[RAKMY]

Hi,
I have a recently rebuilt engine (supposedly by a Suzuki specialist shop) that has a problem with vacuum on #1 cylinder. New crank, bore, pistons.
1977 Carry ST20v. Same engine as the LJ50 but with sidedraft carb (from what I have read).

What we have found so far:
- Compression is solid and consistent on all cylinders @ 150 PSI
- vacuum fuel pump connected to #1. Fuel pump works fine when cranking, but when engine starts and runs for a few minutes it then stops due to lack of fuel caused by fuel pump stopping due to loss of vacuum. As sson as it is cranked it pumpos again fine.
- plenty of spark. #1 plug is wet (with oil I think). Other plugs are dry and blackened.
- when it runs its quite smokey, espcecially just after firing up. I suspect this is realted to 2 stroke oil build up.

So it seems #1 is losing vacuum after the engine fires.

Before the motor is removed again, and stripped down, I am hoping someone may have some ideas on how to isolate what the issue is.

Any help would be greatly appreciated.
thanks

[Boggomobile]

Hi Mate,

Is the fuel tank breather blocked? You could check by bottle feeding directly into the fuel pump and removing the tank from the equation. In other words, is the pump working until the vacuum in the tank stops fuel supply?
Hope this helps?

[RAKMY]

Thanks for the tip. Will check that today as it may explain why it stops but still a mystery why #1 does not seem to fire at all. We can remove be the plug lead while it’s running and it makes no difference… like it never gets fuel.

[RAKMY]

Hi,
Well it turns out the issue was with the fuel pump. A split in the diaphragm allowed it to pump enough on cranking to fill the carby, but when it fired the flow would drop as fuel would be sucked directly into #1 crankcase. So a fuel pump kit and all came good. Found it when connecting a vac gauge up to see what was going on. We happended ot use a clear plastic tube so the flow of fuel was easily spotted.

Thanks for your help.