Volvo Penta Bogging Down and Idles Rough

[talley_ho]

I have a 96 Cobalt with a 7.4 L Volvo Penta DuoProp that was running ok but after running for an hour or so became very hard to start, would die frequently at idle, idles rough, and now runs very sluggish and will only attain 3100 RPM at WOT. I have not had a chance to trouble shoot yet but the boat was layed up for over a year and I suspect bad gas and/or clogged fuel filter. It is carburetted with a Holley 4 brl. I just purchased the boat so I do not know if any fuel stabilizer was added sooo....any ideas of what might be wrong? Suggestions on where I can begin troubleshooting? I do not believe the boat was properly maintained so anything is an option. All input/suggestions is much appreciated.

 

[Don S]

Re: Volvo Penta Bogging Down and Idles Rough

I would sure start with a full tuneup, cap, rotor, plugs, timing check, advance timing check.
Also do a compression test, change fuel filters (inspect old ones for crud and water). Then you will have some idea where you are at.
Since you just got the boat and expect little maintenance was done. I would sure pull the drive and check the alignment, grease the splined shaft, lube the ujoints and gimbal bearing (assuming you have a DP-S drive).
You also need to find the complete model number of your engine or the SN. Just because you have a 96 boat, doesn't mean you have a 96 engine package.

 

[paisaac]

Re: Volvo Penta Bogging Down and Idles Rough

I agree with Don and he helped me a lot when I had the same exact problem. After you do what he has told you, try a compression check. I would bet your #3 cylinder will not have compression.
Then look up my last posting...

 

[paisaac]

Re: Volvo Penta Bogging Down and Idles Rough

Talley

Check out this web page.

http://www.marinepartsexpress.com/jpg/Flapper Parts Bull.jpg

see if that fits your engine.

Pat

 

[talley_ho]

Re: Volvo Penta Bogging Down and Idles Rough

Thanks everyone for the input. I'll change the filters and check the flapper valve to make sure those are ok. I am now thinking either the anti-siphon valve or screen in the tank is clogged and will verify in a few days when I can work on it.

 

[Maclin]

Re: Volvo Penta Bogging Down and Idles Rough

An engine with a Holley 4bbl can exhibit these symptoms when the internal powervalve(s) has failed. Raw gasoline will run into the plenum of the intake manifold and cause a way-too-rich condition. It won't idle very good if at all, and once underway will be way sluggish as the engine is basically flooded and the spark plugs are gas fouled. Worst part is the fuel bowl(s) will drain itself into the intake until there is no fuel pressure even when the engine is not running. Sniff the oil from the dipstick, if the oil has a heavy gasoline smell then the carb could be leaking thru the power valve.

If this has happened (and after the carb is fixed!) definitely change the oil and oil filter right away. You might even change it once more after running it to temperature for a while just to make sure the oil is fresh and not diluted at all with gasoline.

 

[Maclin]

Re: Volvo Penta Bogging Down and Idles Rough

Meant to add that the powervalves have a rubber diaphragm and are susceptible to rapid deterioration when left sitting with bad gasoline in the fuel bowl(s).

 

[Coors]

Re: Volvo Penta Bogging Down and Idles Rough

The new power valves are anti-backfire. Rebuild, with a holley book

 

[Maclin]

Re: Volvo Penta Bogging Down and Idles Rough

right on, Imported Coors, right on.....


And even the newer ones can get jammed with scale and stuff and not open/close like they should when the engine is running.

Talley-ho, if the carb hasn't been freshened for a couple of seasons then it is due in my opinion. Always replace the powervalve on a tear down, pretty cheap insurance. I take mine apart once a year, but I have lots of experience from earlier hot-rodding days (3-4 tear downs in one day!) so it seems easy to me.


Good luck talley-ho!

 

[talley_ho]

Re: Volvo Penta Bogging Down and Idles Rough

Thanks for all the suggestions. Update: I have removed the fuel line and verified the anti-siphon valve is functional and clean, I siphoned the remaining 8 gallons of gas out of the tank so the pick-up/screen in the tank is not clogged, I pulled the fuel line off at the carb and the small filter/screen is clean.

Tonight I will check the electric fuel pump which is what I now believe to be the problem.

The carb is supposed to be new so I am concentrating upstream from there first.

Thanks again for all the help.