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

Re: Missing at 3500 RPM and Above
 

Plugs?

Re: Missing at 3500 RPM and Above
 

Please elaborate. Will plugs that fire okay at 5,000 rpm no-load misfire at that RPM under load? Does the pressure on the compression stroke go up that much? I don't think so; just on the power stroke.

Re: Missing at 3500 RPM and Above
 

Whenever i have misfire at higher RPM thats the ist place i check, easy to do.

Re: Missing at 3500 RPM and Above
 

What do you actually look for on the plugs? Or, do you mean that you just put in new plugs and problem is fixed? My plugs are NGK B-6L with under 3,000 miles, properly gapped (.025), and look fine (light gray, no deposits).

Re: Missing at 3500 RPM and Above
 

"Light gray"? When I was into reading plugs (back in my snowmobiling days), we liked to have them a light chocolate brown; like a freshly broken open Hershey Bar.

Re: Missing at 3500 RPM and Above
 

That light brown is what I liked on my flatheads in the olden days, but does not seem to be the case with modern alcohol blend fuels. I am already running a colder plug than is usually recommended. That is, NGK B-6L versus the hotter NGK B-4L.



Am I the only one wondering where the light brown went?

Re: Missing at 3500 RPM and Above
 

The light brown went the way of unleaded fuel and modern additives. Most plugs in a good running engine will now stay almost white for quite a while, eventually getting some color. Same with the light gray tailpipes....all you see is either black or almost no soot at all.

Re: Missing at 3500 RPM and Above
 

Yes, compression pressure does go up that much but it's throttle opening that does it rather than load per se'. 5000 no load takes very little throttle opening and the cylinders don't get a full air charge but full load wide open does for sure. Lots more resistance to the arc jumping the plug gap under load at high rpm.

Re: Missing at 3500 RPM and Above
 

Issue resolved?

Re: Missing at 3500 RPM and Above
 

After getting my broken door glass replaced I finally got around to checking to see if fuel flow was restricted. The electric pump pushed a nice steady stream through the filters, mechanical fuel pump, and pressure regulator. The mechanical pump also pumped a decent amount, through turned-off electric pump when cranking the engine.

So, back to the ignition as primary suspect. I replaced the Bosch blue coil with the Pertronix Flamethrower I had left from when I removed the Pertronix Ignition. I took the opportunity to check both coils with my trusty Simpson 260 meter. The Pertronix measured 1.5 Ohms in the primary windings, as labeled. The Bosch measured 2.6 Ohms; not right. I have not taken it for a test run yet, but hoping the high resistance of the Bosch coil could be the problem. But why would the Bosch coil work okay no load and break down when winding up in second gear? Maybe because the no-load test was with a cold coil and the street test it was hot?

Re: Missing at 3500 RPM and Above
 

If you are 12 volt, the Bosche Blue at around 3 ohms is the correct coil. The 1.5 ohm coil is for 6 volt, no resistor. If you run that on 12 volt, current (amperage) will be double what it should be. It may work fine and will give a hot spark. Petronix used it. Then again, points or coil may fail in time due to over-current.

Re: Missing at 3500 RPM and Above
 

I had the dash resistor bypassed with the Bosch Blue. I will put that back in for the 1.5 Ohm Pertronix coil and give it a road test.

Re: Missing at 3500 RPM and Above
 

Here is a good video on the Sun 504 Distributer Machines. I used one on a 289 to setup the timing curve on a Mallory distributor 45 years ago. Probably ten years ago I had a chance to buy one cheap, so I brought home. It took me a while to find the flathead distributer adapter and I bought it. I haven't used it yet. I paid as much for the flathead distributor adaptor as I did the entire 504 machine. When the distributer is working correctly all eight lights will be flashing at the same spots. If the points are bad the lights will start jumping all over the place. It lets you check to make sure each cylinder is firing exactly when it's supposed to be. Checks for worn bushings or a distributor cam. Checks the advance. I worked in a fleet with 400 vehicles for 30-years, and we didn't have a distributer machine, we did have a sun scope but no distributer machine. You don't really need one, except for checking the alignment of each cam lobe, but they are fun to play with if you have the distributer off of the engine. Mostly, it makes a nice-looking cabinet for storing my flathead distributor parts in.

https://www.youtube.com/watch?v=8EqUH2ZnSSY

This one is not a flathead but it' still good.

https://www.youtube.com/watch?v=CWbPeWZtAxg

Re: Missing at 3500 RPM and Above
 

Issue resolved.
I mis-remembered having the resistor bypassed with the 2.6 Ohm Bosch blue. It was in the circuit, probably resulting in too low voltage at the coil with the points closed.

With the 1.5 Ohm Pertronix flamethrower coil and the resistor in the circuit, the engine wound right up to 5,000 rpm without losing power. Volt meter shows 13 volts at the coil wit the points open and ~8 volts with the points closed.

Thanks to all for your help.