Stalls and hesitates when choke is open

[Dennis Detweiler]

39 P8 carter carb. Engine dies or stalls when accelerating unless I set the choke about 1/2 closed. Same symptoms when the engine is warm.  Plugs are black but no carbon buildup. It won't run smoothly on the road unless the choke is 1/2 closed.  Rebuild the carb? Manifold leak?

[desoto1939]

Have you tried to time the car with a timing light and also test what the rpms are at idle and also have you adjusted the screw that sets the idle mixture.  running rich.  Do you have a users and service manaul onthis car?

 

Rich Hartung

[Silverdome]

Too many variables and not enough information. Condition of carburetor and fuel system? When was the last time it ran correctly? And so on so forth.

[Plymouthy Adams]

sounds like it is time to go through the carb and clean it up

[greg g]

Put a vacuum gauge on it, sounds like a leak downstream of the throttle plate.

[Dennis Detweiler]

I bought the car a month ago and just finished replacing the whole brake system, repaired the tranny, etc. When I bought the car it had the rough running problem. I also replaced the fuel pump, with no positive results. The old fuel pump didn't have the filter screen in it, so maybe the carb has some crap in it?  I don't know if the carb has been rebuilt? It looks fairly new, but if so, may have had a botched rebuild. I was told, the engine was rebuilt 10,000 miles ago, which was 20 years ago. It has recent new plugs, wires and coil. The last owner (deceased) did some rewiring, body work, paint and upholstery. His restoration looks pretty good except for the wires that were replaced needs a little detailing yet. I'm somewhat of a 68 year old shade tree mechanic and the rough running seems more like vacuum or carb. I have the shop manual for 39. On the highway, it purrs along, but I hear and feel misfire like a fuel issue. I can get rid of some of it by slowly pulling the choke on. Then when I pull up to a stop I have to push the choke toward open to get it to idle better. Would the idle mixture cause it to run rough and miss on the highway?

It came with a spare Carter carb which probably needs a kit. There's also a rusty Stromberg carb in the trunk. I have a timing light.

I'll read through the fuel and carb section in the manual.  

Worst case, a leaking intake manifold gasket? Or, worse yet, a bad valve. However, it doesn't have that puffing at the tail pipe like a bad valve.

[Silverdome]

Start with the basics. With engine idling turn the idle mixture screw in until it starts to stall. If it doesn't stall when completely screwed in it most likely is a vacuum leak. If i starts to stall back it out while counting the turns to see when it starts to stall. Split the difference and turn back in, for example if it's three turns between in and out then turn 1-1/2 turns. Check the rubber fuel line near the tank it may look good on the outside but be collapsing on the inside. Put a clear fuel filter inline to see if it is pulling junk from the tank. Take the top off the carb and inspect for sediment in the bowl. If the car sat for a long time clean the carb and fuel pump.

Good luck and keep us informed on the progress.

Edited October 19, 2017 by Silverdome

[martybose]

I'm surprised that no one has mentioned the accelerator pump yet.  Soaking the leather piston in oil and reinstalling cured the hesitation back a hundred years or so ago when I had the stock carb on my motor.

Marty

[Dennis Detweiler]

Thanks guys!

When I bought the car, I drove it about 2 miles to my girlfriends farm. Oil was dripping from the bottom. My first thought was rear main. However, the fuel pump was loose and had no gasket. There was a new pump in a box in the trunk, so I installed it and no more oil leak. I thought the old pump was the likely culprit for having to run the choke half on to keep it running, but the new pump didn't help.

I ordered a new carb kit from Mikescarburator. Hopefully, that will cure the problem. If not, it has to be a vacuum leak? I'll install an inline fuel filter for good measure. Like I said, the old pump had no screen in it, so there is likely sediment flowing into the carb.

I'll post on this again when I find the problem. It's getting toward Winter here in Iowa, so I may not have a chance to work on it much longer. I don't have a heated garage.

After the fuel problem is cured, I have to figure out why the steering is a little squirrely on the highway. I have a new tie rod end and lower control arm in the trunk. I adjusted the steering worm gear nut. It helped, but something else is still loosey goosey. I'll have someone rock the steering wheel back and forth while I'm under it.