Carb Issues

[beast8812]

I have a 98, 5.7 motor with a 2 barrel carb on it. I keep having issues with the idle being too low and it causing the boat to cut off at idle. I adjust the idle up and the boat will run fine for a few days, and then all of a sudden the idle problem will randomly come back. I have had adjusted the idle up 3 or 4 times ran fine for a few days each time and then the problem returns. For example yesterday I started and stopped the motor a few times with no issues, then we stopped for lunch and when I turned the boat back on it would barely idle, ran a few miles and tried idling again and it would just shut off after about a minute. Should I just rebuild the carb, or is there possibly a electric choke problem? Any suggestions are welcome.

 

[makonnen]

Re: Carb Issues

98 5.7 2BBL Mercruiser

I'm dealing with the same problem too except mine is much more intermittent. So far, the problem only happenend twice this YEAR (put on about 40-50 hours of engine time so far).

The two times that it happened, the carb idle was too low, sometimes stalling, boat was shaking, poor throttle response at low speed, but high speed is fine with no concerns (no miss, no stumbling).

The first time, I soaked the carb in carb cleaner as what I usually do to begin a carb diagnosis and to my surprise it went away for about 4 months. A few weeks ago, it suddenly started doing it again while out fishing. Then after about an hour runing at 2950 RPM / plane speed, the problem fixed itself again.

In between these two times, the carb performs PERFECTLY.

This is odd because with carb problems, they usually don't fix themselves like that.

I'm thinking it might be something in the idle circuits, idle ports, the air vent going to the idle ports ... or perhaps a clogged fuel filter screen at the fuel intake on the carb, perhaps a batch of bad gas or maybe water?

Regardless, I'll be doing a carb overhaul.

Mercarb Marine Carburetor Rebuild - Part 1 of 2 Teardown - YouTube

Mercarb Marine Carburetor Rebuild - Part 2 of 2 - YouTube

 

[slothman]

Re: Carb Issues

pull the fuel line that goes into the carb, crank it over and make sure you have a steady stream of fuel coming out. this will tell you if the fuel pump is working sufficiently . I would also check that little filter that is right inside the front of the carb.

Also try this to rule out the fuel tank as a possible issue: stick the fuel line in a seperate gas can and see if the problem still occurs. If the engine runs good with the seperate gas can, you know the fuel issue is with the gas tank (maybe anti siphon valve)

 

[beast8812]

Re: Carb Issues

pull the fuel line that goes into the carb, crank it over and make sure you have a steady stream of fuel coming out. this will tell you if the fuel pump is working sufficiently . I would also check that little filter that is right inside the front of the carb.

Also try this to rule out the fuel tank as a possible issue: stick the fuel line in a seperate gas can and see if the problem still occurs. If the engine runs good with the seperate gas can, you know the fuel issue is with the gas tank (maybe anti siphon valve)

Thanks for the ideas. I'll look into that stuff too.

 

[achris]

Re: Carb Issues

Next time you get the idle speed right, mark the screw. It sounds like the screw is 'walking out' on the bracket. When the idle speed drops again, have a look for your mark. I suspect it will have moved...

Chris......

 

[beast8812]

Re: Carb Issues

Next time you get the idle speed right, mark the screw. It sounds like the screw is 'walking out' on the bracket. When the idle speed drops again, have a look for your mark. I suspect it will have moved...

Chris......

Is there a suggested way to fix this if that's the issue. Would blue Loctite cause any issues?

 

[Bondo]

Re: Carb Issues

Is there a suggested way to fix this if that's the issue. Would blue Loctite cause any issues?

Ayuh,.... If the screw Is backin' out,...

It should be surrounded by a coil spring to provide tension,...

Just stretch the spring abit,...