not burning fuel

[stug]

I am running a '87 4cyl merc. with a alpha 1.
I had her on the water today and she ran great. after sitting a few minutes I am am expeirienceing a loss of rpm and main acceleration.
engine it will speed up slowly but when i crank the throttle open, it almost seems there is gas not firing in a few cylinders . it chugs and doesnt speed or pickup rpm's, so i lower throttle a bit and the engine runs fine.

I am worried 2 cylinders arent firing properly, thus causing my lack of power.

she was running like a dream then i sat for 15 minutes anchored,....... then this?

I will start with a compression test on the 2 in question. along with checking plugs and wires. this is too wierd

 

[Don S]

Re: not burning fuel

Sounds like a carb or fuel delivery problem to me. Maybe high temp in engine compartment or the engine itself causing a mild vapor lock.
What is your outside air temp, engine temp etc.

 

[stug]

Re: not burning fuel

outside air temp is 85 or so. compartment heat is normal around 100-140. fuel filter is clean, plenty of gas is at carb. honestly to me it sounds like there are cylinders not firing under a load

without trans engaged the engine hums. the load is causing the problem

 

[Don S]

Re: not burning fuel

An engine will rev 10,000 rpms while only firing on 2 cylinders when not under a load. That is basically a non test
When was the last time it had a full tuneup. Points, condenser, cap, rotor, spark plugs, dwell set, timing set. You know, all the good stuff.

Also look at this.
http://forums.iboats.com/showthread.php?t=167561

 

[stug]

Re: not burning fuel

well i have found the problem.

blown head gasket

im taking the head into a machine shop to be sure im not warped at all.

it blew between 2 and 3

probably due to overheating the engine a few times?

heres a few photos

 

[Don S]

Re: not burning fuel

Look at the head and the block in the area of the blown head gasket. Bet they are eroded away also. They either need machined flat or replaced or you will loose the next gasket as well.

 

[stug]

Re: not burning fuel

here is a shot of the head and the block area where it blew. the area doesnt look too bad. But if it is warped slightly it will cause early gasket failure.

quick question,
The head is aluminum or cast ?

This boat got overheated a few times, due to the bad raw water impeller

i will start with a machining of the head. i really dont wanna yank the block out to have it machined untill completely necesary

 

[Don S]

Re: not burning fuel

Before you waste your time with the head, get the block checked. A machinest will have a quality straight edge to put across the section between the cylinders to make sure it's either ok now, or can be machined flat. If it's too much, it won't hold the gasket.

If you overheated the engine more than once before you found the problem, perhaps you should also get a temp switch and make an alarm that will go off around 200? which is well below the temp that will damage your engine, but well above the normal temp also.

 

[stug]

Re: not burning fuel

thanks don I appreciate your input. I will bring the boat with tommorow to the shop. the block work machining sounds like a nightmare though :/ .

can he jump into boat with his straight egde and check block in parking lot?

 

[Don S]

Re: not burning fuel

can he jump into boat with his straight egde and check block in parking lot?

I would hope so!

 

[stug]

Re: not burning fuel

ok heres whats up.

The machinist hopped into boat this morning and checked the block and head. His straight egde was 42 inches long. too long to easily check. It was so long he had to adjust the angle to get it aligned on block . I noticed him getting fluctuated readings while talking to me about the engine...
I/E he readjusted the straight edge and I saw the gap on block change...


long story short, I had him resurface the head. Im gonna toss on athe head with a new gasket and cross my fingers.

 

[180shabah]

Re: not burning fuel

Two words:

Buddy Boat