Johnson 76 25hp WOT no power

[lmifl]

Johnson model 25EL76E

Motor ran great 4 times out. Since then 4 more trips loss of power to 1/5 speed at WOT.

Does not break up or stall or bog down

Cleaned/Rebuilt carb, replaced all fuel lines and bulb. cleaned tank etc.
tank cleaned,new fuel.

No improvement. Finally did compression test. Electric start
wot,nuetral,both plugs removed, 4 cranks 2 to 3 seconds each
Results: 80PSI cycl1 80psi cyl2.

Checked again after warm up 85psi cyl1 82 psi cyl2.

I noticed yesterday that on the upper portion on starter side of motor
that I saw very tiny bubbles of gas where the rear of the manifold meets the crank case, when running. Gasket plate to crankcase area.

Is this the source of my loss of power thus low compression. Shouldn't I be around 100 on each within 10/15%.

Checked the fuel pump seems ok.

Idles OK

Confused

 

[crxess]

Re: Johnson 76 25hp WOT no power

Don't worry about the compression. Both cylinders are close.

Order and replace the Gaskets for the manifold plate. If Exhaust is leaking out it is possible exhaust gasses are also drawing into the back of the crank chamber. That will cause running problems.

 

[lmifl]

Re: Johnson 76 25hp WOT no power

Thanks for the advice. However I've run it several times on the water with the cover off no difference on WOT Gasses blown away.

 

[crxess]

Re: Johnson 76 25hp WOT no power

No, you are missing it. There is an outer and inner palenl. Each has a gasket. if the inner is also blown it willdraw exhaust in and loose manifold vacuum.

 

[lmifl]

Re: Johnson 76 25hp WOT no power

Gotcha. I didn't understand thta this would effect mainfold pressure.
Thanks

 

[jbjennings]

Re: Johnson 76 25hp WOT no power

Exactly where is that bubbling coming from? Is it under the exhaust cover? If so, then you definitely have a problem. As said, if those gaskets are bad then you may have water squirting through your exhaust ports into the cylinders which will ruin them.
If the bubbling is coming from the seam between the crankcase halves it's probably no big deal and not worth fixing.
I'd fix those exhaust cover gaskets, eyeballing the pistons and cylinder walls as best I could in the process. You can also check the spark plugs and look for milky water on your plugs signalling water intrusion into the cylinder form that bad exhaust gasket.
I'd also be absolutely certain I tested spark, WITH A SPARK TESTER. I'm thinking you may be running on one cylinder.
Last of all, 85psi is really not good at all on that motor. It should be about 115-120 psi. However, compression gauges are very often wrong. You should also keep spinning the motor until the gauge reads as high as it will read to get an accurate measurement. Leaking exhaust gases wouldn't affect your compression measurements at all, they just might ruin your motor and cause bad compression.
Just my opinion,
JBJ

 

[lmifl]

Re: Johnson 76 25hp WOT no power

Jennings

Thanks for the advice.

Yes the fizzing is between the crank case halves. Better description of the area. Very small, area.

Doing the compression test after changing testers twice(First got 0 readings).
I did it full throttle,nuetral cranked 2-3 seconds 4 times on each cylinder.


I've cleaned the motor off after each running in a barrel to see any further evidence could be found.
I'm running Champion J4C at .030 gap.

 

[lmifl]

Re: Johnson 76 25hp WOT no power

Finally got it running at WOT.


Put orignal fuel back on and used a nylon tie to secure fuel line to tank to make it snug with tank connector.

Apparently did not sit snug enough with just the clip.


Ran great again on water.

Thanks for the all help and guidance.