air/fuel mixture.
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Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
air/fuel mixture.
Shimmed the stock needles 1 washer front and back, reinstalled, synched the carbs and now have throttle stumble/hesitation when i crack the throttle. Pulled the choke out a bit and it helped the problem. My question is am i understanding this correctly. Pulling the choke richens the mixture therefore i am running too lean. I didnt adjust the mixture screw when i had it apart
so i need to somehow turn the screws out to richen the mix right? Any one have an idea how to turn those without taking anything apart?
so i need to somehow turn the screws out to richen the mix right? Any one have an idea how to turn those without taking anything apart?
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World Champion
Joined: Dec 2004
Posts: 105,287
From: Fulton, MO
So the stumble wasn't there before you shimmed the needles? If that's true then there is another problem. Needle height will not affect off idle response. Something you did when you put things back together is causing this. You have the petcock vacuum line hooked to the back nipple, not the bottom nipple, right? Everything's tight? Hose clamps, crankcase vent hoses, airbox to carb screws, v-stacks in correctly?
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Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
Vacuum line is in the right spot. hoses and clamps tight as well as airbox screws etc.. It stumbled slightly before with debaffled pipes as in i would blip the throttle and get hesitation not immediate revving of the motor. So you dont think its the air/fuel mixture setting? Even with the problem subsiding with the choke out?
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MotoGP
Joined: Aug 2006
Posts: 2,934
From: altoona, pa
it's easy to miss something like the front carb not being seated correctly, etc. If you use a ratchet strap to hold the tank up from the front, it's so much easier. get back in there and take the air mixture screws out with a tweezer, needle nose or similar and slot them with a dremel cutting wheels so you can adjust with a flat screwdriver. Screw all the way in and back off 2.25 turns out. Adjust TPS to 490-500. spray all rubber with silicone to help seat carbs easier and all the other hoses. Take your time and double check everything with a good light during assembly. When you get the carbs synced well, it should be able to idle smoothly at 800 rpms, and 1000-1100rpms should be fine for riding.
Like Hawkrider said, something is probably askew, but you'll get it figured out.
Like Hawkrider said, something is probably askew, but you'll get it figured out.
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SuperBike
Joined: Jan 2008
Posts: 1,697
From: Beaverton, OR
I don't think it is mixture screws as that really only adjust idle.
So the hesitation you had to begin with did it get better with the washer adjustment, or did it not seem to make a difference?
So the hesitation you had to begin with did it get better with the washer adjustment, or did it not seem to make a difference?
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Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
It wasnt as bad before the washers. I developed a flat spot after putting on a set of devil high mounts so i did some looking on here and decided to shim the needles.
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Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
If i open the throttle slowly it is fine but its when i crack it fast (like you would when you down shift if you do that) thats when it "stumbles" and then it revs.
Thread Starter
Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
it's easy to miss something like the front carb not being seated correctly, etc. If you use a ratchet strap to hold the tank up from the front, it's so much easier. get back in there and take the air mixture screws out with a tweezer, needle nose or similar and slot them with a dremel cutting wheels so you can adjust with a flat screwdriver. Screw all the way in and back off 2.25 turns out. Adjust TPS to 490-500. spray all rubber with silicone to help seat carbs easier and all the other hoses. Take your time and double check everything with a good light during assembly. When you get the carbs synced well, it should be able to idle smoothly at 800 rpms, and 1000-1100rpms should be fine for riding.
Like Hawkrider said, something is probably askew, but you'll get it figured out.
Like Hawkrider said, something is probably askew, but you'll get it figured out.
. Thanks nath
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Squid
Squid
Joined: Sep 2009
Posts: 42
From: estonia,Tallinn
Only shims wount help,you must rejet the carbs.Starting at top end revs(main jets)then middle revs(needles)and then pilot jet and miksture screws.Use search "rejetting" and you find alot to read about rejetting.
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Back Marker
Joined: Feb 2010
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From: Western PA
Last edited by steve29; Jun 7, 2010 at 07:08 AM.
2nd mouse gets the cheese
SuperBike
Joined: Jan 2008
Posts: 1,697
From: Beaverton, OR
It may seems weird though but just because you added aftermarket pipes doesn't mean it automatically needs to be richened. On Springbubba's bike he had D an D pipes and it had a nasty stumble and miss. So we thought it had to be lean so we upped the mix on the needle and it got worse so we leaned the needle even more then stock and it went away.
I don't know if this is the same thing that you might have but the lesson is don't rule something out even though it seems unlikely. Oh and FWIW ever since the god damn ethanol jetting has seemed to be harder and the rules haven't seemed to apply as much. Maybe it is just me IDK.
I don't know if this is the same thing that you might have but the lesson is don't rule something out even though it seems unlikely. Oh and FWIW ever since the god damn ethanol jetting has seemed to be harder and the rules haven't seemed to apply as much. Maybe it is just me IDK.
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SuperSport
Joined: Feb 2010
Posts: 667
From: NY State
+1
+1
I have had both situations. I can tell you where I ended up with my Factory 1.1 install:
Front 182mj 50pj 3rd clip from top 1.5 turns out
Rear 185mj 50pj 3rd clip from top 1.5 turns out
Staintunes, BMC, TPS set to 500 ohms
I could fine tune this a bit more I am sure, but this works way better that what the PO had in there.
50pj seemed big to me, that is s the size that factorypro includes so I replaced the 45"S" pj with them. They work. I have some 48pj on order which I will try at some point.
+1
I have had both situations. I can tell you where I ended up with my Factory 1.1 install:
Front 182mj 50pj 3rd clip from top 1.5 turns out
Rear 185mj 50pj 3rd clip from top 1.5 turns out
Staintunes, BMC, TPS set to 500 ohms
I could fine tune this a bit more I am sure, but this works way better that what the PO had in there.
50pj seemed big to me, that is s the size that factorypro includes so I replaced the 45"S" pj with them. They work. I have some 48pj on order which I will try at some point.
Last edited by residentg; Jun 7, 2010 at 01:41 PM.
Thread Starter
Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
Hmmm. Plenty to choose from so i guess i will go back to the drawing board Thanks for all the help guys. cornandp, i wont rule anything out. Thanks for the tip. I'll be back with results.
Thanks for all the help guys. cornandp, i wont rule anything out. Thanks for the tip. I'll be back with results.
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World Champion
Joined: Dec 2004
Posts: 105,287
From: Fulton, MO
Start with mixture screws. See where you are now. If you're at 1.5 t/o then go to 2.0 t/o and sync the carbs. Then see what you're at. Since everything's tight and installed correctly AND choking it makes the stumble go away then this should make things better for you.
Thread Starter
Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
Start with mixture screws. See where you are now. If you're at 1.5 t/o then go to 2.0 t/o and sync the carbs. Then see what you're at. Since everything's tight and installed correctly AND choking it makes the stumble go away then this should make things better for you.
. Thanks man.
Thread Starter
Senior Member
Superstock
Joined: Apr 2009
Posts: 395
From: Columbus, OH
Talk about reviving an old thread lol. Yes I got the bugs all worked out. It only took 5-6 times of putting everything back on and tearing it all back off. But she still runs like the day she came off the assembly line.
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Squid
Squid
Joined: Mar 2014
Posts: 47
Whether it helps or not, the way I tune a mixture screw, which usually affects up to 1/4 throttle is with an IR thermometer. My old bike, someone had used an O2 sensor to set it exactly right and measured the temps so the rest of us could easily set our air/fuel mixture right. For that bike, 500-550*F right at the first bend in the headers put the bike right at stoich. I would assume it would be similar for this bike. Between the 4 cylinders, there was as much as 3/4 turn difference between cylinders on the old bike with them all running stoich.
I know he figured out his issues (4 years ago), but still figured I'd post this info.
I know he figured out his issues (4 years ago), but still figured I'd post this info.
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