4.3l merc sputtering at WOT

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

I cleaned the carb filter pretty easily I will bring some tools with me on the water just incase it stalls out again. This way I can check the filter and see if it really is causing it.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

Here is a video of her running. Let me know if anyone hears anything that sounds bad?

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

VID 20130624 200029 724 - YouTube

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

anyone? It seams to have a strange sound at idle but its gone the second you rev to as little a 1k

 

[Eric 3.7LX Alpha 1]

Re: 4.3l merc sputtering at WOT

It kind of sounds like a misfire.

When was the last time it got the treatment?

Plugs, wires, cap, rotor, points & condenser (if it has them), check/adjust timing if needed.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

have not changed the plugs or wires yet.. Ill run over to advance auto tomorrow and grab a set. I think they were replaced recently but your right I might as well do the whole tune up.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

i ordered a tune up kit for the cap and rotor. Do you think plug wires need to be replaced? Pretty sure they are not factory... ill grab plugs locally

 

[NHGuy]

Re: 4.3l merc sputtering at WOT

The wires are marine specific. They need to be longer than truck wires to reach around those water jacket exhaust manifolds.

 

[boozer1966]

Re: 4.3l merc sputtering at WOT

I have an '84 Regal Medallion with a Merc 140. Exact same symptoms as you describe. I have replaced the entire fuel system (sans tank) from vent to carb and all ignition components with only moderate success in improving the problem. I think its a loose ground or broken wire somewhere in the wiring harness. Good luck.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

new MSD wires, NGK plugs installed. Cap and rotor replacements be here tomorrow. Looks like the plugs were replaced recently, but put the new ones in anyway just to rule it out.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

cap and rotor installed. Looks like the previous own replaced the plugs and cap before selling but the rotor was so rusted up and stuck on the distributor had to do the flat blade screwdriver and hammer trick to split the plastic casing.

There is defiantly a SLIGHT difference in the idle but only slightly. At least it is noticeable.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

ok so today I took her out again for alittle more testing.

Got to the boat ramp and she started right up as usual. Let her warm up and right when I was about to cast off the trailer she just died. Went to check for spark and again nothing.

After a hour or so of trouble shooting turns out I had spark at the coil, but no spark after the distributor. So Remember I just replaced these parts.. If you pushed down on the distributor the spark came back and she would crank.. then all of a sudden she was fine.

Launched her and took her out. All i have to say is MAN she is WAY smoother than last time I had her out. I did not have the same issue I did with the clogged fuel filter like I did last time. New issue popped up though. Hit a large wave or jolt the boat she would sputter and back fire out the carb and then catch back up again.

Maybe float in carb is getting stuck? Maybe it is time to rebuild the carb? Suggestions?


side note: only managed to get her to about 31mph.. at WOT seams pretty low? I didnt trim at all I just left her down for testing. If I would of trimmed up you think it would of increased top speed? I check via GPS and speedo they are identical.

 

[Another retired guy]

Re: 4.3l merc sputtering at WOT

You say you had to press down on the cap to get it to start, so there is still a problem there! If the cap centre electrode is not making good contact with the rotor that may explain why she was backfiring when hitting a wave. The vibration is causing an intermittent loss of spark?
Re speed - yes, altering trim will affect speed. Check this article

Trim Your Boat

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

Ok well I fixed the cap issue, the gasket that came with the off brand cap and rotor kit was to thick so I picked up a mercrusier part instead and that seams to be good.

Now I still get the backfire issue (out of intake ) but it seams to be related to the carb now.. Out of water testing (on muffs) shows that if I hit WOT from idle it will POP and then catch up and start going. But if I rev up to 1000 for a second then throw it to WOT it does not do this. Do I need a carb cleaning/rebuild?

Also I got my new fuel/water separator installed also and cleaned out the screen at the carb which was dirty AGAIN. Starting to think I need to remove the metal line from the pump to the carb and shoot some air through it.

Trying to get her out to Lake Anna this weekend.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

bump

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

could really use some advice on if I need to rebuild the carb or not.. dont wanna just throw parts at it here.

 

[1ruralmailman]

Re: 4.3l merc sputtering at WOT

Just my two cents,but seein the crud in that filter I would put fresh fuel and dry gas in it and try that first.then info improvement would move on to rebuilding the carb.

 

[sptjet90Reflexx]

Re: 4.3l merc sputtering at WOT

Took her out on lake anna past weekend and on Saturday I dropped her in and she ran great for the 2 hours we had her out. No sputtering no coughing nothing. 0 to WOT without any hesitation. Top speed is alittle lower than I expected though.. probably have a ski prop on instead of a speed prop.

Left it at the dock over night, she took alittle longer than normal to crank but she still cranked. Usually she cranks easier than my truck. and its fuel injected lol. let her warm up and took her out. Went to WOT and bam backfiring out of the carb again. she was running as long as it was under 4000 rpm then all of a sudden the ignition system just died. no spark after the coil so something with the distributor AGAIN so I finally said screw it and bought the EST system.

 

[Badfish95]

Re: 4.3l merc sputtering at WOT

I am very interested in what solves your problem. My brother is having the exact same issue on a 87 OMC 4.3 in a 17.5' Four Winns. I feel terrible because I gave the boat to him and it has had nothing but problems since.

He has done the same things:
Plugs, cap, wires, points and had the carb cleaned(not necessarily rebuilt). The boat has even been looked at by a local marine mechanic and they haven't been able to solve it. They put a different distributor (points)in it and the same problem persisted.
They also tried an electric fuel pump and the problem persisted.

My brother is getting pretty discouraged. The engine was pulled recently and rebuilt. I'm wondering if a wire got pinched somewhere during installation.

Please keep us informed on your progress!