Apologies for the off topic post, but I couldn't find any motorcycle forums.

I have a 1973 Honda CB350 with twin carbs. Had to do a top end rebuild last year to replace piston rings, and ever since then I can't get the carbs adjusted quite right. I can get them close, but there always seems to be a little bit of discrepency between them.

I've adjusted the throttle cable and idle speed screws according to my manual, as well as the idle mixture screws, and that [mixture screws] is what I'm having trouble with. I'm experiencing symptoms of both too lean and too rich mixtures and I'm having difficulty deciphering if it's just one carb or both.

It's obviously an old bike with over 30k miles on it, so I don't expect to be able to set them exactly to spec, but I'm wondering which would be more acceptable- to have the mixture rich or lean. I don't think lean is the answer as that causes the most trouble, but I wanted other opinions on it.

Sorry if I'm not being clear- just got off work and I'm ready to go to bed- I'll check back later to see if you guys can offer me any advice and if necessary, clarify the issue.

Thanks in advance.

 

A little rich is better, that will prevent off idle stumble and make better power.

 

Not sure how you set them up, but you should set them up one carb at a time. This is how I do it:
1. Set the carb mixture and and idle screws to what manual suggests for ballpark settings to get you started.
2. Make sure throttle cables are set correctly to open and close both carbs equally.
3. Pull the spark plug wire off the plug on the opposite side cylinder of carb you are going to tune and attach a spare plug to it and rest it against the motor. (It's hard on the electrical system to leave the empty plug wire firing and not grounding while running the engine.)
4. Now, start bike using only this carb and cylinder(you'll need to keep your hand on the throttle at first until you can raise the idle screw to maintain idle by itself). Now adjust the mixture screw counter-clockwise and as it starts to stumble, turn clockwise to richen it and back-off slightly from where it begins to stumble again. Lower idle again, and re-set the mixture again to attain smooth running, but always stopping before stumble at the richer-end setting. Repeat this process until the bike idles low, smooth and on it's own.
5. Now, replace the plug wire on the opposite cylinder and remove the plug wire from the engine side of the carb you just tuned.
6. Repeat tuning process on the opposite side carb as used in step 3, remembering to unplug the spark plug wire of the just tuned side so you are not using that cylinder's spark.
7. Turn bike off and re-attach both plug wires. Start bike back up again and it will idle really fast as it's now running on both cylinders, so at this point, you need to back off the idle a 1/4 turn at a time on each carb equally until you obtain the desired idle.
Ride it around a little and make sure it runs good and check the plugs for colour. tan/brown to slightly dark is best. Yes, better a little rich then lean

Hope that helps.

 

I will give your tuning method a try 94shorty- I didn't think about pulling the plug wire on one side. My manual says to tune the left carb first which I have been doing. I'm sure the throttle cables are set correctly so it's just a matter of getting the mixture set just right. If it doesn't work then I will do as Conanski said and keep them set rich enough to keep it running smooth.

Thanks for the advice guys.

 

Well the rain hasn't really let up enough yet for me to make any adjustments, but while I'm waiting, 94shorty I was wondering if a screwdriver would work just as well as a spark plug? Only wondering because I don't have any spare plugs I can use, so it's either a screwdriver or pull the plug and let gas spray all over while I'm making the adjustments.

 

No, don't remove the spark plug from the opposite cylinder. You can still run it without grounding the plug wire, nothing should happen, but it is hard on the ignition system. Just don't do it all the time.

 

Okay thanks.

...

[A moment later.] Actually what I could probably do is cut off the fuel supply to the carb I'm not tuning- that way the wire is still grounded but the cylinder isn't firing.