720 gti not starting (will run once going)

[smaguire93]

2000 Gti 720

rebuilt the carb and replaced grey fuel lines

now ski won’t start. If I put some fuel down the carbs it starts right up and runs until stopped. However try to start it again no joy.. fuel into carb and bang off she goes again.

anyone any suggestions on things to check/ trouble shooting?

 

[smaguire93]

One thing which may or may not be irrelevant. I replaced the pulse line with normal fuel line (same size as original hose) could this be causing less pulse when turning over from start. Then once running the increase pulse cause fuel to flow. Carb fuel check valves both pass the blow test. Could be a red herring just thinking out loud.

 

[mikidymac]

A soft pulse line could cause issues and unless they are physically damaged you don't need to replace the pulse lines.

Did you follow the carb rebuild sticky and only use genuine Mikuni parts?

 

[smaguire93]

Yeah followed the sticky and genuine parts. I’m abit stumped. Runs so well once started with a little fuel down the throat. Then just nothing on the next start up

 

[smaguire93]

Well today it started working however new problem now. It bogs down then backfires on acceleration. This is turning into torture

 

[mikidymac]

Something isn't correct with your carbs.
Also you really need to be running with the air cleaner box on.

 

[smaguire93]

I’d agree. Going to take them apart and rebuild again.
When I took the carb off there was no gasket below it. (My old 720 also didn’t have one). I decided to put a gasket just below the carb where it attaches to the rotary valve cover. Could this cause backfiring?

 

[mikidymac]

I’d agree. Going to take them apart and rebuild again.
When I took the carb off there was no gasket below it. (My old 720 also didn’t have one). I decided to put a gasket just below the carb where it attaches to the rotary valve cover. Could this cause backfiring?

All of them require a gasket, you really risk a runaway engine and a lot of issues not having a base gasket.

 

[PorknBeans]

Agree 100% that a gasket is required at the carb's base. This would be causing an air leak and causing the back fire.