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1968 Hot Start Problem

Gregpet

Well-known member
Joined
Feb 4, 2009
Messages
51
Location
Dallas, TX
My car starts right up when cold but after a 15-20 minute drive I have to crank the engine 4-5 separate times to get it to start again (this is after the car has rested for 10-20 minutes).

Recently I had the carb rebuilt and re-installed by my mechanic and I have replaced the distributor and added Pertronix electronic ignition. I set the initial timing to 12 degrees BTDC with no vacuum hoses connected. The engine seems to run very well (thankfully). No issues with rough idle or stalls when driving.

This seems to be a timing issue but I'm not sure how the fact that the engine is hot would effect timing(?) Or maybe a carb setup issue? I had to switch from a dual diaphragm to a single diaphragm distributor (all Dallas Mustang had) so I'm also wondering if I now have the vacuum hoses hooked up properly (I now have a vacuum hose that is plugged since I now only have a single diaphragm distributor)...Would this cause hot start issues?

Thanks in advance for any help/guidance...

Greg
 

mechanicalguy48

Well-known member
Joined
Dec 8, 2008
Messages
77
Location
Poulsbo Washington
Sounds like hot start problems related to heat soak. When you run the car up to temperature then let it soak for awhile some engines are prone to percolate the fuel out of the carb float bowls. It may take awhile for the float bowls to fill, thats why you have to turn it over so much. Isolating the carb from the manifold is usually the answer to that. It keeps the carb cooler and also being carefull where your fuel lines are routed. Some people dont put back the spacers and thick gaskets(these isolate the carb) at the carb base when they rebuild or they run their fuel lines touching the motor. Either of those things could cause fuel percolation. Test it out by getting the motor hot and then after a 20 min soak in hot weather open the fuel bowls and see if you have any fuel there. If thats the problem it will be obvious. Other sources are starters that are near the end of their life and drawing too many amps after heating up(thus turning the engine over slowly and dropping avaolable voltage) , coils that break down under heat and dont provide a hot spark when hot.
 

robert campbell

Well-known member
Joined
Apr 10, 2007
Messages
4,321
Greg,
Please do not take offense from this. Many younger owners (do not know your age) have grown up with new fuel injected cars. They have not experienced an old cranky carburetor fed engine.

Reading right out of a Ford owner’s manual with some left out and some added.

Cold Starting V8:
To operate the automatic choke and the fast idle, first press the accelerator pedal all the way to the floor, and then release it all the way. Now start the engine. Fast idle will run the engine a little faster than normal. Sharp taps on the accelerator will allow the engine to step down off the fast idle cam steps.

Warm Starting V8:
If the engine is warm, it is not necessary to “set” the fast idle. (In fact any pumping on the accelerator will more than likely flood the engine). Simply press the accelerator pedal down about one inch and hold. Turn the key until it starts.

Many owners do not know to open the throttle the “one inch” or so. This allows the carburetor to introduce a larger amount of air to atomize gas “droplets” that may have formed in the carb and intake. My cars will grind a bit if you do not do this. And if the car experiences heat soak, you may want to open the carb half way. But try to cure some of the problems as Steve mentioned. A carb that continuously drains out when hot, “washes” the cylinder walls of oil and this increases wear on the next start.

Hope none of this is offensive.

Rob
 
OP
OP
Gregpet

Gregpet

Well-known member
Joined
Feb 4, 2009
Messages
51
Location
Dallas, TX
No offense taken at all! That is great information. Although I don't consider myself young any more - I don't think I have owned a car without fuel injection (until this one).

I did get the sense that I was flooding the engine while trying to start it hot (and pumping the gas pedel) so I think you are exactly right. The car is getting some paint work right now so I won't be able to try it until this weekend.

One quick clarification. You said: if the car experiences heat soak, you may want to open the carb half way. Can you expand on this - what do you mean by 'open the carb half way'?

Thanks again for everyones help.

Greg
 

robert campbell

Well-known member
Joined
Apr 10, 2007
Messages
4,321
Greg,
The manual recommends you push the accelerator down and inch of so. I estimate that at ¼ throttle. So pushing the accelerator down two inches may get you close to ½ throttle. More air if the carb has experienced heat soak. I like to use another word to define heat soak. “Percolating”. The intake and carb are hot enough that the gas “kinda” boils in the float bowl. The gas is boiling and expanding in the float bowl and raises the gas level up enough to drain down out of the carb into the intake. This causes the hard start when hot.

It is important that when you try to start hot that you do not let you foot off the gas for each time you turn the key to start it. That exasperates the problem further by adding gas via the acceleration pump each time you move the accelerator.

So prepare yourself to hold you foot one or two inches down for the duration of the hot start try.

I assume you are running a stock carb with a one-inch spacer under it? Sometimes if the car runs a bit hot and it is Sunday driver so to speak, dropping to a 160-degree thermostat can help it run cooler. I would not recommend this for a daily driver that runs a bunch in the winter. It would create other problems.

Rob
 

Midnight Special

Well-known member
Joined
Nov 5, 2005
Messages
3,713
Location
Grass Valley, California
...My 351C does this all the time. Raise the hood after shut down when hot and you can hear it "hissing" at the carb. I sometimes hold the pedal almost full down to get it re-started, but when cold, it fires right up....

I've never heard of "heat soak". Great info! Thanks!!
 
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