not running right once warm

[mikeybikey82]

hey guys, i have been riding my bike to work for the last week, its about a 8 mile trip each way, no speed limit over 40 mph. when i start out, either in the morning or the afternoon, the bike runs like a dream! its awesome! then about halfway home it starts to get a little sputter at partial throttle, i wouldnt even say 1/4 throttle. doesnt matter what gear, or what rpm i am in, its really weird, and it goes away when i get on it or when i come to idle.
ive been through the carbs a dozen times, it has 135's and 42.5's for jets in both carbs. ive adjusted the mixture screws to 3 turns, inline fuel filter.....all that looks good but i must be missing something? any ideas? sorry for the essay...
Mike

 

[drewpy]

partial throttle usually is the transition stage between the pilot system and mains.

mine does it to some degree, check the height of the needle, try raising lowering it. If the engine is warm its an indicator the engine is running rich.

Check spark plugs to confirm.

 

[mikeybikey82]

well i could not find any way to adjust the needle height on my carbs. they didnt look anything like the pictures in the manual. they had a flat plate with 4 holes in it that used 2 screws to connect it to the base of the plunger. then one hole lined up with a hole that went into the air passage of the carb, the other was blocked off. the needle itself had a circlip on it, and a round piece of plastic that keyed into place in the plunger base, but i saw nothing that would allow me to adjust height. anybody know anything about this?
Mike

 

[drewpy]

no more grooves for the circlip?

 

[mikeybikey82]

nope, there was only the one groove that it went into.

 

[drewpy]

you can compensate by putting washer/s under the seat to raise the needle (richen the mix)

 

[Travis]

Yeah some needles aren't adjustable and don't have the different grooves so all you can do is shim them up with tiny washers like drewpy said, or get new needles.

I would check the air filters and replace the plugs first.

Did this problem just start happening this week? How did it run last week? Or last month? Did anything else change on the bike?

 

[OliverB]

You didn't post the year of your bike. Helps us all if you post such info in your sig.

Have you ever replaced the small "O" ring at the bottom of each idle mix adjustment screw?

 

[mikeybikey82]

sorry, its a 1981 speciall 2. this is the 2nd set of plugs ive put in it in the 4 months ive owned it. it has always done this, but gotten way better when i patched up the intake boots and made new gaskets for those. nothing has changed, it had pods on it when i got it and i replaced those so the air filters are brand new. i replaced the o-rings in the bottle of the float needle area, but i didnt know there was one in the idle mix screw area.
i did pull the plugs last night and am running lean on that side, i think. the plug was white and looked hot, while the other side was black and sooty, but not too sooty.
its just weird, at idle and the rest of the throttle it runs awesome. ill look for some washers to raise up the needle on that side and check the o-rings oliver suggested. thanks guys, you too drewp.
Mike

 

[OliverB]

The symptom you describe is the same I experienced after getting my '80 Special last year. On the top of each carb there is an air mix screw that has a very small "O" ring at it's bottom. Easy to miss because of it's small size and often gets stuck down in the hole. My o-rings were kinda squashed and hard. They are a cause of air leaks into system and did the exact same thing to my idle after warm as you describe. Replacing them worked miracles with my bike. I also replaced the choke rod seals at the same time and plan to replace the butterfly shaft seals this year. Sometimes the tips of the O.E. idle mix screws get broken off when someone cranks them down too hard. Mikesxs sells a kit of two screws and two o-rings for cheap. The new screws don't have quite as thin a needle and probably won't break as easily. Go with the 3-3.5 turns out to start then fine tune from there. I started with 3 turns out and tweaked it to somewhere between 3-3.5.

Hope this helps. Any way, if you have not replaced them, it is an easy, cheap update. Worked the same miracle on my son's '81 but he had to drill out the factory plugs on top of each idle mix screw.

 

[mikeybikey82]

ok awesome, i will take those out when i get home and check on those o-rings. i have an assortment of o-rings that im sure will have one that i can use for now and make sure thats the issue. im glad this forum is here or i would have no idea where to look for half my problems, haha. thanks oliver.
Mike

 

[crush1776]

Just as an FYI, make sure the o-rings you have are fuel resistant, regular plumbing type ones will break down pretty quick, exacerbating your problems.

Yeah, I said it: exacerbating....

Woops, old thread sorry. I was doing a search then brainpooted. Problem solved?

 

[jigm400]

just to give you a heads up i was having an issue like this when i first put my bike together. it ended up being an air leak that only made is self evident when the motor what "hot" and the bike would high idle and sputter. i took the carbs back off and sanded the engine serface where the carb boots go and used a little silicone on the boots when i put them back on. it all went away. plug issue and bike running funny.