I'm trying to cure black fouled spark plugs and a lack of power in my '50 Merc equipped with 2 Ford 94's, a Mallory dual point and an unknown (not too lopey) cam. Plugs are Autolite 216. Gap is .028. Points are gapped at .020. Switched to 3.5 Hg power valves from 7.5. Lowered float settings 1/16". Now it refuses to start. I do have spark. Plugs get wet after briefly cranking engine. Does the power valve operate all the time? (unlike the accelerator pump) Does the dual carb set-up, combined with the cam demand the 7.5 Hg power valve? Any thoughts on why the engine runs so doggy? (it used to start and idle fine.) Right now I'd be thrilled just get it running. Thanks folks! Matt
Perhaps a better timeline would help. Is this correct; It used to start and run fine At some point it still started ok but ran roughly and rich You changed the power valves and lowered the floats now it won’t start at all. Power valves do change the mixture at a given load but shouldn’t cause a no start, unless their diaphragm has holed. I would return it to the original spec and see if it starts. What happens when you try to adjust the mixture?
Could this have to do with the power valves not seating correctly? I know the regular Holley power valves have more radius where it transitions from the threaded area to the flat where it should seal against the body. I fought this on some 94’s on my 292 until I realized they were different than newer style Holley power valves. If they don’t seal, they just dump gas similar to the diaphragm having a hole or leak.
Yes, as above, the correct power valve for the 94s are not the same as the newer style PVs at the seat area. You need to get the PVs from a source dealing with 94s.
But to answer your question, no , a power valve cannot keep a car from starting. Unless it has fouled the plugs so much they won’t fire. You can squirt gas into the intake with out a carb and the engine will fire off! Bones
You may have lowered your floats to much check and see if your getting fuel to the intake if not adjust the floats up.
As others have noted . . . your PV's are probably not the correct ones. You cannot use regular Holley (modern) PVs. I suggest getting them from Daytona. Daytona Parts Home
This was a better resource before all of the pictures disappeared but there is still some good information. Holley 94 - Power Valve Issue + Source for Valves? | The H.A.M.B.
I put my 94’s together with the plastic style power valve seal and mine would not start. The plastic style washer did not seal so fuel just leaked past it flooding the engine. Might want to check to see if they are leaking raw fuel into the intake. I went back to the fibre ones and the sealed up:
GREAT info gentlemen! I'll be in the garage this w/e doing surgery (lol) and will update you all. Thanks! Matt
Here's the latest: I made sure the fiber washer is seated properly on the PV of Ford 94. Set the carb body on a little stand so I could look underneath it, put some gas in the bowl and watched it drip, drip, drip out of the PV. Bought the current 3.5 PV from the local speed shop. No brand name on it. Gonna contact the company you folks suggested. Any other thoughts? At least now I know why my plugs are black and it barely ran.
I was just changing the power valve in my Demon (4150 Holley). I went from a 8.5 to a 10.5 just as a test. When I tried to crank it, it was popping and backfiring and barely wanted to run. Went back to a 9.5 (still testing) and it started much better but not great when cold. Back to an 8.5 and it starts normally. So that's what happens when your power valve opens too soon, and I think if it's your power valve that you're dumping too much fuel (edit: I went back and read and I guess you know that now). Since you went the other way, IF your only change was the power valves, my money would be on them not seating/operating correctly. If you switch back to the originals, does it start?
Sorry if I was redundant with my power valve problems. The 3.5s seem to be working, once I got the gaskets to seat properly. Four idle mixture screws (2 per carb) set to 1 1/2 turns out. No backfiring. Car starts immediately. Plugs still get black and sooty after a few minutes run time. Time for a good run on the road? Can a weak coil cause black, sooty plugs?
apparently ! Once your plugs are fouled, can they be cleaned sufficiently to still be used ? I am going through something similar, with the larger version of same carb on a sbc. After around 300km of driving, now only runs for about 5 minutes, before the plugs soot up. Lots of things affect this, so here are some of the things that google ai suggest: (may or may not be helpful) 1. Carbon Fouling: Rich fuel mixture: When the air-fuel mixture has too much fuel, unburned fuel can deposit as soot on the spark plugs. Dirty air filter: A clogged air filter restricts airflow, leading to a rich mixture. Excessive idling: Prolonged idling can cause carbon buildup due to incomplete combustion. Low-speed driving: Similar to idling, low-speed driving can also contribute to carbon fouling. Faulty fuel injectors: If a fuel injector malfunctions, it can deliver too much fuel, leading to carbon deposits. 2. Oil Fouling: Worn piston rings or valve seals: If these components are worn, engine oil can leak into the combustion chamber, fouling the spark plugs. Leaking head gasket: A damaged head gasket can allow oil to contaminate the combustion chamber. Damaged PCV valve: A faulty positive crankcase ventilation valve can also cause oil to enter the combustion chamber. 3. Other Causes: Incorrect heat range: Using a spark plug with the wrong heat range (too hot or too cold) can lead to fouling or premature wear. Incorrect spark plug gap: Improper gapping can affect spark plug performance and lead to fouling. Engine overheating: Extreme heat can damage the spark plugs and lead to deposits. Coolant leaks: Coolant entering the combustion chamber can also foul the spark plugs. Poor fuel quality: Low-quality fuel can contain contaminants that foul spark plugs. Faulty oxygen sensor: A malfunctioning oxygen sensor can cause the engine to run too rich, leading to carbon fouling. also : incorrect timing or carburetor settings. Too much fuel pressure for those carbs. I am back to one known good carb, and still trying to eliminate each of the above. Seems to be a bit of a process as my knowledge of the combustion engine is quite limited, (but rapidly expanding). One of my current concerns was washing the bores with the leaking power valves. I hope you resolve your issues and come back to let us know.
Usually you can determine leaky power valve on Holley carb by hard hot starting . Leaking they drain fuel bowl into the intake
I read on this site that 1 1/2 turs out is a good baseline to start at for correct idle mixture. I'm open to experimentation. Car now starts right away since I switched PVs from 7.5 Hg to 3.5 Hg. Plus, they don't leak. A friend recommended I take it out and DRIVE it to burn the carbon/soot away. He said idling won't clean the plugs. I think he may be right. Once again, thanks to all. This thread has been a WEALTH of info to this flathead/94 carb rookie!
You are correct. I have experimented at less than that with duals and single and they just won’t run at 1 turn out or less. 1&1/4 to 1&1/2 seems to work for me. Don’t ‘force’ them all the way in when you do turn them in as a starting point, as even that can damage the orifice according to Bruce Lancester on here.
The Jalopy Journal
