Any Ideas?

[DanR]

My Commodore Blue '67 Sunbeam Alpine has a new rebuilt 1974 Mustang II 2.8 V6. It was bored .060 over all new pistons, etc., Jose grind cam from DeltaCams. Mallory distributor, Ofy 4bbl with a new Holley 390. Run only 93 octane non-ethanol.

I've had it on the road a good bit since installation. It will get you to a fast speed very rapidly. Runs strong in all gears, at least to me it is pretty swift.

Driven on several short trips with very little trouble breaking in and getting the bugs out.

Only difficulty after many hours of having fun and enjoying the car is when slowing down and coming to a stop (not a fast stop) the engine will slow down to an idle for a minute or so then cut off.....I can start it up again, sometimes immediately other times it might take a bit of cranking on the starter, it will run good then when it idles back down ... for a minute or so then..... cut off!

Went thru the valve adjustment three times Friday afternoon. Runs for a minute or so then cuts off! Nothing changed.

Checked the fuel levels two or three times. Runs for a minute or so then cuts off! Nothing changed!

Checked timing several times. Runs for a minute or so then cuts off! Nothing changed!

Checked all the wiring from ignition to the distributor. Runs for a minute or so then cuts off! Nothing changed!

Took it on the road for a few miles and it ran great. Slow down and come to a stop, the idle drops down to normal, then cuts off! Nothing changed.

I then, removed the "new" Holley 390 and replaced it with another "new" 390 Holley. Went thru all the necessary steps and let it idle on it's own. Ran for a minute or so, then cut off! Nothing has changed.

Went thru the vacuum checks and found nothing.

Checked for leaks around the intake manifold, nothing found!

Man what a study in automotive mechanics

 

[Ratical]

Float level? Or ignition coil?

 

[Bill Blue]

What is your ignition system? I had similar problem "back in the day" with a Fiesta. Was ignition (DuraSpark II?). While screwing around with the carb, the ignition module would cool off enough to run for a while.

Bill

 

[DanR]

Thanks for the response....

I'm using the Mallory electronic distr with all they recommended. Mallory coil and resistor.

DanR

 

[tigretr]

Dan,
I had this issue forever when I would pull up to a light the motor would idle down and stall. Every time I rebuilt my motor I kept putting the same spark plugs in I had used the previous time. It wasn't until I rebuilt my motor the last time that I blueprinted EVERYTHING and I noticed the spark plugs I was using weren't long enough to reach the combustion chamber. The electrode was still way up in the threaded bore. Worked ok at elevated RPM's because there was enough fuel and turbulence to get the spark to propogate but at idle neither of those were true and off she went.

I would recommend making sure you are using the same plugs others are using and then put your motor at TDC and do some measuring to make sure you don't have some strange head that keeps your plugs from reaching the charge.

That worked for me. Hopefully it solves your problem.

Brian

 

[alpine_64]

Dan,

Brian's suggestion is an interesting one.

Im thinking along a basic line.. Based on your description.. It happens after a longer run .. Have you tried letting the car just idle for an extended period.. Get it up to temp.. Then in neutral give it 3000rpm constant for 20 sevonds and lift off and see it it stalls..

Im wondering if it has a heat soak issue .. Fuel line, carb heat soak perhaps.. Its fine at higher rpm when flowing but whe you lift the fuel flow slows... Then when you stop it vapourises the bowls or line dry out and stall. It would also explain the inconsistent restart after.. Just a thought.

 

[tigretr]

Dan,
I just reread your original post and realized I forgot to mention that restarting after the motor stalled in my case was also a drag. It would often take quite a bit of cranking to get it fired back up again after it stalled. This led to a number of stressful green lights as traffic stacked up behind me.

Some times I would even get a nice big backfire as it was cranking. But this was only after it stalled. First start of the day never really had any issues.

Food for thought.

Brian

 

[sd_pace]

Dan it sounds like the fuel line has a close spot by the exhaust pipe issue somewhere, it could be anywhere along the line... it dont take much

 

[MikeH]

Are you using a carb spacer?
Have you tried a new PCV valve?

 

[MikeH]

Float level? Or ignition coil?

I think a coil problem would be more evident under power. At least it was in my Mustang. It would run fine until hot, then when accelerating, it would develop a nasty miss. Although it did die at a stop light and would not start. Towed it home. It fired up the next morning.

 

[Charles Johns]

heated ignition troubles

A little tech info from an old electronics tech...ME! Get a can of "freeze" or similar product at Radio Shack or other electronics store, then spray the suspected part and see if the car starts. In an old TV repair class the engineer told us, "Solid State components either work or they don't"...to which we said, BullS*#@! We all had a can of cold spray to shoot on components to see if our suspected part was the problem. Many a time in a customers house, that cold spray cooled a part long enough to temporarily fix the problem. It is then just a matter of replacing the suspected part. It still works on CARS just like TV's and stereos! Give it a try.

 

[Cactusmasher]

modified Alpine

I don't know what electronic ignition you guys are running but here's what happened to me. Over the years I have owned mostly Fords from Mustangs to trucks. All of them that had the Ford Duraspark electronic ignition had this same problem as described by many of you.

I learned to carry a spare "brain box" with me at all times. When the same or similar problems you describe started occurring, I switched out the "brain box" and all was well again....until the next time the brain box crapped out. The problems start out intermittent and you can restart the engine until it just fails altogether.

The key to fixing the problem permanently is to move the brain box out of the engine compartment, such as inside the passenger compartment under the kick plate on the passenger side floor and put heat shielding around it.

The first V6 conversion I built, I polished the fins on the brain box and hung it proudly on the firewall in the engine compartment. Painted it black crinkle paint and with the polished aluminum fins looked pretty sharp with all the other shiny stuff. After I sold it, I got a call one day from the new owner that the electric system went dead and the car would not start or run. I had him replace the brain box and the problem was cured ( temporarily I'm sure ).

Engine compartment heat is what kills the brain boxes in the Ford Duraspark system. From what I gathered from the previous postings on this thread, it sounds like I'm not the only one that used the Duraspark system. I hope this information is helpful toward fixing some of the problems you guys are having.

 

[SoCal'beaming]

Yep ... Same symptoms and fix with the early(70's) Chrysler/Dodge/ Plymouth's electronic "Brain Box" ... changed out many 'till they get moved outa' the eng. comp. and even then they didn't last long.

........ David

 

[DanR]

Float level? Or ignition coil?

Checked and rechecked the float levels

I am utilizing the Mallory recommended coil. Seems to be fine and does not get very hot.

DanR

 

[DanR]

Dan,
I had this issue forever when I would pull up to a light the motor would idle down and stall. ..........and I noticed the spark plugs I was using weren't long enough to reach the combustion chamber.......... Worked ok at elevated RPM's because there was enough fuel and turbulence to get the spark to propogate but at idle neither of those were true and off she went.

I would recommend making sure you are using the same plugs others are using and then put your motor at TDC and do some measuring to make sure you don't have some strange head that keeps your plugs from reaching the charge.

That worked for me. Hopefully it solves your problem.

Brian

I will check on the plugs tomorrow (April 4th).... out of town today.

DanR

 

[DanR]

Dan,

Brian's suggestion is an interesting one.

..... It happens after a longer run .. Have you tried letting the car just idle for an extended period.. Get it up to temp.. Then in neutral give it 3000rpm constant for 20 seconds and lift off and see it it stalls..

Im wondering if it has a heat soak issue .. Fuel line, carb heat soak perhaps.. Its fine at higher rpm when flowing but when you lift the fuel flow slows... Then when you stop it vapour rises the bowls or line dry out and stall. It would also explain the inconsistent restart after.. Just a thought.

I can start cold, after warm up it will idle for a short time then die. Tried it after long runs different rpm's ,.... still same thing. I have looked very closely at the possibility of vapor lock. Nothing appears to be getting hot or even warm all along the fuel line.....It will not die or cut off if the rpm's are above 800 or at least not yet.

DanR

 

[DanR]

Dan,
I just reread your original post and realized I forgot to mention that restarting after the motor stalled in my case was also a drag. It would often take quite a bit of cranking to get it fired back up again after it stalled. This led to a number of stressful green lights as traffic stacked up behind me.

Some times I would even get a nice big backfire as it was cranking. But this was only after it stalled. First start of the day never really had any issues.

Food for thought.

Brian

Brian, what you say is about a "Copy" of my situation.... As I said tomorrow I will check,

DanR

 

[DanR]

Dan it sounds like the fuel line has a close spot by the exhaust pipe issue somewhere, it could be anywhere along the line... it dont take much

Steve, I have run several checks along the fuel line and can't find any hot spots nor even a warm one....

Had vapor lock on my 409 Z11 in my '58 Impala that acted on a "consistent basis" not like this at different times and temperatures .

DanR

 

[DanR]

Are you using a carb spacer?
Have you tried a new PCV valve?

Mike, I am not using a spacer! I have one, as a matter of fact I have two different ones. Did not think they would make a positive difference. And they would add height to the carb and breather,

Have a new PCV!

DanR

 

[DanR]

A little tech info from an old electronics tech...ME! Get a can of "freeze" or similar product at Radio Shack or other electronics store, then spray the suspected part and see if the car starts. In an old TV repair class the engineer told us, "Solid State components either work or they don't"...to which we said, BullS*#@! We all had a can of cold spray to shoot on components to see if our suspected part was the problem. Many a time in a customers house, that cold spray cooled a part long enough to temporarily fix the problem. It is then just a matter of replacing the suspected part. It still works on CARS just like TV's and stereos! Give it a try.

CJ, Never heard of that! I will try about anything

DanR