Yamaha 4AC, low RPMs unpossible to keep

[marsalek]

Dear guys,
as a new member I wanted to introduce myself. My name is Karel and with my dad we bought an older (pre 2000) Yamaha 4AC engine. We are using it only on holidays in Croatia, so quite seldomly. After some years of service, it has developed a problem. It cannot idle or stay at low RPMs. The engine goes off immediately. At higher RPMs it works well. My dad cleaned the carburetter, changed the gasket between the carburetter and the cylinder, but with no success in curing the trouble.

So any hints are welcome.

Thanks in advance!!!
Karel

PS: a link to a repair manual would be appreciated as well

[J.W.W.]

Karel, what type spark plug do you have in it?
You should have NGK B7HS or BR7HS.

Some people accidentaly fit B(R)7HS-10.
This is also possible when B7HS is not vailable, but will only work if you set the spark plug gap at a distance of 0,7mm.

Gr. Wouter

[ollyit]

clean the low speed idle jet with thin wire, very small and probably hidden under a rubber grommet

[marsalek]

Dear Guys,

thanks for the replies. I will try cleaning the carburettor again, this time by myself. If this does not help, we will have to open the engine and see, if the shaft seal on the crankshaft is still OK. This is at the moment the only place, where it can get false air.

As the engine is now some 1000 km away from me, this will take some time. But if there are any other tips, there are always welcome :-)

Regards
Karel

[marsalek]

Dear guys, the problem has been just cured completely :-)

After sealing the round rubber plug at the shaft, the engine can idle or stay at low rpms without any problem.



Best regards
Karel