Backfire through carb - sputtering

[rocketman]

Hi All,

I'm a noob to the site. I have a 72 F250 Camper special with the 390 cid in it. I've owned it for about a year and only has about 70k miles on it. I wonder if you might be able point me the right direction on this. Idling - it's pretty good. But as soon as I put it in gear, it acts like it's not getting enough gas or something. Under load, it backfires through the carb pretty bad. It runs, sputters, backfires, runs, runs, sputter/backfire... etc. It actually runs better ( at temp ) in cold weather. In hot weather - frustratingly bad. And stalls at the lights and stop signs as well.

Any thoughts on the problem? It's a pretty old beater but I'd like to keep it and get it running dependably all seasons and pull my horse trailer.

Thanks and glad I found this site!

Shawn Pierson
Eagle Mountain, UT

[Whateverman]

sounds like your timing is off too me (too far advanced) thats where i'd start

[elgemcdlf]

Shawn don't get caught believing the truck has 70K for mileage. Normal mileage for a truck this age would be 410K. Since the odometer starts over every time you hit 99,999 mileage could be anything unless you are the original owner. With that said I would be looking at timing. You might pull the valve covers & check for any problems with the rocker arms. Check for slop in the timing chain. Check the points.

[Donnie]

....You have come to the right place for help..A lot of good folk's on here...We may ask you more question's. Like: how easy does your truck start, is your choke working as it should? Are you getting any valve "ping" ? Timing ??already mentioned....vacuum leak. Check ALL hoses.
Automatic or standard shift? Fuel filter? Runs better in cold weather or just when the engine is cold...Plug's or wires? Excessive fuel use?
Happen all at once or come on gradually? Let's start here........others will chirp in soon with more opinion's...HTH.....Donnie

[TexasTruck72]

Check your points. I just went through this same list of symptoms on my truck. Put a new set of points in and adjusted my timing, problem fixed.

[rocketman]

Thanks guys. Hope I answer your questions.

Doesn't start very easy. No smoke. I don't know if the choke I working. In the winter months, I have to hold the butterfly open until it warms up or it just goes back to sleep.

Not sure what you mean by all at once. Can you clarify for me?

I put in new gas filter last year as well as new plugs, new cap, rotor, and points from O'Reilly auto parts.

It does seem to leak a little gas out the accelerator pump gasket area. I did a carb rebuild last year, again using O'Reilly parts.

I could take the valve covers off. It does go through gas pretty badly.

[Donnie]

Repair the leaking accelerator pump....set your points & lube the dist cam so it doesn't wear the rubbing block in the dist...Should have gotten a capsule of lube with your points...Did you replace the condenser? ADVANCE your timing until it grunts when you try to start it....then back off slightly until it starts easily.....WHAT I MEANT WAS : did this condition happen suddenly, or has the truck been GRADUALLY getting worse?
What carb are you using? can you post a photo of your carb? let's find the choke unloader..It will open your choke for you after cold starts...Donnie

If you are not sure of anything that I post , question me.......some times I expect you to know how to do something that you may not know
Troubleshooting a problem on line W/O knowing your skills.....can be a futile effort for both of us , OK ?

[sargentrs]

Like Donnie asked "what carb"? If it's an Auto lite 2100 they have a habit of the accelerator pump cover warping allowing gas to leak and causing vacuum issues. At least mine did

[rocketman]

Hi Guys,

Man - you guys are good. Donnie - it happened gradually and got worse and worse. I put these points on last fall. They shouldn't be bad already but they are. Check out the pics I have listed here. ( Assuming my pics upload works. ) If you download the pic and zoom in a lot, you can see the point face is bad. At least I think it is. Why would I keep going through points? I don't remember if I added grease to the cam or not. The cam isn't really greasy though. So - probably not. ( Ugh. )

The carb is the Motocraft two barrel. ( see the pics there too. ) I don't know if the video will work or not. I remember that after I had rebuilt the carb, I couldn't understand how that accelerator pump housing could leak. But it must be warped like you said. So - I guess I have to purchase a new carb then? If so - any recommendations?

[rocketman]

Here are some pics of the carb as well.

[sargentrs]

You may be able to save that accelerator pump cover. Take a piece of 100-150 grit sandpaper and wrap it around a hard flat object like a 2x4 or flat metal bar, preferably the metal. You can also tape it to a counter top or workbench. Remove the acc pump cover and, gasket surface down, start rubbing it across the sandpaper. Stay in straight strokes and rotate it 90* every few strokes. You'll immediately start seeing the high/low spots on the face of the cover. Once you have it to where you've sanded the entire surface, switch to a finer 220 grit for a few strokes to smooth it out. Put a new gasket on and you'll be good to go. Don't overtighten the screws putting it back on, snug is fine. It's a soft metal and cracks/warps easily.

[rocketman]

OK. I'll do that today. How do I test if the choke is working?

And guys, thanks a ton. Sorry I'm not as up to speed on this stuff. Should I use points and condenser from Napa or something? Maybe I'm not installing them properly and it's wearing them out abnormally.

I'll post my results on the pump cover later today.

[Donnie]

I see no grease on your dist. cam....I can't really see the color of the point surface, but it should be gray & no pitting or transfer of metal..
If one side of your points has a high spot & the other side a low spot or the color is not gray..that could be excessive voltage or a faulty cond.
Replace the points & cond, lube the cam, set them at.016 & do the timing thing...The black inside your carb is showing your complaint.
When you replaced the acc. pump, did you pull the little orange check valve into your float bowl & then snip off the tip...
Also use your thumb nail to test your float if it is a black "plastic" material...These soak up fuel and become heavy, just nick it , if it is wet at your nick, replace it...if it is brass leave it alone, just set it..
The diaphram on the top of your carb in the rear is the choke unloader...they deteriorate, but are available & adjustable..
The way that the choke works: the spring in the bakelite cover will close the choke when you hit the throttle on a COLD engine, this will close the choke plate,,,,then as the engine starts-vacuum is supplied to that unloader & it will pull your choke open a predetermined amount & allow the engine to get some extra fuel until the spring in the choke housing warms up & opens the choke. NAPA should have this part
The adjustment for the float & the unloader should be included in your rebuild kit instruction's
also do a Sarge said, flat sand your pump cover, you need a good squirt of fuel,,,Agood spark at the right time & U should be OK......Donnie
Were your points worn out of spec...like closed/? I would get a set of "Standard" brand points...Or from a Ford dealer...not today

[rocketman]

Thanks! I'll get to work on that today. I think that my points are totally closed. I'll get the new parts and get them mounted and get a timing light on 'er as well and post the results. I hope this is it. That would be great. I can do the work but because I don't understand the mechanics behind things so well, I end up, well, here.

On my way!

[rocketman]

OH MY GOSH! My points were trashed. I have a new truck! I changed points, condenser, rotor, and lubed up the cam. Checked the wiring, set the timing, checked the vaccum advance... In fact I advanced the timing a bit and holy crap! Smooth and fast!! What happened! This things a rocket compared to before. The timing change made a huge difference. ( no spark knock... )

You guys rock. As soon as I can I'm putting the Pertronix ignition system on it. I still have to fix the Accelerator Pump housing by sanding it. But I'll get to it next weekend.

Thank each of you for the tips!