RPMs jumping/cutting/skipping with fast idle engaged, possible cause?

SweetD

Petty Officer 2nd Class
Joined
Jan 19, 2010
Messages
153
2005 BRP Johnson 90hp carb'd two stroke Model# J90GLSOB.

When running the motor and engaging the fast idle lever, the RPMs will initially increase to about 2800 RPMs. After a few seconds the tach starts jumping around, basically skipping/cutting out and in significantly. If I bring it back down to idle (disengage the fast idle lever) it idles normally.

Motor is sometimes harder to start than usual. I've also lost top end - consistently won't go above 4800-4900 RPMs and normally tops out around 5700 RPMs.

Motor sometimes bogs and quickly stalls out when I give it throttle above idle speed in gear, sometimes it jumps right up.

Thinking rev limiter/power pack may be going. I know of the CDI-based troubleshooting and testing guide just have not attempted it yet as I have not had the chance to pull the boat and I need to get a DVA adaptor.

Main question is the first part above with the fast idle engaged and the tach jumping all around, motor missing hard, etc. - symptomatic of what possibly?

I appreciate any feedback. Trying to get through the rest of our short season up here in the NE.

Dave
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,454
Use a timing light to see if you can pinpoint a cylinder with a spark issue.----VRO oil out put tested ?------Compression tes should be done too.----Post your numbers.-------Carburetor plastic float bowls are known to warp as well.
 
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