motor problems

[jif102]

I had a few days on the boat and developed motor problems. I have a 1986 Larson 21 ft with a mercuiser MCM 228 engine SS# 4930867. I have a Holley 4 bbl carb on it. I have been having problems with the rpms. I used to get about 3200, which is low, this weekend I could only get 2200-2500. On a cold engine I was getting 3000 but it would pop through the carb. It doesn't miss and idles smooth at low speed. There is no top end. I put new dist cap and rotor this summer as well as new plugs and wires. I am going to do a compression test tomorrow night. What else should I be looking for? Can it be a simple carb problem or bigger engine problems?

Thanks

 

[firehog6305]

Re: motor problems

how old is your fuel?

 

[bjcsc]

Re: motor problems

Sounds like a timing issue to me. If you have an advance timing light, you could check to see if your advance matches your spec'd curve or check points. I am not savvy enough to know what ignition system you have, or what it uses for advance, but I would be suspect that it is not advancing the timing based on your description...

 

[Bondo]

Re: motor problems

Ayuh,..........

Change the Fuel Filters....... She's Starving for Fuel..........

 

[jif102]

Re: motor problems

The gas is 3 days old. It might have been in the boat clubs tank for maybe a week. They go through it pretty quick.

I have a slight clicking but nothing that is really loud. I have a timing light but need to find the directions for it.

I have a few opions from mechanically inclined members of the boat club. A few people are saying I am having problems with the carb and some are saying I am having problems valves and some are saying it is timing.

I hope it is something easy and cheap.

It has a Mallory Distributor

 

[jif102]

Re: motor problems

fuel filter was changed when I put the boat in the water in May but I will pick one up here tomorrow.

 

[jif102]

Re: motor problems

Well, I did some more looking around tonight trying to find my problem. I took my fuel lines off the carb and cleaned the mesh baskets. There was a little in there but not much. I cleaned the inside of the primary and secondary bowls. I reset the secondary float level. It was a little low.

I took it out for a run and when I hit 3000 rpm it would pop back through the carb.

I did a compression test. My low was 145 and my high was 160. I did notice one of my plugs was really carbon coated. I just put them in on Sunday.

I feel a little better with the compression numbers close. I need to learn how to check my timing. I have a light but have no idea as to how to adjust it.

What else could it be? Could I still have a plugged carb?

Thanks
John

 

[Bondo]

Re: motor problems

Could I still have a plugged carb?

Ayuh...................

 

[Limited-Time]

Re: motor problems

I'm with Bond-o, you have a fuel delivery issue. Your going lean on the top hence the backfire (lean pop). Time to check the fuel system.Look for Don S post on the subject.

 

[Don S]

Re: motor problems

Testing your boats fuel system

 

[jif102]

Re: motor problems

Ok, one more update. I went out today and found that the fitting where the fuel hose connects to the gas tank was loose. I fixed that. I also found that one of the screws holding the dist. cap down was stripped. What kind of problems would a loose dist cap cause?

I ran the boat after fixing the tank connection but not for long. The engine did not sound right. That is when I found the loose dist cap.

I hope that solves the problem.