1994 Volvo Penta 7.4 GL acceleration problems

[mtboatin]

Hoping for some help!

1997 Cobalt 272 that I've had now for the last 3 years.

Quick story. When I purchased the boat it had sat almost 3 years with 100 gallons of fuel in it. Secondaries were glued shut from age. Added one of every snake oil I could find to the tank. Replace the impeller, changed fuel filter, and fluids and ran till it ran out of gas on the lake. Carried enough gas with me to get it back to shore. Change the fuel filter again filled up with fresh fuel. Got secondaries functioning.

Ran pretty good for the next season and a half.

Then if I floored it from a Idol when we were tubing or skiing it would bog down and then finally take off. First thought was accelerator pump. Wasn't consistent. Seem to only do when it was warmed up then shut off for five or so minutes and restarted it would rear its ugly head. Would sometimes stick it in neutral and rev it up a little to clear it out or try to ease into it. It progressively got worse. Since then I overhauled the carburetor and nothing terrible jumped out at me.

Threw the carburetor back on and it made little to no difference, out of the water anyway. A quick jab of the accelerator will actually sometimes stall out. Couple times I got a ball of flame out of the carburetor so I'm thinking rich. Tried backing off the accelerator pump adjustment a little to no avail. Pulled the spark plugs and they weren't real pretty. Put new OEM plugs in which made it start more quickly and crisper and made blipping the throttle crisper but still seeing the problem.

Thinking of replacing cap and rotor if for another other reason just due to age.

I would think jetting as a possibility except that it ran pretty good for about a season and a half and nothing was changed. The reason I would think about playing with jetting is due to Elevation change. We're about 3,200 ft here in Northwest Montana and I know the boat came from Lake Havasu originally. It had been here a few years on the water prior to me purchasing it so not the main problem.

 

[mtboatin]

Some additional info

785 hrs

 

[mtboatin]

I'm still dealing with this problem.

I overhauled the carburetor. No better. Went through the carburetor again just a double check things. Still doing the same. Bought a remanufactured carburetor and found accelerator pump leaking fuel and then the rear float not sealing and pouring fuel out the secondaries. Fix this and planning on taking it out tomorrow to see if there's any changes. They're going to try and Source a cabin worker tomorrow for it . Maybe a coil . Would appreciate any help.

 

[Fun Times]

Do you recall what size power valve number is being used now? I believe Volvo's generally run a 2.5.

Since you had a fire ball, might be time to check ignition timing to ensure it's still at 10 before top dead center... also make sure the dizzy is tight by carefully trying to move it by hand.... Did you try a new cap and rotor yet?

Spark plugs getting near black like that also could suggest there's a bit to the high side of too much fuel pressure 'or as you mentioned, jetting needs to be slightly adjusted. Checking fuel psi might become needed if it continues out on the water.

Hopefully the backfire flame wasn't an indication of a valve train issue.... Compression and leak down test might become needed as well.

Are you putting down new OEM or aftermarket carb base gaskets as sometimes gaskets could be cut out wrong and blocking a vital hole.

Carburetor

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[Scott Danforth]

If it's backfiring thru the carb, your timing is off

When you rebuilt the carb, did you pass a fishing line thru each passage?

Where were the transfer slots set? What is your float level? What PV valve? And did you check to see if the accelerator nozzles are plugged? (Common issue on a boat that sits)