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Discussion Starter #1
Ok, so I've meticulously restored this 72 Honda CB 350 and I can't get it to run right. I rebuilt the carbs as well as pretty much everything else, but when I start it, it revs way up without even touching the throttle. Before it started doing this, when you revved it up, it would be really slow to return to idle. It acts like a vacum leak but I can't find one. I balanced the carbs as best as I could. Any suggestions (short of throwing it off a cliff) would be greatly appreciated.
 

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is there a fuel leak at all? check the oil to see if there is any fuel smell in it...maybe a stuck needle or something like that.
 

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Discussion Starter #3
There's no fuel leaks that i can detect. I have had the carbs apart about 3 times and everything seems to be working as it should.
 

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i have NO idea about that bike... but i DO know that i had a similar problem on my 03 r1 when i installed the throttle slide stops... the bike would rev to about 8K bately twisting the throttle and it would take forever to return to idle, yea i retraced my steps and found out that the problem was from the rubber boots on the throttle body were LOOSE, causing air to come in and makin it rev like that... just check the boots, mine were rubber with a metal clamplike thing around em, and i had to get a ft and a half long allen head t handle to get to each clamp... yea thank god for pep boys!!!
 

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How are you checking for vacuum leaks? I usually use Gumout carb cleaner and spray the boots one at a time. If the motor revs or bogs then there is your leak. You can also take some water in a spray bottle or some spit on a finger and while its running spray or spit and wipe on the headers just off the head. It should sizzle away, if not that carb is your problem.

How did you sync the carbs also? If it is slow to idle down that is typical for the carbs to be out of sync. But could also be attributed to the vacuum leak.

Tread
 

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Discussion Starter #8 (Edited)
Tread70 said:
How are you checking for vacuum leaks? I usually use Gumout carb cleaner and spray the boots one at a time. If the motor revs or bogs then there is your leak. You can also take some water in a spray bottle or some spit on a finger and while its running spray or spit and wipe on the headers just off the head. It should sizzle away, if not that carb is your problem.

How did you sync the carbs also? If it is slow to idle down that is typical for the carbs to be out of sync. But could also be attributed to the vacuum leak.

Tread
I used a propane torch and blew propane over the boots. I am going to check them again. it seems that is the most likely culprit. There are what look like vacum hose nipples in the tops of the boots for some reason. I have them blocked off but perhaps they are still sucking air. The carb syncing procedure is pretty primative if you follow the manual, there really is only one adjustment on these carbs for the main air screw and syncing is done manually by adjusting the cables and stops.Thanks for the suggestions!
 

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Tread70 said:
How are you checking for vacuum leaks? I usually use Gumout carb cleaner and spray the boots one at a time. If the motor revs or bogs then there is your leak. You can also take some water in a spray bottle or some spit on a finger and while its running spray or spit and wipe on the headers just off the head. It should sizzle away, if not that carb is your problem.

How did you sync the carbs also? If it is slow to idle down that is typical for the carbs to be out of sync. But could also be attributed to the vacuum leak.

Tread
Don't throw it off the cliff just yet, those bikes are classics.

It sounds as if there is either a vacuum leak or your carb is fouled still. If you left fuel in the carbs for too long and didn't get it completely cleaned, it will have a hard time maintaining a constant RPM. If your carb is still gummed up it will act very much like a vacuum leak.

If you have ensured there are no vacuum leaks with your carbs or intakes, and it sounds as if you have, I would try and clean the jets/passages of those carbs again.

Let us know how it turns out. Good Luck!:thumbsup:
 

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here is how i fixed my sv with the same problem. does it have the rubber boots that go to the airbox from the carb? the screw that holds it down to the carb was tightened down to where it was touching the throttle control on the carb and pushing it open. stupid fix but worked for me. check the clamps that go down over the rubber boots to the carbs and see where the screw is set at. i moved mine to make it better access and found that i had tightened it down touching the carb throttle plates/control.
 

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there is a throttle cable junction under the tank, check it out, and throttle cable function thru out. There is also choke plate linkage between the two carbs. See if the slides are free to move up and down. Look for carb diaphram cracks. Intake boots. I had two of these, when they run good they are an absolute hoot to ride. When they give you trouble, they will make you lose your religion. good luck, if you fix it you have a real interesting classic, that is fun to ride.
 

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Discussion Starter #12
Update: I got new boots and went through the carbs again. I got it to start and idle well, balanced the carbs. The only thing it is doing now is when you twist the trottle more than 1/4 turn or so, it doesn't return to idle right away. If i close the choke it goes right back down. I know it's nothing external (cables linkages etc.) and the carb slides seem to be returning like they should. I'm thinking that maybe thats just the way these things run? I also have pod filters and 12" bullet mufflers on it and I didn't re-jet it. Thanks alot for your inputs. This is my GF's bike and she wants to ride it before the snow takes over in Siberacuse!
 

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Sounds like you still have either a vacuum leak, a clogged jet/vent, or the carbs need re-synced. If you synced them, I asume you used gauges. So that leads me to believe you have a vent clogged or jet. Do you have some pics of the carbs. I assume you have plugs on the ports for the sync's. If I remember right and mind you its been a while since I played with a 350. But I believe one should go to the petcock or they should all be plugged off or at least linked together.

Pics would help out but I guess you probably have a manual.

Tread
 
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