4.3 Mercruiser idling problems.

gotons · Jul 6, 2009

I've got a 1991 4.3L Mercruiser that is having some idling issues. The first start of the day, it fired right up in neutral without having to give it any throttle and idled there for a few minutes while I let the TWRA guy retrieve and trailer his boat. The boat ran great for probably an hour or two, but eventually started having idling problems. The boat wouldn't start without giving it quite a bit of throttle and wouldn't idle at all. As soon as I would get it started, I'd drop it down to idle and it would instantly stall. I could smell a hint of gas like it was possibly flooding the carb, but I can't 100% tell. I'm going to check to see if the plugs are fouled up on Wednesday, hopefully not as their brand new but it should be telling. I was wondering though if there is anything else I should check while i'm poking around.

OH, a little more information... It wasn't old gas, I filled up right before I put in. I did read though there is an issue with the 3.0 with the 10% ethanol, but i'm not sure if that issue is also occurring with the 4.3's.

Any and all help is greatly appreciated guys.

Gotons

WAVENBYE2 · Jul 6, 2009

Re: 4.3 Mercruiser idling problems.

1991 4.3L why are you using ethonal ? Being an older engine I use the 89 oct gas, ethanol isn't good for the engine either it prob burns to hot, I subscribe to boating world magazine and there is a whole artical about ethanol being bad for your engine, If gas wasn't so high I would be using the Premium gas, but Med. 89Oct runs great too. Just my own experiance

gotons · Jul 6, 2009

Re: 4.3 Mercruiser idling problems.

This might be the problem. Would this explain the gradual loss in the ability to keep the boat idling, or would it happen from the start?

I'm still sitting at a little less than half a tank of gas, (I think, gauge is being a little wonky), should I just go ahead and fill it up with premium and take it out again?

WAVENBYE2 · Jul 6, 2009

Re: 4.3 Mercruiser idling problems.

You could pull your plugs to see if they are white from burning to hot. But Yes I wouldn't use ethonal Use a better grade of gas and your performance will improve a little, I wish I could send you the artical, interesting. but ya stay away from ethonal you don't need it, cost less at the pump but could cost alot more in engine damage in the long run, Happy boating and be safe!

gotons · Jul 6, 2009

Re: 4.3 Mercruiser idling problems.

Thanks a bunch, the info is greatly appreciated. I'll pull the plugs this week and reply back with what I see.

I wish I could give you rep or something.

WAVENBYE2 · Jul 6, 2009

Re: 4.3 Mercruiser idling problems.

What do you have your 1991 4.3L in? What boat?

gotons · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

It's in a 1991 17 'Glassport.

IVAZ · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

WAVENBYE2 said:
1991 4.3L why are you using ethonal ? Being an older engine I use the 89 oct gas, ethanol isn't good for the engine either it prob burns to hot, I subscribe to boating world magazine and there is a whole artical about ethanol being bad for your engine, If gas wasn't so high I would be using the Premium gas, but Med. 89Oct runs great too. Just my own experiance

His problem is not 10% ethanol. Thats all we have here and my 1988 4.3 runs fine with it.
The op needs to verify spark if he already determined he is getting gas.

searay3 · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

When was the last complete tuneup? Could be fuel filters, dirty carb, water in fuel, weak ignition, etc, etc. Get a baseline with a tuneup. Once you have a good ignition system, start looking at fuel delivery....

gotons · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

I think I'm going to check the plugs and fuel filter tomorrow if I can find it. It sat with very little gas in it over the winter. I wonder if my filling it up Saturday caused to loosen some garbage in the tank and it's clogging the fuel filter. I'll post back Wednesday with what I find. If anyone else has any other suggestions, I'd like to hear them.

Thanks!

IVAZ · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

I don?t have any new suggestions.
If you haven?t changed the filters (all of them) I would definitely do that.

scipper77 · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

gotons said:
I think I'm going to check the plugs and fuel filter tomorrow if I can find it. It sat with very little gas in it over the winter. I wonder if my filling it up Saturday caused to loosen some garbage in the tank and it's clogging the fuel filter. I'll post back Wednesday with what I find. If anyone else has any other suggestions, I'd like to hear them.

Thanks!

sitting with very little gas can lead to water in the gas from condensation. Do you have a water separator??

WAVENBYE2 · Jul 7, 2009

Re: 4.3 Mercruiser idling problems.

This is why I don't use ethanol,
http://www.fuel-testers.com/marine_boat_ethanol_problems.html
Newer boats might be built for ethanol but my older engine wasn't and thats why I use the med. grade gas. Read the artical especially the end chapter.

gotons · Jul 26, 2009

Re: 4.3 Mercruiser idling problems.

Just wanted to give an update. I took the carb off and noticed that it had a rattle to it. The rattle was coming from the electric choke, so I took the plastic off of it and found a screw that had vibrated out and was keeping the coil from opening (or closing) properly and not adjusting the choke. I put the screw back in tightly and replaced the carb. The boat now idles fine.

Now, when it's idling, and I hit the throttle a little bit, the carb makes an "airy" sound and the boat stalls. If I hit the throttle hard, it gets through that little hesitation and seems to run fine. It's just easing on the throttle a little bit kills it. I think I've got the electric choke adjusted right, but is there something on the throttle arm that needs to be adjusted? There is a screw that seems to adjust the arm by way of a spring, but I'm not sure what it's purpose is. I've enclosed a picture of the right side of the carb.

I can't get the attachment button to work, so I've provided a link to the picture instead of just posting it in the thread. I don't want to shrink it down and make it harder to see.

Carburetor Picture

gotons · Jul 27, 2009

Re: 4.3 Mercruiser idling problems.

Just to add a little more information. I have tried adjusting the electric choke to the 5 preset little ticks. I've got it set that where it's idling fine, but still having the issues with increasing the throttle.

bchoate · Jul 27, 2009

Re: 4.3 Mercruiser idling problems.

gotons said:
Just to add a little more information. I have tried adjusting the electric choke to the 5 preset little ticks. I've got it set that where it's idling fine, but still having the issues with increasing the throttle.

Try backing out the idle mixture screw about an eighth of turn (counterclockwise) at a time and see if this helps

gotons · Jul 27, 2009

Re: 4.3 Mercruiser idling problems.

Is that the screw in the picture?

4.3 Mercruiser idling problems.

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