1988 90hp runs rough

[BQUICK]

Have a 1988 90hp 2 stroke that runs real rough almost as if plug wires were crossed. Has good compression (115-120). Strange thing is that it idles high even with throttle closed and even tried backing off timing. Usually motors that aren't running well idle too low. Tried cleaning carbs. Checked that all three cylinders were getting spark. They are.
Was going to check fuel pump diaphragm next.

Any ideas?

[99yam40]

have you pulled and cleaned the carbs and done the link and sync as the manual calls for after installing the cleaned carbs?
need to make sure carbs a set and synced together properly.

What did the timing look like before you changed it and what is it now?

Did you use the timing light to see if all plugs where sparking a steady spark?

Did you inspect carbs to make sure they are closing off as they should?
this would be part of the link an sync

[BQUICK]

Yes, did link and sync. But now I see the magneto link plastic connector is broken. I have another one. What is the initial length supposed to be? I need to do static timing.
\Which cylinder is #1 top or bottom?

\Thanks

[99yam40]

top is #1

I have no idea on length, but your service manual should have some kind of info on timing

[BQUICK]

Had a thought....could it be running in safe mode due to oil and temp wires not hooked up?

[pstephens46]

What did Rodbolt say? It shakes like a dog passing peach pits.....

[ausnoelm]

Had a thought....could it be running in safe mode due to oil and temp wires not hooked up?

Doubt it, but....how did you clean the carbs? Have you checked for air leaks?

[TownsendsFJR1300]

Yep, an air leak, leaned out carb will cause a high idle.

Did you pull out EVERY JET and physically look thru each one to see light thru them? Just spraying carb cleaner doesn't count...

[BQUICK]

Yeah, clean all thru....
Where might it have air leaks? Carb gaskets new even looks like new intake gasket. Reeds look intact and seated.

[TownsendsFJR1300]

As 99Yam posted, timing too could be the issue.

Advancing it will raise the idle..

Did you check the base timing?

[BQUICK]

I actually moved the magneto lever around and it ran rough and high idle advanced or not. Never seen anything like this.

Manual says to disconnect rev limiter and try if running rough. I'm going to try that next.

[99yam40]

Still no idea what the timing is set at or you just refuse to tell us.

Is it in spec or not.

adjusting the timing and idle RPM is part of the link and sync

[BQUICK]

Waiting to receive 3 cyl manual so I can set static timing before firing up again. All my manuals are V6.

[robert graham]

Mine is a 1990 C90 2 stroke similar to yours and the "very rough running" and "high idle" combination seems like an odd combination....I'm very interested and curious what this could be.....maybe a faulty signal from the electronic control module?....Please keep us posted with what you find on this...

[ausnoelm]

An air leak on the engine side of the carb can cause your symptoms.., as can an air leak in the crankcase sometimes cause erratic idle and poor running, but, that said, get your timing fixed first seeing as it's broken.