Engine will only idle high.

[StickyWidget]

I have a 76 75HP Evinrude, I am trying to figure out what would make an engine want to only idle higher that then recommended RPMS.

Currently on muffs, and in a bucket (water only up to the cav plate) it will not idle below about 1100 RPM, After running in the lake it was more like 1300 not in gear.

Recommended in gear is 750, I think it was closer to 1000 in gear in the lake.

I have cleaned the carbs 3 times and made sure that all passages are unobstructed.

Spark jumps 7/16 gap, with strong zap

Compression 115-120 on all 3 cylinders.

WOT peaks at about 5400 RPM.

In this video at about 36 seconds you hear an RPM drop. If I lower the idle anymore than this you hear about the same sound more frequently and it dies.

I can get it to idle in gear albeit high rpm, and I can get it WOT if I quickly advance throttle. I am hoping that what ever is causing a high idle might be mucking up my mid throttle transition.

Any ideas?

 

[multimech]

Re: Engine will only idle high.

The high idle could be caused by the carbs not being synched and linked, like one throttle plate open. Check it. A flooding carb could cause a high idle, by introducing too much fuel into the engine at idle. An air leak can cause too high an idle. It can also blow your engine at high speed. Get some carb cleaner and spray it at the halves of the block (where they meet up).

Hope these help.

 

[StickyWidget]

Re: Engine will only idle high.

If you had an air leak between the blocks wouldn't that throw the compression off one or more of the cylinders?