Running Rough When Hot

don's 37

don's 37

Senior Member
I'm sure this has been posted before but I'm having quite the issue with my '37 fordor! When the engine starts getting hot on a warm sunny afternoon drive by the time I can get it back home the engine is bearly running and it sounds like it has a heavy cam in it. Eventually it will shut off on it's own. It runs excellent when cold. I installed a Skip coil, new condenser, and the generator is charging at 10 amps while driving. Does this sound like a carb problem then? Tomorrow I'll pull the plugs and see what they look like. I do know that when I get home I'll lift the hood and the carb is so hot you can't even touch it. It's like touching an exhaust manifold! Any ideas? Thanks Guy's! Don
 
the heat is boiling the fuel out of the carb, take the manifold off and plug the exhaust cross over passages in the manifold just behind where carb mounts, use two real copper pennys to do that, the passages are to heat the carb on freezing days, but flatheads dont need that extra heat on the carb, put a 1/2" to 1" phenolic spacer under carb to insulate it from excessive heat
 
Which type fuel pump are you using? The '47-'48 glass bowl FP's can be more prone to cause gas heating/boiling problems because of the bowl and screw bails close proximity to heated engine parts. G.M. has been doing some heat rise monitoring of different engine component temperatures relative to the problems we are having with today's ethanol enriched gas.
 
Anything is possible. But, this still sounds like an ignition problem. If your carb/fuel experiments don't seem to be helpful look at the ignition resistor, coil, points, primary wiring, or condenser.
 
ford1 said:
use two real copper pennys to do that, the passages are to heat the carb on freezing days, but flatheads dont need that extra heat on the carb
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Maybe I'm doing something wrong, but when I was just installing my intake a few days ago I thought this would be a great idea. Dug up a couple pennies and put one in the heat riser hole....it was like putting a coin in a slot machine...it fell thru the hole, out the exhaust port and hit the header with a crisp *ping* and rolled out onto the floor.

Whats up with that?:confused:
 
I've seen those pennys blow out, some don't fit tight, I use a regular cup block plug. BUT, it depends on the climat where you live, up here in Maine I don't recomend blocking those heat riser holes in a daily driver. We don't get the hot weather like down south, and it makes poor gas mileage. Install one of those spacers under the carb ought to be all that needed. Walt
 
Could it be something as simple an an over-rich mixture? Incorrect float setting (too high) faulty or leaking power valve. anything that makes the mixture too rich.

Mart.
 
Your problem is the hot gas. First get an insulated spacer from gadgiteer@aol.com or call Bob Shewman 1-610-933-6637. And reduce the heat riser holes from .675 to .325 Start with this which will greatly reduce the heat in the carb bowl which don't want to be over 115. If it still gets hot you will have to take measures to reduce the heat in the fuel supply line and the fuel pump. G.M.
 
In answer to one question I am using the original style fuel pump, not the one with the glass bowl. If I go with the heat phenolic spacer I would have to install longer carb studs, correct? How hard is it for these to come out? Another question I have is that I would probably have to rebend the throttle and choke rods too? What about spark plugs? Could a wrong heat range cause this too?
 
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Before i done anyhthing drastic, i would run it till i had the problem you mentioned and then i would check the spark. If is real weak yellow or none at all i would check coil, condenser, and resister. Marv
 
Don Your problem is the temperature of the gas in the carb. You need to get a hand held laser pointed thermometer, cost about $35.00. You will need it even after the carb gets cooled from doing what I told you in my last post. Guessing don't solve these problems. The carb temp when hot now is over 125, this new gas boils in the 125 to 130 range. The base of your carb is in the 125 plus range and the intake maniflod below the carb is in the 200 range. With the heat riser holes reduced and the spacer the base of the carb will be in the 98 to 102 range. When the base of the carb is cooled you get additional cooling from the ventury cooling action of the carb. Bob's ventilated spacer comes with 3 longer studs and two new gaskets. Specify which type of carb to get the right shape spacer and gaskets. Put two nuts on the old studs and tighten them together then back the studs out useing the bottom nut. Do the same replaceing the new studs useing the top nut to tighten them. Don't jamb the unthreaded center section of the stud down in the manifold or it could break. A dot of lock-tite will hold them in place. G.M.
 
Good info George! I took my fordor for about a forty mile spin on Friday and as soon as I got home I started taking temperature reading everywhere that made sense to me with my laser thermometer. It was amazing to see what those temperatures read on places like the intake manifold, the base of the carb, the bowl of the carb, the fuel pump body, glass bowl, bail screw under the bowl, the brass fitting on the flex hose, and the firewall. I will be making some changes soon to reduce the critical temperatures. Thanks for your eye opening helpful demonstrations while in Punta Gorda this March.
 
LOL Hey Walt, you live in maine and you can only drive your cars 3 months out of the year, so even if the passages are left open it wont make any difference because your car and carb are frozen and you cant drive it any way, LOL you need to come out to sunny california and enjoy the coast line cruises
 
Scott H, if you have the boiling carb problem and the weather is above freezing all the time plug those passages, just cut two flat pieces out of a TIN can big enough to cover the holes put them on the block then the manifold gasket on top, the gasket is thick enough to let them squish into it, dont use aluminum wont last
 
JM It would be interesting for you and others to post the outside temperature, how long the car was driven and the temperatures of the spots you took the readings. This way as this problem occures more as the outside temperatures rise more people will be able to identify the problem promptly without disturbing other parts of the engine. This is not to say coils and condensers won't still act up on hot engines. It's unlikely one of Skips coils will have a weak spark but condensers can act like a bad coil. An email from a guy a while ago had a bad coil and replaced it with his rebuilt by Skip. He thought he still had problems and was told to check the spark at each plug wire. He replied he couldn't get near the wires or he gets zaped with the new coil. He was told it would only take 8 zaps and he would know they were all fireing. G.M.
 
Ford1 I used thin aluminum with a .265 in each and took it apart a few months later. the bottom of the aluminum in the .625 riser hole was coated with black carbon protecting it from burn out. I also opened the holes to .375 It may burn the holes but I doubt it as the manifold is a dead end hole and the exhaust isn't running through it like an exhaust pipe. This seems to reduce the heat in the manifold and heat the carb base enough so it don't stumble when it's cool.G.M.
 
Marv said:
Before i done anyhthing drastic, i would run it till i had the problem you mentioned and then i would check the spark. If is real weak yellow or none at all i would check coil, condenser, and resister. Marv
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I agree. There are a lot of "solutions" being thrown at you without much discussion of first accrurately diagnosing the problem. Like Marv said, first determine whether it's a fuel or ignition problem then test and eliminate possible problems by diagnoses rather than just throwing possible solutions at it until you have identified the problem. Then you'll know exactly what solution to "throw" at it.

Here's my method of testing for ignition problems while driving:

I take my timing light and hook it up and put the sensor on the high tension coil wire. Then I tape down the trigger on the light so that it's always on. Then I stick the light on the cowl and shut the hood to hold it in place so I can watch the light while I drive. The light that is reading every spark coming out of the coil should burn steadily all the time. If it blinks when the engine spits and sputters you know it's spark and have to diagnose and fix that first. If not, then you know it's fuel and diagnose and fix that in ways as has already been suggested. But, for me, I like to start with the spark since it's easy to test while driving as I have described.

You ought to read this thread before assuming it's a fuel/heat problem: http://www.fordbarn.com/forum/showthread.php?t=69400&highlight=timing+light
 
Ok Guy's! Thanks so much for your help. I am pretty sure it's fuel related and not spark. I'll start looking into a spacer this week. Happy V8ing!
 
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