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RPM issue not prop 2000 90hp

T

turbochargeit

New member
2000 Johnson 90hp OIS carburetor motor use to run 5600rpm same prop

Fuel side is all rebuilt or replaced - on portable tank, no air leaks
Can't get past 4200rpm unless trimmed half out of water, then 4800rpm
Squeeze bulb at WOT no change, bulb stays up and in correct direction
Hit primer at WOT drops rpms 200-300
New lines are 3/8" old were 5/16"
Starts easy, runs fine, just will not open up, 8-10 mph slower
Last couple inches of throttle control does nothing
Throttle plates open full and not over opened
Timing advances, follow cam roller replaced
Control cables are good and same as before
Quikstart works and S.L.O.W. checks out good
7/16 spark jump in open air on all four, new Champion QL76V plugs
Compression 135 on all four

Stumped?

How to check fuel pressure at VRO2?
 
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Re: RPM issue not prop

has the boat gained any weight? water logged?

have you done a comp check? since the problem started?
 
Re: RPM issue not prop

No weight gain or water. Bone dry below deck, very light boat.
Would go slower with more load but never lost that much rpm with more passengers.

Comp check 135psi on all 4 cylinders (added that in edit)
Seems fuel starved, but no indication of lean condition.
 
Re: RPM issue not prop

You note trimming it very high helped = possible exhaust restriction.

Might have a build-up of (salt - if saltwater run) or minerals/crud (freshwater) or even excess carbon resulting in excessive back pressure.

Since your compression is good, if the ignition checks out and you can't find a fuel issue, pull the leg and have a look...
 
Re: RPM issue not prop

galamb said:
You note trimming it very high helped = possible exhaust restriction.

Might have a build-up of (salt - if saltwater run) or minerals/crud (freshwater) or even excess carbon resulting in excessive back pressure.

Since your compression is good, if the ignition checks out and you can't find a fuel issue, pull the leg and have a look...
Click to expand...

Thanks for the reply.
This motor only has 60-80 hours on it, and is flushed every time out, restriction in exhaust is unlikely. I think trimming it very high is just freeing up the prop.

I am not sure if ignition is good, can you recommend any way to verify coils and power pack?
 
Re: RPM issue not prop

Following the link & sync procedure on my 1990 225 did wonders for its performance. Don't know if that applies to your new fangled motor. If it does, I would consider it.
 
Re: RPM issue not prop

If your timing advance at WOT is off, you will experience low RPM please check this also
 
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