Topic: Help, fuel shooting out of the intake of the Carburetors

[Jcold98]

Hello.
I have a 1972 cb750 I’m getting started. When I attempt to start the bike I’m getting occasional shots of fuel back through the intake side of the carbs. My motor was idling pretty decent before I took it about and put it back together so I’m hoping it’s a small mistake. I had the carbs rebuilt but didn’t touch anything on the motor.

[ekpent]

 Is the engine running now or can you not get it started ? Fuel line hooked up to the correct nipples ?. Floats set correctly and not sticking down ? Fuel vents and lines all clear ?

[Jcold98]

I’m having trouble getting the engine started, the floats are set and the petcock running to the to fuel fuel nipples are correct. As I attempt to start it, I get a most of fuel out shooting out the intake aide of the carbs as well as an occasional backfire that sounds like a gunshot haha

[Bodi]

Ignition coils reversed can cause some pretty severe backfiring through the carbs but usually only flame and smoke blows out: raw fuel without an ignition isn't usual.
Possibly cam timing is out so the engine is blowing out the intakes rather than the exhaust, or tappets are adjusted incorrectly (way too tight).
This is an interference engine so if the cam is out of time you may have damaged valves and/or pistons.

[PeWe]

Did you take the ignition advancer apart?
If yes, shift blue and yellow wire connection from point plate to main harness behind oil tank and see if it will work better.

[Jcold98]

I’m running the DYNA S electronic ignition.


I had the engine idling a couple months ago and after a couple weeks it would no longer start. The starter would engage but the engine would no longer start. But when it did start the idle was VERY rough and it had to idle very high, maybe 1/4 throttle almost.

[PeWe]

Ok, if it can idle the rotor must sit right.
The barely seen dot at left when 1:4 is up if I remember correctly.