Engine runs terrible when cold, great when warmed up

[1 Wild R/T]

My 67 Dart had 5.7 volts with Ign ON. The 75 Power Wagon had 6.4. Both start and run fine with no choke in 60 degree weather and above.

Slide a hotter cam in & tell me how they do...

 

[Kern Dog]

Ha! Yeah...
The Dart has a 280/474 and the Power Wagon is stock.

 

[dieseldazzle]

I would start with the basics and do a compression and leak down test, just to eliminate anything mechanical. You said it ran fine with no choke when cold and then out of the blue it runs like crap until warm? Id look into something more mechanical that is masked with a warm engine like a low cylinder etc. You seem to have most of the common crap dialed like vacuum leaks, ignition timing, voltages and crappy cali fuel. I will agree with WILD RT that this new fuel is garbage. We have over 50 cars that sit around so I do feel that pain.

 

[Kern Dog]

I would start with the basics and do a compression and leak down test, just to eliminate anything mechanical. You said it ran fine with no choke when cold and then out of the blue it runs like crap until warm? Id look into something more mechanical that is masked with a warm engine like a low cylinder etc. You seem to have most of the common crap dialed like vacuum leaks, ignition timing, voltages and crappy cali fuel. I will agree with WILD RT that this new fuel is garbage. We have over 50 cars that sit around so I do feel that pain.

I looked back at my notebook that I keep for the car. This started in June. The gas in the tank was full in February but it may have been filled up the month before that. My other cars can sit for longer periods and start up fine. Maybe having lower compression and milder cams allows them to run on crappy gas without too much trouble ?
I like the idea of doing a compression check. Maybe with the engine cold it might reveal something. It gives me an excuse to replace the spark plugs too.
First up, I am going to pump out all the gas in the tank and refill it with fresh 91 octane. I'm even going to drain the fuel bowls to get all of this old gas out.

 

[91r/t]

Kern do you even know what cold is??? You are in Cali man! Haha hope you can get this problem nipped in the bud.

 

[BB BELLA]

have you checked fuel pump volume/pressure when cold?

 

[Mike67]

Oh, I have the budget but I figure that if I can't figure out a carburetor setup, I'd be far worse when an EFI problem pops up!

Most of the efi set ups have diagnostic tools. The best thing is that they constantly change the tune based on optimum AF ratios. You can go from sea level into the mountains and never worry about it again!

 

[Darter6]

For fun look up Project Farm on You Tube. He did a comparison on gas new vs old. As stated above the year old gas was hard to light with a grille lighter.The fresh fuel lit off by barely a wave near it.

 

[Don Frelier]

Before you go and drain all the fuel and change it out.
Have you tried pushing the choke closed with your finger or sliding your hand over the carb opening while it's running?
That's the way we do it up here in the cold.

 

[Sweet5ltr]

Kern, I can tell you - on our diesel fleet vehicles - old diesel that was six months old wouldn't allow them to run [08' 6.6 Duramax]. Sloshing in 5-gallons of fresh diesel with the old diesel, they fired right up instantly.

I'm sure you noticed my picture yesterday, of what looked like gold paint flaking & the sludge in my regulator housing, this occurred after only 3-5 months of sitting. Most likely you have some build up plugging one of the orifices [which you need to verify]. I would start with just adding a few gallons of fresh fuel, maybe a bottle of seafoam. If that doesn't clear it up, then start diving in deeper.

 

[dvw]

Have you checked the gap on the distributor pick up? Should be .008"-.010". Swap a coil from another car and test. Your coil voltage looks fine. One more test. Coil voltage should come up during cranking as the ballast resistor is bypassed. Have you watched the choke? One kick it should fully close. Then open about 1/8"-3/16" when first started. If it doesnt open it'll load up. If it opens to far it'll fall on it face. Is the fast idle screww adjusted so the engine runs about 2500rpm warm?
Doug

 

[oldbee]

Seem to remember reading that elec. choke should not be wired on the coil feed also. Otherwise, just what r/t & Doug say.

 

[Kern Dog]

Thanks. The choke is wired to a 12V supply at an auxiliary fuse box.

"have you checked fuel pump volume/pressure when cold?"
No, I have not. I figured that if the accelerator pump was working and the float bowls had gas, it would run.

"Have you tried pushing the choke closed with your finger or sliding your hand over the carb opening while it's running?"
Yes I have. It made no difference.

"Have you checked the gap on the distributor pick up? Should be .008"-.010". Swap a coil from another car and test. Your coil voltage looks fine. One more test. Coil voltage should come up during cranking as the ballast resistor is bypassed. Have you watched the choke? One kick it should fully close. Then open about 1/8"-3/16" when first started. If it doesnt open it'll load up. If it opens to far it'll fall on it face. Is the fast idle screww adjusted so the engine runs about 2500rpm warm?"
I have tried different distributors, coils, ECUs, ballast resistors, I've jumped the wires together on the ballast and none of it makes a difference.
The choke butterfly was closed until I started the car. It opened and stayed open. It was 66-70 degrees when I was working on the car so I thought that maybe it was too warm for the choke to operate.

One more thought for now:
Two weeks ago I put on a Holley 750 from my '67 Dart. It started and ran much better so I suspected that this Demon 850 needed a rebuild. Last night it occurred to me that the Dart carburetor still had the Dart gasoline in it when I installed it. Maybe the problem is as simple as the old gas ?

 

[themechanic]

"The simplest solution is most likely the right one."

Occam's Razor paraphrased

 

[Don Frelier]

If closing the choke plate and covering the throat with you hand has not effect, then I believe you have a primary circuit restriction in the carb.
I'm surprised it runs OK when warm.
You need to clean it or put a clean carb on it.
Keep us posted.

 

[slepr1]

I tried lighting 1 yr old gas with a bbq lighter and it wouldn't even catch.

 

[Kern Dog]

If closing the choke plate and covering the throat with you hand has not effect, then I believe you have a primary circuit restriction in the carb.
I'm surprised it runs OK when warm.
You need to clean it or put a clean carb on it.
Keep us posted.

I did. It was just rebuilt.

 

[Don Frelier]

Vacuum leak?

 

[Kern Dog]

*** UPDATE *** *** UPDATE *** ***UPDATE *** ***UPDATE ***
Good news.....The problem might have been the gasoline!
I pulled a spark plug to get a look. It was blackened from running rich OR from the bad gas...?. I decided to replace them so I bought another set and gapped them to spec. Aluminum heads so the threads got some Anti-Sieze.
A cold cranking compression test showed 178 in cylinder #1. I don't recall ever checking the numbers after installing this cam. The Lunati I had way back was around 165 at the advised install centerline. I advanced it 4 degrees and the numbers moved close to 170.
The gas was pumped out of the tank and the carburetor bowls were drained. In went 15 gallons of fresh 91 octane. It wouldn't get spark again so after some checking, I replaced the Chrome MP ECU with a known good orange box. I checked the distributor air gap and buttoned it all up to try to start again. It took a moment to get fuel to the carb but once it fired, it ran GREAT! It idled barely rougher than when it is warm. Great throttle response. I set the timing to my 18 initial, 32 total number and adjusted the idle mixture screws. It was idling in the 10.5 to 11.o range....waaaay too rich.
I was having a hard time getting the AFR to the 14 range. If the screws were fully bottomed out, the numbers go up but then it wants to stall out. I've read before that the ethanol blended gasoline may need to run at a number richer than a pure gasoline tune and I am inclined to believe it. In the past, The car has seemed to run stronger with it set to numbers that would usually seem to be too rich. I was able to get it to idle in Park in the 13.5 range. I left it there.
This carburetor comes with #85 primary and #92 secondary jets. I have it to #83 and #90 to lean it out. I've had #82 and #80 in the primaries and could tell that it had lost power.
So I did go against the traditional practice of only making ONE change at a time. People say that when you make multiple changes, you don't know which change had solved the problem. I still suspect that the gas was to blame. If it runs shitty the next time I start it, I'm back to square one!
Finally:
The heater and A/C system that I installed recently gave me a heater for the first time since I bought the car in March 2000! That dude works, too. I was cruising today, 58 degrees out with the windows down and the floor heat was hot on my legs. That is GREAT!
Oh yeah....This car does great burnouts.

 

[themechanic]

Hallelujah!