wierd fine tuning idle stuff

[joeybaggadonuts]

bike: 78 honda cb400t . stock airbox. different pipes, but still 2 into 2 annd same diameter.

my high rpm riding is wonderful. very responsive and good control. but low rpm and idling gives me sone trouble here n there. when i start the bike, it has a wierd idle. it only idles when the petcock is at off. but itll die after a bit and spew gas out overflown. and then give me trouble starting and getting it to idle nice again. no matter how much i mess with choke and petcock. once i get a nice idle. i hop on and itll run on one cyl with petcock cracked towards on. it dies in full on. then after 10 minutes. i start it again in petcoxk off and choke half. ill ride it, once i get up goin ill turn petcock to 5/6 on. and choke at 1/4 and it runs great both cylinders for a while. but itll die if i stop and let it idle for a bit. idle is set at about 1500 atm. im trying to to tune it down to 1200. but it gets bitchy when its too low.

dont want to bring it to a shop to fine tune yet, so any advice/diagnoses

 

[Titan performance]

Have you checked to see if your carbs are clean and the slow running jets clear?

 

[joeybaggadonuts]

a couple weeks ago i recleaned them because they were off. so im 95% sure they are clean. still, they are carbs, so miniscule dirt could block it. so im not counting dirtiness off the list yet. but i want to check other possibilities first

 

[Sonreir]

Check timing and compression first. Any problems in those areas can mask or stack upon carb problems.

 

[joeybaggadonuts]

i have a cdi, so i dont need to check timing correct? but compression ill get checked. although i know its got decent compression, ill check it with a gauge when i can.

 

[joeybaggadonuts]

and thanks i appreciate the replys guys

 

[Sonreir]

i have a cdi, so i dont need to check timing correct? but compression ill get checked. although i know its got decent compression, ill check it with a gauge when i can.

It depends on the setup. I'm not familiar with the 400 twins, but a lot of electronic ignitions still use a pickup located on the end of the cam which may require some rotation in order to dial in the timing. It's still worth checking, but you'll need a strobe light to verify it.

 

[joeybaggadonuts]

It depends on the setup. I'm not familiar with the 400 twins, but a lot of electronic ignitions still use a pickup located on the end of the cam which may require some rotation in order to dial in the timing. It's still worth checking, but you'll need a strobe light to verify it.

Thanks I'll look into it. that might be the last thing i check after compression and a carb reclean but its good to know other possible causes.

 

[NvgtrWiggles]

Double check your floats. Maybe there's something messed up about 'em.

 

[joeybaggadonuts]

Double check your floats. Maybe there's something messed up about 'em.

like maybe they're getting stuck?

 

[crazypj]

You don't have float height set correctly, it sounds too low

 

[joeybaggadonuts]

that would cause idle problems and overflow problems?

You don't have float height set correctly, it sounds too low

 

[crazypj]

:

 

[joeybaggadonuts]

lol... gotcha

 

[crazypj]

;D

 

[joeybaggadonuts]

Still haven't had time to pop the carbs off and take a look. also need to look up how to properly measure the height... but besides that, could the problem be that they weren't synced while on the bike? I benched synced them but never tuned them while on the bike. Have to get around to that. but could that be the problem?

 

[joeybaggadonuts]

raised float height. rode great! for a week.... now its back to where its started... ? leaking gas out of overflow again when i have it idling with petcock in on. for a week it idled perfect with petcock in on position and no gas overflow. but now its back. any guess on what the problem is? check for cracked floats? maybe? something else?

 

[Maritime]

sounds like floats went off again. check the float bowl gaskets, if they shift they can have the float catch and stick down. They can be picky. I had a float that was sticky for a few days and I just tapped the bowl and it would un stick and be fine for a while then f up again. I found it was shifting to the side a bit and I just bent the hing a slight bit to prevent the side to side play and been good for a few thousand km's. Yor gaskets are o rings I think?? and can get loose and pinch when putting the bowls back on. At least you can pull them and check with the carbs on the bike.

Cheers and good luck.

Maritime.

 

[joeybaggadonuts]

thanks maritime! tonight ill pull the bowl and check to see if the float slides. if it does ill make sure it cant go side to side and ill also make sure its not catching on the o ring.