I rarely have problems with my truck, but just last week I picked up a used Edelbrock 1406 and swapped it on to see how it'd run. Having sat six years, you can imagine the spitting and stumbling and such that resulted. My real problem came, however, when I reinstalled the Motorcraft 2150 that I had just taken off a day or two prior.

The week before the switch, I was noticing that I was smelling gas fumes when I'd first start the truck. The exhaust has always smelled pretty rich, but this was more than I was used to. I was smelling raw gas as well as the rich exhaust. Despite this, the truck ran normally and had very good power and throttle response, but horrible mileage.

After taking the Edelbrock back off and putting the 2150 back on, I can get it to start, but it won't stay running unless I'm constantly mashing on the gas. It won't idle at all or hold steady RPM. If I'm not pumping it while it's running it will sputter out and die right away. I even had a flame pop out of the top of the carb as it was sputtering out this afternoon, but I'm thinking that was from me pumping the pedal so much that it had a small backfire and ignited. It went out on its own, fortunately.

I replaced the power valve with a brand new one from NAPA; there was fuel all over the old one as well as in the little cap piece that screws down over the PV. With the new power valve I did notice the exhaust tone sounded a little different than before, though performance didn't change any. This could be from my having reset the idle mixture screws to the baseline 1.5 turns out, though

So far I have done the following:

- Set idle mixture screws to 1.5 turns out from bottomed-out (not too far off from where it was originally)
- Checked carb gaskets (I did have to reuse one for the spacer but I bolted everything down tight, and it wasn't damaged)
- Checked for loose vac lines, found a cracked cap, replaced it
- Made sure vac advance was hooked to ported vacuum
- Checked for fuel spray upon throttle application (accelerator pump is OK)
- Replaced power valve (old one was shot and covered in fuel) and installed new gaskets for PV and its cover
- Checked fuel output from fuel pump, pump is OK
- Checked for fuel-fouled plugs (pulled three random ones, one was a bit dark but dry, I cleaned it)
- Spark is OK
- Plugs are about two years old but in good condition
- Wires are new
- Cap and rotor are in good condition
- Timing has not been changed from where it was before the swap
- There is fuel in the tank (I overlooked this once...lol)


At this point I don't know of any other things I can replace without having to disassemble the carb, and I don't think I have the gaskets handy for it anymore. I do plan to replace the carb as soon as I get my rebuild kit for the Edelbrock installed, but if possible I'd like to see if I can get the truck running so I can have a vehicle of my own to drive so I don't have to use my mom's Cherokee so much.

Thanks in advance.

 

How are you putting a 4bbl carb on the 2bbl manifold or the other way around? Sounds like you are using an adapter which can lead to problems.

You are checking the right things, but it sounds like you have a big vacuum leak somewhere. The only other thing I can think of is your old carb had some sediment in the bottom of the bowl, and when you took it off it got sloshed around and stirred some of this dirt up and now it's clogging things up.

 

Has it backfired since you replaced the power valve? If so, you may have damaged the new one. But, if it backfired then there is something wrong beyond the power valve

I agree with Dave that it sounds like you have a large vacuum leak. Pumping it squirts raw fuel into the mix and helps to cover up the lean problem. While I kinda doubt that it would be enough to do that, it is very possible to have a hole in the vacuum advance diaphragm. But, you said that you have it hooked to ported vacuum, so it shouldn't cause much, if any, problem at idle.

Do you have EGR? If the valve is stuck open you will have a lot of problems at low RPM.

 

I have a stock 2bbl manifold and I got an adapter so I could run the Edelbrock until I can afford an intake. The Edelbrock actually ran okay with the adapter, but it had some issues on account of sitting up so long.

I did reuse the old spacer gasket as I mentioned earlier, but the gasket between the carb and the spacer is new from the 4bbl adapter kit. I'll see if I can find a new gasket for the spacer and see if it helps any.

It backfired right after I cranked the truck after replacing the power valve. This was the first time it's done that since I've had this carb installed on the truck.

That's what I thought, though I thought that it would at least run somewhat okay with a leaking carb spacer gasket, if that's in fact leaking. I could try unhooking the vac advance hose and capping the vac nipple on the carb base.

No, I don't have EGR. I have no emissions parts at all on my truck aside from having the stock intake with the little oblong hole next to the passenger side carb hole. It does look like that little hole is somewhat uncovered even though I have a decent sized gasket from intake to spacer, but it's been that way for years and I've never had any issues from it.

Also, I called my uncle today and told him what's happening, and he said that it sounds to him like the timing chain might have either jumped a tooth or just be stretched out. What's ya'll's thoughts on that?

 

It could be the timing chain, but it wouldn't do this by just being stretched. That's a very gradual process and it won't go from running ok one day to not idling the next due to wear and/or stretching.

But, when it is stretched and you have poor running with jerking, backfiring, etc the chain can jump and come down in another spot on the sprocket. Then it won't run well at all. However, if you put the E'brock back on and it runs sorta ok then it isn't the timing chain but carburetion. Or, fuel induction might be more correct as it might not be the carb but the manifold and/or gaskets.

Have you tried going to the E'brock again? If it runs the same as the 2150 then we'll know it isn't the carb, although it still might be the intake. And, it could be the timing chain. If it runs ok then it isn't the timing chain and isn't the intake - gotta be the carb.

 

Well I put the E'brock back on today....and it idles.

Sort of.

It sounds like it's firing on every other cylinder, yet it runs pretty smoothly with no backfiring whatsoever. If I ease into the throttle and get the RPM up, it will actually hold the RPM and then it roars to life and sounds like it's supposed to, I'm thinking from the secondaries kicking open.

I'm pretty sure once I rebuild it, it should idle right and run properly. If not then we know I need a proper 4bbl intake, though I do hope the adapter works good enough to do me til I get some money for an intake.

Makes me wonder what made the 2105 go nuts. A friend said it sounds like the floats got stuck, but once I get the Ebrock installed and running I'll tear that 2105 apart and figure out what's up with it.

 

I think the problem with the 2bbl 2150 is, it's a 2bbl lol

 

It ran perfect for ages til it saw that 1406 come along. lol.

I can't wait to see what my gas mileage is with the E'brock though. Hopefully it'll be better than what I was getting.

 

It's almost impossible to get the secondaries to open just sitting in the driveway, on any carb except one with mechanical secondaries. I think you still have a problem. And I don't like that hole you mentioned that is uncovered. Unless it's covered somewhere else by a gasket underneath. That hole sounds like a EGR hole, and it should leak exhaust, or vacuum.

Don't get side tracked. It would be a very rare occurrence for another problem to crop up while you are messing with something else. There is a 99% chance that the problem is caused the carb swapping, I would keep concentrating on that area.

 

Agree, 100%. It sounds like things are way lean and pumping the throttle is giving enough gas from the accel pump to keep it running. But, as you get some R's on it the amount of air via the carb is much higher than the leak so it'll run.

 

When I had the cast iron intake, once I took all the spacers and gaskets off, got the gaskets wrong once and that big EGR hole. All it leaked was exhaust, engine ran fine other than an exhaust blowing leak under the hood lol. Only took two minutes to fix it.

 

Is there a way I could put an old EGR plate under the carb adapter to seal up the hole until I get an intake? I think I have one in a box somewhere. I'd just need to use longer bolts than what the kit came with.

If I absolute have to get an intake I can, but if possible I'd like to make this work til I have a little more money.

 

I don't see why you could not use a EGR spacer, and then make a block off plate where the EGR goes. Everything usually fits better if you do use the spacer in my experience.

 

Others have said they made a block-off plate with an old soda can and it held nicely. I'm surprised that aluminum, and especially that thin, would work but it appears to do so.

 

I have done that myself with aluminum flashing I had laying around from some roofing work. It worked fine for the few years I used it, but I have to wonder also how long it would last before it was eat through. A piece of stainless shim would be more permanent.