PCM 351 Vapor Lock Issues

[biggsie]

Don't be intimidated.... Read my post about Holley carb tuning. There isn't much to it, good luck!


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[chris young]

I'll second what biggsie says. BTW if you go to the Holley site and the Summit racing site, read everything, and watch all the videos regarding tuning the 4150/4160 vacuum secondary carburetor, you will have all the info you need. Start with the Holley videos, they are short and break the carb down into all it's individual circuits, and how they work.

I still haven't heard, have you looked into the barrels to see if there is fuel dripping? If it is and it continues to drip for a bit after the motor is shut down, you have float issues, if it doesn't, don't mess with the floats they are probably ok. It is highly unlikely that they are adjusted so low the you are running lean, and running rich due to float adjustment is obvious by the dripping.

Good luck.

[CJD]

A little tip from those like me, who couldn't go a week without tweeking their Holleys...

The bowl and valve block gaskets are made from a paper material with a coating that seems to glue them to the surfaces, making them stick hard so they tear and cannot be re-used...not to mention that they are a real pain to clean off the faces of the parts. Spray them with silicone spray before installing and they come off easily and can be re-used a handfull of times before they get too messed up. Saves a lot of money while you get the jets, PV's, and ports all tuned.

[lively]

They make Holley blue gaskets for race application that you can remove them as many times as you like


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[Supra_Comp]

Ok folks, an update.

So I had the carb looked at by the company who re-built it and he said the floats are set perfectly, he even had it on a test motor and said it works just fine.

So being completely baffled, I called SKIDIM and talked to Vince. Walked through the situation with him twice and he started talking about ignition issues that can arise. So the boat does have an electronic ignition conversion (Mallory) with the 3 wire hook up. He said the coil could be bad and is heating up which causes symptoms similar to heat soak and carb problems, and it is also the wrong application (Accel Super Stock 1.4 ohm) which tests out ok using a multimeter according to specs but Vince also said it could be the wrong resistance for the dizzy.

Now comes the head scratching part. As I was looking at the wiring, I began to ponder about how all of this is hooked up. I found the link below showing how a normal PCM 351 should be connected with an electronic ignition:



So when I look at my setup, I have the following.

Red wire from dizzy is direct to + of coil.
'Pink' wire from ignition source is direct to + of coil.
I then have a purple wire coming from + of coil to one side of ballast resistor, but other side of resistor is only hooked up to the choke on the carb and what looks to be the old 'igniter' wire for the old dizzy that is abandoned.
Green Wire from dizzy goes to correct - of coil.
Brown wire from dizzy goes to correct ground.

As a summary, the ballast resistor is essentially doing nothing because the coil and distributor are getting a full 12V source and the power to one side of the resistor is coming via the coil. Now I have read that the resistor may not be needed for certain coils that are 1.4 ohms and higher (internally resisted?) but my assumption now is to eliminate this issue by buying the correct lower resistance (0.7 ohm) coil and hooking up the ballast resister in the fashion shown above.

Apologies for the long post! Anyone have any comments on this?

[ssa]

Mine has a Accel Super Stock coil installed also by a previous owner. It isn't wired according to the above diagram but it works and I figured if its working leave it alone. For whatever reason the red wire coming from the ignition module is connected to the positive terminal of the coil and the coil is fed through the ballast resistor. So you may be able to wire either according to the diagram or how mines hooked up without replacing anything. Your ignition module may also be the problem if it was the kind requiring the resistor and it hasnt been wired in.

[lively]

Ok folks, an update.

So I had the carb looked at by the company who re-built it and he said the floats are set perfectly, he even had it on a test motor and said it works just fine.

So being completely baffled, I called SKIDIM and talked to Vince. Walked through the situation with him twice and he started talking about ignition issues that can arise. So the boat does have an electronic ignition conversion (Mallory) with the 3 wire hook up. He said the coil could be bad and is heating up which causes symptoms similar to heat soak and carb problems, and it is also the wrong application (Accel Super Stock 1.4 ohm) which tests out ok using a multimeter according to specs but Vince also said it could be the wrong resistance for the dizzy.

Now comes the head scratching part. As I was looking at the wiring, I began to ponder about how all of this is hooked up. I found the link below showing how a normal PCM 351 should be connected with an electronic ignition:



So when I look at my setup, I have the following.

Red wire from dizzy is direct to + of coil.
'Pink' wire from ignition source is direct to + of coil.
I then have a purple wire coming from + of coil to one side of ballast resistor, but other side of resistor is only hooked up to the choke on the carb and what looks to be the old 'igniter' wire for the old dizzy that is abandoned.
Green Wire from dizzy goes to correct - of coil.
Brown wire from dizzy goes to correct ground.

As a summary, the ballast resistor is essentially doing nothing because the coil and distributor are getting a full 12V source and the power to one side of the resistor is coming via the coil. Now I have read that the resistor may not be needed for certain coils that are 1.4 ohms and higher (internally resisted?) but my assumption now is to eliminate this issue by buying the correct lower resistance (0.7 ohm) coil and hooking up the ballast resister in the fashion shown above.

Apologies for the long post! Anyone have any comments on this?

this is a PCM wiring diagram and you need to use this with a coil that is externally resisted . They used them for points and condenser dizzys but like mine and a lot others I have the YL Mallory dizzy electronic . It does not like internally resisted coils at 1.4 ohm . Buy a cheap 20$ coil from napa should say use with external resistor on top . And wire from solenoid to dizzy the way this diagram shows



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[CJD]

Just my feeling...if you cannot find direct documentation from the coil manufacturer saying the coil can take the full 12v...then I'd go safe and use the resister. Also, as I am sure you know at this point, it sounds like you need to replace the coil you have!

[Supra_Comp]

Great info guys, found the diagram Lively posted.

I am a bit confused only because the coil would say to 'use with an external resistor' but the diagram shows to put a by-pass for electronic distributor. Any clues? My theory is to wire the resistor in without the by-pass and see what happens. Found a 0.7 ohm coil, so I will re-wire and give it a shot.

[lively]

I talked to skidim when I did mine , HEI like full 12v but these external mount coils and Mallory dizzys do not . I ran into the same issue like a month ago and I posted videos of my findings . Mine had a accel coil 1.4ohm internally resisted and the coil was suffering from heat of excess voltage and would not provide enough spark for long periods of time . I then ordered a ballast resistor and coil from napa and wired it just like that diagram shows . Do not follow the msd or dizzy diagram because you want the + input from dizzy to + coil and the. To ballast . My coil without this setup was reading like 189 degrees at operating temp of 180 but now that I changed it . It runs at 90-120 degrees . And my spark is big and fat from 1" away from ground .


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