Hi Folks,
Here is a pic of the new 20 pilot jets along with the 17.5's I plan to replace. (later 3 jet carb)
Supposedly Mukini jets, they have the right "mukini quality" square marking, but the small lower emulsification tube is much narrower. This is a bigger jet so I would expect it to be set up to have more fuel in the emulsification tube which might be why the tube is smaller and has smaller holes (to let less air into the air/fuel mixture) but the fact that there is a ring on the old one might indicate it is a different jet? Those lines often mean something!
Can anyone remember if there was a difference? Does this look right.
Thanks!
OK, I think I've found part of the problem,
The rejetting wiki states on two places that that "Pilots = N224.103 or VM28/486 (apparently they are the same)". When talking on the phone the supplier had no N224.103 so I asked for and ordered VM28/486.
Now that I'm googling a bit deeper it seems they are NOT interchangeable - I found this following info over on a suppliers site
"The Mikuni N224.103 pilot jet has a total length of 28mm with a 2.5mm outside diameter of the thin end tube with the bleed holes. This jet is also identified by the machined groove next to the size stamping. Be careful not to confuse this jet with the VM28/486 which has a 1/2 mm smaller diameter end tube."
I'm assuming these are not in fact interchangeable. Can anyone confirm? (or deny ;) )?
If so, it might be a good idea to update the wiki if anyone here is in charge of that.
http://wiki.gstwins.com/index.php?n=Upgrades.Rejetting
Hi Folks, I've done a deep dive on the mukini jets to try to get the answer to this.
From what I understand, the VM28/486 (with the thinner emulsion tube) is used on carbs with limited space that have a smaller air chamber around the vacuum side of the pilot jet. In this case the N224.103 jet (with thicker emulsion tube) will not even fit and one will damage the body by screwing it all the way home.
Conversely, carbs designed for N224.103 jets (like ours) will have a larger opening and will be able to accept either pilot.
Jets of the same number will flow the same amount of fuel with the same vacuum applied, hower the mixing/emulsifying of the air+gas may be less efficient with a VM28/486 pilot in a N224.103 spec carb. Whether this will have any noticeable effect is not clear but doubtful.
I sucked it to see what it tastes like and she runs fine with the VM28/486 #20 pilot so, for a single data point, it seems the N224.103 and VM28/486 jets are interchangeable. However, I might still get a pair of N224.103's just to be on the safe side.
Cheers
HnN
"Sucked it" as actually running the bike with it I hope?
I can't imagine mouth to mouth with a carb jet is precise enough. Plus last time I tried, unleaded 89 tastes awful :sad:
Hehe, yes, sucked meant testing on bike.
Checked the plugs this evening - they look a little better but still look quite lean.... (although my bum tells me things are much better).
As well as getting the N224.103 pilot jets, I might go for a bump on the midrange jets to 62.5 to see what happens.
Cheers
Hi Folks,
Having some time to waste I bumped my mid mains up to 62.5 and my mains up to 137.5 (against Buddha's recommendation), because well - more is more, right?
Nope, he was right, less is more, it definitely felt softer with the 137.5 and 62.5s (2004, K&N drop in and stock everything else).
Will change back over the weekend. Or maybe I'll go back one step at a time. Mains, test and then mid-mains.
Dealing with a problem on another bike I've been told (as has been stated here) that reading plugs on the porcelain is not easy with modern fuel. However, it can still be read on the base plug ring. This worked quite well for me. My base ring was quite sooty with the larger jets. See pics below.
Interestingly bike lost power terribly at around 6000 RPM but that went away when I cleaned all connectors (especially those related to coils/ignition) and installed new plugs. The spade connectors to the coils were quite dodgy/loose.....
Base ring on my plugs is always black regardless of jetting. With today's fuels, reading plugs is iffy. IMHO.
Sent from my SHIELD Tablet K1 using Tapatalk
Interesting Update -the major flat spot at 6000 did not go away but it is much reduced.
I changed the mains back to 135 and went for a ride - seemed great - then as my elevation went from 1000 feet to around 3000 feet it came back, but less strongly. Then as I dropped down in altitude again it went away.
Seems to indicate that I am borderline rich with the 62.5 mains (as Buddha told me .....) and that at altitude it gets richer and bogs down.
Buddha, does it make sense that a too large mid-main could do that. I know carb troubles should be throttle related rather than RPM, but with aggressive throttle use up hills this is a consistent stumble between 6 and 7 k and its fine after 7 k - pulls really well.
With less aggressive throttle the stumble is still there but less pronounced.
I hate jetting carbs, I'm just glad I've got a known good setting to go back to.... Hopefully.
I don't think a mid main increase is ever necessary unless you're doing K&N and pipe, and even so, I don't see how it can be better than needle and 1-2 washers.
Also Less isn't more either. Correct is more, and thanks for all the experiments.
Further those pilots being interchangeable and whatever - it may have got some weird outsourcing differences, I'd be shocked if you get the other part number and find the jet is like your original 17.5. Its likely the same crap you have in a different baggie with a different printed part #.
Cool.
Buddha.
Hey Buddha,
I did get the new "proper" N224.103 part recently, and it is the same as the original (thicker emulsion tube). See picture below. The two outer jets are the same two as the old jets in the original photo (the bottom two). In this case, at least, I can confirm the info "from google" that the N224.103 has the large emulsion tube and the VM28/486 the smaller.
But, there always is one isn't there.... the holes on the side of the emulsion tube in the new part are 3% smaller than the originals. Probably no practical difference but interesting nonetheless....
Never know what one's going to get in those baggies ;-)
HEHE, "interesting" response when I told the supplied that the emulsion tube holes were slightly different to stock. Seemed ok but interesting that they are different. One would assume the 8 side holes would be identical in a specific jet part number, as opposed to the jet sizes that do obviously change under any specific part number.
Don't read to closely is it gets a bit circular fast. However, the Jets do seem to work fine....
Hello,
I must point out that this product is manufactured according to the Japanese carburetor sample, so the data is not wrong.
I also believe that the diameter of the atomizing orifice you are talking about is different, but all the atomizing orifices of your N224.103 you mentioned are only one diameter size, which is obviously not the fact.
Actually, carburetor manufacturers will make corresponding optimizations according to the products sold in different regions, and atomizing holes will also make corresponding changes. Because of the air and humidity in many areas, or the temperature is not the same. For example, the frigid climate and the tropical climate are different, so they will make relative changes.
In fact, the slight change of the atomization hole does not affect the use of the product. Generally, it can be adjusted by using the air-fuel ratio screw, or by changing the size of the jets, which does not affect the use.
But if you insist that all N224.103's atomization holes should be the same, I will respect your ideas, but at the same time my experience and the actual cases I encountered, I can say for sure that not all Atomization holes are the same.
If you think that my product is a problem, I can refund it to you. I am very happy that we can explore this issue rationally.
OK changed the mains back to 135 and now have 20/60/135.
Funny how the mind can jump to conclusions. The stumble at 6k to 7 k RPM was still there. However, this time I did what I should have done right at the beginning and marked my throttle to identify exactly at what throttle opening the problem occurred.
I realised that altitude had nothing to do with it, it was the fact that I was opening the throttle more while climbing, and that the engine was working harder going uphill. If I limited my throttle to at most just over 3/4, there was no dead spot while accelerating from 5k up to 8k. If I went WOT there were bad stumbles at 6 to 7 K. This was worse uphill but still noticeable on the flats. This happens in different gears (and hence different speeds)
I'm guessing that the main jet at 135 is too rich for my setup on my particular bike (stock exhaust + K&N drop in). But it's strange that it should manifest only at one place on the rev range when at WOT and not over more of the range. The pulls like a champ from 7k up.
I'm wondering what happens at 6K that affects this???
what happens at 6K, and under that kind of load, is that vacuum increases enough to pull the slide far enough to open the main jet.
I think it's more likely it's lean than rich. Usually the bike will run great when rich down to probably 12:1 or even richer especially under high load/WOT... some FI cars map down to 10:1 or so at high revs and WOT without any kind of damage other than continued running this way will increase carbon buildup and shorten the life of the catalytic converter ... but it's unlikely your bike is going to have that problem.
I think under WOT/high load/>6K RPM running as rich as 10:1 is probably close to ideal as long as at part throttle or less load you get back closer to 13:1-14:1 and very light load you get close to 14.7:1.
Not that any of that matters except to quantify why I think it's more likely too lean than rich. What was Buddha's recommended jetting for a K&N drop in filter? Could be needle shimming will get the job done better than jetting up, since the needle shim will mostly affect how quickly it enriches under given vacuum (load) conditions.
Hi Josh, thanks for helping me think through this.
The reason why I think it's rich is that by dialling back the jets from 62.5/137.5 down to 60/135, the problem was reduced but not completely eliminated.
Also I did not have this with the old jets (57.5/127.5 iirc).
If I go WOT at 4k it's fine until it gets to 6k and then it stumbles a few times between 6 and7k. After that pulls well.
My plan of attack is to try 132.5 and see what happens and if still there to try the 127.5 to get a reset/ baseline test condition.
I'm feeling a bit lost as I don't have an understanding of how the mid-main mystery jets work and their potential impact on this. are they just a constant feed into the throat varying only by venturi vacuum, are they fed through the needle somehow? How do they impact over the range of throttle movement....? Who knows.
Cheers
HnN
Quote from: herennow on May 30, 2018, 03:45:31 AM
Hi Josh, thanks for helping me think through this.
The reason why I think it's rich is that by dialling back the jets from 62.5/137.5 down to 60/135, the problem was reduced but not completely eliminated.
Also I did not have this with the old jets (57.5/127.5 iirc).
If I go WOT at 4k it's fine until it gets to 6k and then it stumbles a few times between 6 and7k. After that pulls well.
My plan of attack is to try 132.5 and see what happens and if still there to try the 127.5 to get a reset/ baseline test condition.
BTW IDK at all about the 3-circuit carbs but what this sounds like to me is maybe it is too rich at that point due to excessive overlap between mid and main jet, or in other words your main jet is opening too early.
Reasons for this would be diaphragms are worn out (too flexible), return spring under the slide is missing or bent or whatever, or if you shimmed the needle, maybe un-shim it and see how that goes.
But IDK what the right jetting with the K&N drop in filter is. Try it with a paper filter and see if that helps. The thing is with the K&N you might be lowering the air velocity under all conditions and you definitely change the behavior of the carbs and how the circuits interact. It's a finicky system. There's no performance gain with the K&N, it increases engine wear and makes it potentially difficult to tune, so I would say the easiest thing is just to switch back to the paper filter.
"hmmmm", says stroking beard, "Insert, what insert?"
My bike came with the K&N filter so I never researched it. I had no idea there was such a thing and don't know if it has it or not. looking forward to finding out this evening. Major "doh" moment if I've been jetting while aiming at a moving target...
FYI, Re the three-stage CD carbs, Haynes manual says this:
"There are a number of hybrid instruments found on
motorcycles. One of these is part fixed-jet and part CD in func-
tion. At tickover, metering is controlled by a normal pilot circuit,
independent of the main carburettor and automatic in opera-
tion, as in most instruments. As the butterfly valve is opened,
more air is admitted, and fuel is drawn from the primary main
jet located on the engine side of the valve. Further opening of
the butterfly causes the secondary main jet to be brought into
action, this being located centrally in the instrument as in con-
ventional slide or CD types. Up to this point (idle to low speed)
the carburettor has functioned as a fixed jet instrument, but
from here on, the vacuum induced begins to act on the suction
chamber, and the instrument functions as a CD type. This
additional sophistication is designed to give an ever smoother
transition between the idle and low speed stages."
Someone kicked an old 70's Honda manual my way where they also use prim/sec main jets on a CD carb:
They say this:
"Primary and Secondary Main Fuel Circuits:
The carburetor illustrated in Fig. 35 & 36 divides
the main jet system into primary and secondary
circuits. The purpose of this design is to provide
a smoother transition from low speed to inter-
mediate systems.
As the throttle valve starts t0 open and induction
port vacuum extends upstream, fuel is discharged
from the primary main jet nozzle before the
secondary circuit becomes operative (Fig. 35j.
As the throttle valve opens farther, fuel is dis-
charged from the secondary main jet nozzle
(needle jet), and the vacuum piston begins t0
rise (Fig. 36).
Fuel is delivered from both primary and secondary
circuits throughout the operating range of the
vacuum piston. Fuel mixture adjustment can be
made by replacing the main jets with jets of
larger or smaller diameter."
Hope this sheds a little light on the working of our carbs.
Based on this, and if the restrictor is not present, I might first go back down in size on the mid-main (primary main) just for the hell of it and then the main (secondary-main) after that if no difference. If the restrictor is present, taking it out might sort out all my problems - but that's a long shot as it would be way too easy..... ;-)
I wonder if the jetting chart would look something like this for our carbs (blue added in by me):
Quote from: herennow on May 29, 2018, 01:10:38 PM
If I limited my throttle to at most just over 3/4, there was no dead spot while accelerating from 5k up to 8k. If I went WOT there were bad stumbles at 6 to 7 K.
This is a dead giveaway sign of a slide rising too fast. Plug one hole with a 4-40 nylon screw and cut flush (absolutely not at all recommended) or train your wrist ( :thumb:)
Cool.
Buddha.
Hi all, just checked - no restrictor ring on the filter..... Damn!
Buddha, in the test runs I did, I would go WOT sometimes at 4 K and sometimes at 5 K. In both cases the bike would run fine until it reaches the magic 6k rpm mark and then the stumbles would start until around 7K. If the slide was rising too fast would I not get this problem at, or close to, the time I go WOT, rather than at a later specific RPM?
Note stumble was more pronounced when the engine was working harder (going uphill).
Thanks!
I've had it do that with the stock filter. Putting a pipe on it will get it to the disaster zone. And maybe even a stock pipe is close.
Cool.
Buddha.
Thanks again for the input folks. Mr 72, I think you might have something after all. I went for a ride and repeatably found the situation where *slightly* closing the throttle gives me noticeably more power than when WOT.
In classic slide carbs, which I am much more comfortable with, this means that the main is too small (running lean up top), does this also hold for CV tye carbs?
As an aside, I checked float levels again (just to make sure). I checked before I restarted jetting, but now fuel level was way too high again. Adjusted them back but can only think that maybe I bumped the floats while changing jets that caused this.... Be careful out there folks!
Cheers
HnN
Quote from: herennow on June 04, 2018, 06:38:58 AM
In classic slide carbs, which I am much more comfortable with, this means that the main is too small (running lean up top), does this also hold for CV tye carbs?
Not exactly, but maybe coincidentally.
The following is all just theory, IDK precisely about what can be done to tune your carbs.
In a CV carb, it's VACUUM AND VACUUM ALONE that opens the main jet by virtue of pulling the slide up. The needle is attached to the slide. So to get more fuel, the slide has to move up and pull the needle out of the jet. The position of the slide at a given vacuum level is determined by the diaphragm and spring tension. The amount of opening of the main jet at a given slide position is determined by the needle profile and needle position (shimming). Shimming the needle pulls it "up" more giving more fuel at lower slide position, making it run richer at lower vacuum levels.
The issue with the K&N drop in filter is that it will reduce vacuum and therefore cause the slide position to be a little lower, so you might have to shim the needle to compensate. It may also reduce velocity of air enough to require a bigger jet so you will get more fuel per unit volume of air since the air is moving through more slowly. This air velocity issue will also affect the mid jet to some degree but not the slide/needle/vacuum issue.
There's also the effect of how quickly the slide moves up, which is a result both of the spring tension and also there are holes in the slide that allow air to pass through sort of like a poor man's damping and change the rate at which the slide goes up. In my old SU carb tuning days there was oil in the damper on the carb and we could change the oil to change this rate of enrichment under transient vacuum conditions. Anyway, if the slide is going up too fast then it will be too rich too quick. I think this is unlikely. A wideband O2 sensor would tell the tale and is about the only way to reliably know for sure but my guess is the slide coming up too slow is a more common complaint especially if you've put in a less restrictive air filter so there's less total vacuum.
If slightly less throttle results in more power then that sounds to me like it's lean on the main jet; less air = richer = more power, more air = more lean = less power. I'd say put the paper air filter back in and see if this situation improves. If so, be done with it. If not, then I'd look really hard at the condition of the diaphragms and springs on the slides, and if you are certain they are good to go, then look real hard for vacuum leaks. If you're absolutely sure there are no vacuum leaks then shim the needle and see if it gets better. Last resort: bigger main jet. My point here is that I think changing the vacuum condition likely led to this condition, and changing it back could remedy it.
BTW I have the opposite problem ... 3K rpm very small throttle opening I get a consistent stumble which I am quite confident is lean condition. I think the solution to my problem is going to be shimming the needles, but it only shows up when riding around parking lots looking for a space, so it's not really bugging me. Actually I have likely a too-big main jet (127.5) and could probably put 1-2 washers on the needle and go back to a 125 and it would work better. Next time I have the tank off I might actually do all that. By then maybe I'll need another round of carb cleaning. It has been about 3K miles.
Very good points.
Any modifications often require extra tuning for best performance. For example, I use 127.5 mains on my liter bike. Everyone says, "Oh, they're too small, blah blah blah." Throttle response is crisp and she flat hauls a$$; the front wheel comes up when shifting into 4th at speed. It took a bit of tuning to get her there.
I found this (http://www.factorypro.com/tech/carbtun.html)to be a great resource when tuning CV carbs.
That looks like a really good resource. Simple, easy to understand, makes a ton of sense.
The big key facts that are easy to miss are: 1) high flow air filter doesn't mean more air, it means slower air and less vacuum; 2) opening the throttle does not directly cause the slide to come up, that is caused by vacuum ... then it's easy to understand why a higher flow air filter may result in lean condition because of less vacuum and lower air velocity.
Thanks for the inputs folks. Interesting - yesterday I bought this for another bike:
https://www.plxdevices.com/ProductDetails.asp?ProductCode=897346002870
Think it's going to come in handy here too.
I'd like to check a couple of logic items with you though:
The first is the effect of a free-er filter (I'm not trying to defend the K&N, it came on the bike and I might well buy a new one to test, and I also don't want to argue at all- just trying to understand!).
I understand that the K&N will let more air through (less resistance). This lower resistance will lead to a lower pressure differential between atmosphere and intake manifold.
However, this will also mean that more air will pass per given amount of time (lower resistance = higher current). This greater amount of air will lead to a greater velocity, not lower as stated before?.
Secondly, Assuming the carb respects Bernoulli (yeah right...) would that not mean that at higher throttle openings (very little constriction for a venturi effect) the greater airspeed from a free flow filter would obviously mean more air, but also more gas sucked by the Bernoulli vacuum effect due to the higher velocity? Of course its hard it say which would win out at any given point. I know CV's are designed to "not rise too fast" as a slide type carb would but it can obviously happen. Bottom line is I have a hard time deciding whether a slide rising too fast would;
a. Momentarily lean out the mixture too much by letting in too much air before the gas delivery can catch up, or
b. Momentarily richen the mixture by letting in too much gas from the needle as it opens quickly.
My gut feel tells me "a", as I think the vacuum will reduce momentarily (less restriction), and the velocity will decrease momentarily at the main jet (greater area) until the engine speeds up and velocity increases. This would lead to less gas for a short time.
This is hard to explain but I hope you can understand my questions.
Wow, carbs are complicated
EDIT - just realised that CV carbs mean "constant velocity" of airflow, will have to rethink the above in respect of this realisation.
cheers.
This sound exactly like what I was discovering.
http://gstwins.com/gsboard/index.php?topic=72399.0
I think Buddha's suggestion for better throttle control is the right answer
Quote from: herennow on June 04, 2018, 01:33:02 PM
I understand that the K&N will let more air through (less resistance). This lower resistance will lead to a lower pressure differential between atmosphere and intake manifold.
Well sort of. The K&N could potentially let more air through, if such a need were to arise. On a GS500, it will not need more air. But the vacuum will be reduced as you point out.
Quote
However, this will also mean that more air will pass per given amount of time (lower resistance = higher current). This greater amount of air will lead to a greater velocity, not lower as stated before?.
No, this is not correct. There will be no more air. The engine still displaces 487cc, so it will still draw in that amount of air (and fuel) with each cycle while the intake valves are open. Since the total rate of flow (volume over time) remains the same but the pressure is lower, the velocity has to necessarily be lower. Since the velocity is lower, the amount of fuel picked up by the air as it passes over the jet would be lower, which is half of the reason you might need a larger jet. The other half of the reason is since there is less vacuum the slide will be lifted less and result in the needle being at a lower position than it was designed to be so the jet is more closed.
Quote
Secondly, Assuming the carb respects Bernoulli (yeah right...) would that not mean that at higher throttle openings (very little constriction for a venturi effect) the greater airspeed from a free flow filter would obviously mean more air, but also more gas sucked by the Bernoulli vacuum effect due to the higher velocity?
It's just like that only opposite because it is lower velocity.
QuoteBottom line is I have a hard time deciding whether a slide rising too fast would;
a. Momentarily lean out the mixture too much by letting in too much air before the gas delivery can catch up, or
b. Momentarily richen the mixture by letting in too much gas from the needle as it opens quickly.
It's b. The throttle position meters the amount of air, the needle (and slide) position meters the amount of fuel, generally speaking. I mean, the slide does restrict the air flow a little bit, but not nearly as much as the throttle plate.
Quote
My gut feel tells me "a",
No, it's b. And that's because as you mention in a moment, in a CV carburetor, the whole objective is that the air velocity is constant. The only thing that changes is the position of the throttle plate and slide which together limit the cross-sectional area through which the air can flow so a high throttle opening and low slide results in more air restriction (low rpm) and a high throttle and high slide results in less air restriction (high rpm) but in both cases the velocity of air remains approximately the same. If it's not working this way, something is wrong, and it will be difficult to tune. When you make a change to the vacuum behavior you wind up imbalancing this system and you have to compensate somehow. That's why vacuum leaks are a tuning killer and a lower-restriction air filter is much like a vacuum leak in terms of the effect on the engine.
The thing to remember here is that it's the engine's demand for air that causes the volume and rate of flow, not the air filter's restriction. In other words, your bike will make the same power and consume the same amount of air with no air filter or with a Briggs & Stratton air filter. Only difference will be the velocity and vacuum so you will have to tune the carbs accordingly. To actually consume (or demand or use) more air per cycle you would have to change the cams and/or valves, add displacement or add forced induction. To add to the total rate of airflow you could do those things plus increase operating rpm. You know an engine operating at 12,000 rpm will use 33% more air than one at 9,000 rpm and will also make 33% more power all else being equal, and it would require an air filter (as well as valvetrain and head and intake tract and exhaust etc.) capable of flowing that 33% more air.
Quote
EDIT - just realised that CV carbs mean "constant velocity" of airflow, will have to rethink the above in respect of this realisation.
Yep!
Quote from: herennow on June 04, 2018, 01:33:02 PM
b. Momentarily richen the mixture by letting in too much gas from the needle as it opens quickly.
It does this, but in simpler terms a big inrush of air will get fuel added to it, the engine can only eat up so much cos its flow is limited by cams and exhaust etc. The air column hits the back of the closed intake valve and rebounds which results in more fuel getting added as it flies past the venturi this time going toward the air filter. Then ofcourse the intake open and the air flies to the engine, making it add fuel again etc etc
This is the single biggest reason a K&N lunch box without pipe can likely never be jetted right. Of course training your wrist and closing off 1 hole in the slide could help, but I have never experimented with that and I am not about to mangle a few $100 worth of unobtanium parts to find out nor do I have an O2 sensor fitted stock exhaust pipe. And besides O2 sensor will just read rich, I guess that fall on its face feeling combined with rich reading can indicate that while a steady state at that same throttle position may be much leaner indicating pretty much the slide rising problem.
Cool.
Buddha.
Interesting Stuff, I hope that I will be able to shove the O2 sensor up the GS500's bum, I mean the exhaust pipe ;-) when it arrives. That hole is pretty small and I am not really keen to drill and weld a bung on the exhaust itself (I bought this for an older carbed bike with almost a 1" exhaust that I can shove the sensor up). I know this is not the most accurate way to install the sensor but I'm looking more for relative AF ratios than exact ones.
Buddha, did you use a logging recorder or look at the dial in real-time? How fast does the reading change to reflect instantaneous conditions?
Mr72, I'd like to unpack your comment a bit:
QuoteSince the total rate of flow (volume over time) remains the same but the pressure is lower, the velocity has to necessarily be lower.
You are of course correct that the bike always sucks the same 487 cc volume. The throttle butterfly dictates how many "gasps of air per minute/RPM" the engine can breathe. That got me thinking about how the different air filters work, because, if one can never flow more air at a steady state, what exactly do they do? The only answer I could come up with is that more restrictive filters create higher pressure drop resulting in less dense air and hence less oxygen and thus less power? Free-er filters would conversely have less pressure drop, so more O2 molecules per given volume? Or does it just lead to lower rpm, like closing the throttle a teeny bit?
Obviously, this density change would be very small - assuming that there is none for argument's sake, my understanding is that the volume and the area that the given volume flows through, would define the velocity of the gas. (m/s = (m3/s) /m2 ). Would that not indicate that even with the pressure being lower, the velocity is still the same (going back to the CV name)?. if this is the case velocity vacuum (Bernoulli) effect would be minimal and most effect would come from the slightly lower pressure differential not raising the needle as much = less gas?
Finally, I might one day test out closing one hole temporarily with a plug of silicone to see the effect. For now its "right-hand modulation" for me.
Thanks for this interesting discussion folks.
Its arrived!! - my air-fuel ratio sensor (works with a smartphone app via Bluetooth). See picture below
I look forward to finding out what is causing the 6 k RPM flat spot.
While waiting I had a look at how the slides work when the bike is running with an endoscope end stuffed in the airbox. I was quite surprised to see how much the slides are moving all the time, even at steady revs. Probably due to the time taken for a cycle on each cylinder, when the intake valve is closed the pressure will drop. This happens very fast and my cheap endoscope could not capture the movement at revs much above idle.
This got me thinking that (seeing as the movement of the slide is so fast), and the fact that blocking one of the slide holes will not change the end point of the slide but only the speed that it takes to open to the point when the pressures are equal - maybe it is better changing spring tension rather than the holes of the slide? Changing spring tension will make the valve open earlier, if weaker (or later if spring is stronger) and might be a more beneficial modification than blocking holes. I might buy some spare springs and play with stretching them or shortening them after I've understood what my A/F sensor is telling me.
Devilishly complex, these simple carburettor things!!!
Quote from: herennow on June 25, 2018, 06:22:26 AM
Its arrived!! - my air-fuel ratio sensor (works with a smartphone app via Bluetooth). See picture below
That's a really cool tool. I kinda want one.
Quotemaybe it is better changing spring tension rather than the holes of the slide?...
Devilishly complex, these simple carburettor things!!!
Better not to change any of it. As you say, it's a carefully balanced system and seemingly simple changes have side effects that are difficult to predict. The engineers of these bikes are near magicians for making them work as well as they do. I find it hilarious the arrogance of most of us shadetree mechanics who think we know so much more than those engineers!
The diaphragm also offers both some spring action and damping, as well as the flexibility of the diaphragm affects how quickly the slide will open or how much vacuum it takes to pull it up. That's a wear item and a small pinhole or tear will make it useless. So that's one thing that can be replaced to perhaps restore original function. But the springs don't wear and while the sides may wear I don't think it's significant enough to warrant changing anything unless they stick.
It's just funny, we're so simple-minded about this stuff, we think "more airflow through air filter means more air means MORE POWER better get bigger jets so I can make MORE POWER" and it's just wrong. Then we make this one wrongheaded change (not you, but in general) and wind up chasing all kinds of other "problems" to try and compensate for something that worked just fine if we just undid our first change.
Without screwing it into the headers you will never be able to get a real world 6K or 4K or - more precisely 1/2 throttle or 3/4 throttle reading without a dyno.
If its bolted in the exhaust, you can just ride it and you can read it if its sitting on the tank or dash.
Also it needs heat, it warms up with the exhaust gasses flowing through it and then starts reading accurately. Till then it is likely off to the lean side. That's a 20min time frame at a minimum @ rpm and load. My dyno guy way back when I put it on the dyno had to let it idle and rev and idle and rev and still wasn't getting good temp in it cos a bike that's jetted rich warms up much slower cos its exhaust is lower temp and it also has liquid gasoline cooling down the sensor if you were that rich.
Cool.
Buddha.
Hey Buddha,
The manual states to install the unit at more than 24 inches from the exhaust port. I plan to shove it up the exhaust hole to around that distance (attached to a spring steel guide rod which will be clamped to the exhaust) would that prevent me from testing at 6k RPM?
Interestingly, the newer sensors (LSU 4.9 +) have integrated heaters built in to avoid the heating up issue.
" reaches operating temperature of 700 to 800 degree Centigrade (1,400 degree F) within 20 seconds or less using its internal heater"
Cheers
Brett