Flathead hard start when hot

Hotrodvideo

Hotrodvideo

Senior Member
The flathead in my '32 starts up fine when cold but after it warms up and shut it off and let it sit for awhile I have a hard time starting it.

It's a rebuilt 81a but I adapted a 59a crab style distributor with dual points.

What should I check first?
 
heat soak boils your fuel from your fuel pump and your float bowl. You smell gas, so you naturally hold the foot feed to the floor thinking it's flooded, so, no vaccuum to help prime the hot pump. Meanwhile, your old coil also experiences the heat soak in addition its own built up heat, and fails to produce adequate spark.
 
I too suspect the condenser but if your using 94 Carbs you may want to check the power valve or gasket for it.
 
Before we start guessing what do you mean by hard start? Does it turn fine but not fire? Does it turn too slow?
 
Many of us that use our flat motors regularly are experiencing the same issue and I attribute it to the new ethanol enriched fuels lower boiling point. These fuels are designed to be used with fuel injected engines not carburetors. When you engine gets up to operating temp and is shut off the heat sink high point of the engine is the carb. The cool down point of the engine is the highest point as heat rises, so all the heat from the engine moves to the carb and begins to evaporate the new design fuel from the carb leaving remaining fuel low in the fuel bowl. Because the engine cranks so slowly the fuel bowl takes some time to refill and thus the hard start issue.

My approach has been to mix my store bought ethanol fuel with racing gas fuel to raise the vaporization point and prevent this carb percolation issue. Unfortunately if you go on a long trip you cannot always replenish the race gas so I try to look for gas stations that sell non ethanol fuel.

I think this is may not be the exactly correct answer but its what I have done to cut down the hard start issue. My other option has been to carry a can of spray starting fluid and on hot days or long drives when restarting a hot engine give the air filter a good dose of starting fluid to help get the engine fired faster and the fuel pump to bring in a new batch of cooler fuel. Welcome to the new world..
 
ford38v8 said:
heat soak boils your fuel from your fuel pump and your float bowl. You smell gas, so you naturally hold the foot feed to the floor thinking it's flooded, so, no vaccuum to help prime the hot pump. Meanwhile, your old coil also experiences the heat soak in addition its own built up heat, and fails to produce adequate spark.
Click to expand...

The fuel bowl is vented, so you wouldn't have vacuum there no matter what.
 
Last edited:
I grew up with "flatties." They were the most dependable engines on the road. Always started on half a revolution hot or cold, covered with snow or water. My Dad never had one overheat and never, no matter what the conditions, had one fail to start. When our neighbors couldn't get their Chevys, Pontiacs, Buicks or Chrysler Products to start, my Dad would be on his way to work in our '35 Ford. This was in 1948. So all that being said, I recently sold my '48 Merc. just because of the problem you're having. I went through three 94 Carbs before I found the problem. It was exactly what Dick Spadaro said in his reply. Ethanol, Ethanol, Ethanol !!! In fact I put one of Dick's insulators under the carb and that "cured" the problem for the most part. That came with other issues though. On initial start, the inside of the throat of the carb would ice up and cause a very rough idle until she reached normal temperature. Our wonderful Politicians here in New York have seen to it that un ethanol fuel is no longer available on Long Island. Try getting a full season out of your lawn mower or other implements including boats. Bottom line? There is a 90% chance, in my opinion, that ethanol in your fuel is the culprit. OMO and experience!
Rich O.
 
Hotrodvideo said:
The flathead in my '32 starts up fine when cold but after it warms up and shut it off and let it sit for awhile I have a hard time starting it.


May I suggest you take a look at what Old Henry posted on
2-4-2014 in response to my thread about gas tanks and related.

Re: 48 coupe- lets talk gas tanks and related

He added an Airtex electric fuel pump in order to get the gas flowing again when the car vapor locked. The way he has it, he can then turn off the Airtex and run on the stock fuel pump. I think I got that right.
Click to expand...
 
ford38v8 said:
Nothing to do with the fuel bowl being vented. I can see the confusion, though, as I failed to say that choking it down would help prime the pump.
Click to expand...

Could you explain?? Cuz if that's the case, why do people bother with an electric pump to prime the mechanical pump??

I thought the venturi vacuum just pulled fuel from the bowl, not up from the tank to the pump.

Seems if the fuel bowl is low, then there's no fuel for vacuum to pull through the passages, and because the bowl is vented, would only draw air.
 
Last edited:
1952henry said:
Could you explain?? Cuz if that's the case, why do people bother with an electric pump to prime the mechanical pump??

I thought the venturi vacuum just pulled fuel from the bowl, not up from the tank to the pump.

Seems if the fuel bowl is low, then there's no fuel for vacuum to pull through the passages, and because the bowl is vented, would only draw air.
Click to expand...

So... my theory sucks. However, the later 94's having the internal vent tube could still benefit from choking, so ya think I might save face after all? :o
 
I sent my distributers to bubba, my coils to skip, i dont run eth gas. All is well. Cruised the 36 for a hour straight. Stop.... Then Stop and go. Idled the engine for 20 min after up to 200. Turned it off. Cranked right up... Not my experience before and maybe just lucky.

As posted condensor or coil is alway suspect.
 
Just to clarify, I'm using a stock mechanical fuel pump and dual 97's on an Edmunds regular dual intake.

It's a 12v system and the condenser is a fairly new 12v and mounted on the dist in the stock position. I've heard that some guys move it off the dist, away from the heat source.

Once the eng warms up and I shut it off for awhile, it really takes a long time to start it, lots of cranking and I usually have to pump it like crazy and then it starts up and runs rough for a minute.
 
Hotrodvideo said:
Just to clarify, I'm using a stock mechanical fuel pump and dual 97's on an Edmunds regular dual intake.

It's a 12v system and the condenser is a fairly new 12v and mounted on the dist in the stock position. I've heard that some guys move it off the dist, away from the heat source.

Once the eng warms up and I shut it off for awhile, it really takes a long time to start it, lots of cranking and I usually have to pump it like crazy and then it starts up and runs rough for a minute.
Click to expand...

What's the outside temperature when this occurs?? Sounds to me like hot weather and vapor lock in the fuel pump or gas boiling in the carb. after heat build up after shut down. For the carb problem you need a carb base insulator. Contact Bob Shewman gadgiteer@aol.com or 1-610-933-6637 he has the best one I have seen. The pumps vapor lock problem on hot days with the new gas is an unresolved problem at this time. G.M.
 
New? Last summer, new dual point that was all checked out on a distributor machine, etc. The Mallory condenser quit. Maybe 150 miles
of driving on it. Replaced with a Vertex mag condenser and no problems. NAPA has an Echlin and I think the part number is a FA82.
Just because it is new, does not indicate it is good.
 
You have 12 volts and should spin fast enough.
I would go with a 12 volt selinode 2 post the ign post run direct to coil.
Ford used that fix for years.
 
You must log in or register to reply here.
Back
Top