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Joe, Marine Mechanic
Category: Boat
Satisfied Customers: 7251
Experience:  ASE, electronics, Marine mechanical and electronics, pwc, wiring, all around repair tech,
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I have a 1990 120 HP V4. I have lost about 1000 RPm and no

Customer Question

I have a 1990 120 HP V4. I have lost about 1000 RPm and no power to get boat onto plane. Fuel bulb is tight the entire time, no change when pumped, also coils test ok. Could it be the power pack or the trigger switch? Motor acts like its running retarded and not advancing the timing.
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?
Customer: I have checked the coils, replaced plugs and checked fuel filter.
Submitted: 4 months ago.
Category: Boat
Expert:  Joe replied 4 months ago.


Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.

Are you feeling and misfires and have you checked compression and checked timing?



Customer: replied 4 months ago.
Compression has been checked, All cylinders over 135. Timing has not been checked It ran fine when we went out and run to our fishing spot. I then shut the motor off, and we used my small 9.9 to troll around and fished. Restarted motor ran fine. The next day when we unloaded is when I lost the RPM's and MPH. I was down 1000- 1200 RPM and about 10 miles per hour. That is when I tried to pump the primer bulb to make sure we had full fuel, and also changed spark plugs and checked coils. None of these made any difference. It has been on the water several times after that and no changes with anything I have tried. Motor acts like it is retarded and not advanceing the timing. No hole shot and low top end power.
Wondering if the power pack is failing, or maybe the trigger switch failing.
Expert:  Joe replied 4 months ago.

If the shear pin on the flywheel were to slightly twist it would throw your timing off. Have you noticed rough running or misfires?

Customer: replied 4 months ago.
The motor shakes more at idle now than before, do not notice a misfire during trying to run WOT Just no hole shot, hard to get up on plane and low RPM and MPH. It all happened the second day out. The first day motor ran fine. Motor ran fine putting it onto the trailer, nothing was hit with the prop or lower unit to cause shear pin to move. I can check it tonight.
Customer: replied 4 months ago.
If it is not the shear pin, what else could it be?
Expert:  Joe replied 4 months ago.

Shear pin on the flywheel is what I am referring to, and it does not take hitting something to cause this. You would want to put a spark tester on this motor and check all cylinders to see if they are all firing the same, one down, or misfires, weak, so on.

If spark is strong and no misfires than I would check timing and then next move onto possible fuel issues, as it would be likely an issue with the carb and fuel delivery. The carb may very well need to be cleaned and rebuilt.

Thank you!
- Joe

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Customer: replied 4 months ago.
O.K. Thanks, ***** ***** check the shear pin tonight when I get home and see if it is bad, also check the spark. If not that I will move to the carbs. So you don't think it is in the electronics?
Expert:  Joe replied 4 months ago.

"Electronics" control ignition side so if there are no problems with ignition (which is what I am having you check) then I would move on to the carbs and check them.

In terms of the flywheel shear pin you wouldn't have a sheared pin but instead a slightly twisted one which would throw the timing off and cause problems trying to time it. It should be straight and not twisted off center what so ever.



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