Low speed miss - 200 Ocean Pro

[dingbat]

This is the second season I’ve struggled with a misfire, for lack of a better word, coming off idle.

Could be missing at idle but a spark test turns up nothing. Plugs don’t show anything and there is no audible evidence of a miss at idle.

It’s only obvious for the first couple of seconds of heavy throttle before it “catches” and runs strong.

Seems worst when cold. Don’t notice it as much, it at all once the motor warms up

Brought the boat home yesterday to clean it up after 3 weeks of fishing. In doing so, I noticed one of the exhaust ports was full of coagulated oil.

Not unusual when trolling for hours in cold water, but unusual in that it was just the right side exhaust port. Nothing at all in the left.

Got it me thinking...at what rpm does the motor transition over from the idle to high speed jet?

Thinking maybe a partially blocked idle jet and the “catch” is the translation to the high speed jet

1997 Ocean Pro 200

 

[boobie]

Do a compression test on it and report back.

 

[jakedaawg]

Idle and off idle circuits do not quit working as the butterfly passes them.

The off-idle circuit is an air bleed until the butterfly passes it, then it becomes a fuel bleed. **At least this is true in many cases.

Fuel coming from main nozzle is a gradual thing technically. In many cases it may not feel that way.

Too determine RPM you would need to observe butterfly angle as the off idle ports are just exposed and check the tach. All boats will be different partially due to prop and weight of vessel and such.

I've been proven wrong before but I believe the above to be at least generally true.

 

[jakedaawg]

An excess of unburnt fuel while experiencing a miss would tend to point toward spark or compression before fuel starvation.

 

[dingbat]

Do a compression test on it and report back.

Hard to get accurate numbers. Starter will not stay engaged with all the plugs out.

Nothing showed up on plugs.

Did noticed the remains of a “puddle” of dried fuel in cowling below port (offending) carb stack.


102 105
105. 105
98. 100

 

[boobie]

When you run into the problem of starter not staying engaged when doing a compression test with all the plugs out, use one plug and install it in different cylinders and starter will stay engaged.

 

[dingbat]

Follow-up.....

Replaced four of the six OE ignition coils as PM a year or two ago. The other two coils looked and tested good so I left them.

While both coils still looked and tested good, replacing both resolved the "misfire" issue coming off idle.

Thanks for the input