The Stovebolt Site Forums The Shop Area Engine Shop Carb help please.......

Once started and I begin to drive, it sounds like the motor is backfiring through the carb. It coughs and bacfires once or twice while I'm giggling with the choke knob. Once the choke is out a bit it usually stops. Once the engine is hot I push the choke all the way back in. Occasionally when I'm pulling up a hill it backfires again until I pull out the choke slightly. Do I need to adjust the distributor or make an adjustment on the carb. I know very little about how a carb works.

Thanks for any suggestions why it's backfiring.

Spot

Have you set the timing? How?

What is your idle speed (in RPMs)?

Is this a recent problem - have you done something with the carburetor recently (if yes, what, and was it running OK before)?

sounds like fuel starvation, low flaot level, weak fuel pump?

In additions to the before mentioned problems, a bad vacuum leak will also cause these symptoms. How's the hose to your wipers?

What engine and carb?Some info please.

Pete

Thanks for the comments everyone. Now here's some more info...

No, I have never set the timing but the truck runs beautifully after it's warmed up and not backfiring.

Have no way to know the RPM's at idle but it's not very high.

No, I have not done anything to the carb. This problem is an ongoing one since I've owned the truck 2 yrs.

I installed a new hose from carb to wiper motor when I bought it. I assume there are no holes and connections are good.

Engine is a 1950 216 CID.

Thanks guys,

Spot

So..... when it's warm/hot it all stops.........first of all that's weird, When you shut it off and wait 3 minutes, does it start nice and run nice? It may be an old tired fuel pump getting itself "primed" and pressurized from engine RPM. Chances are there are two things wrong, like a carb that needs rebuild or like the guys are saying vacuum leak at some gasket or carb part that swells after starting. Or carb bowl leaking down (maybe bad needle valve seat)and weak pump takes too much time to refill. To sputter and backfire, then run good, isn't a usual occurrence. Visibly check what your choke is doing when you move the knob.(take off the air cleaner) Sometimes the cable operated butterfly will open or not open and close and not close and you are choking when you think your not and visa versa. Make sure the plug wires are on the correct plugs, etc. You/we will find it if you do the necessary work and experimentation. Bartamos

I would rebuild the carb it sounds like it's running lean,after it's warm does it sound like it's popping thru the exhaust as it's at idle or as you're driving?After you have it out for a drive pull the plugs out how do they look what color are they?The color of the plugs will tell you if you're carb is running lean rich and a vac.tester will tell you if you have a vac leak some where.hook the vac gauge to the wiper port good vac is 21 inches.

Pete

Bartamos and Pete......thanks for your comments. I've about decided to tackle the job of doing my first carb rebuild. I've never done any carb work but figure I should teach myself.

I've checked the plugs before and saw what I expected....black plugs. Yes, the truck is running rich, but that is because I have to run it with the choke longer than I would like. I've never had a car with a manual choke but I think I should be able to push the choke in sooner. The truck just coughs and sputters too much early in the drive if I don't have it out slightly. As it warms and then gets hotter I don't have to use the choke for smooth running as much. The cough or sputter is more like it dies for a second when I'm pushing in on the accelerator then it starts back up. It's for only a second....thus the "cough". I pull the choke back out at that time and it purrs like a kitten. Something is wrong so I'll tear down the carb and install a kit hoping that will solve the problem. I'm sure I'll post ????'s once I begin that journey!!

Thanks,

Spot

How long had you been driving it, warmed up, before you checked the plugs? It's OK to let it cool down before pulling them out, but they were hoping you would see what they look like after a good drive.

If you do rebuild the carb, here is some interesting reading. Not truck carbs, but still:

http://home.insightbb.com/~cdpumphr/the_carb_chronicles.htm

If it dies for a second when you press the gas, that sounds like the accelerator pump. I see a Carb rebuild in your future.

It bothers me that you say "it purrs like a kitten" after a few minutes. "truck runs beautifully". If an engine purrs and runs and accelerates and goes all day like that. The carb is not far off of correct.. After you get it warm, get out, take off air cleaner and see if gas squirts inside the carb when you operate throttle. If it squirts the ACC pump is OK. It's the starting phase that's broken. You are out of gas in the bowl or semi leaking fuel pump or choke mechanism screwed up, cold plugs, weak ignition system.........ballast resistor,,,

6v or 12v

Have you checked for vacuum leaks?

Bartamos, I drove the truck last night to Sonic and it acted like it always does when it's cold. After I got home I pulled the air cleaner off and watched when I pulled the acc. rod. It squirted gas alright but it wasn't a steady stream, and it ran okay. Of course it was hot and running well. It's only when it's cold that I have problems. I should just resign myself to a carb rebuild and then see if that solves the problem. Logic tells me that's what the problem is.

BTW, it's still all original 6 volt.

Thanks,
Spot