Missing at 3500 RPM and Above
 

With electric fuel pump through the mechanical pump, I am pretty sure it is not fuel starvation.



Chevy valves from Flathead Jack, height and notch for flathead. Zephyr type valve springs from the 70's. Johnson lifters. So I am pretty sure it is not valve float.



Recently rebuilt crab type points distributor. I doubt the points would float at 3,500, but?? Tubman condenser.



New Hewlett Packard solid core spark plug wires, BUT, - I am using a one foot piece of spiral wound ignition cable between the coil and distributor to suppress the ignition noise, which otherwise really kills my radio. I will replace that with solid core and report back. Can anyone recommend an alternative for suppression of ignition noise?



What else should I be looking at?

Re: Missing at 3500 RPM and Above
 

Sure sounds like point float to me. A quick run on a Sun Machine could confirm or reject this theory

Re: Missing at 3500 RPM and Above
 

Michael
I am getting my 504 back the end of the week.....how do you tell on the Sun that the points are floating? On the degree wheel lights???

Re: Missing at 3500 RPM and Above
 

You rebuilt the crab distributor - new points? Spring tension at spec for points? Condenser - check with a multimeter to see what Mfrd the condenser is when at operating temperature. If all of that is okay, I would run the distributor on a Sun machine or equivalent. Does the missing take place before engine gets to operating temp or after operating temp is achieved? Coil getting to hot and breaking down? When did the missing show up - after the distributor rebuild? Sun machine - degree wheel lights will not be steady if points are floating. Measure point resistance with ohm meter - should be zero. Points clean and free of cam grease. Pivot points on the points binding - drop of oil cures that - I have had that happen. Report back.

Re: Missing at 3500 RPM and Above
 

You need to figure out if it's fuel or igntiont. It could be starving for fuel if the tank outlet was clogged. My dad's '32 roadster would run at a low rpm but run out of gas at higher rpm. I found it by mounting a 5-gallon tank of gas on the floor and going for a ride. The problem went away.

The electric fuel pump should me mounted as close to the gas tank as possible and the fuel filter there also, between the electric pump and the tank. I only use the electric pump to prime the system, then I run it on the mechanical pump. There are two kinds of electric pumps. One is closed when the power is off and one is open. You want the one that stays open so the mechanical pump can draw fuel through it.

Re: Missing at 3500 RPM and Above
 

I had a similar problem. Turned out the fuel line was too small . Or more correctly, small and had a slight kink in the line causing a flow restriction.

Re: Missing at 3500 RPM and Above
 

Distributor was from Third Gen and has only a few thousand miles on it. I will pull it to check that the points are not pitted and still properly gapped.

Does anyone have an idea of what the points spring preload tension should be? 3,500 RPM seems pretty low for point float, but not my expertise.

Re: Missing at 3500 RPM and Above
 

Before the rebuild I would have never revved the engine that high, so I don't know the prior state. Missing is with fully warmed up engine. Coil is the blue Bosch on that folks on this forum prefer; only 5 years old. Condenser is the Tubman product, which is ceramic parts inside of a brass can. Doubt that would go bad but the points should tell the tale.

Re: Missing at 3500 RPM and Above
 

I will check fuel flow at the output of the mechanical pump; both mechanical only and with electric pump through the mechanical pump. The electric pump is inside the frame rail just in front of the left rear wheel.


Now that you mention it, I am more suspicious of fuel flow. Ran fine in the Fourth of July parade; it was very slow moving and a very hot 93 degree day. Surprisingly, the engine did not over heat but it would not restart after being parked for half an hour. In spite of the electric pump I could see bubbles in the clear lines from the mechanical pump to the three deuces. No bubbles and started easily the next morning, in spite of a low battery.

Re: Missing at 3500 RPM and Above
 

Put distributor on Sun machine to eliminate it as a cause. With NOS Ford script points I can get a solid 5k RPM with a crab on my machine. I have had 2 of those blue Bosch coils fail when hot. Cool off and will work but unreliable. Engine never overheats. Moved new coil to inner fender panel and problem went away.

Re: Missing at 3500 RPM and Above
 

Do you know what the specified spring tension is on the NOS Ford points?


I have the coil up off of the front of the intake manifold, which I thought would be a cool enough location. You can see that and the Tubman condenser in the photo. Do you think the right fender would be enough better? I have a PertroniX flamethrower coil, the 40,000 volt one. Can I use that Pertronix coil with a points distributor and solid core wires?

Re: Missing at 3500 RPM and Above
 

Re: Missing at 3500 RPM and Above
 

Spring tension should be 20-24 oz. Mark

Re: Missing at 3500 RPM and Above
 

I had an issue with the engine missing if I would pull onto the highway and run it up at higher RPM to speed. Turned out to be fuel starvation even though I use a electric fuel pump. Adjusted float slightly higher and it never happened again.

Re: Missing at 3500 RPM and Above
 

The springs on the points are elongated to increase tension on the points. I push the springs over as far as possible to get the max tension. I wonder where the springs are set - least tension?. A Sun machine will narrow the problem - you will see the flashes on the degree wheel - steady and consistent - OK - bouncing - problem - point float and that can be caused by low tension on the point springs. I have a 221 with max 1 cam, dual 97s and it will turn 5500 rpm in 2nd per Snap On dwell tach.

Re: Missing at 3500 RPM and Above
 

If you bought the distributor from us or we built it, I will gladly run it on the machine for assurance that there is no issue if you wish...

Re: Missing at 3500 RPM and Above
 

You'll have more than 8 arrows flashing on the degree wheel

Re: Missing at 3500 RPM and Above
 

Easy test to check for points bounce:


Run the car in neutral to 3500+rpm. If it misfires, points may be the problem. If it doesn't, and only misses or loses power under load, probable fuel problem.


Points will bounce at the same rpm whether loaded or not. Should make an analog dwell meter twitch too.

Re: Missing at 3500 RPM and Above
 

Finally got around to doing the no-load RPM check. It wouund right up to 5,000 RPM (briefly) and ran fine for a while at 4,500 rpm. So, no valve or point float. I will raise the fuel pressurse setting from 2.5 to 3.25 and check the fuel filters.

Re: Missing at 3500 RPM and Above
 

Don’t forget fuel pressure and volume are two different measures. I had a similar problem and it was the size of the fuel line that restricted the amount of fuel I was getting at the carb . My pressures were fine . Good luck , it can be very frustrating.
Gary