95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

I purchased a 1995 Mercury Tracker 90 HP that lost oil pressure due to oil tank issue (now removed) The mid-range power is poor although it idles fine. Compression is as follows:
Cylinder #1= 100... a leakdown test was performed to 90 PSI and it held at 55 PSI
Cylinder #2 = 120
Cylinder #3 = 120
No leakdown was performed for cylinders #2 & #3 as compression was good and equal.

Question: What is a reasonable cost to rebuild the #1 cylinder or, what do you all think I'll need to do to get this thing back to running condition?
I appreciate any and all of your suggestions and opinions.
Thanks,
reccrew

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

Your powerhead is healthy. Leave it alone.

I would investigate the mid-range circuits in your carbs. It seems to me that one or more are going lean in mid range and/or the ignition stator is not advancing correctly.

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

JB,
Your advice is very much appreciated...I'm not much of a mechanic and was concerned over the 16% variance between #1 and 2 & 3 cylinders. Was really hoping I didn't hear, you need a new powerhead.
Thanks,
reccrew

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

A decarb treatment would do no harm. A cylinder weakness would not affect power only in midrange.

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

Thanks I received some bad info that a cylinder weakness was the likely issue and of course that was from the guy selling powerheads. I decided to put it up until late winter & deal with the repairs. I winterized today. I ran the motor at idle with about 16 oz. of Seafoam in 2 gallons of gas, sprayed Seafoam liberally into each carb & then removed plugs and sprayed it into the cylinders. Waited about 20 minutes and on start-up it smoked like a mosquito fogger I ran it another 1/2 hour then hit the cylinders again with Seafoam vs. fogging oil and put it away. It may need further de-carb before I get the carbs and stator looked at: I think you're right on the money and appreciate your support.
Regards,
reccrew

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

reccrew said:

Thanks I received some bad info that a cylinder weakness was the likely issue and of course that was from the guy selling powerheads. I decided to put it up until late winter & deal with the repairs. I winterized today. I ran the motor at idle with about 16 oz. of Seafoam in 2 gallons of gas, sprayed Seafoam liberally into each carb & then removed plugs and sprayed it into the cylinders. Waited about 20 minutes and on start-up it smoked like a mosquito fogger I ran it another 1/2 hour then hit the cylinders again with Seafoam vs. fogging oil and put it away. It may need further de-carb before I get the carbs and stator looked at: I think you're right on the money and appreciate your support.
Regards,
reccrew

Click to expand...

The "decarb" process usually requires new plugs when finished. Course with surface gap maybe not. After you finish the decarb and subsequent engine cleanout of the crud, recheck your compression. You may find it in the normal range of 10-15% between cylinders.

That engine's timing goes from about 5 degrees BTDC at idle to 20-25 at 3000 rpm. There is a stop on the timing linkage that prevents further movement while the butterflies in the carbs continue to open to bring your rpms up to the rated 5000-5500 value with the throttle set to wide open (WOT). Sounds like you are at the cross over point when you have your problem.

So, other information may be needed to help you. Is timing correct, does engine run up to spec rpms at WOT, is the boat still "in the hole" and coming up onto plane at this rpm or is it still in the hole? Did the decarb solve the problem?

I just finished working over the carbs yesterday on mine and I doubt there is anything in there that would cause this specific problem. If it were crud in the carb clogging the high speed jet (which turned out to be my problem), your WOT rpms would be low.

HTH,
Mark

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

reccrew said:

........... I winterized today........ I ran the motor at idle with about 16 oz. of Seafoam in 2 gallons of gas, sprayed Seafoam liberally into each carb & then removed plugs and sprayed it into the cylinders. Waited about 20 minutes and on start-up it smoked like a mosquito fogger I ran it another 1/2 hour then hit the cylinders again with Seafoam vs. fogging oil and put it away. It may need further de-carb before I get the carbs and stator looked at: I think you're right on the money and appreciate your support.
Regards,
reccrew

Click to expand...

You 'de-carbed'and you have treated the fuel for winter but until you fog the motor with fogging oil you have not fully protected the bearings and cyls from rust.

Please finish winterizing your motor to ensure a nice long lifetime.

Re: 95 Mercury 90 HP, low compression & mid-range power loss: Your thoughts?

CharlieB,
I actually fogged with Sea Foam Deep Creep" I've used it in the past with no issues but this is an older motor so I'll investigate and follow your lead with fogging oil as necessary. Thanks for the advice and ironically, I'm not too far east of you...just across the Missouri River.
Regards,
rec334