351 stalls after exiting freeway

[nickjames138 15]

My 1969 Mach fires right up in the morning and drives great....for a few miles and then starts stalling and will not start back up. I let it sit for 15 minutes and it starts right back up and drives great for a mile or less and starts stalling again. Thoughts?

 

I have a 351w with I'm assuming a big cam because it sounds great. I know it wasn't producing enough vacuum to stop the new wildwood brakes with a master cylinder and power brake booster, so I switched to a manual wilwood break booster which helped the brakes considerably. It was also running fine (a little rich) before I put on vintage air AC. As the mechanic put AC on he bumped down the timing and carb. I tuned the carb back to running rich and it's still stalling.

 

I've heard it could be the distributor (which I believe is new), could be the lock in torque converter not releasing after driving on the freeway, or it could be the electric starter heating up?

 

Thoughts please!!??

[Dave R. 85]

Could it be the coil heating up and quitting? Standard ignition or a MSD/Pertronix set-up? Sounds electrical. Something is overheating, breaking down, cooling off and then working again. Dave R.

[1969_Mach1 333]

Does it only die when coming to a stop like the topic of your post suggests or at any speed?  If its only when coming to a stop it might not be an ignition issue.

[nickjames138 15]

I believe the guy who had it before me put an electric ignition on it. It only does after I've driven it on the freeway or far on back streets then slow down at a stop. It always dies of i drive on the freeway and exit. A couple hundred feet after I exit it dies. Then I have to coast to the nearest safe spot and let it sit for a while before it will start back up.

[barnett468 418]

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wha carb d you have?

 

if its a holley style, set the gas level to just below the inspection holes with the engine idling . . if i has clear windows you must remove them.

[nickjames138 15]

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wha carb d you have?

 

if its a holley style, set the gas level to just below the inspection holes with the engine idling . . if i has clear windows you must remove them.

It's an edelbrock.

[1969_Mach1 333]

Do you know what carb is on it?  I had a Holley cause behavior just like you are experiencing.  That was a long time ago.  With what I know now it could have very well been debree floating around in the main well of a metering block and occasionally plugging an idle fuel restrictor.  After 20-30 minutes of driving when I would come to a stop the engine would shut off.  Mine would restart but I had to keep my foot on the throttle because it would die at idle.  I would have to wait 15 minutes or so before it would idle again.

 

After it dies have you been able to start it and keep it running by holding the throttle open some and not let it idle?  Or will it just not start at all for at least 15 minutes?

 

You mentioned torque convertor locking up and not disengaging, is it an overdrive trans in the car?

 

Do you know what distributor and ignition system is on it?  Still really cannot rule out something there.

[Max Power 74]

When it does, take off the gas cap and see if it sucks in air. Then see of it restarts right after that. This almost sounds like a vacuum lock problem.

[1969_Mach1 333]

I didn't think of something that simple.  Good possibility.  It should be a vented gas cap.

[nickjames138 15]

When it does, take off the gas cap and see if it sucks in air. Then see of it restarts right after that. This almost sounds like a vacuum lock problem.

Thanks man. I'll try it later today and see what happens and let you know.

[danno 128]

I am really not much of an expert, but I remember vapor lock issues occuring from similar situations.  I don't think the conditions of vapor lock can occur on a carb car, but still wonder.  If the problem is related to the engine being at full temp, and not when it cools down, it could be a fuel issue.   Maybe try a non-oxygenated fuel in it?  In Minnesota we can buy gas without alcohol in it at select locations.  Try that, nothing to loose?

 

I would tend not to think it is an electrical problem. There is nothing special about the ignition system when it slows down after running at full speed.  If it would die on the freeway before you slow down, then maybe.  It is easy enough to verify; the next time this happens, and it will not re-start, see if you have spark.

[nickjames138 15]

I am really not much of an expert, but I remember vapor lock issues occuring from similar situations.  I don't think the conditions of vapor lock can occur on a carb car, but still wonder.  If the problem is related to the engine being at full temp, and not when it cools down, it could be a fuel issue.   Maybe try a non-oxygenated fuel in it?  In Minnesota we can buy gas without alcohol in it at select locations.  Try that, nothing to loose?

 

I would tend not to think it is an electrical problem. There is nothing special about the ignition system when it slows down after running at full speed.  If it would die on the freeway before you slow down, then maybe.  It is easy enough to verify; the next time this happens, and it will not re-start, see if you have spark.

I think you're right! I probably need to reroute the fuel line away from the engine? My engine is incredibly hot! Really fast

[barnett468 418]

see my post on your other thread

[1969_Mach1 333]

Edelbrock recommends, on their own website, to use an insulating spacer like a 1" Phenolic spacer between an Edelbrock carb and an aluminum intake manifold to prevent the fuel from percolating in the bowl's of the Edelbrock carb.  The other option is to block the heat crossover passage in the intake manifold.  The heat crossover is really not beneficial on an aluminum intake.  Especially if you have a manual or electric choke and no EGR valve like with these cars.  If you suspect the fuel line is getting too hot causing vapor lock, covering the fuel line with an insulating sleeve is one option.

[barnett468 418]

get it hot then go around 25 - 28 mph and slam on the brakes . . if it dies, you gas level is too high in the carb.

 

if you have a heat cross over in the intake and it is connected, i would disconnect it.

 

yes a 5/16" phenolic spacer or 5/16" thick paper carb gasket can help if it is carb fuel boiling.

 

if the fuel line is 1/2" away from the engine and 1" away from the exhaust it is ok.

[Max Power 74]

I think you're right! I probably need to reroute the fuel line away from the engine? My engine is incredibly hot! Really fast

I was thinking of that as well, but you mentioned it happens after 15 minutes on the freeway, but it takes longer while driving back streets. Usually not being able to dissipate heat is a big cause of vapor lock, and you can get rid of heat easier on the highway than back streets. That's why I leaned towards your fuel tank not venting properly.

 

But, vapor lock is a funny thing. Could be either.

[nickjames138 15]

I was thinking of that as well, but you mentioned it happens after 15 minutes on the freeway, but it takes longer while driving back streets. Usually not being able to dissipate heat is a big cause of vapor lock, and you can get rid of heat easier on the highway than back streets. That's why I leaned towards your fuel tank not venting properly.

 

But, vapor lock is a funny thing. Could be either.

True, but it doesn't stall on the freeway when I hit traffic. It only stalls after a LONG drive then exiting freeway and turning onto another street. I just drove it today 5 miles up the street and back (which is a long time to drive in Los Angeles' traffic) and it was fine. HOWEVER, I do remember that when I get on the gas and hot rod it a little bit that's when I start having issues. I drove very slow today and didn't give it a lot of gas off the line. Usually when I'm on the freeway I open it up here and there. When I'm at full throttle it starts to get choppy (almost like i'm pushing the accelerator in and out although I'm not).

 

I was thinking about cutting a hole in the hood under the hood scoop to cool the engine as much as possible. Has anyone done this? I'm afraid of making a big change like that and ruining the hood. 

[1969_Mach1 333]

True, but it doesn't stall on the freeway when I hit traffic. It only stalls after a LONG drive then exiting freeway and turning onto another street. I just drove it today 5 miles up the street and back (which is a long time to drive in Los Angeles' traffic) and it was fine. HOWEVER, I do remember that when I get on the gas and hot rod it a little bit that's when I start having issues. I drove very slow today and didn't give it a lot of gas off the line. Usually when I'm on the freeway I open it up here and there. When I'm at full throttle it starts to get choppy (almost like i'm pushing the accelerator in and out although I'm not).

 

I was thinking about cutting a hole in the hood under the hood scoop to cool the engine as much as possible. Has anyone done this? I'm afraid of making a big change like that and ruining the hood. 

 

The description of the issue is s little confusing.  "Choppy" sounds like a sudden off and on like the ignition is being turned off and on or valve float is occurring.  This would indicate either something is wrong in the ignition system or there is a valve spring setup issue.  "Like I'm pushing the accelerator in and out" sounds much more gentle and gradual which would usually indicate a lack of fuel.  Air restriction into the carb will also cause similar effects.  Is there a better description of the issue?

 

FYI:  In general with carbureted engines when you let off the accelerator and let the throttle return to idle, the fuel mixture gets extremely rich.  High engine vacuum during that time is pulling fuel from every circuit in the carb.  I wonder if the overly rich mixture during those times is causing the engine to die.  Then the wait time is needed to let a flood like condition clear out.  Maybe somebody else will have input on this thought.  Or maybe that thought doesn't pertain to this issue?

[Brian Conway 264]

 Mach1 I think your onto something.  Next time you, Nick, pull off the freeway and the car stalls;  try starting it as if flooded.  Gas pedal floored and stay floored while the engine cranks over.  Brian

[barnett468 418]

 When I'm at full throttle it starts to get choppy (almost like i'm pushing the accelerator in and out although I'm not).

 

I'm thinking about cutting a hole in the hood under the hood scoop to cool the engine as much as possible. Has anyone done this? I'm afraid of making a big change like that and ruining the hood. 

 

That is not electrical, it is fuel related and can be called surging  . . Your carburetor obviously needs tuning.

 

Do NOT cut holes in your hood.

.

[1969_Mach1 333]

+1 barnett468, those were my thoughts as well.

[Rsmach1 71]

+1 with Barnett468. Have you checked your fuel filter lately?

[shaun071 62]

I had a similar issue with a Mazda RX7 after it being in the bodyshop for a repaint. Both fuel filters were clogged as was the mesh filter at the carb fuel inlet.

[barnett468 418]

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can you pull out the front spark plug on both sides and post a photo of them?

[nickjames138 15]

That is not electrical, it is fuel related and can be called surging  . . Your carburetor obviously needs tuning.

 

Do NOT cut holes in your hood.

.

I'm not really good at tuning the fuel/air screws on the carb. I'll tell you my symptoms and maybe you can give me some insight. First off, the car REAKS of gasoline. Anytime it idles for 5 mins I smell like i worked in a gas station. I know old cars smell like that, but I get headaches from the strong gas odor that comes from my car. It starts and drives fine when it's been sitting over night. I drove it the other day a few miles around back streets being really gentle with accelerating and cruising. It ran fine and I made it home. However, if I hot rod it around town or drive it on the freeway it stalls after being driven hard. I'm guessing when it's at it's hottest it stalls. Also, It hesitates off the line. It has one gap in accelerating then takes off. I replaced the fuel filter, I know the fuel line sits right on the block, and it has an Edelbrock carburator. What would you suggest?