Engine Problems

[jif102]

I have a 1986 Larson Delta sport 21 ft cuddy cabin. It has a 350 ci engine with a Holly 4 bl carb. Over the 4th of July I started to have problems with it. The problem is as follows.

Once the boat is running in neutral at the docks it will idle good for 2 to 3 minutes. When the motor is running you can increase the rpms with no misses. The motor will sit and idle fine. There is no missing. Then after about 2 minutes or so the motor starts to struggle and the rpms drop and finally it stalls out. There is no smoke in the exhaust and no gas smell at the exhaust. After you get the motor running (some time it starts right back up others it take 2 tries) it will idle good and do the same thing.

I don't think it is an electrical issue. If it was electrical I would assume there to be a miss in the engine with it is idling.

I am thinking it is in the fuel system but I am not sure where to start looking. I changed the fuel water separator and it does the same thing. Today I am going to look at the tanks internal strainer and pickup tube. Is this a sign of fuel pump problems? Has anyone seen this before? I am trying to get some ideas as to what to look at.

Thanks for the help.

 

[Barracuda Bill]

Re: Engine Problems

I have heard of a similar problem. Engine would run fine until reving up, then would stall. The problem was the check valve on the gas tank outlet.

 

[jif102]

Re: Engine Problems

Ok. I went out today and worked on the boat. I pulled the siphon valve off the gas tank and put in a hose barb. It was a little rough starting but then it idled nice for about 15 minutes. I turned it off and it started right back up. I thought I found the problem. After eating and talking with some people, about an hour or so. I went back to the boat. It was hard to start. It cranks strong. When it finally started it was back to before. It would round for about a minute and then die. Sometimes it starts right back up other times it takes some trying. After having it die on me a few times I went home. I did check the distributor cap and it was clean and dry.

Any suggestions?

Some additional information on the boat. The carb is a holley 4075. I put it on late last summer. I had to go to smaller ports because I was running super rich. It was putting gas out the exhaust. I went .061 to .059. I think I have a size in between. Could I have to go up one size?

 

[jif102]

Re: Engine Problems

Just an update.

I changed fuel filter, no difference
removed the anti siphon valve, no difference
changed plug wires, no difference
Fuel pressure at carb inlet is 5.5 psi

Next steps, are to remove the stone filter in the carb inlet and change plugs. I am running out of ideas on this one.

Any one have any ideas why the boat will stall when you leave it in idle?

 

[fossill]

Re: Engine Problems

When it does this is there fuel in the carb when you look down the bore while cycling the throttle and is there spark happening? I would start with a major tuneup for starters.

 

[searay3]

Re: Engine Problems

Check the choke operation. Sounds like it starts fine cold, choke closed, then starves of fuel after it opens. Could be an indication of a carb issue, regardless of the carbs age.

 

[Alpheus]

Re: Engine Problems

I would start with a major tuneup for starters.

Right. Just blindly throw money at it without diagnosing and then fixing the REAL problem...

It sounds like a fuel issue. When the boat stalls out after running for a few minutes have someone pump the throttle and see if the carb it shooting fuel via the accelerator pump.

Check your coil and see if it has any cracks or flaws and check to see if it is becoming very hot while boat is running.


PS

GO STEELERS!!!