Topic: can't get to idle right

[schneider419]

i have a 1972 350f that idles at 3,000 rpm in neutral. if i am riding, and leave it in gear and brake to 2,500 rpm or so and then pull in the clutch, it idles down to about 1,000 rpm. it takes off kind of lazy. once i am off of idle it runs good. i have rebuilt the carbs, blew out the passages, and balanced the carbs at 3 lbs vac. each. i think that the float levels are ok. i even have an old set of idle jets and opened them up just a tick, thinking it is lean, but it acts the same and now back fires once in awhile after it warms up. when i try to adj. the idle it either goes to 3,000 or falls off under 1,000 and dies. whats up?   

[TwoTired]

Air leak between carb and cylinder?

[MRieck]

Air leak between carb and cylinder?

I agree. Synch the carbs too once you cure the vacuum leaks.

[74cb750]

Ahh, just went thrgough this and the problem was cracks in the carborator bowl gaskets. Small, but irritating. Check to see if they are in properly. michel

[schneider419]

thank you all for your fast response. i'll try to do your ideas in the next few days ,and let you all know what happens.

[gaijin]

I'm just tackling this same problem on my 400f. I tried synching the carbs Friday but while it idles more smoothly it still likes to idle at 3/3.5k and then drop back down to 1k eventually. I checked for leaks from the airbox to the carbs and from the carbs to the cylinders and didn't find anything, so next step will be to rebuild with carb kits... Definitely post how your repairs go!

[Bob Wessner]

Any chance any of these are because of sticky throttle (grip, cable, carb linkage)? Maybe vibration eventually lets things settle down.

[egar]

I also am having the same problem. The idle varies at times and is sluggish in moving the bike along when I'm going through the gears. I throttle up from gear to gear and its as if the engine is trying to catch up. The rubbers sleeves between my carbs and the engine are probably original and have some fine surface cracks in them. Can't that really make that much difference? If so, is there a good source besides EBay?

[schneider419]

no, i checked the throttle slides with the air box off, and they are smooth from closed to w.o.t. i'll try to keep y'all informed

[gaijin]

Thought I'd let you guys know how my repairs went. I rebuilt my carbs yesterday (a busy day  ) and finished putting the bike in order today, resynched carbs as well. Replaced worn needle jets, gaskets, the works. The gaskets were in real cruddy shape, perhaps they were leaking? I'll never know now. Reset the idle screws to 2 turns out, set the throttle stop screw so it idles correctly. Now my bike runs better than it ever has since I've owned it, pulls like a champ. Idles great now too.

The previous owner had trouble getting it to idle, so instead of rebuilding the carbs he turned up the throttle stop screw so it idled at 1200 *cold*, which meant it idled at 3000 when it was warmed up . Now that it idles beautifully I've turned it back down to what it should be, 1200 when warmed up, and it runs much better.
GL to you guys, hope you get those issues solved! Now for that cam chain rattle...

[written_black]

I've go the same problem on mine, before and after a rebuild. I got them sync'd up, but it idles up. I'm going to investigate my boots and see if thats where the problem is. Is also possible for the intake to be leaking air off of the engine if the gasket went bad?

[wing01blue]

Hello everyone I`m new to this board  although I`ve owned my 2 bikes a 72cb500/4 and a 76 cb750 for a few years. Just my 2 cents but if you checked for vacum leaks and synched and adjusted the carbs and everthing checks out then check your advance mechanism to be sure its operating smoothly or the springs arent worn out and are not allowing the weights to return. Good luck

[schneider419]

hey i know it's been awhile but here is what i found so far. i went and checked the timing , and found the point gap on no. 2 & 3 cylinder to be at .004' open and the gap on 1 & 2 was .006'. i guess i didn't tighten the screws enough. also i retarded the timing just a fuzz, like i set the timing at the edge of the mark instead of at the middle. also i closed down the open gap on the points to .010' for more time for the condenser to charge. it seemed to help alot.

[heffay]

harry~
this thread is faq material in the making...
yes friends, i too have the same problem with idle
my solution:  stay out of the city!
no but really, all the helpers on this thread have it pegged... vacuum leaks and a good carb synch will solve all... why haven't i done this?     ummmmm, school, work, i like to ride it rather than fix it, BEER!