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'96 Monsoon Not running right after warmed up


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Damsel in Distress! My partner says its all in my head but I dont think so!

Issue: Idles great, revs great, runs out at 4800 rpm when it first reaches 140deg. After that, when you give it throttle, it just doesnt go. Give it a lot of throttle then it jumps but looses 200rpm off WOT. In between giving it the gas and it going, engine seems to be running bad like its missing. Never backfires.

What I have done so far: Replaced spark plugs, wires, cap, rotor and fuel filters. Basically, I have exhausted all the suggestions so far posted on this fine forum. Many BIG thanks to those that posted the filter and cap NAPA part numbers. No water in the oil. Do not notice any smoke from exhaust. HELP! Its driving me crazy!

1996 sunsetter lx with 320hp 350 efi monsoon engine. only 180hours.

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Damsel in Distress! My partner says its all in my head but I dont think so!

Issue: Idles great, revs great, runs out at 4800 rpm when it first reaches 140deg. After that, when you give it throttle, it just doesnt go. Give it a lot of throttle then it jumps but looses 200rpm off WOT. In between giving it the gas and it going, engine seems to be running bad like its missing. Never backfires.

What I have done so far: Replaced spark plugs, wires, cap, rotor and fuel filters. Basically, I have exhausted all the suggestions so far posted on this fine forum. Many BIG thanks to those that posted the filter and cap NAPA part numbers. No water in the oil. Do not notice any smoke from exhaust. HELP! Its driving me crazy!

1996 sunsetter lx with 320hp 350 efi monsoon engine. only 180hours.

Theres a power reduction mode if things are not working so well.

Is the buzzer working?

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Checked the Indmar manual and it specs a 143 degree t-stat.

How would I tell if the tranny is hot? I do not notice any smoke or burning smells.

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Are you losing rpm at WOT in gear (as opposed to in neutral)? If so, could there be any damage to your prop?

Also, is the air intake/flame arrestor clean? I assume you properly gapped the spark plugs when you changed them.

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Prop seems fine. I have visually inspected and also, since it gets to 4800RPM with no vibration when its been running less than 15 minutes.

Cleaned the spark arrestor at tune up time and yes, gapped the plugs to spec.

Also, thought about the tranny question. I dont think the tranny is slipping. I say that since the engine is not picking up RPM, its just not speeding up at all as I apply throttle. Its all really weird. I have taken it to the shop before but they dont run it at the lake or give it time to exhibit the problem.

Thank you for offering the suggestions. Keep 'em coming.

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Prop seems fine. I have visually inspected and also, since it gets to 4800RPM with no vibration when its been running less than 15 minutes.

Cleaned the spark arrestor at tune up time and yes, gapped the plugs to spec.

Also, thought about the tranny question. I dont think the tranny is slipping. I say that since the engine is not picking up RPM, its just not speeding up at all as I apply throttle. Its all really weird. I have taken it to the shop before but they dont run it at the lake or give it time to exhibit the problem.

Thank you for offering the suggestions. Keep 'em coming.

I don't know much about other models, years & the engines they used, my 95 Sunsetter has a Mercruiser - although I think it is the same thing basically small block Chevy, Some of the add on parts are different, not knowing all the history of the manufacturers, I read an Indmar manual and it was quite different than the Mercruiser manual. 140 sounds cold on an older style engine.

Is it bogging down from wide open or more like it won't open up?

Edited by SFD
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It just will not open up. Revs in neutral just fine but put it in go mode and it runs like junk. Yes, the indmar is a fuel injected small block chevy engine.

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It just will not open up. Revs in neutral just fine but put it in go mode and it runs like junk. Yes, the indmar is a fuel injected small block chevy engine.

Compression check? - could be losing your power there.

Fuel pump pressure check? - could be affecting the EFI.

Vacuum pressure check? - could be affecting the EFI? or what I don't know.

Spark plug firing order - Guessing at - 18436572 ? - If the right two are crossed it will still run smooth but take all the power out.

Major water in the fuel? - Add some Heet?

Distributor cap cracked? - Pull off & check for arc lines inside?

Steve

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  • 2 months later...

Update. Turns out the problem was the throttle linkage and opening the butterflies. The secondary linkage rod was binding on the pivot rod and the secondary butterfly was not opening up at the right point. I loosend the linkage and pulled it out so the linkage rod would not hit the pivot rod. Can anyone instruct me how to adjust the linkage correctly? The secondary butterfly is past 90deg at full throttle.

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