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Discussion Starter #1
Heya,

Currently working in a cb 750 on a go-kart frame. I want to get a service manual for it but I don't know what model\year it is. The 2 inside cylinders aren't firing, carbs are clean and plugs are powered\clean too, also carb 1 is pissing fuel out the overflow while idle. Would appreciate some advice, am doing it myself as a project so workshop is a no go.

Can't post pics or links without 15 posts, maybe I can email/Skype whatever them.

Cheers
 

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ZAMM Fanatic
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2,730 Posts
Spray some starter fluid (ether) into the boots for cylinders 2 and 3. If they start firing, you've got a carb problem.

If they don't, check for spark on those two cylinders. If you've got spark but still no firing...

Check compression.
 

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Discussion Starter #3
Definitely got a spark on them, will try the starter fluid. I've yet to build a air filter, I am assuming that may be causing some strife, have been testing in a relatively clean environment.
 

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Discussion Starter #5
Nope, the order is correct. I've got a friend coming over this weekend with some compression testing gear. This thing is stumping me. I may have to take the block apart and check the pistons next...

Cheers.
 

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Ace Tuner
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2,910 Posts
The #1 carb dumping fuel from the overflow indicates a float or float valve problem. (Valve stuck open)?
The #2 & 3 cylinders not running but having Ign fire could also indicate a float valve problem.
The float valve could be stuck closed not allowing fuel into the carburetors. Try draining the carbs to find out if they are dry.
I'm guessing varnished up float valves along with other internal carb parts and passages,

I recommend giving the carburetors a clean bill of health before you disassemble the engine.
 

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ZAMM Fanatic
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You can check for compression with your thumb.

I would never disassemble an engine for failure to start unless I had total lack of compression (valves not movign or stuck) on one or more cylinders.

If I did have zero compression on one cylinder, I MIGHT squirt a little oil in it as sometimes excess fuel can wash the cylinders so well that the rings don't seal.

Rule out everything else first. Fuel, air, compression, well-timed spark. Which one are you missing.
 
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