Major Flat Spot only at WOT

[werase643]

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

[The Buddha]

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.

[werase643]

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

[The Buddha]

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.

[quiktaco]

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?

[The Buddha]

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.

[quiktaco]

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?

[The Buddha]

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.

[dgyver]

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.

[The Buddha]

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.

[quiktaco]

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?


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?


Thanks

[dgyver]

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.

[quiktaco]

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?

[dgyver]

The carb missing the cap will run lean and like crap. 

[quiktaco]

Ok, I'll cap it and go from there.

[quiktaco]

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.

[quiktaco]

Anyone know why I still have this flat spot?

[quiktaco]

Anyone?

[The Buddha]

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.

[quiktaco]

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.