Langdon HEI problem, I think

[Powerhouse]

I was having probs with my car...similar but not exactly the same.

I tested igniton parts, took apart the carbs and cleaned them, then I took the electric pump out of the system and put the old stocker back in. When i took the the elec pump out I noticed the fram see thru plastic fuel filter had some sediment in it so I replaced it. When i disconnected the filter on the "out" side the fuel didn't come pouring out as it should have. when I disconnected the "in" side...fuel cam out of the line from the tank as expected. I think the filter was clogged somehow...looked clean to me.

I should have stuck to the old game plan when diagnosing car trouble....START WITH THE CHEAPEST PARTS FIRST.

[martybose]

Well, I had a theory that maybe the ignition switch was having a problem because of all of the electrical stuff that I have added. So I bought a new ignition switch, then made up a panel that had a pair of 70 amp relays feeding fuse panels, one for the ignition side, one for the accessory side. This way there is no additional load on the switch at all.

Finished all of the wiring today, checked it all out, started the car up, everything seemed fine, so went for a drive.

I made it one block before it went back to 3 cylinder mode, so clearly my theory was wrong. But this time I had a laser pyrometer with me, so I now know conclusively that the back three cylinders went dead, as the exhaust header temps were down a bunch, while the front cylinders were fine.

So I guess I'll pull off the back Carter-Weber and tear it down. I didn't see anything wrong when I looked in it before, but what the hell.

Damn, this is really getting to me.

Marty

[Dodgeb4ya]

Possibly rear carb isn't getting fuel or not suppling it. My big truck 6 twin carb engine does the same thing cold upon sitting a month or so-rear 3 cyls won't fire till rear carb gets filled (front carb fills 1st and fast , then takes a bit longer for the rear carb to fill and supply fuel to the 3 rear cylinders. The engine kinda drones till the rear 3 fire.

Do you have a fuel filter on the rear carb too- maybe it's partially plugged up?

Bob

[martybose]

Possibly rear carb isn't getting fuel or not suppling it. My big truck 6 twin carb engine does the same thing cold upon sitting a month or so-rear 3 cyls won't fire till rear carb gets filled (front carb fills 1st and fast , then takes a bit longer for the rear carb to fill and supply fuel to the 3 rear cylinders. The engine kinda drones till the rear 3 fire.

Do you have a fuel filter on the rear carb too- maybe it's partially plugged up?

Bob

No separate filter; there's two inline to a Y-block that feeds both carbs. A while ago I pulled the tops off of both carbs after one of these episodes, and the fuel level was the same in both. No obvious smoking gun, but I'll look inside for something awry.

Marty

[Don Coatney]

Is your intake manifold to the back 3 cylinders icing up internally? Did you shoot temperatures on the intake manifold as well as the exhaust manifold? Is the rear intake manifold cracked and sucking air? Did you pull and read the spark plugs?

[martybose]

Is your intake manifold to the back 3 cylinders icing up internally? Did you shoot temperatures on the intake manifold as well as the exhaust manifold? Is the rear intake manifold cracked and sucking air? Did you pull and read the spark plugs?

I didn't check the intake temperature, but I don't think it ran long enough to ice up, and it does have a working hot water pipe running though it, and it was already warm.

It is an Edmunds manifold that has a plenum for all six cylinders. I haven't pulled the sparkplugs yet, I was too annoyed to work on the car any more. Thinking about the last few trips, the change to 3 cylinders almost always happens as I am shifting gears; 1st to 2nd yesterday, 2nd to 3rd the last time. Maybe something to do with higher fuel rate or higher vacuum as I lift off the throttle to shift? Many things to think about ......

Marty

[oldodge41]

Any chance you have something floating around in the gas tank that restricts the fuel pickup at times? Fuel may slosh around during your upshifts. I had a problem with my '41 that I thought was vapor lock, turned out I had a big chunk of old varnish-like substance that had broken loose from the tank floor and would block the pick-up point. I had flushed the tank a couple years earlier but this was apparently stuck fast and eventually broke free. My car had sat for 25+ years though.

[T120]

I'm not familiar with Carter-Weber caburetors.It might be interesting to swap position of the carburetors (front to back) and note any significant change

[Don Coatney]

In my drag racing days I would do a full power shift. However I would not recommend that you do so.

[Don Coatney]

I few more thoughts. I once was responsible for operating a V-16 cylinder ammonia refrigeration compressor. This was shaft driven by an electric motor from one end and had a common crankshaft for all 16 cylinders. One day it was noted that 8 of these cylinders (the ones furthest away from the electric motor) quit pumping. After much deliberation all to no avail we elected to disassemble the compressor. Found the crankshaft had broken right in the middle allowing the 8 cylinders closest to the motor to work but the other 8 to not work. Now I wonder if you dont have something crazy such as your carburetor shaft being split. Only working when cold and as soon as you drop the throttle to shift the vacuum pulls the butterfly closed even though it appears the shaft is moving from the outside.

So I am in agreement with Ralph D25cpe. Swap the carburetors front to back. and see what happens.

[yourpc48]

I read all the posts and all the normal suggestions have been made. I dont know what weber model your running but if the model your using has a power valve you may have a bad diaphram in the valve. Holleys had this problem too. Just another of many suggestions. Since you know it drops the back 3 I would try the back carb. Hope this helps.

[martybose]

Thought I would put in an update to this long-running thread. I've been so annoyed with this issue that I have literally left the car sitting for about four months since the rewire job proved not to be the answer. Since I had confirmed that the problem is the back 3 cylinders, my suspicions had turned to the back carb, which looked fine the last time I took it apart. This week I decided to bite the bullet, so I ordered a new Carter-Weber carb to try a shotgun approach to my problem. I decided to pull off the rear carb yesterday in preparation for the pending arrival of the replacement carb. I took it off and set it on my workbench. Just for giggles I pulled off the top of the carb to see if there was anything foreign inside, and everything looked clean as a whistle. I pulled out the jet carriers and they looked fine, just like the last time.

Then I did something different. For those that don't know, the main jet system in these carbs is a three piece affair about 2" tall that press-fits together. I took it apart, and to my surprise found something that looked like a 1/16" diameter hairball sitting in the middle section on top of the lower jet! I can't figure out where it came from, or how it even go in there, but it certainly isn't supposed to be there! So I spent the rest of the day going through the jet system and the carb body with carb cleaner and compressed air trying to flush out anything else that might be hiding in there (I didn't find anything else). Today I'm taking apart the power valve system to check it, then may put it back together, charge up the battery and risk taking it out for a spin again; wish me luck!

Marty

[Don Coatney]

Good luck! I hope you found the problem? As the saying goes if you think it is electrical is is probably fuel related.

Have you installed your dual master cylinder yet?

[yourpc48]

Sometimes you just have an "AH HA" moment.

[Mark Haymond]

I helped a friend with his 48 Plymouth with an stock engine that would start fine, run fine, but stall at a stop sign after a run up to 50 mph. We tried a different good distributor, coil, spark plug wires, and carb with no success. He called me a few days later and said he had a vacuum leak on the intake manifold and that a new gasket cured his problem. The heat from a run at 50 mph would change the temp and shape of the manifold such that he got a vacuum leak at a stop sign and his idle would die. Not the same as your losing a few cylinders but awfully close.

[807kirby]

just my 2 cents, I had a harley the would drop one cylinder when hot. It seamed to be cured with a better ground wire to the frame! I chased this problem for a year! It also had electronic ignition.

[martybose]

Well, I drove it about 5 miles this afternoon, with no signs of my problem reoccurring. One thing I did note, however, was that it was idling quite a bit higher, which is a good sign; earlier in this thread I had commented that I had to turn up the idle screws to get it to idle, so I turned them back down when I got back to the garage.

I did note that removing and reinstalling the carb messed up the synchronization of the linkage a bit, so that's next, followed by reinstalling my HEI and wide gap plugs. Then maybe I'll be back where I was about 3 years ago!

Don, yes, I did complete my installation of the dual master cylinders, so now I have front disk brakes and the dual master cylinder. It stops much better now!

Marty