not running good at low rpm

[Jayh1813]

So it has been been really nice in ct the past few days. So Friday i decided to take out the bike and make sure she is ready for a long season. Well i rebuilt the carbs over the winter. But once i took her out it had no power in the low end. Now i don't have a rpm gauge so im not sure the engine speed. If i had to guess i would say it started to pick up and run ok around 1500. But once i get off the gas the engine will start to run up with out any throttle. I have to let out the clutch a little to bring the rpm down.

I have pod filters and a short exhaust. I up-sized the pilot jets one size. They are the stock 71 carbs. My needle jet is right in the middle. I know no one can trouble shoot carbs via the internet but any guidance would be appreciated. Especially with the engine running up in rpms

 

[peanut]

what happened to the problem of only running on one cylinder last October ? you never replied
http://www.xs650.com/forum/showthread.php?t=22886

Did you fix that issue ? what was the problem ? is this current issue related to that do you think ?

 

[Jayh1813]

The previous one cylinder issue was carb related. The person I had rebuild the carbs screwed up. So I rebuilt them again myself. im going to play around with different needle jet positions and air/fuel mixtures and see if that will do it. But the engine running up in rpm has me completely stumped.

 

[sonicarb13]

Have you checked the carb boots between the carb and engine? If they are cracked and leaking air it could cause that. Spray carb cleaner around them with the engine running and see if the rpm's change. Also, did you ballance your carbs when you last put them on?

 

[peanut]

I am not familiar with these carbs yet and its a long time since I messed about with twin carbs on cars or bikes but first thing I would check is the buttterfly return springs on both carbs.

Do the carbs have seperate double throttle cables? or a single cable with butterflys linked as on the later carbs ? maybe make sure that the cable/s are not being pulled or pressed anywhere along their length.

How about the needles have you checked that they are fixed securely ?

last thing I can think of is the slides themselves gradually rising . Did you check the diaphrams carefully for splits and holes and are they seated properly .

I wouldn't mess about with the jets until you have this rising rpm licked or you'll never get the carbs synched and the mixture right

 

[Jayh1813]

Thanks peanut. It has 2 cables. They run nice and smooth. I know for a fact that one diaphragm had a split in it. The P.O. had a piece of scotch tape over it.... When I saw this I took the tape off and painted one liquid electrical tape. Its definitely holding strong. Its a little more stiff than the actual diaphragm but I think it's ok. I will check the boots today and go over the cables again today too just to make sure no snags. Thanks guys

 

[XSLeo]

A sticky advancer rod can cause the idle speed issues you are having. When you pull the weights out by hand and release them, do they snap closed? If not you need to pull the rod, clean out the cam and clean and polish the rod. Fresh lube in the bushings and seals in the cam. In the cam there is what they call a labyrinth seal, A steel bushing with grooves in it. Clean out the old grease in the grooves, replace with fresh grease. A moly grease is recommended.
Air leaks on the carb holders or throttle shaft seals are common causes too.
Does your engine have the crossover tube between the cylinders under the carbs? If so your air leak may be there.
Leo

 

[Jayh1813]

Thank Leo! You gave me enough stuff to check to keep me busy for a week! I'll keep you updated. I have a day off tomorrow and its going to be really nice so ill get into it.

 

[Brian G]

quote >>Spray carb cleaner around them with the engine running and see if the rpm's change.

I'd be very careful spraying carburetor cleaner around a running engine. Most of them contain acetone, toluene, methanol and possibly propane and/or diacetone alcohol - Whoooosh!

WD40 should do the same thing and is a bit less volatile.

Regards,

 

[peanut]

i read somewhere that carb cleaner can turn into mustard gas in ideal conditions . That'l mess up your day

 

[Jayh1813]

Got it running guys. I think the vacuum leak was where the carbs meet the motor. And as for the flat spot right off idle i raised the needle and adjusted the mixture screw out 1 3/4 turns. Now it runs 99%. There is one little spot in the high end but that's if I'm wide open.

Thanks guys for all your help. Much appreciated.