Idle problem with 9.9 MSHU

[svsunbeam]

I have a 1996 MSHU F9.9 4 stroke with an Idling Problem! HISTORY: The motor sat unused in my garage for a few years. Was told by local Yamaha mechanic that most problems with this motor are fuel related so I have replaced (WITH NEW) the carburetor, fuel pump, electrothermal valve, fuel tank and all hoses. Have sprayed Yamaha combustion chamber cleaner into intake and am running Yamaha ring free cleaner in the gas. Motor starts on 2nd pull but will not idle down... you have to keep wiggling the throttle to keep it running at lower rpm. Runs great at med to full throttle but at fast idle speed the rpms go up and down without moving the throttle. Anybody got any ideas????

[arny]

You probarly have a crankshaft sealing issue.Need to take out the crankshaft and replace the labyrint sealant between the connecting rods.New and improved seal is made of aluminium,not rubber as the old one. Take of the carb and reed plate,and you will be able to take a look inside for smal rubber parts.

[svsunbeam]

Idle problem with 9.9 MSHU 4 stroke

Arnie,

Thanks for the reply! Does this work the same on a 2 stroke and a 4 stroke? And is there any way to do this without a complete teardown of the powerhead? I looked at the parts diagram and didn't see anything called a labyrint seal, just top and bottom oil seals. Could you suggest a part number?

Thanks
Thomas

[arny]

Ooops,assumed it was a two stroke as they might have this problems before 2000. 4 strokes with such problems might have an air leak between carb and intake manifold.

[svsunbeam]

Idle problem with 9.9 MSHU

Arnie,

Thank you very much for replying with a tip!

Things have been a bit quiet out there! It seems that this is one of those off the wall problems that nobody wants to touch. I've been scratching my head for several months on this one and it has been taking a lot of the fun out of running around in the dinghy. It used to idle down so slow and so quiet that I couldn't believe it could keep running but not anymore. Always interesting coming up to a dock.

Anyway, I'll surely try it. I'll remove the carb and manifold and re-assemble with a layer of akumpucky in between. What would you recommend??? RTV??

Thanks again,
Thomas