Volvo penta 4.3 running rich

[Jb44]

Hey all,

Can’t seem to solve this one! I’ve got a 96 four winns sundowner with a VP 4.3GL. It’s idles poorly and is running rich, verified by fouled plugs and exhaust smell. All my plugs keep fouling matte but one fouls wet and smells like gas on cylinder 6. Compression holds at 175 in all cylinders. Recently rebuilt the carb and adjusted idle mix countless times, cleaned distributor points, replaced plug wires, replaced ignition coil and cleaned plugs up. Any ideas? Really stumped by single shiny plug.

 

[Bt Doctur]

check the fuel pressure. Do not blow off a pressure check because the pump is mechanical

 

[Jb44]

check the fuel pressure

I was thinking this may be the issue but I’ve had the same pump and it used to run great. Will test anyway though!

 

[Scott Danforth]

A single shiny plug is not firing or is being steam cleaned by water in the combustion chamber

 

[Jb44]

A single shiny plug is not firing or is being steam cleaned by water in the combustion chamber

Will test with inline spark tester today. Would compression test rule out head gasket leak? Or should I fork out for a leak down tester.

 

[Lou C]

A '96 should be a Vortec engine with an electric fuel pump.
Holley 2 or 4bbl carb?
When you went through the carb did you replace the needle valve and check the float height?
Also, sometimes rich running is due to clogged air bleeds, make sure to blow them all out.
Lastly, are the idle transfer slots over exposed?

 

[Jb44]

A '96 should be a Vortec engine with an electric fuel pump.
Holley 2 or 4bbl carb?
When you went through the carb did you replace the needle valve and check the float height?
Also, sometimes rich running is due to clogged air bleeds, make sure to blow them all out.
Lastly, are the idle transfer slots over exposed?View attachment 381640

Lou, that is correct it is a vortec head with electric pump. It’s a 2bbl and I replaced needle and adjusted float height. I soaked it in acetone and blew it out really well. Will double check air bleeds. Are these idle transfer slots just under the throttle plates? I did not adjust the plates but will check now as I go back through the carb.

 

[Scott Danforth]

Run fishing line thru all the carb passages vs just blowing them out

 

[Lou C]

Lou, that is correct it is a vortec head with electric pump. It’s a 2bbl and I replaced needle and adjusted float height. I soaked it in acetone and blew it out really well. Will double check air bleeds. Are these idle transfer slots just under the throttle plates? I did not adjust the plates but will check now as I go back through the carb.

yes you can't see em unless the carb is off the manifold

 

[Jb44]

Thank you all for the advice. Went back through distributor and cleaned it up a bit. Missed some corrosion under the rotor. Also went back through the entire carb and used fishing line (great tip) and air blasted all the passages again. Double checked all clearances and we seem to be back in business!

 

[jimmbo]

Lou, that is correct it is a vortec head with electric pump. It’s a 2bbl and I replaced needle and adjusted float height. I soaked it in acetone and blew it out really well. Will double check air bleeds. Are these idle transfer slots just under the throttle plates? I did not adjust the plates but will check now as I go back through the carb.

You adjusted the Float Height. Is it set to spec? Holley quite often use hollow brass Floats, which occasionally develop pinhole leaks and gas gets inside. Shaking them usually reveals gas inside.
You say the Compression Test shows 175, did each cylinder take about the same number of rotations to attain that?
A leaky intake gasket can cause a hard to trace Air or Coolant Leak, check to see see if any Intake to Head Bolts are loose around #6.
You have replace some of the Ignition Parts, but not the Plugs. Examine #6 carefully for Carbon Tracks on and/or Cracks in the Ceramic Insulator, or just try a new Plug

 

[dubs283]

Faulty power valve gasket will cause a rich running condition at idle on a holley carb

Gasket needs to be replaced even if it appears sound

 

[jimmbo]

Faulty power valve gasket will cause a rich running condition at idle on a holley carb

Gasket needs to be replaced even if it appears sound

Good Catch, I forgot about that nugget.

Or a pinhole leak in the Diaphragm

 

[Lou C]

I have found the Holley carb I tried on my engine far more prone to rich running than the Quadrajet that came on my engine, I tried a brand new 4160 on mine and had no end of rich running troubles, gave the Quadrajet a good cleaning and rebuild and it's been fine.

 

[jimmbo]

Replacement non OEM Carbs often need Calibration. Factory Carbs, had that work done long before before being sold, by engineeers

 

[Lou C]

Well I bought the exact carb that Holley designed for the 4.3 V6 and it was a total waste of money. This carb is unlike other Holley carbs in that it doesn't have a power valve but the main jets were made bigger to compensate.

Holley 0-80492 600 CFM Marine Carburetor-Aluminum

All Holley Marine Carburetors are designed to meet Coast Guard specifications. A marine carburetors fuel metering system is calibrated to compensate for unique engine loads found on boats. The J-style vent tubes direct fuel/fumes back into the carburetor for safe operation while on rough...

www.holley.com

this one, it wasn't that expensive when I bought it but prob $450-500.
if you scroll down you see that it is calibrated for the OMC and Volvo 4.3s.
but the one I got was no end of trouble
After rebuilding the Q-Jet I took that Holley completely apart and found the clutch bolts holding the rear metering plate were loose, it could have been that, but there was no way I was going to even bother trying it again the old Q-Jet performed so well. Personally while Holleys are more or less universal and infinitely tune-able, I don't think their quality control or customer service is adequate. I should probably put it up on Ebay, or Craig's list lol. Sitting on a shelf in my garage.