Bass Boat Forums
Outboard Motor Forums (by brand) => Mercury/Mariner Outboards => Topic started by: TerryF7532 on May 09, 2015, 01:58:50 PM
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I had a bad ignition module on a 1990 XR4(carbs)(0C291052) changed it thinking it would fix the low WOT rpm problem, but it did not. when taking off, it seems to get to 4000 rpm and wollow trying to get out of the hole, with the throttle at wide open, and then on plane, it will only get 5000 rpm at full trim. any ideas will help me trace the problem, it seems run ok at idle and once on plane it is ok at slow rpm, but cant get 5400 at wot. have not change anything from original set up, it used to be just fine. i know it is 20+ but should still run better than it is.
thank you for the ideas (hmm)
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Terry,
Just taking a wild guess here and I mean a wild guess, are the carb jets clean?
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@Coop any suggestions for this problem?
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Sounds like a fuel problem to me.
Mine did the same thing and I rebuilt the carbs and fuel pump and it worked great after that.
The floats were bad.
Good luck.
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But......
Have you changed your plugs lately?
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yes the plugs are new, that was how i found the bad ignition module, # 3 wasnt firing, all the others show they were firing. do i need to have the carbs removed and cleaned or can i use a carb cleaner in the gas to clean them?
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You can try it in the gas, that would be an easy fix.
But you will probably have to take them off and rebuild them.
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Stator maybe
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I'm tending to think it's not a carb problem, but more electrical or electronic, as @JackJ has suggested. But I could be 100% wrong.
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I might be able to help I went through this same problem a couple of years ago. Before you start spending money on experiments try this. (not my brilliant idea got it from a mechanic) Take the cover off the motor and the air cleaner so you can see the carbs. Have someone run the boat on the water under load. Watch the fuel flow in the carbs. It should be the same in all carburetors, not one start off good and then peter out. Full flow stream through all together. You might see the problem if not probably is electrical but like others have said sounds like fuel. It was in my case. After I spent almost a hundred dollars trying to fix not the problem. Good luck. This test is free.
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Take the cover off the motor and the air cleaner so you can see the carbs. Have someone run the boat on the water under load. Watch the fuel flow in the carbs.
And this is assuming that your fuel lines are clear, so you can see the fuel in them, correct?
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No. Watch the jets inside the carbs. You'll see a stream of gas. That stream has to be consistent and steady the faster the engine runs the greater the stream. If it changes in a carb that carb needs to be cleaned. Usually is only one that does it, but realistically if one is dirty its foolish not to go ahead and clean them all.
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OK. Gotcha!
Definitely a great tip. Thanks (y) (y)
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thank you for all the suggestions, i will try the carb stuff first, on the weekend when i can get it out on the water. I will keep you all posted to what i find out.
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Sounds good @TerryF7532 (y)
I hope it's a cheap, easy fix that gets you back up and running again (yes)
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Im sure it prolly wont be, but thats how it goes, i am going to take the cover off and look in the carbs like suggested and run some good carb cleaner thru, and see what it does after that. it may have to go to the shop for this one.
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(y)
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Im sure it prolly wont be, but thats how it goes, i am going to take the cover off and look in the carbs like suggested and run some good carb cleaner thru, and see what it does after that. it may have to go to the shop for this one.
Well, look at it this way. If it does go to the shop, you will have eliminated a lot of their troubleshooting, which should save you some cash.
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So today i replaced the old fuel hose from the tanks to the engine, (what a pain to find one long enough), checked again for spark to #3 have spark. plug looks just like when i put it in, doesnt look the the other 5 with burn marks on the center, so figured it has no fuel, put on the muffs, started it, pulled off wire on #3 did not seem to make a difference, held my hand over carb(#3) it has suction, and you get a big backwash of fuel if you cover it and it snubs the motor out. pulled the plug many times it still doesnt look like its used. tried 3 different ones. when i hold it up to the block there is spark every time i check it so not sure whats going on. compression 110 - 115 across all 6
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Still sounds like a bad stator to me, or a coil pack that is on its last leg but fires just enough to make you think it isnt it.
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Cant get in until after Memorial day but the mech will have her purrrrring again soon
thanks for all the help and great suggestions
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All fixed now, besides the ign module, the coil and plug wire were also no good. so now she runs great and back to 5400 rpm no problem.
thanks for all the help
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@TerryF7532 Thanks for the update! Glad it's fixed and running well again (yes)
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Good deal.. (y)
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Good to hear you got'er goin.
P.S.- Check your oil injection tubing and fittings, all of it, if you havent in 5-6 years. You might want to do that.