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79 CB750 - Starting issues, carburettor?

After messing around I settled on 75 pilots
and 110 mains on my “79.

Stock airbox with 8 - 3/8 inch holes drilled in the bottom of the box for increased air flow.

A clear plastic in line fuel filter right before the carbs, the kind you see on lawn mowers, well worth the 8 bucks.

Loose chain givin good advice.
Good luck my friend.
 
Last edited:
Loose Chain said:
This thing you are calling a fuel syringe, is it applying pressure in the line? If so that will force the valves off the seats in the carbs and flood them. Go to a junk yard and get yourself a fuel tank off a lawn mower, and then hang it with a piece of wire from the handlebars and let gravity do its thing. Also you mentioned earlier that you put larger jets in for some reason, so put the stock ones back in. This will eliminate some of the things that could be causing your problem. Get a fresh set of plugs also. You are probably going to have to change the oil at some point too because you will have fuel in the oil after all this flooding.
Click to expand...
Nah it’s fully open, it’s got 100ml capacity

I’m not pushing any fuel into the carbs, it’s gravity fed
You can even see it in the video
 
Chudman1 glad you're back, i'm sorry i can't stop laughing but i bet you're ready for a break down. it starts and ticks over on full throttle ,? what's going on there then , are you sure they are opening up fully if so it should be hitting 1 zillion revs
 
kirky said:
Chudman1 glad you're back, i'm sorry i can't stop laughing but i bet you're ready for a break down. it starts and ticks over on full throttle ,? what's going on there then , are you sure they are opening up fully if so it should be hitting 1 zillion revs
Click to expand...
Throttle definitely works
It’s getting too much fuel so it’s completely bogged
 
Leaking valve/valve seat AND a clogged overflow tube. If that's not the problem then you have a hole in your float AND a clogged overflow tube. But then it could be................you have a leaky valve/valve seat AND a clogged overflow tube AND a hole in your float.
 
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Chudman1, you said only the plugs in cylinders 1 and 3 were black. Is there fuel in carb boots 2 and 4? When you're changing the jets, you'd might as well set the float height on all 4 and pay special attention to 1 and 3.
 
mrtwowheel said:
Leaking valve/valve seat AND a clogged overflow tube. If that's not the problem then you have a hole in your float AND a clogged overflow tube. But then it could be................you have a leaky valve/valve seat AND a clogged overflow tube AND a hole in your float.
Click to expand...
The floats are fine and the over flows definitely work
 
They're plastic, then?
If so, I would suggest changing the jets and doing a valve job before anything else.
 
Chudman1 said:
Okay
I went down the the bike shop to look for a part and had a chat with the mechanic, he said if the butterflies are closed and it’s reving up there’s a leak at the manifold boots
Click to expand...
That topic has come up before. Did you change out those clamps? Did you look for any cracks in the rubber? Are all 4 carbs closing properly?
 
Chudman1 said:
I hadn’t run into this issue until now
Click to expand...
Not this particular issue but the topic of vacuum leaks and wrong clamps causing vacuum leaks have come up and that will cause the problem you are having. Brett mentioned the method for checking for vacuum leaks.
 

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