4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

[doodeesdaddy]

can anyone help? I have 1990 187 xl eclipse I/O with a 4.3L v6 mercruiser with thunderbolt IV ignition the motor isnt the same that came with the boat older by a couple years i was told. Starts good. Idles good. Runs good up to 2500-2700 rpms then fluctuates up and down in power and speed. checked compression good in all cylinders got spark. problems noticed vacuum leak at base plate of carb cap and rotor dirty ordered those. What should i do first for losing power and speed?
also outdrive has up and down movement by hand really sloppy........any suggestions would help thanx

 

[Bondo]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

can anyone help? I have 1990 187 xl eclipse I/O with a 4.3L v6 mercruiser with thunderbolt IV ignition the motor isnt the same that came with the boat older by a couple years i was told. Starts good. Idles good. Runs good up to 2500-2700 rpms then fluctuates up and down in power and speed. checked compression good in all cylinders got spark. problems noticed vacuum leak at base plate of carb cap and rotor dirty ordered those. What should i do first for losing power and speed?
also outdrive has up and down movement by hand really sloppy........any suggestions would help thanx

Ayuh,.... Welcome Aboard,... Check the fuel filters for what's inside 'em, other than gas,...

You gotta isolate the slop in the drive, 'n ID what's loose...
Then We can tak 'bout Fixin' it...

 

[achris]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

Ayuh,.... Welcome Aboard,... Check the fuel filters for what's inside 'em, other than gas,...

You gotta isolate the slop in the drive, 'n ID what's loose...
Then We can tak 'bout Fixin' it...

Hey Bondo, how on earth did you make heads or tails out of that post???? and what is the 'base plate of the carb cap'?

Lost.....

 

[doodeesdaddy]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

Hey Bondo, how on earth did you make heads or tails out of that post???? and what is the 'base plate of the carb cap'?

Lost.....

forgot to put a period between the word carb and the word cap.......any suggestions?

 

[Ion66]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

I have pretty much the same issue with my 86 205 V6. I've had the carb rebuilt, new fuel pump. New coil. New cap/rotor and pickup. The cap/rotor and pickup were all in rough shape. Now it starts perfectly, idles perfectly and leaves the marin fine, comes up to plane strong, then starts missing over 3500 and will not pull past that. Once it starts missing, its has a hard time coming back up to plane unless it's been sitting for a while, like if we stop and fish for 40 minutes. It's much improved, but the miss/hesitation is still there.

 

[Bondo]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

I have pretty much the same issue with my 86 205 V6. I've had the carb rebuilt, new fuel pump. New coil. New cap/rotor and pickup. The cap/rotor and pickup were all in rough shape. Now it starts perfectly, idles perfectly and leaves the marin fine, comes up to plane strong, then starts missing over 3500 and will not pull past that. Once it starts missing, its has a hard time coming back up to plane unless it's been sitting for a while, like if we stop and fish for 40 minutes. It's much improved, but the miss/hesitation is still there.

Ayuh,.... Look for a fuel restriction,... startin' at the tank...

 

[Bondo]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

forgot to put a period between the word carb and the word cap.......any suggestions?

Ayuh,.... Whatsa matter,..?? ya didn't like Mine,..??

 

[doodeesdaddy]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

Ayuh,.... Welcome Aboard,... Check the fuel filters for what's inside 'em, other than gas,...

You gotta isolate the slop in the drive, 'n ID what's loose...
Then We can tak 'bout Fixin' it...

ok ive gone further with my boat and im getting the same results. before i go any further and spend any more money i got a really good deal on a chevy 350 hooked up to a omc outdrive still in boat all hooked up and all in perefect running order. with controls gages and all. can i swap my 4.3 mercuriser and mercruiser outdrive for the chevy 350 and omc out drive? is the hole cutout the same for all or most outdrives will the omc outdrive fit and will the bolt patterns match up or do they make an adaptor kit/plate to swap outdrives. i know the outdrive and motor will fit together because they opperate correctly in the wrecked boat but will they fit in my boat and work? any info or feed back on this would be greatly appreciated .

 

[Bondo]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

ok ive gone further with my boat and im getting the same results. before i go any further and spend any more money i got a really good deal on a chevy 350 hooked up to a omc outdrive still in boat all hooked up and all in perefect running order. with controls gages and all. can i swap my 4.3 mercuriser and mercruiser outdrive for the chevy 350 and omc out drive? is the hole cutout the same for all or most outdrives will the omc outdrive fit and will the bolt patterns match up or do they make an adaptor kit/plate to swap outdrives. i know the outdrive and motor will fit together because they opperate correctly in the wrecked boat but will they fit in my boat and work? any info or feed back on this would be greatly appreciated .

Ayuh,... OMC went Out of business, Over a Decade ago...

Why, O Why, would ya want to stuff that obsolete junk into yer hull,..??

 

[joewithaboat]

Re: 4.3L v6 mercruiser with thunderbolt IV ignition loses power at high rpms

ok ive gone further with my boat and im getting the same results. before i go any further and spend any more money i got a really good deal on a chevy 350 hooked up to a omc outdrive still in boat all hooked up and all in perefect running order. with controls gages and all. can i swap my 4.3 mercuriser and mercruiser outdrive for the chevy 350 and omc out drive? is the hole cutout the same for all or most outdrives will the omc outdrive fit and will the bolt patterns match up or do they make an adaptor kit/plate to swap outdrives. i know the outdrive and motor will fit together because they opperate correctly in the wrecked boat but will they fit in my boat and work? any info or feed back on this would be greatly appreciated .

You don't want to spend the time or money to give your current drive system a tune up soooo.... now you want to swap in an older outdated system in instead???? I'm guessing you have V8itus LOL

Stick with your current set up, 4.3/mercruisers are a good set up.

 

[#motorboater]

I had a similar problem. The boat would randomly lose rpm's when on plane or cruising. It ended up being an issue with the main power wire from the battery feeding to the cockpit. There is an inline fuse for it near the battery, mine was in a black boot style fuse block with a 35 amp fuse. If I bumped it, it would cut power. I ended up cutting it out and replacing it with a new auto style fuse block. Runs like a top now. It was a lucky find and only found after I replaced the plugs, wires, distributor cap and rotor and rebuilt the carb. Good luck

 

[Rick Stephens]

+1000 on staying with Mercruiser. Stay far far away from OMC.

 

[nateo]

Is card adjusted properly? Is timing set correcting? If you swapped motors why not keep the merc outdrive, seems like would be less work. One time I had a problem with my car missing. Asked a gear head buddy of mine and he said to inspect spark plugs wires for damage. He was on right on the money first suggestion.

 

[Fun Times]

I had a similar problem. The boat would randomly lose rpm's when on plane or cruising. It ended up being an issue with the main power wire from the battery feeding to the cockpit. There is an inline fuse for it near the battery, mine was in a black boot style fuse block with a 35 amp fuse. If I bumped it, it would cut power. I ended up cutting it out and replacing it with a new auto style fuse block. Runs like a top now. It was a lucky find and only found after I replaced the plugs, wires, distributor cap and rotor and rebuilt the carb. Good luck

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[NHGuy]

As Bondo said, you probably have a fuel restriction. To confirm, you can run the engine off a portable tank to see if it holds high rpms.
To chase the issue, pour out the contents of the fuel water separator into a clear jar or ziplock bag. Replace the separator, they are not reusable.
You can also inspect the fuel lines. if there are signs of cracking they need to go. If they crack, air can enter the suction side causing your issue. If they look original you'd be smart to change them out any way. 25 years is a long time, rubber has a lifetime and there can be internal fails that you can't see.
Get the marine rated line at a boat supply. To attach the lines to your boat get screw down zip ties at your local home center. The stainless clamps are reusable, you use 2 at each end, that's the rule.
There's an anti siphon valve at the tank, I removed mine and cleared it out with some carburetor cleaner and I stuck a plastic probe in it to make sure the little ball moves on it's spring.
It also would be smart to remove the tank sending unit to inspect the tank interior for debris.
BTW you need to do this check no matter which engine you end up with.

 

[Fun Times]

As Bondo said, you probably have a fuel restriction. To confirm, you can run the engine off a portable tank to see if it holds high rpms.
To chase the issue, pour out the contents of the fuel water separator into a clear jar or ziplock bag. Replace the separator, they are not reusable.
You can also inspect the fuel lines. if there are signs of cracking they need to go. If they crack, air can enter the suction side causing your issue. If they look original you'd be smart to change them out any way. 25 years is a long time, rubber has a lifetime and there can be internal fails that you can't see.
Get the marine rated line at a boat supply. To attach the lines to your boat get screw down zip ties at your local home center. The stainless clamps are reusable, you use 2 at each end, that's the rule.
There's an anti siphon valve at the tank, I removed mine and cleared it out with some carburetor cleaner and I stuck a plastic probe in it to make sure the little ball moves on it's spring.
It also would be smart to remove the tank sending unit to inspect the tank interior for debris.
BTW you need to do this check no matter which engine you end up with.

Sorry NHGuy, guess I should have closed this so you wouldn't have wasted your time on this older topic though you were probably typing while I was posting above..