MKII stalls after reaching operating temperature

[o2bdriving]

Hello all. My stock MKII runs well when cold but after about 15miles dies like it's fuel starved. Starts back up but dies shortly thereafter as I limp home. Changed needle valves, adjusted float levels (Holley 4B 80783-1), tightened the sheet metal screw holding the ground wire on the LP SU fuel pump, pulled fuel line to fill a glass jar. Can hear the pumping ticking away so presume the points are operational. That all seems fine but I'm open to your ideas. Couldn't find a fuel filter in the usual locations (b4 Fuel pump/b4 carb) so guessing that they didn't add one back during the restoration. Thinking of adding an electronic fuel pressure gauge to monitor the pressure when it craps out.

A few have suggested that it may be electrical and change the condenser in the DP Distributor (C5OF-12131-B). Out of desperation, I took it to the local speed shop that says that they specialize in American muscle so figured that they'd know a 289. Turns out they like EFI and didn't know much about carbs but offered to take a look. Found plug 1 wire was loose. Aside from effing up my interior door handle (grr), they suggested changing the Ballast Resistor to see if that helps. Hmm.

Again, it runs strong when first starting out but STB after it gets hot. If I left anything out that would help in the diagnosis, let me know.

Thanks

Steve
7034994886

 

[ABSunbeams]

Could be a plugged fuel line, if the tanks were never cleaned out(age old problem).
I had an issue with a bad condenser that would shut down when it got up to temp, cooled off and would start right up. Changing to petronics solved that issue.

 

[Theorangetiger]

What kind of carb spacer do you have?

 

[o2bdriving]

What kind of carb spacer do you have?

No spacer. Carb sitting atop F4B manifold.

 

[Theorangetiger]

You might want to consider a spacer. I had this issue back when my MK I was my daily driver. There's a real possibility that the warmed up engine is boiling the fuel in the carb bowls and causing starvation. I was running a Holley straight on top of an F4B then.
Check everything else - fuel pressure, spark etc. after it has warmed up to eliminate them first.

 

[KenF]

I use to run this heat shield setup on another SBF. You may have to trim a bit to clear the linkage. If height clearance is an issue, you can remove one or more of the shield/gasket pairs.

https://www.summitracing.com/parts/mrg-3710

 

[venice532]

Hi Steve, I had the same symptoms with an alpine years ago. It would happily run for about 15 minutes and then it would start to sputter.
When I popped open the gas cap I heard air getting sucked in.
It turned out the vent on the cap was clogged and the negative pressure that formed was fighting with the fuel pump.
This might not be the culprit here but it's worth checking.
regards
Bob

 

[TAH_Tiger]

A phenolic spacer did the trick for me. Mine is only 1/4" so doesn't interfere with hood spacing.

 

[o2bdriving]

I use to run this heat shield setup on another SBF. You may have to trim a bit to clear the linkage. If height clearance is an issue, you can remove one or more of the shield/gasket pairs.

https://www.summitracing.com/parts/mrg-3710

ordered one.

 

[o2bdriving]

A phenolic spacer did the trick for me. Mine is only 1/4" so doesn't interfere with hood spacing.

Likely do the same to gain some separation.

 

[hottigr]

You can add these gasket/spacer combos until you run out of head room- serves as a heat shield and adds a little ram effect:

 

[o2bdriving]

Hi Steve, I had the same symptoms with an alpine years ago. It would happily run for about 15 minutes and then it would start to sputter.
When I popped open the gas cap I heard air getting sucked in.
It turned out the vent on the cap was clogged and the negative pressure that formed was fighting with the fuel pump.
This might not be the culprit here but it's worth checking.
regards
Bob

Thanks Bob. Was thinking about that too. I'll check the vent. Didn't hear any great sucking sound when I popped the gas cap. Car mostly sat for the last decade so shaking out lots of little things.

 

[Warren]

The MK2 fuel filter location is under the rear of the car by the spare tire bulge. It's a mess to change being at a low point on the tanks so be ready to get soaked.
Bob is right many other vented gas caps fail. We hope you are not going to have to deal with the flaking epoxy in the tanks. I don't really believe in those see through fuel filters by the carb but it takes some vapor lock questions out of the picture. A spacer is great for a big complaint that a hot sitting motor percolates fuel easy vaporizes all in the bowl when parked. After a long drive I pop the hood and vent the garage. That keeps the eau de garage smell down some too

PS if you can stand the sight of a extra wire of a Pertronix it's a set and forget as there's so much else to do.

 

[mr55s]

I had a bad ground strap that would start and not start the car, check connections. Also the ceramic ballast in the mkll could give you grief.

 

[SunbeamTgr]

I think I may know the source of your misery, that is, IF that Holley is the "center pivot" style of fuel inlet. Going on 7 years ago, we fought a similar problem on the return to Oregon from SUNI in Colorado Springs. The car would run fine for a while, then start to bog, losing power. Seemed to have good fuel pressure, and to help, we bought bags of crushed ice to improve fuel pump pressure. Made it all the way home with some creative driving!! I was certain is was a fuel related problem. I FINALLY found the problem! Both carburetor fuel filters, front and back, were badly restricted. I will never forget the euphoric feeling when I blow tested those two filters and knew I had finally nailed it!!
Gary Haslip

 

[o2bdriving]

The MK2 fuel filter location is under the rear of the car by the spare tire bulge. It's a mess to change being at a low point on the tanks so be ready to get soaked.
Bob is right many other vented gas caps fail. We hope you are not going to have to deal with the flaking epoxy in the tanks. I don't really believe in those see through fuel filters by the carb but it takes some vapor lock questions out of the picture. A spacer is great for a big complaint that a hot sitting motor percolates fuel easy vaporizes all in the bowl when parked. After a long drive I pop the hood and vent the garage. That keeps the eau de garage smell down some too

PS if you can stand the sight of a extra wire of a Pertronix it's a set and forget as there's so much else to do.

Thanks, hoping that the tanks are still clean. Somehow that missed putting the fuel filter back when they restored the car. Not visible under the hood either. Will double-check the inlets on the carb for some inline dbaggery.

 

[o2bdriving]

I had a bad ground strap that would start and not start the car, check connections. Also the ceramic ballast in the mkll could give you grief.

Thx, I'll swap ballast resistors.

 

[o2bdriving]

Ok, looks like the general consensus is heat buildup along the fuel delivery system. Will work on isolating the fuel line and carb from the heat.

1. Will add insulation on the fuel line that runs between the engine block and header.
2. Will add heat shield under the carb and build up the gasket.
3. I Will check that system is venting
4. Adding electronic fuel pressure sensor/gauge to ensure the pressure is maintained while crapping out.
5. Will swap out ballast resistor and coil. I'm just about ready to go pertronix. This one looks like I can keep the stock coil and ballast resistor. 1281.pdf (shopify.com)
6. Have a spare SU Fuel pump too. I had seen a diagram where someone added a valve to cut off fuel so they could change the filter without draining the tanks.
7. Anything else?
8. Thanks to all for helping with a plan of attack.

 

[Warren]

Here's how they put the filter on at the factory. There was a stock plastic Fram there . If you are changing things having the filter on the intake side of the fuel pump makes sense. I fashioned a super fine screen on the intake side as I wanted some pump protection and the correct but questionable stock appearance.
When it's having it's out of fuel problems is there visible raw fuel from the accelerator pump discharge tubes. I would also think of a big filter like shown as a nice way to maintain pressure.
Can it be that hot in Va. this time of year.

 

[o2bdriving]

Here's how they put the filter on at the factory. There was a stock plastic Fram there . If you are changing things having the filter on the intake side of the fuel pump makes sense. I fashioned a super fine screen on the intake side as I wanted some pump protection and the correct but questionable stock appearance.
When it's having it's out of fuel problems is there visible raw fuel from the accelerator pump discharge tubes. I would also think of a big filter like shown as a nice way to maintain pressure.
Can it be that hot in Va. this time of year.

View attachment 13552

Nah, it's in the 50's/60's as the high. 70ish next weekend. Was almost 40 when we teed off this morning. Don't notice any fuel discharge when it's acting up. Changed Ballast Resistor and went for a ride but not long enough to get very warm. Mostly just to make sure it was functional. Will take it for a longer ride tomorrow while I wait for the heat shield and fuel pressure gauge to arrive. Then I'll place the insulating sleeve on the fuel line, the heat shield under the carb, and the electronic fuel pressure sensor on the fuel line. If the pressure is low or gets low when it craps out, I'll change out the old SU for the new one from my spares box. Pic below is what was there before the resto. I do plan to add a filter back but will have to drain the tanks first.