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Bucking problem

willie

willie

Forum Mentor
Past Site Supporter
I'm looking for some advice for solving a performance problem I'd describe as bucking when running at 1/8 throttle under low and no loads. This is on my bone stock 1100G. The following have been done or are correct: coil relay mod, valves set, carbs synched, o-rings replaced, inline fuel filter added, carbs rebuilt with floats sets to spec and every passageway completely clean. The bike starts and runs perfect except for this problem which is a real pita.
I can feel the same bucking when I'm coasting with no throttle at all. It almost feels like I'm riding over some bumps but the pavement is smooth.
I have tried shimming the needles and turned the pilot air screw in and out a total of 1 turn in either direction but have not noticed any affect on the bucking.
Any advice would be appreciated.
Willie
 
Are the engine RPM's "bucking" or is it possible that you are feeling a brake drag/hang up? :-k
 
Do you have a Carb colortune to look at the ignitions at idle to see if they are variable? Also have you measured the output from the coilds to see if this is some kind of weird early failure? Do you have the original petcock? Could that be giving you low level irregular gas flow with a small vacuum leak?

Just wondering
 
Youre lean in your pilot circuit, or the pilot needle transition...
 
TheCafeKid said:
Youre lean in your pilot circuit, or the pilot needle transition...
Click to expand...
Thats what I've been thinking but would've expected a turn of the air screw in either direction to make a difference. Do you suggest that I go OUT a couple of turns from stock? Also, is shimming the needle going to help? I'm leaning (pun intended) towards doing that again to see what happens.
Thanks
Willie
 
tlepac said:
Do you have a Carb colortune to look at the ignitions at idle to see if they are variable? Also have you measured the output from the coilds to see if this is some kind of weird early failure? Do you have the original petcock? Could that be giving you low level irregular gas flow with a small vacuum leak?
Click to expand...

I don't have a colortune and havent measured coil output. It does have the OEM petcock but I don't think its fuel starvation in that respect because each "buck" lasts less than a second. Like hitting a bump.
Thanks for the ideas.
Willie
 
Dave8338 said:
Are the engine RPM's "bucking" or is it possible that you are feeling a brake drag/hang up? :-k
Click to expand...
Interesting thought but I'm convinced its the engine and not the brakes. I rebuilt the calipers and replaced the pads and they're working great. The tach needle doesnt respond quickly enough to see the "buck".
Thanks
Willie
 
I would say it is as simple as lugging the engine, Or your chain is loose and the drive train is catching up to the slack repeatedly.
 
The tach needle doesnt respond quickly enough to see the "buck".
Click to expand...

Which makes me think that it is not carb related. IF it is...it will be the pilot circuit as mentioned.
 
i can only presume that you mean "surging" .... opposed to bucking which means nowt to me.. if that's the case then your pilot circuit is lean. is everything stock on yer ride ?
 
Where are your pilot screws set at now?? generally, ive found them pretty much all over the board in stock set ups... they did whatever they needed to do to get the bike to run well, and cover EPA standards.. You need to set them using the highest idle method, but i would guess a good starting point is around 2-2.5 turns out..
 
Clone said:
I would say it is as simple as lugging the engine, Or your chain is loose and the drive train is catching up to the slack repeatedly.
Click to expand...

It happens when coasting too so its not a matter of lugging the engine. In fact, it runs smoothly under load even if I am lugging it. Its a G model so I'm confident its not a loose chain.
Thanks though.
Willie
 
Down here by the beach 19801000G with California carbs I need 2.5 turns approx. That's 40 pilots & 180 air jets.

Interestingly - I switched to a Canadian setup with 42 pilots & 160 air jets & needed about the same...

Dan :)
 
Hey TCK, I started with the screws out 1 3/4 turns as thats where they were from the factory. I was the one who removed the plugs so of that I'm certain. I have them out 1 turn from there for a total of 2 3/4.
I just pulled one of the slides out to make sure everything was stock. It wasn't. I have a .020 shim under the needle. I apologize for not mentioning it. I'd forgotten that I put the extra shim in each carb when I was messing with the carbs before the WV rally.
If memory serves me right, for once, it was common to place the nylon spacer under the clip too, as opposed to it being above the clip like it is from the factory. I'd appreciate your thoughts on doing that too please.
Where to from here? Back the screws out another 1/2 and/or mess with the shims?
Thanks again and keep those comments coming folks. ;)
Willie
 
Put the spacers back how they were from the factory if you are shimming the needles with washers. Try that, get back to us..
 
I second checking the chain tesion. Too tight will also cause problems.
 
Having a shim UNDER the needle wont do squat. Shims ABOVE the needle will make it leaner. To richen, remove the plastic spacer and use shims of less height of the spacer.
 
TheCafeKid said:
Put the spacers back how they were from the factory if you are shimming the needles with washers. Try that, get back to us..
Click to expand...

The nylon spacers are and have been where they were from the factory (ie. above the clip). My comment/request was for your opinion on the idea of moving the spacer under the clip. So....now that I have the tank off and one diaphragm cap off, I'm going to put the extra shim under the clip as it was, back the screws out another 1/2 turn each and go for a ride before the sun sets. I'll report back this evening.

Now to address Mr Gearhead's comments re: shims and spacers above the "needle" will richen the mixture. Ah, forgive me for sounding dumb and all but, it was my understanding that its shims and spacers placed under the needle clip that affect the mixture by effectively raising the needle. Am I mistaken about this?
Thanks again, one and all,
Willie
 
willie said:
Now to address Mr Gearhead's comments re: shims and spacers above the "needle" will richen the mixture. Ah, forgive me for sounding dumb and all but, it was my understanding that its shims and spacers placed under the needle clip that affect the mixture by effectively raising the needle. Am I mistaken about this?
Thanks again, one and all,
Willie
Click to expand...
The spring under the clip forces the needle up against the plastic retainer, by adding a washer/shim under you are just increasing the springs pressure pushing up on the needle. Think about it.
 
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