The Stovebolt Site Forums The Shop Area The Electrical Bay diagnosing ignition system

1954 pu with 235 engine, engine overhauled 5000 miles ago. converted to 12 volts
was running great until it started losing power under load. idled fine.
found the phenolic block going through distributor was cracked. replaced.
engine continued to lose power under load
have checked point gap to be .017
no vacuum leaks
have removed coil (12 volt requiring external resistor)
Resistor shows 12 volts on both sides (doesn't sound correct)
any other suggestions would be appreciated.
Thanks

Hello Frank,

1. Do a fuel pump test at fuel pump outlet. This will show if you need a pump or the upstream delivery is blocked.
2. Depending on how and when the "resistor" was checked we can advise. Probably not the resistor because motor starts OK, the resistor and points keeps it running until something "fades"....like fuel supply. Do the pump first. The procedure is on Stovebolt a lot. Put hose or fuel line, off of carb inlet/pump outlet, into a water bottle, disconnect center dizzy tower/coil "plug wire", crank and watch bottle start to fill. Need pulsing steady pumps with reasonably good volume. Do this outside in the yard. Report.. Leave the electrics alone til then. You can check spark at a spark plug. You are obviously initially getting good spark and carb has gas in it. Either could get weak/insufficient under load.

Thanks. Will give the fuel system a check.

To check the voltage drop across the ballast resistor, the points MUST be closed, engine stopped, ignition in the "run" position. If the points are open there's no current flow, and no voltage drop across the resistor. Normally, 12V into the resistor will yield about 9 to 9.5 volts at the coil + terminal with the points closed.
Jerry

Thanks for all your help. I had the coil and condenser off at my last post. i had checked the vacuum by installing a rubber tube into the diaphragm on the distributor. when i sucked on the tube the whole distributor turned. I was only expecting the internal plate to turn. when i looked at the shop manual the figure that shows the distributor does not show the vacuum advance diaphragm. I've included a photo of the distributor. this is the dist. that was on the truck when i got it. In messing around with the distributor i found it would move beyond the vacuum advance. Checked the timing and it was off. retimed and it runs fine but cannot figure out how to tighten the timing down. There is a clamp on the back of the distributor, but it is tight. Not sure how to attach a picture. will look into that and put it in another post.

i checked the resistor and got 9.6 volts at the coil.

thanks again for your help.

These distributors work differently from others you have seen. The entire distributor rotates to advance the timing. When I first saw it operate, I was surprised. It took me a minute of investigating to figure out that it's spoda do dat!

Obviously i was shocked also. was this an original Distributor or some kind of an aftermarket. can you describe how you tighten it down in place? Thanks i thought i had lost it.

That's the original GM design for these describblers.

It fastens to the engine pretty much like any other. There is a clamp with a bolt on it.

Installation instructions can be found in the 1948-1952 FSM on page 12-29. Not sure what page it is on in the 1954 manual.

The bracket that holds the vacuum advance bolts to the engine block, with a slot in it that allows for a limited amount of timing adjustment available. For more radical movement, loosen the pinch clamp, which would allow for 360 degrees of movement. The motion of the distributor housing caused by the vacuum advance cannot, and should not be restricted- - - -that's a "feature-- - - -not a bug"!
LOL!
Jerry

Been away for a few days. thanks for the clarification of the adjustments for timing. How tight should the pinch clamp be. i tightened it pretty tight but it still allowed the dist to turn past the vacuum advance.
thanks for your help.

The pinch clamp should be tight enough that there's a definite stop at the end of the vacuum advance movement. It shouldn't turn after that. Crank it down a bit more if it still turns.

Your clamp may be jacked up. They are made out of stamped steel. If you continue to have issues, you may want to pull the distributor and check for obvious distortion.
Before you put it back it, do yourself a favor and find an Allen head bolt to replace the slot head clamp bolt. You'll be able to apply a lot more force on it. That flat head screw location makes it difficult to put much tightening force on it with a screwdriver.

Carl - I’m kinda wondering if the problem you describe is my problem here…

https://www.stovebolt.com/ubbthread...54349/lousy-running-235.html#Post1554349

i took the screw out of the pinch clamp and replaced it with an allen head screw. It made it much easier. timed the engine, tightened the octane bolt and tightened the pinch clamp screw. had to loosen the pinch clamp screw a little to allow the vacuum advance to move freely. engine is running very good. thanks for all of you help and comments.

Something is VERY wrong if the pinch clamp has to be loosened to allow the vacuum advance to move freely. Remove the vacuum advance assembly from the housing and figure out what's binding.
Jerry

I believe i had tightened the pinch clamp until the dist would not turn . i only loosened it enough tro the dist to move with the vacuum advnce.

I would strongly suggest that you learn how the advance system on a stovebolt engine works. The pinch clamp has exactly NOTHING to do with how the vacuum advance makes the housing move in the engine block. All it does is establish the initial position of the housing. Something is wrong that you haven't discovered yet.
Jerry

Let me tell you what i did. You can tell me what i have done wrong.
Loosened the octane bolt enough to turn the dist.
Loosened the Pinch clamp screw.
Timed the engine with light by turning the dist to get the ball on the pointer.
Tightened the Octane bolt.
Tightened the Pinch clamp screw.
The dist had no movement for the vacuum advance to move it.
Slightly loosened the pinch clamp screw. The dist could then respond to The vacuum advance.

I do appreciate any comments.
Frank

This is my first rodeo with this type of Dist.

Check your private messages (the flashing envelope icon at the top of the page).
Jerry

Be sure to get back with us after you talk to Batman. (Some call him Hotrod Lincoln. I call him Batman. Don't let his mildmanerdly ways confuse you. He IS Batman.)

Keep trying if you get a busy signal or a voice mail- - - - -my wife and her sister in Ohio spend hours on the phone- - - -sis has some kind of unlimited long distance plan. I call it their electronic umbilical cord!
Jerry

Look closely at the pictures in this Ebay ad. There are TWO pieces there that move against each other. Bolt the slotted bracket tight to the engine in the middle of its travel, set the initial timing by turning the distributor housing, tighten the pinch clamp, and let the vacuum advance move through its limited range of motion to adjust the timing for load conditions on the engine- - - -acceleration, cruise, passing, etc.

www.ebay.com/itm/266847684437?

Jerry

After my conversation with Hotrod Lincoln i reset the timing using a static timing method he suggested with a test light. Worked easy and the engine runs smooth. The cracked phenolic block led me off on a wild goose chase and i think the timing had shifted because the bolt holding the distributor had loosened and allowed the distributor to turn and the timing to shift.
Thanks to all for your suggestions and especially to Hotrod Lincoln for his willingness to have a phone conversation to discuss.
Frank

Like I said,
Nanah nanah nanah nanah,
nanah nanah nanah nanah,
Batmaaaan!