Yamaha T9.9 problem

[<rkahr>]

I have a T9.9 4-stroke which runs fine at normal speeds but won't idle. It will surge up and down at idle and eventually die. Adjusting the idle speed up will prevent it from dying but it will still surge quite a bit.

Any ideas?

Thanks.

[<rkahr>]

Also - once the engine cools down the problem
goes away. It has to be run for a while to develop
the problem. Switched to an external tank, nothing
changes.

[<Steve>]

Sorry I cant help you with your question but maybee you can help me. There is a hole just above the oil drain plug on my 9.9 Do you have any idea what it is for? Nothing seems to empty out from there! Thanks

[<gvb>]

I have had the same problem. It is caused by the electrothermal valve or a dirty carb. Do the easy thing first: remove the electrothermal valve inspect it for damage and connect it to a 12vdc battery. Verify that the plunger slowly extends over about 5 minutes. If not, replace the valve. If the valve moves correctly, remove, disassemble and clean the carb. reassemble and install. Reinstall the electrothermal valve. If the operation is still not smooth, with the engine running and thourghly warmed up, adjust the tiny screw on the top of the electrothermal valve to a "best lean mixture". Good Luck