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I purchased a 1976 CB200 a few weeks ago as my first bike. I knew it didn't run, but I was excited to pick up a new hobby of working on bike engines. I got my license ten days ago - and haven't gotten to ride yet!

I've cleaned the carbs and replaced the jets and gaskets. At this point I think my problem is a vacuum leak in the intake manifold or a balancing issue with the carbs... but what do I know?


Thanks for taking the time to help me fix my bike :)
 

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#1.... You NEED to set the mixture screws to the factory settings, NOT FULLY CLOSED!!!

The correct setting for a CB is 1&1/4 turns out (plus or minus 1/8) from GENTLY bottomed... IF you TIGHTENED them in you have probably done permanent damage to the carb bodies and will likely need to replace them....

#2 ... The throttle stop screws (the projecting knurled ones) should be backed out until loose, and if you'll phone, we can proceed from there.....
 

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That’s where I started - I had to close them to get it to idle. I’ll move them back there and update. Thanks.
 

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That "Plus or Minus 1/8 turn" is the normal limit of allowable adjustment from the factory setting....
...I allow slightly more to compensate for ethanol in the fuel....
 

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It should be screaming, with the idle stop screws run all the way in, instead of just barely idling. If you close the choke partway, while it's running, what does it do?
 

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Ok here they are at factor settings - I found a PDF of the owners manual that said that factory is one full turn out from closed.
It comes on super strong and then chills out. Someone on reddit told me to spray the intake manifold with carb cleaner to see if there's a vacuum leak... the engine stops the second I do it but I don't know if that's coincidence.

Battery's dead now so I can't try much more until tomorrow. Video is here, thanks for you time :)

 

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I'm not quite sure how this form works yet - here's a video of factory settings (i posted it below too). The engine quits the second I sprayed the intake manifold so i'm thinking maybe I have a vacuum leak and they need to be replaced? Owner's manual said 1 full turn, but i've found 1.25 online. similar results which makes me think it's a leak.

thanks for viewing.

 

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The video shakes so much you can't see much, did you push the choke lever back down after it started?
 

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I did.
I'm thinking a vacuum leak in the manifold is likely... which is why it ran OK with the air adjustment screws all the way it - it was getting air from somewhere else. But I don't know much about these things.
I recharged the battery so I can do a bit more trial and error today. I'll post some results.
 

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an easy test is to spray some sort of flammable agent like carb cleaner at the intake manifolds. If the engine changes idle (up or down), thats a clear indication of an air leak. I know that much.
 

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an easy test is to spray some sort of flammable agent like carb cleaner at the intake manifolds. If the engine changes idle (up or down), thats a clear indication of an air leak. I know that much.
I actually sprayed carb cleaner on the manifolds at the end of that video - right when the engine died. It could have been a coincidence... but my battery also died so I couldn't keep testing. I'll give it a few more goes today.
 

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Have you tried new spark plugs in it? Kinda sounds like it's only running on one cylinder.
 

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Discussion Starter #13
I think that’s the next step:
Oil change
Float adjustment
Spark plugs

I sprayed some carb cleaner to check for vacuum leaks - nothing
 

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Here’s an update - it runs but it’s all over the place.
I’m gonna try try to change the oil and replace spark plugs today

https://youtu.be/D8arf8IV6hs
 

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I think Mike is right about the idle screws being in all the way, it seems you're using the choke to keep it from running away to 5000 or higher. the choke is closed in the upward position, once running the choke should be all the way down. Nice jello, BTW, almost looks like the video was done from a drone :lol:
 
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