1986 90hp evinrude only reaching 3800 rpm

[Handsome Transom]

I recently just re-powered my 1975 18' starcraft bow rider with a 1986 90hp evinrude (no power tilt). I've been taking it out with my family and it seemed to run fine but I've started to notice that is doesn't to rev up as much as my previous 1975 85hp merc. I went ahead and installed a tachometer and found that with my normal load (~6 people, a cooler) the boat planes very slowly and reaches 3800 rpm at the most. I've tried the two most inward tilt positions and squeezing the bulb. The boat has a 13.25" x 17" prop on it which is the usual for this motor. It seems like its something as simple as the throttle going all the way but with the throttle control lever all the way forward, the linkage lever on the side of the motor is bottomed out. I could try bypassing that linkage line and pushing the linkage that is right on the carbs but that could get very dangerous.

Has anyone ever had this problem? I first though it was the wrong prop size but its barely reaching 3800 rpm, and it should be closer to 4500 rpm before estimating prop sizes.

 

[racerone]

Should be running at 5300 RPM at full throttle.------Verify the tachometer is on the right setting.------Most important to do a compression test on that V-4 crossflow.----Post your numbers.------Sounds like it might be running on 3 of 4 cylinders too.---Check for spark on all leads.

 

[Handsome Transom]

Ok I'll do that tomorrow. Thanks!

 

[oldboat1]

Might try tilting the motor away from the transom. Bow may be plowing, particularly with heavy load.

 

[Handsome Transom]

No spark on upper port side plug. I’ll buy a new coil and try that. Anything that could cause that plug not to spark?

 

[jimmbo]

Swap a couple of coils, see if the problem remains on #2 or moves with the coil

 

[oldboat1]

You can test the coils with a standard multi meter. Test resistance with meter set to 1K ohms. Touch red lead to coil post, and black lead to mounting bolt -- should see 4 or 5K ohms resistance. Check them both -- if the same, it's not a coil issue. Also do a simple continuity check from plug to plug on each wire (connector in the plug). No continuity can mean a bad wire, but more likely an issue with the contact between the wire connector and the inner wire core.

 

[boobie]

I agree with Jimmbo. Swap a couple of coils around before you spend any money.

 

[Handsome Transom]

Swapped the coils. It’s not the coils. Can’t find any disconnected/frayed wires. When turning it over I get around 5.9v between the coil and the power pack thing on the 3 cylinders. Getting 2.9v on the cylinder not getting spark. Should I replace the power pack?

 

[jimmbo]

For an 86 90hp and 115hp

https://maxrules.com/graphics/omc/wiring/1986_90_115.jpg

 

[Handsome Transom]

Ok thanks. I can’t find any information on how to trouble shoot this particular problem. My plan is to check the volts on the brown wires from the stator to the power pack. If all four of those are consistent I’ll replace the power pack.

 

[Handsome Transom]

It was the power pack. Runs great now.