Ran great until I stopped for ice cream

[1938FordPickup]

Been having a problem for awhile now, engine cold, runs great, pulls great, no issues, after about 20-25 miles or about short of an hour, things start getting bad. At low engine speeds, things are seemingly good but higher rpms, the engine starts to stumble or bog and making it back home on a wing and a prayer. My goal goal is to be able to drive the truck all day long and all night. Looking at the basics, everything is stock on my 1938 Ford Pickup, I was thinking vapor lock or the vacuum brake setting has changed. I believe something has loosen or slip since last fall but I'm drawing a blank. When I was out, I pulled the choke to check a lean condition, made it much worse. So ignition is the next thing to check, new coil and condenser, same issue. Need to know which way the index on the side of the distributor is retarded or advanced (Up is ... and down is ...). The vacuum brake, what is the normal adjustment at 1000ft? I try to run premium fuel every-time, add 8oz of MMO every-time. Looking for some suggestions on testing or how to correct this. And if anyone has a suggestion on a battery powered timing light, that would greatly appreciated.

[Henryat1140]

I'm no expert. . . .

But from reading numerous posts and experiencing the same symptoms, the problem was the coil.

We are lucky to have a few people available who can rebuild the coil and distributor.

These are parts that, once serviced, give lots of trouble free miles.

The common symptom of a bad coil is as you described, runs OK cold, misbehaves when hot.

Look up Skip Haney in Punta Gorda FL, he's the gold standard for coil rebuilding. For distributors, there are several so I don't want to mention one and leave someone else out.

Hope this helps,

Henry

[1938FordPickup]

I've read here about Skip, definitely an option, swapped out a coil and condenser already, so leaning towards vacuum brake and/or distributor plate index moved.

[Henryat1140]

No offense to you, but until/unless you have a Skip Haney rebuilt coil, and a distributor rebuilt by Charlie NY, Skip Haney, or Bubba's you can not tick those items off your troubleshooting list.

I am speaking from experience on this.

Just my 2c

Good Luck

Henry

[Kurt in NJ]

When you go out for a drive check to see how much of a gap you can make at a plug wire before you get a miss, then check again when you start to have the problem, weak spark can show mostly at higher speeds.


the vacuum brake screw should be backed out as far as you can without pinging--look in owners manual


moving the timing adjustment up will advance the timing


I never assume that just because a part is new that it also is good

[Tinker]

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Originally Posted by Henryat1140

No offense to you, but until/unless you have a Skip Haney rebuilt coil, and a distributor rebuilt by Charlie NY, Skip Haney, or Bubba's you can not tick those items off your troubleshooting list.

I am speaking from experience on this.

Just my 2c

Good Luck

Henry

I really have to second this one. Has made my flathead life more enjoyable.

It could be something else. What kind of fuel?

Great 38 truck by the way!!!

[richard crow]

when it starts runing bad take a voltage reading at the coil . check all the wire conections from the ign switch. your restor could be at fault also .there designed to reduce voltage as it heats up if it,s an orignal its 74 years old & could be reducing two much voltage.

[Old Henry]

Originally Posted by 1938FordPickup

At low engine speeds, things are seemingly good but higher rpms, the engine starts to stumble or bog and making it back home on a wing and a prayer.

I had these symptoms that first off was a plugged fuel filter that lets enough gas through for low speeds but not high. Might check that if you have one.

Second, that's just how my engine acts when it's vapor locking in hot weather. Solved that with a backup electric fuel pump for those occasions.

Originally Posted by 1938FordPickup

The vacuum brake, what is the normal adjustment at 1000ft?

As has been said, run the vacuum brake out as far as possible without pinging. Setting does not cause the performance problem you're having, just pinging.

Originally Posted by 1938FordPickup

I try to run premium fuel every-time,

There is no need for premium gas. It is no better gas, only reduces pinging in modern high compression engines. Does nothing for flatheads. You can run the lowest octane available and get as good of performance as premium.

Originally Posted by 1938FordPickup

And if anyone has a suggestion on a battery powered timing light, that would greatly appreciated.

Here's a battery operated timing light for $100.00 but my 12 volt light works fine on my 6 volt system. http://www.automotive-diagnostic-too...p/atd-5598.htm

One thing I do with a puzzling problem like yours - I hook up my timing light and put the sensor on the high tension coil wire so that I can see every spark in the light then run the light wire under the hood with the light on the cowl so I can see it through the windshield then drive. If there is an ignition problem it should show up in the light. If you have the problem and the light is steady you can rule out ignition and focus on fuel.

[Cecil/WV]

I second what Henry says-stop wasting money on premium gas!

[G.M.]

If you have Skip rebuild your coil I would have him do your distributor also.Then you have one person to deal with if what was done didn't work. I think there are readers that could confirm this. Skip is more into water pumps and coils and does the distributors to compliment his coils. He has two Ford~Heyer distributor strobe machines that the certified Ford rebuilders and Ford dealers used to check and set the distributor to Fords factory specs. These machines include a coil tester, condenser tester, vacume pump with a site glass with mercury that rises to indicate the vacume. This is used to test and set the vacume brake and to see that the vacume cylinder is not worn. A worn piston or cylinder won't lift the leather brake off the wheel or plate. With the vacume leaking past the piston, the piston just sits in the cylinder jiggleing up and down. The points are not set with a feeler gauge but with a built in dwell meter. Each set of points are set separately to a specific dwell with the other set insulated. Then the total dwell has to read to a spec in the instructions. Some of the after market points won't come into the correct range. The distributor is run at various RPMs with a built in varable speed air driven motor and a strobe light shows the timeing is right on the mark when properly set. I rebuilt 3 of these machines, Skip has 2 and I have one in Pa. They are all set to a master distributor kept in a plastic bag so we can periodicly check them. The reason Skip has 2 is so he has a back up as it takes more than a few minutes to trouble shoot and repair them. In most cases there are no adjustments required when the distributor is installed on the engine. Skip also writes the left and right point settings in the housing after it comes off the machine. The phonalic shoes that ride on the are going to wear after a number of years which changes the gap and could be reset to the original settings. Use the numbers marked in the housing. There is no specific gap that fits all, the machine settings determine the gap. I would check the gap on any rebuilt distributor and write it in the housing if it was done an stobe machine. If it wasn't done on a machine I wouldn't trust it. G.M.

[alan]

are running a ballast resistor? if so when it goes to causing problems, put a jumper wire across the contacts and see if anything changes, second is the coil getting too hot, even the new one to touch?

[IVT1]

Don't stop for ice cream

[41ford1]

Your problem sounds like something is affected by heat. Check ALL the wiring and connections from the battery to the ignition coil. That includes the ground sides of points, condenser and coil. Heat will make a loose connection go high resistance. The problem goes away when cool. X2 on Skip, Bubba and CharlieNY for fixes on ignition components.
Todays fuel is a problem above 90°F ambient. It will cause vapor lock symtoms when the fuel reaches 125°. This is real easy to reach on a flathead o a 90° + day. Look for posts by GM on this issue.
The alcohol also loosens the varnish put down by the real gas. A probable, but not likely, complete fuel system clean out may be needed.

Oh yeah. Don't waste your money on premium. I tried. The 59 A-B in the pickup and the 215" six in the 53 Courier run BETTER on 87 octane.

[Dec211975]

I would check fuel and ignition first but it could also be a lose baffle in you muffler or a collapsed exhaust pipe, I don't know if your exhaust pipe would be single wall or double wall, but with a double wall pipe if you hit a puddle while driving the inner wall can collapse and the outer wall will look normal. you should be able to check this with a vacuum gauge as you drive at normal speed (constant) you vacuum will drop off. You could also check exhaust temp with an infrared temp gun and look for a drop off in temperature along the pipe.

[G.M.]

When the distributor is changed to electronic or a coil adaptor and brand X coil installed it becomes harder to locate the problem. When stock parts are used there are simple tests and information in the Ford Service Bulletins that will help solve problems in an orderly fashion. Also if a problem happens on the road it's an easy fix. This is what I see over the years on differant forums. G.M.

[Brendan]

Originally Posted by Henryat1140

No offense to you, but until/unless you have a Skip Haney rebuilt coil, and a distributor rebuilt by Charlie NY, Skip Haney, or Bubba's you can not tick those items off your troubleshooting list.

I am speaking from experience on this.

Just my 2c

Good Luck

Henry

i have a Skip coil in my 36 pickup, i took it for a 100 mile drive tn the morning it was ab out 60 deg out side on the way home it was up into the mid 80's the old truck never missed a beet

[G.M.]

Brendan almost any stock old Ford coil will work in the 60 to 80 degree outside temperarure range with no problems. It's when it gets in the 85 plus range the heat starts to effect the insulation qualities of the coil and they start having voltage loss internally. When this happens the spark is reduced from a nice bright 1/2" jumping spark to a fuzzy little yellow spark 1/8" long. A weak spark don't have the power to jump the plug gap under compression.The compression blows the arc out like a candle. I have a Champion plug tester that has it's own spark generator. The plug is screwed into a chamber with a viewing window. You can push a button and watch the spark jump across the electrods of the plug, then you can adjust the pressure of air blowing into the chamber watching a pressure gauge. I have seen them where they look good until the pressure gets to about 25 lbs and the spark disappears. This could be the case with some of the posts that everything checks out but the plugs wires when shorted to ground do not make the engine shake a little at slow idle and still jump an arc to ground. Look at the plug and it will be wet if not fireing. Just swap the plug and see if the problem moves with the bad plug. You are good to go at any temperature with Skips coil plus it will last as long as you own the car. He don't offer a life time warrantee but has never charged anyone in 18 years to repair one other than a few that left the ignition switch on. A bad condenser can act the same as a bad coil when hot. G.M.
I forgot were used call these 10, 15 or 20 mile coils before knowing the real cause.

[nbrskn]

I am just a luker and not a computer perason. My 46 merc would quit when hot sometimes. Up under the dash are some relays. replaced them and that fixed the problem.


nbrskn

[George/Maine]

I would remove the dist claen and adjust the points .015 the dwell is built into the cam,if only had a air gap of .005 they could wear and the points would be made forever on that set,or intermitent.The match book or feeler is the tool.
There aren,t many fords around here, they must have made it home,stopping for ice cream.What did we do before the internet.

[1938FordPickup]

Ok, ditching the premium gas since a few have suggested it. I have been adding MMO (8oz to each re-fill) to the tank. Any of the lead additives a good idea?

Did some searching on the forums and I get the recommendation for Skips, seems like an option. Did a few things yesterday, swapped out the Ford coil for a external coil (Napa coil with an internal resistor and bypassed the ballast resistor) a plate adapter and a new condenser. Today was about 90 out and ran the truck for another test, same issue, but no ice cream.
The index on the side of the distributor is in the middle and the vacuum brake is adjusted till pinging occurs. Question, screwing the vacuum brake adjuster in or out does what to change the advance curve?
Another question, could a hot engine effect spark plug wiring? checked the cylinder head temperature at each plug, seemed even except one cylinder was hotter. What could cause that?