It seems like I have a fairly unique problem. There's tons of posts about a flat spot, but no one says anything about it only at WOT. At least not like my symptoms are.
Bike runs great. I've got warm up time to around 20-30 seconds for it to be ridable, and about 2-3 minutes for it to be smooth. The problem is when the bike is hot and cold. It also happens if I turn the throttle gradually or snap it open. When I hit wide open throttle, the bike will just hit a bad flat spot. It seems to happen around 4.5k-7.5k. Seems to decelerate slightly during that range, then kicks in again after the 7.5k and is strong through redline. If I come off the throttle just 1-2 mm, then it seems to be fine, and runs strong all the way through.
Previously, I had a lunchbox, 140 mains, 40 pilots, DJ needle on slot #2 (previous owner's doing), stock exhaust, and 4 turns out. Bike ran great, but was slightly lean, (hence so many turns out) but no flat spots at any throttle position.
Now, I have the lunchbox, 147.5 mains, 40 pilots, DJ needle on slot #2, custom muffler on stock pipes, and 1.75 turns out. The flat spot was a lot worse at 4 turns out, and was way too rich. I took it down to 2 turns and it was still bad, then to 1 turn. 1 turn the flat spot seemed less, but still bad, but it would climb RPM's at idle because it was too lean. I brought it out to 1.5, then to 1.75. The flat spot is still bad, but the RPM's don't climb anymore. (yes I adjusted the idle screw, and no I don't have any leaks)
What I'm thinking is that the needle is being pulled too far out of the jet, and it is just being overwhelmed with fuel at full throttle, so maybe lowering the needle to the #1 slot (lowest slot), would keep the needle inside the jet enough, and would keep this from happening. (don't know how far the needle is actually coming up, so this is just talking out of my ass.
As far as I know, the slides aren't raising too fast, because it happens if I come on it gradually, and if I snap it open.
Please help. I'd really like to fix this, cause it's a major pain. Thanks
Quote from: quiktaco on April 15, 2008, 02:36:37 PM
Now, I have the lunchbox, 147.5 mains, 40 pilots, DJ needle on slot #2, custom muffler on stock pipes, and 1.75 turns out. The flat spot was a lot worse at 4 turns out, and was way too rich. I took it down to 2 turns and it was still bad, then to 1 turn. 1 turn the flat spot seemed less, but still bad, but it would climb RPM's at idle because it was too lean. I brought it out to 1.5, then to 1.75. The flat spot is still bad, but the RPM's don't climb anymore. (yes I adjusted the idle screw, and no I don't have any leaks)
Please help. I'd really like to fix this, cause it's a major pain. Thanks
Sounds like your float levels are too high ? You've kind of confirmed that reducing the richness with the mixture screws isn't enough already, so the float level is my guess. I'm assuming you're right about the slides not moving too fast, and the needles aren't shimmed too high. Are you also certain the needle JETS are in good shape and not letting gas by ?
Not sure on the needle jets. The float level is right at the gasket on both carbs, so I don't think it's too high. I don't think that would only affect WOT either. And the needle jets too. You'd think I'd have a problem throughout the throttle range, right?
I just went for another ride on my lunch, and I also noticed a popping in the carbs...backfiring through the carbs. That's happening at idle, and on closed throttle decell. What does that mean? There's also slight backfiring through the exhaust on closed throttle decell, but that's expected; it doesn't seem too bad, but the carb backfire is a little concerning. Any thoughts?
My idle was climbing again on this last ride also, so I might bring it back up to 2 turns out. Before with the #140 mains the bike ran fine with no problems. Should I drop a size on the mains so I lean it out a bit, then turn out the mixture screws like I had it before? Maybe 145's? Don't know if that would even be the correct direction, maybe I need to up it to 150's? Seems like it would be way too rich though.
Anyone have some other advice?
I pulled the plugs from idle, and it showed that it was lean. I then turned the mixture screws to 2.5 turns out and rode for a bit and did a chop at 5k, and it was lean again. Then to 3.5 turns, and rode for a bit and did another chop at 5k, and it was still lean. So I'm thinking that I either need to bring the needle up to the #3 slot and/or move up to #150 mains, then go from there. That will probably fix the flat spot that I'm having, and the closed throttle RPM hanging. I still don't know about the WOT problem though. What would cause something like that? Is it a lean condition? A rich condition? Something else?
Mains are too big. But you are also using DJ neddles which have a bigger taper.
Dgyver is right. 147.5 will work only with stock needles. heck 140 was too rich with DJ's prolly. I will slowly read your post again, but post how 140's were compared to the 147.5's.
Cool.
Buddha.
Quicktaco - You said ...
Previously, I had a lunchbox, 140 mains, 40 pilots, DJ needle on slot #2 (previous owner's doing), stock exhaust, and 4 turns out. Bike ran great, but was slightly lean, (hence so many turns out) but no flat spots at any throttle position.
Why change to 147.5 from here ??? 4 turns out is perfectly acceptable. I have often had to set them even north of 4. 3 is just a starting point.
BTW if you get past 5-5.5 just put a dab of silicone on the air screw spigot so the screw cannot jump out and fly away. I have actually see a carb with a rubber cap on it as well.
Anyway a bike that is nearly on the spot needs 1 change in 1 thing ... like lift the needle with 1#4 wahser leaving clip at 2, or go to 142.5 mains, or 1/2 turn out on screw ... you are throwing the baby out with the bathwater when you make huge changes on a near spot on setting.
Cool.
Buddha.
Hey ME TOO,
I have the WOT,& Bogg down, & 6000RPM tops, And the fuel starvation problem? can it be a BAD petcock??
I've put in used slides & guides,Diaphrams..I bought form here! But no better, What next? from what I'm reading here the fuel starvation problem is a lot :dunno_white:
Thanks for the replys. The problem is that it was nearly spot on when I had the stock exhaust. I have a free flowing custom exhaust now. I was slightly lean with the 140's and the stock exhaust. But now with the free flowing exhaust, I figured it wouldn't be too big of a jump to go to the 147.5's. I did a plug chop at 5k, after the new jetting of 147.5's and 3.5 turns out, and it was still very white on the plugs. Maybe I'm doing the chop wrong. The bike is completely warmed up, I rode around for a few minutes at these settings, then rev it to 5k for about 5 seconds, then hit the kill switch. If that's correct, then I think I'm still very lean.
Taco - Stock pipe to aftermarket pipe = 1 jet size - if that.
Mustaang - Starvation is fairly common, but 6K is too low for starvation. You're talking 9K+ under load AKA WOT for 10 mins before starvation from the petcock flow rate. You got something clogging up something somewhere ... My vote goes to possum in the pipe ... but hey ...
Cool.
Buddha.
Doesn't hanging RPM's that only comes down under load (like letting out on the clutch some) signify that it's lean? I have no problem dropping down to the 142.5's, but the bike is really looking like it's lean with the 147.5's. Was my description of how I did the plug chop correct, or did I mess it up somehow?
warm it up
install new plugs
ride it on a highway for 5 miles in 3rd or 4th gear 6-9k
cut ignition and pull in the clutch then pull over
then look at the plugs
are they still white?
or dripping wet?
also go back to your last known good settings/jets/turns
and start from there
i bet you gunna go down jet sizes!!!!!
134 is what DJ supplies for pipe and K&N. So werase is right, however no one has got it running perfectly with a DJ in it. If it ran great at 140 please go back there and do 1 small change at a time and start taking notes.
You can be lean with 147.5 only if you are running floats waaaaaaaaaaaay low ...
Plug chop - werase is correct - mostly ...
Here is what I have seen. Install old but good plugs. Older plugs dont self clean as well and you want that to read it.
And you stay under full load (I prefer 6th ... not 4-5 though they cant be too far off) at steady rpm and note the throttle position and rpm for ~5 seconds and kill the motor with the kill switch and pull in clutch at the same time and then pull the plugs. Remember jetting depends on throttle position not rpm. You should mark them on the grip and switch and read from there.
However the difference between plug pull test and seat of the pants feel is under 1 jet size. I nowadays just do seat of the pants feel, jet up and do it again ... so on till I'm past the perfect location.
AKA - jet it up its better, Jet it up again - better, jet it up - better, Jet it up - better, jet it up - worse - stop.
Cool.
Buddha.
Ok, I'll revise my Chop method and see if that works. Since I made the new muffler, I have no known 'good' setting. After it was on, it was way too lean...no doubt about that.
Without a plug chop, what do these symptoms say about the mixture?
• hanging RPM's that only come down with load (release of clutch slightly)
• backfires through muffler
• backfires through carbs
• flat spot on WOT around 4.5k-7.5k
I think that's all of the problems.
I don't want to spend 10 bucks for each set of jets, only to find out that I did need bigger than the 147.5's. Would I be better off buying stock needles from the dealer (i think they're 15 dollars for the two - might be a piece though). That way I could stay at the 147.5's and all the DJ crap would be out of the carbs. I don't think the previous owner drilled anything, so there's no permanent damage.
5 seconds my ass
race bike chop....after WFO FOR AS LONG AS POSSIBLE SO THE READING WILL BE OF THE MAIN JET
Yea this incremental buying of jets really gets on my nerves too.
150's and stock needles will leave you spot on ... needles I have and mains too. How is $20 for 2 of each including shipping.
Man I was thinking you'd finally get the DJ to work on yours ...
Anyway - throw in and ride = stock needles and 150's - 3 turns and 1 washer under the needle - heck I'd toss in washers and the bolts for the bottom too for the 20.
Cool.
Buddha.
Quote from: werase643 on April 16, 2008, 11:06:54 AM
5 seconds my ass
race bike chop....after WFO FOR AS LONG AS POSSIBLE SO THE READING WILL BE OF THE MAIN JET
Yea hold it WFO for as much as you can, as long as that is over 5 seconds ...
Dude - 5 seconds is plenty to color a plug. You want more - knock yourself out.
Cool.
Buddha.
Thanks for the offer. I might take you up on that. I think I'm going to mess around with all the configurations I can with what I have this weekend and see what's better and what's worse. I have allen's for the carbs, so I don't have to pull them...when I put the 147.5's in it took all of 10 minutes. It's going to be harder to shim the needles cause I have to lift/remove the tank and it's almost full.
I'll throw the 140's back in with different needle height's and do different needle heights with the 147.5's. i'll double check that my float levels haven't moved in the last few weeks. And I'll mess with different mixture screw settings. I'm sure between the 140's and the 147.5's I can see what is closest to working and go from there.
If all else fails, then I'll take you up on that deal, though.
READ THIS LINK.... IGNORE the part about premix.... then read it again
this was the first one i found......
http://justkdx.dirtrider.net/printcarbtuning.html
unless you are racing.......you will never stay at WOT for any appreciable time.....therefore.....YOU NEED SMALLER JETS TO GO WITH YOUR NEEDLES!!!!!!!!!!!!!!
you do not have a WOT problem..... you have big frigging stupid budda jeting with a set of DJ needles
Werase you clown ... I never told him or sold him anything.
Now he prolly read it and saw people got 150's etc etc and did it ... he must have missed the part about the stock needles.
You will need to get the upper end sorted in a GS, you will see over 7500 on it for extended periods of time if you are on highways. 7500 rpm is 75-82.5 depending on your sprokets. Its very very useable.3/4 throttle and up you will need to sort it out, maybe the GSXR 1000's dont need their 3/4 and up throttle position on the street, but a GS will need it.
Quiktaco - However with DJ's you may have a different issue as to why you are lean, they supply 134 mains. I dont think they made a big mistake there. I believe their errors are lower down in the pilot range and some other stuff that is hard to explain and that is why they sell you those plugs for the slides etc etc.
Cool.
Buddha.
budda...or is that bubba.....
mark your throttle tube and then look at the throttle position needed to go 80mph in top gear.....it ain't WFO
that baby is on the needle
3/4 th and up is mains. 1/2 to 3/4th is needle. And I routinely run to 90+ and stay there, remember super slab is high speed holding speed and straight line and I ahve the square tires to prove it. Your twisties may not need WFO, but superslabbers do.
Its bubba's wisdom dispensed with a Buddha like manner.
Buddha say:- We fit it with duct tape ... may pease be with you ...
As opposed to ...
Put that there duct tape on it, bubba ... ther rigth ther, that hold it ...
See ...
Cool.
Buddha.
Wow! What an excellent article werase.
I think I have been thinking of certain parts slightly differently than they really are. Of course everything has an affect to other parts, but it seems in much less degree than I had thought.
• Do the mixture screws (that are originally under the brass caps) mostly have an affect at idle and partial throttle, but not too much else?
• The idle circuit mostly has to do with closed to part throttle and consists of the pilot jet, the mixture screws and the idle screw?
• The main jet is fully engaged at full throttle and has nothing to do with the taper or height of the needle?
• The mixture screws do not affect the air/fuel mixture of the main jet once over 1/4 throttle or so?
• So once the main jet is correct, from about 1/4 throttle to about 3/4 throttle has to mostly do with the needle taper and the needle height? So if there is a problem of drivablity (i.e. - a flat spot), then adjusting the height of the needle may fix the problem; if you have the correct taper of needle as well?
And of course all this is only accurate assuming there are no air leaks, the carbs are sync'd and the float height is spot on?
OK the factory article of many years ago and possibly this one (I haven't read this) are both making a lot of assumptions and also tend to be more compartmentalised.
The quick thoughts from my very sporadic memory is this ...
Your needle does affect full throttle. Its taper does not.
You miss the lower jets by enough, you will never get it up on the higher revs to test the mains.
You get the mains right after getting the lower ones right, but after that you fine tune the lower jets too.
Its related by a good bit, especially needle and mains.
I have to read that doc, which I cannot at work. I may post tonight.
Cool.
Buddha.
Yeah, it admitted that it compartmentalized the whole process a lot, just for ease of explanation.
There's a really great graph in this article that shows where things affect the mixture and to what degree. Very generalized of course.
I have a 96, so I've only got the one main. Are you saying that you figure out the main jet after the pilot jet and needle? Or are you saying that you'd set the first main (if you have one) then the larger main?
If you are saying, set the main after the pilot and needle, then does that mean that if your main is close enough, then you can get the rest of the carb tuned pretty close to correct? Then go after the correct size of main for the full throttle mixture?
I still didn't read it. But back in the 80's Factory had an instruction sheet they sent with their kits. I found it to be accurate for what we need to tweak in what range but off for what else it will affect. Like you're lean at WOT, you go bigger mains, and they seemed to say it wont affect much else, but it totally affected your midrange. You had to drop your needle a hair.
I just think from the 140's you had, work 1 up or 1 down form there and small steps for the sweet spot. Pipe is no more than 1 jet size. In fact I run the same jets with or without pipe. 40/125.
See lean bikes make more power, but they run hotter and misbehave at steady throttle.
Too Rich uses up more fuel, runs poorer when accelerating, but runs cooler, starts and settles down better and overall behaves well.
I take it to that too rich spot and back down 1 step. Its only a hair rich.
Cool.
Buddha.
The main will affect ALL throttle positions. It must be selected first and be within 1-2 sizes to be able to set everything else properly.
Yea that's what Factory says ... implying that you can be off a good bit on pilots and tune yourself to the right pilot. While it is correct in the narrowest sense as in (you never change the pilot) try getting your bike jetted with 35 pilots instead of 37.5's.
Or try tuning yourself into float height starting with floats 3-4 mm high.
1-2 sizes of right on mains is going to do squat for the low end. yea it will let you get the needle right which is 90% of the running on it. OK I'll grant them that.
You need to know their assumptions first. Which is, right pilots, right float height and 1-2 sizes off on mains.
Cool.
Buddha.
Thanks guys for all the great info. I think I've decided to put the 140's back in and test out one thing at a time until I find what works best.
In anticipation for the 'one thing' I'm going to test this weekend, I went out this morning and raise the DJ needles 1 slot. When doing this, I noticed two things that I didn't see before. One thing is probably from the previous owner and the other may have just fallen off or something.
Are these white caps supposed to be here? What are the things that they are attached to? Do they need to be removed? If so, do they need to be routed away from the hot engine?
(http://i190.photobucket.com/albums/z307/quiktaco/bottomcaps.jpg)
Here, it looks as though I'm missing one of the caps that go ontop of the carbs. These caps look like they block a passage that goes through that small 'O' ring on top of the carbs. Do these both need to be capped? Do they both need to be removed? What does that passage way do?
(http://i190.photobucket.com/albums/z307/quiktaco/topcaps.jpg)
Thanks
The white caps, I believe are on CA bikes that go to the carbon canister for emissions. Need to be capped without the canister.
The black covers need to have the caps. They are the ports to attach the vacuum gauge to sync the carbs.
Ok, thanks. So what would happen if I ride around with the one top cap missing like it is? Is it going to hinder tuning the carbs? Wouldn't that cause a vacuum leak and make it leaner of a mixture on that one carb?
The carb missing the cap will run lean and like crap.
Ok, I'll cap it and go from there.
So I got to work early today on the bike. I capped the top vents. Don't feel much of a change, but I'll know it's fixed at least. I also raised the DJ needle to the #3 slot (from the top).
I took it out with the 147.5 at 2.5 turns out and the needle on slot #3. Chopped the plugs (the correct way this time) at half throttle and at full throttle. Half throttle was slightly lean, full throttle was way too rich.
I then worked with the mixture screws, and followed the procedure on the poor man's rejetting tutorial, and that put them out to 4.25 turns out. Throttle response is quick now and I don't have the hanging idle anymore. I put the #140 mains back in and went out to chop the plugs some more.
This time with #140 mains, 4.25 turns out, and the DJ needle on the third slot. Half throttle chop was a nice tan color on the plugs. Full throttle looked slightly white to a light tan color. I might be a little lean on it still, but it seems to work.
And now to the problem...
WOT is still causing a bad flat spot. It doesn't seem to do it as much when I go up to WOT gradually. Mostly went I snap it open. Does that mean that the slid is coming up too fast? How do I fix that? There's a small hole in the flat part of each slide, but it doesn't look like it was ever drilled bigger; looks stock. The flat spot is just about as bad as it was with the 147.5's. However, everything else is tons better...especially between 1.5k-3k is a lot smoother. Slow speed manuevering is fairly easy now.
Anyone know why I still have this flat spot?
Anyone?
OK you went from 147.5 and 2.5 turns to 140 and 4.25 turns and your 1/2 throttle went from a shade lean to normal. If you are certain of that I'd not disagree here, slightly lean to normal can be mix screw 1.75 turns. OK I'll agree there.
OK 147.5 was rich up high and 140 was a shade lean. I am guessing you should got 142.5 and maybe 3.75 turns on mix screws. It should be right at full throttle. Lean = heat = lower life etc etc etc. However very very rich is just as bad.
Here is the next dead giveaway though ...
Throttle opened fast = dead spot ... or I call it falls on its face, slow opening = :) ... slow opening = good.
Yes slides comming up too fast. Stock slides have 2 holes on the bottom not including the one the needle goes through. You have just 1 ... and other hole has a white plug ? OK you may have to put a plug with hole in this one and keep it from comming up too fast.
Cool.
Buddha.
You said "OK you went from 147.5 and 2.5 turns to 140 and 4.25 turns and your 1/2 throttle went from a shade lean to normal."
(I also lifted the needle from the 2nd slot to the 3rd slot, so I think that had the most to do with this range being fixed)
Yeah, there's a white plug in the other one. Didn't know that wasn't stock. So what You're saying is I need to completely plug the other hole? Or make the hole smaller, so it lifts slower?
I'm going to chop the plugs again at full throttle, cause I've gotten mixed readings the 4 times I've done it. I think I need to pull them and clean them off, then do it, cause it might be contamination from other times that's making it dark/light/whatever.
Other than the flat spot at full throttle, the bike is running better than ever. I've never had this smooth of a low rpm range. It's a breeze to go slow speed now instead of having to constantly feather the throttle and brake.
Thanks for all the info, it's really helped get this bike running great.
There is a plug with a hole that comes with the DJ kit. That is the plug you need to install. You plug the hole completely and the slide will never lift and it never would rev up.
And no one run to anothet contamination at WOT is impossible. It doesn't even stay on it through 3 econds worth of running.3-5 combustion cycles are all it takes at lower rpm, higher rpm may be 10 cycles. No more.
Cool.
Buddha.
Ok, thanks. I'll see what I can do with the slides.
Could you not learn to open throttle slower ??? I did.
Anyway you are setting a template for anyone running a DJ kit. Add it to the FAQ or wiki when you clean up the things power delivery.
BTW the thinner needle is playing havoc with your sudden WOT as well, most bike with stock needles dont feel like the slide's comming up too fast. The serious stepped taper in the DJ needle is the reason yours is doing that. The gradual taper of the stock needle does not suddenly change the jetting to super rich ... like at 3/4 throttle its good, at 49/64 th throttle is super rich cos the needle has suddenly dropped in diameter to 1/2 its original cross section.
Cool.
Buddha.
Lol. I usually do, that's why it's not too big of deal right now, but for the times when I do crack it open, I'd like it to be dialed in.
Yeah, I'll definitely add it to the FAQ and Wiki. I think that's partly why I haven't given in and just gotten the stock needles, cause it feels like it's so close, and this could help a ton of people out there that have initially messed up getting the DJ kit.
I think you're right about the 3/4 and up throttle position with the needle. The taper is so drastic and sudden, that when I open it up beyond that taper (if it's below about 5-6k rpm's) then it just drowns it with fuel that the engine doesn't want yet. It feels like if I open about 3/4 throttle, then wait for it to raise to about 6k, then snap it open the rest of the way, it's perfect.