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

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.