Hot start troubleshooting

[boilermaster]

Here we go. Another hot start thread lol could use some opinions. 

351c 2V no modifications 

Car starts immediately when cold and runs great. 

Runs good and strong when warm as well. 

The problem comes when i shut it off. 

If i wait less than say 10 seconds after shut off it will fire right back up in an instant.

If i wait longer than that say a couple minutes up to about 15-20 i have to keep the pedall to the floor while cranking.  The starter sounds strong for the first few seconds then slowly gets weaker. I would estimate it takes 5-8 seconds to start. Right before it starts the battery seems to be getting week.

The car does diesel when shut down from time to time.  I rebuilt the carb and am waiting to road test it to see if the dieseling has been solved.

My thoughts

Since the starter sounds strong at first i dont think its a heat sink issue.

I started to think fuel was getting sucked into the combustion chamber and draining the bowl. But it will fire immediately afterit cools.  so i dont think the bowl is getting emptied. 

Still have points ignition and a coil thats probably from 1999 if not older lol.  

Id really like to pinpoint the problem rather than start throwing parts at it. I know it will all have to be replaced anyway but id still like to know what the issues is incase it returns. 

Im down to 2 thoughts 

1 it is sucking fuel after shut down and flooding

2 weak spark because of old components.

Tucaz520,

Did you ever think that the fuel was being sucked up in a heat soaked condition by carbon deposits in the intake tract and combustion chambers ?

Engine run on goes hand in hand with a high idle and HOT spots, and carbon loves these two guys.

If it were mine, I would run some top end cleaner through the old girl.

I would suggest using half of a can, slowly down the carb or pcv valve and the remainder down the carb to stall the engine out, and then let the engine sit for 45 minutes or so.

Now you will have a car that is hard to start, and lots of smoke too.

What octane fuel are you using ?

Have you ever shut the car off hot, and then opened the hood and walk away for that twenty minutes, to see if there is any difference in your condition ?

I have fixed cars with the conditions you describe by removing carbon build up.

Boilermaster 

 

[Tucaz520]

Here we go. Another hot start thread lol could use some opinions. 

351c 2V no modifications 

Car starts immediately when cold and runs great. 

Runs good and strong when warm as well. 

The problem comes when i shut it off. 

If i wait less than say 10 seconds after shut off it will fire right back up in an instant.

If i wait longer than that say a couple minutes up to about 15-20 i have to keep the pedall to the floor while cranking.  The starter sounds strong for the first few seconds then slowly gets weaker. I would estimate it takes 5-8 seconds to start. Right before it starts the battery seems to be getting week.

The car does diesel when shut down from time to time.  I rebuilt the carb and am waiting to road test it to see if the dieseling has been solved.

My thoughts

Since the starter sounds strong at first i dont think its a heat sink issue.

I started to think fuel was getting sucked into the combustion chamber and draining the bowl. But it will fire immediately afterit cools.  so i dont think the bowl is getting emptied. 

Still have points ignition and a coil thats probably from 1999 if not older lol.  

Id really like to pinpoint the problem rather than start throwing parts at it. I know it will all have to be replaced anyway but id still like to know what the issues is incase it returns. 

Im down to 2 thoughts 

1 it is sucking fuel after shut down and flooding

2 weak spark because of old components.

Tucaz520,

Did you ever think that the fuel was being sucked up in a heat soaked condition by carbon deposits in the intake tract and combustion chambers ?

Engine run on goes hand in hand with a high idle and HOT spots, and carbon loves these two guys.

If it were mine, I would run some top end cleaner through the old girl.

I would suggest using half of a can, slowly down the carb or pcv valve and the remainder down the carb to stall the engine out, and then let the engine sit for 45 minutes or so.

Now you will have a car that is hard to start, and lots of smoke too.

What octane fuel are you using ?

Have you ever shut the car off hot, and then opened the hood and walk away for that twenty minutes, to see if there is any difference in your condition ?

I have fixed cars with the conditions you describe by removing carbon build up.

Boilermaster 

After seeing that egr passage blocked with carbon i started to wonder if that might have contributed to the issue.  The dieseling did stop once i turned the idle down.  

There does seem to be plenty of carbon deposits everwhere from intake to exhaust tip lol.

I have two nice black spots on the concrete where the tail pipes turn down.  This thing is still running the stock exhausts from 1973 with the orginal single exhaust crossover pipecut and welded shut lol. 

I suppose a little sea foam wont hurt.  Ill do it before i replace the plugs.

 

[boilermaster]

Here we go. Another hot start thread lol could use some opinions. 

351c 2V no modifications 

Car starts immediately when cold and runs great. 

Runs good and strong when warm as well. 

The problem comes when i shut it off. 

If i wait less than say 10 seconds after shut off it will fire right back up in an instant.

If i wait longer than that say a couple minutes up to about 15-20 i have to keep the pedall to the floor while cranking.  The starter sounds strong for the first few seconds then slowly gets weaker. I would estimate it takes 5-8 seconds to start. Right before it starts the battery seems to be getting week.

The car does diesel when shut down from time to time.  I rebuilt the carb and am waiting to road test it to see if the dieseling has been solved.

Tucaz520,

This may sound kind of corny, but gotta think Fire triangle (air , fuel, heat )

those are what is needed to make Fire (combustion) or in your case dieseling, run on.

the idle was too high, allowing air and fuel into the combustion chamber.

this, left unchecked will allow for combustion because you already have heat.

This incomplete combustion (key off) will make carbon, the carbon stores more heat

making the condition worse.

once you finally get this engine off, the fuel in the carbon deposits boils off.

when you go to restart, you are saturating (sucking up ) all the available fuel to satisfy the carbon deposits, then the engine finally starts and the cycle continues.

the Mo Co had troubles with carbon build up in the 351M/ 400 era.

remember de carbonizing many trucks at the dealership, changed out many a egr valve due to this as well.

Boilermaster  

My thoughts

Since the starter sounds strong at first i dont think its a heat sink issue.

I started to think fuel was getting sucked into the combustion chamber and draining the bowl. But it will fire immediately afterit cools.  so i dont think the bowl is getting emptied. 

Still have points ignition and a coil thats probably from 1999 if not older lol.  

Id really like to pinpoint the problem rather than start throwing parts at it. I know it will all have to be replaced anyway but id still like to know what the issues is incase it returns. 

Im down to 2 thoughts 

1 it is sucking fuel after shut down and flooding

2 weak spark because of old components.

Tucaz520,

Did you ever think that the fuel was being sucked up in a heat soaked condition by carbon deposits in the intake tract and combustion chambers ?

Engine run on goes hand in hand with a high idle and HOT spots, and carbon loves these two guys.

If it were mine, I would run some top end cleaner through the old girl.

I would suggest using half of a can, slowly down the carb or pcv valve and the remainder down the carb to stall the engine out, and then let the engine sit for 45 minutes or so.

Now you will have a car that is hard to start, and lots of smoke too.

What octane fuel are you using ?

Have you ever shut the car off hot, and then opened the hood and walk away for that twenty minutes, to see if there is any difference in your condition ?

I have fixed cars with the conditions you describe by removing carbon build up.

Boilermaster 

After seeing that egr passage blocked with carbon i started to wonder if that might have contributed to the issue.  The dieseling did stop once i turned the idle down.  

There does seem to be plenty of carbon deposits everwhere from intake to exhaust tip lol.

I have two nice black spots on the concrete where the tail pipes turn down.  This thing is still running the stock exhausts from 1973 with the orginal single exhaust crossover pipecut and welded shut lol. 

I suppose a little sea foam won't hurt.  Ill do it before i replace the plugs.

 

[Tucaz520]

Here is an update for anyone that might Google this having the same issue.

Disclaimer what I'm about to say makes no sense but its observations in my particular case.

Recently got back on this csr after letting it sit for a while. Life happens. The major thing was u finally got it registered and insured so I could start driving it more I stead of quick trips through back roads for fun.

I was still fighting with the hot start issue but had learned to live with it. I made it a habbit of taking at least 30 min before starting the car. You know how hard it is to waste 30 min at a gas station lol.

Anyway with all the driving I had been doing the radiator sprung a leak. I went ahead and replaced it with a champion aluminum one from Jegs. Not expecting anything except no more leak i went back to driving it around to run errands etc... I made a quick run to the parts store to pick up some dry sweep and just on a whim I decided to try and start the car even though it had only been off a few minutes. To my surprise it fired right up. Next a quick run to a gas station on the way home. Put my usual $20 in and called it good. Fuel gauge is inop so I just make it a habit of putting fuel in it everytime I go out. Again I was sure it was gonna have the hot start issue. Turned the key and wow it fired right up again and has been doing so ever since the new radiator.

Now I've been working on cars long enough that I would laugh at anyone telling me they replaced the radiator and their car starts better.

But I'm guessing now that with the old radiator the car was always just on the verge of overheating despite a normal reading on the factory guage. This then lead to a heat soaked starter and caused the hard start..

Another aluminum foil hat theory. The rad cap was bad and again the car built up heat and pressure but not enough to over heat. Instead it pressurized the system to the point the water pump impeller was unable to rotate and causing the hard start issue.

I can't prove either one of those all I know is ever since I put in the new radiator the hard stsrt issue is gone.

Ok feel free to laugh I sure am

 

[c9zx]

Your first theory is plausible but, I think more likely the fuel in the carb was percolating during heat soak causing the hard start. I've seen a few times. Just a thought. Chuck

 

[Tucaz520]

I'm just glad I dont have to duck in embarrassment when it doesn't start at the gas pump lol.

On to the next issue that should show its head any second now.

 

[Don C]

I agree with Chuck, most likely carburetor heat soak. Plus, your new radiator is probably much more efficient, mostly due to deposits in the tubes of the old one. Coolant continues to circulate through the engine even when it's not running, when it is hot and the thermostat is still open. Hot water, like hot air, rises, goes into the radiator, cools, and the cooler water descends, enters the block and gets heated again, helping to keep the carburetor from getting so hot.

 

[c9zx]

I'm just glad I dont have to duck in embarrassment when it doesn't start at the gas pump lol.

On to the next issue that should show its head any second now.

Owning and maintaining an old car is a bit like playing "Whack-A-Mole". Chuck