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Hi, new to the forum. I hope someone can help with an issue I'm having with a 90hp 1990 v4. I bought the boat about two months ago and knew of the problem prior to purchasing but also knew it's history and got a great deal. The motor will start, idle and run all day at 1500 rpm but once it hits open water it bogs. It won't stall but can't get past 2k. It shakes and sounds like it's missing. I've ruled out any fuel issues as both carbs have been rebuilt, primer bulb and fuel lines changed and fresh gas. Compression is 95-100 on all 4 and supposedly the leak down tested good when the last mechanic checked last year. All four have a strong spark and no fouling of the plugs. I'm sure it's a stupid solution but don't want to throw money at every electrical component until I find the problem. Any advice on how to diagnose would be greatly appreciated. Thanks!
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Jac, you don't needed to throw money at new parts, but a good service manual for testing the components would be a big plus.
Probably the first step would be to back into water deep enough to run motor in gear while on trailer (if still secure on trailer to run up till missing) check each plug with timing light to see which cylinders are miss firing (if not secure enough on trailer, may have to tie up securely at a dock to do this test.)
Once you can identify which cylinders are missing, part of your problem is known. If you can do this test when dark enough, you might even see if plugs, wires, or coils are shorting to block (bright arcing), sometimes not noticeable until under load at slightly higher RPMs.
Many times misfiring under load, is an indication of weak insulation allowing spark to jump to ground. There are other areas that can cause these same symptoms, but finding if misfiring, and what cylinders, will confirm electrical problems. It does sound like you've gone through the fuel system.
Good luck post back if find anything, when able. -
Check that the motor is not going into slow mode. See if the motor is overheating if not, Disconnect the tan wire from the high temp sensor, if the motor how runs right the sensor is bad or the powerpack is bad, let us know what you find.Comment
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Thanks Solarman, I checked the coils as you said and did notice an arc on the #2 cylinder coil and replaced it. Didn't make any difference so I ended up taking it to an mechanic last week who charged me 700.00 to replace the flywheel, stator and another coil, same problem. He was closed for the weekend so I'll call him Monday morning but can't afford another big hit like that, hopefully he'll stand behind his work. I've already changed the power pack and new wires and the rectifier was changed last year by the previous owner. I have it tied off at my dock and can run it up to the 2000 rpm where it starts to bog.
Coueytwo, I don't believe this model had the slow mode feature but I'm not certain how to tell either. It's not overheating and the problem will occur consistently wether it's warmed up or not.
Thanks again for your help guys and I'll let you know what the mechanic says.
Unfortunately there's a shortage of good outboard mechanics in my area so if you have any other ideas, I'm all ears.Comment
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Jac, see if you can find the neutral / shift switch on your motor, can you test, or byp*** it to see if it makes a difference? Some of these switches have been known to affect one side of motor when hitting 2k RPMs.
Good luck. Post back when able.Comment
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Hi solarman,
Can't find a shift interrupter on the motor but there's a neutral safety switch in the control. Could this cause the problem? Or possibly the ignition switch?
ThanksComment
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I think that NSS in control would prevent starter cranking motor. The neutral/ shift sensor/ interrupter would be located at/ around shift linkage on the motor.
Good luck.Comment
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