Volvo Penta 5.7GL runs bad?

[Ricky_rich]

I recently bought a Wellcraft Excel with a Volvo Penta 5.7GL.

Have problem with the engine, feels like it?s misfiring or don?t get enough fuel when I?m trying to get the boat up to plane. Lack of power and running uneven . I changed the spark plugs because they were black, with lots of carbon build up. But it didn?t help, and the new plugs go black right away.

I have cleaned the distributor cap because there was some oxide there, but no difference. I also checked that I had sparks on all the plugs.

And I think there is a bit too much smoke coming from the engine on idle.

Where should I start?

 

[Scott Danforth]

start with the basics
check compression
verify contents of fuel filter
make sure the clear hose from the fuel filter does not have fuel in it
clean/rebuild the carburetor

 

[Ricky_rich]

What's the deal with the clear hose from the fuel filter? What is it for, if not for fuel?
Guess I'll start on the fuel side...

 

[Scott Danforth]

No Title

its a tell-tale vent hose if your fuel pump fails, that hose fills up and the excess fuel is pushed into the carburetor and it runs really rich forcing someone to take a look.

without that line, the excess fuel would be dumped into the bilge........


..........boom

 

[Maclin]

Ricky_rich regarding "clear hose from the fuel filter" hopefully you meant Fuel Pump?

 

[Ricky_rich]

No Title

This is how my plugs look after just being run for 30 minutes. Engine running rich? The fuel filter is also new.
I have to check that hose next time I'm at the boat. But if pump is pushing gas into it, does that mean that the ordinary fuel line is blocked?

 

[jimmbo]

No it means the fuel pump diaphragm has a leak. Instead of dripping into the bilge, the leaking fuel is routed to the carb where it is burned and makes the engine run lousy making you want to fix it. One of the reasons Marine parts(carbs, fuel pumps, starters, alternators, and others) are different than auto parts

 

[Maclin]

Those plugs have had a "rich" life, too much fuel and not enough air I would say.

Is it hard to start? Do you need to have the throttle open past 1/3 to get it to start? Because it sounds like the carb is flooding, and if it is a Holley then it could be the internal power valve has ruptured. If that happens then fuel goes nearly unfettered from the fuel bowl into the intake manifold plenum.

 

[Ricky_rich]

Engine is a bit hard to start when cold, but when it's warm it's no problem. I have a two barrel Holley carb.
Yesterday I checked that I didn't have and fuel leaking from pump to carb through that hose.
I also run the engine from a separate tank with fresh fuel, in case I had water in the big tank.
Changed distributor cap and rotor.
None of these tings made any difference. Engine runs a bit uneven on idle, and feels like I loose a cylinder or two from time to time when giving throttle? I'm really lost here..

 

[Bondo]

Ayuh,.... You've got a Carb problem,.....

Rebuild the Carb,....

Changin' ignition parts does nothin' for the induction system,....

 

[Ricky_rich]

Carb rebuilt kit ordered, I'll get back to you with the result when the job is done.

 

[Ricky_rich]

Back here again now. Have rebuilt the carb with a new power walve, needle valve and gaskets and so on. Put it back in the boat today but made no difference against before. Also changed the fuel filter today, but no difference. Tried to make a few videos when engine is running. Maybe sounds better on the video than in reality. But listen closely; you hear how I lose a cylinder from time to time. And with engine lid closed, I can hear a kind of BOOFF sound from time to time. Hard to explain...

 

[Ricky_rich]

Video with closed engine lid, more obviosly when egine missfire

 

[BarryTurano]

Sounds like it is laboring. Maybe a vacuum leak. When the motor box is closed it sounds like it is gasping for air. Is the motor box vented? If so are the vents clear?

 

[Ricky_rich]

Running the engine without airfilter and open lid, still runs bad. So I don't believe there is lack of air. Get a feeling that I'm loosing a cylinder... Some vibration when the engine runs bad.
Did a compression test, and here are the result.

1. 10.5 bar
2. 10.5 bar
3. 9.0 bar
4. 10.5 bar
5. 10.5 bar
6. 8.5 bar
7. 9.0 bar
8. 10.0 bar

I also tried new sparkplug cables, but made no difference.

 

[BarryTurano]

I'm not sure how to equate Bar to PSI. But from what I am told there should be no more than 10% difference between cylinders. You may want to have a leak down test done to see if you have a bad valve. How does your oil look are there water droplets or does it have a milky color, from a bad head gasket? Do you see or smell any exhaust coming from the valve covers?

 

[Chigwalla]

Did a compression test, and here are the result.

1. 10.5 bar = 152psi
2. 10.5 bar = 152psi
3. 9.0 bar = 131psi
4. 10.5 bar = 152psi
5. 10.5 bar = 152psi
6. 8.5 bar = 123psi
7. 9.0 bar = 131psi
8. 10.0 bar = 145psi

Next step is a wet compression test.

 

[BarryTurano]

Does not appear to be terrible. Obviously #6 is the worst. I would again suggest the leak down test to insure your valves are holding. How many hours on the motor?

 

[Ricky_rich]

I just bought the boat so I don't know about the hours. But both boat and engine are from 1997.
Have to get me one of those leak down testers.
One test I was thinking of is to remove one spark plug cable at a time, to se if they all makes the same inpact. What do you think about that?

 

[BarryTurano]

Leak down is a vacuum test. I can't tell you how it is done. Best would be a mechanic to do it correctly. Pulling plug wires will just show spark condition. Spark does not seem to be the issue. Your compression and or valves is probably the root cause.