[richa610]

This has probably been asked before, but I haven't found it using search.. so..

Just got my 350 up and running - excited about that. However, I have two issues that may be linked.
1. Bike will not start or run without the throttle manually held a little open. I assumed that at 'idle' the throttle is supposed to be completely closed (meaning that the throttle body in the carb is completely closed). Manuals had no info on this at all, so I don't know if I'm wrong or right. I tried getting it warm and adjusting the idle screws on the carbs, but that really doesn't do anything (perhaps they're gummed up), but I wouldn't really expect it to since the throttle has to be open for the bike to "idle" rendering the adjustment screws pointless (right?).
2. Since I can't close the throttle and have the bike stay running, I can't get the RPMs down very fast. I open the throttle, RPM's get to 4-6K, close throttle, RPMS then SLOWLY go back down to about 1.2K. This is a problem when riding and shifting (especially shifting). Again, I think this is due to not being able to close the throttle all the way.

Upon inspecting the carbs very very closely, I see three pinholes that may be the problem (these are located on the 'engine' side of the carb). One I think is the idle mixture 'vent' where air and fuel goes through to the cylinder when at idle (this being the front most hole). The next two are covered when the throttle is completely closed, but I assume these two are more of the same kind of thing. Are these likely to be the problem?? I've had so much trouble with these carbs and so little trouble with everything else that I kind of regret not spending the big bucks to get them ultra sonically cleaned - so any 'cheap' fixes would be really really helpful.

[I've cleaned and replaced jets (with correct sized jets), cleaned carbs, replaced needles (again, with the correct size, double checked), and replaced idle screws (double checked too)]

 

[richa610]

May have answered my own question-

I got the Dunstall type pipes, but forgot to put in extra baffles, I was so excited that it ran. No back pressure=pretty bad running bike. Probably causes the idling problems too.

Throttle cable was the one cable I didn't replace, but It probably needs it because it isn't as responsive as I think it should be- Throttle sticks open and doesn't snap back closed (though in the afore mentioned problems, I had closed the hand throttle and the carb throttle bodies were closed as well) as fast as I want it to. I'm going to order some baffles and see how they work.

 

[richa610]

This is starting to bother me. I've re packed the mufflers- I think I've accomplished a stock like exhaust system when it comes to sound and backpressure. Cleaned and checked all parts of the carbs again. I've also checked timing (its almost perfect), tappet clearance, points gap and I've made sure the carbs are synched. The weird part is that the engine responds fine when its colder, right after its started. When I take it out for a ride, after about 10 minutes of running it starts to act up - I'll be driving along, and stop, start, shift from first to second and while I pull the clutch in and let off the gas the engine races so when I shift into second or third it lurches. Thing is, it doesn't happen every time, probably about 50 percent. I'm at a loss as to why this is still happening.

 

[HerrDeacon]

Strange one :shock: Have you checked for air leaks where the carbs meet the engine. A leak in one of these rubber holders could cause erratic idle and symptoms like you mentioned. Also, when checking the carbs have you checked the float heights? I had a similar issue recently with my KZ and found that one of the float needles was a bit worn (ridge around it) and was causing it to not totally shut off the fuel. Was causing similar behavior to what you're experiencing.

 

[richa610]

I'm going to start posting the rest of this stuff on my build thread... (1971 CB350 started by yours truly).