84 F-150 300I6 - EFI Manifolds - Duel Exhaust - Stock Intake & rebuilt carter 1bbl - EGR tube/valve & O2 sensor removed
After I drive @ highway speeds for about 10 miles my exhaust manifolds glow & at lower RPM's it seems to hesitate a lot & it sounds like it backfires in the carb (lots of popping noises) The carb is about 2 months old & ran ok after it was adjusted by a local shop & timing set right, after I put on the EFI's it ran great for about 1-2 weeks then starting running a described above - I have checked & replaced every vaccum line & cap. I can floor it everywhere I go & it runs ok after it gets wound up, but no power under a load. After rebuilt carb & duels the fuel mileage was a little better, but now it's worse than before. Some advice please...this is driving me crazy

 

you need to adjust your timing and you need to richen up the carb

 

How do I richen up the the carb?

 

find the idle mixture screw turn it all the way in until it stops then back it off 3 turns i would use a vacuum gauge to get the best reading i would not drive it until you get this fixed you are causing a lot of harm to the engine

 

Turned the idle mixture screw as above & it's still doing the same thing. Could my carb be screwed up? It ran perfect for a few weeks after the carb was adusted the first time, then just one day it started running poorly. Could no EGR valve or O2 sensor cause this problem?

 

I also changed the fuel pump about the same time the problems started...I don't remember if it started right after that or not. I've done a lot of work to this thing so far. Could a faulty pump cause a lean condition?

 

Forget all about the mixture screws everyone unless you have an IDLE problem. That is all they effect. They have nothing at all to do with popping, backfiring, power problems. They are IDLE MIXTURE SCREWS. They do not get out of adjustment unless someone changes the setting or some other condition like vacuum leaks arrise. Any vacuum leak will cause the need to compensate with the mixture screws which contrary to under the tree belief is not a repair.

A faulty fuel pump can cause the ultimate lean condition. No fuel. Very, very, lean. I don't think a pump will cause a running lean condition. I don't think any of this is your problem. It is probably going to be something to do with the ignition system. Many perceived carburetor problems are caused by ignition troubles.

 

I would think a carb problem would still be a problem @ higher RPM's, but it runs really well @ higher RPM's - When I take off that it sort of hesitates. Hesitates is the best description I can come up with, sometimes it will not hit a lick when I floor it but it will pop, buck & sputter & very soon it starts to accelerate, still sputtering but it stops that @ higher rpm's. It also takes a little while to start, like it's not getting fuel, after it sits for a while. So now I'm back to ignition problems (timing) BTW, what is the correct timing for this motor...10 Deg BTDC, is that right? Out of time can cause the manifolds to glow right? It seems like I saw that in another post. Will be checking it tonight if my buddy brings his light by. I'm getting an Offy intake & holley 390 very soon, so I don't want to put a lot of $ in this setup, but I don't want to harm the engine either. Anyone got a Offy intake for sale & maybe a carb trade - I've got a Holley 600 CFM that's in great shape, but a little to much for this motor. Also a Carter 1 bbl (reman) that I will not need anymore, only a few months old.

 

This is getting complicated. The latest description sounds like carb troubles. The hesitation and then catching/hard to start sounds like a bad accelerator pump. A quick check is to remove the air filter top and work the throtlle by hand. Every time you push the throttle back you should see a shot of gas down in the throat of the carb. If you see nothing or a weak dribble you have a bad pump diaphragm more than likely.

Now as far as hard cold starts the accelerator pump can cause that but the choke could also not be working properly. Check operation of the choke with a cold engine. It should move freely with the throttle open a bit and if automatic the choke should close on its own as soon as the throttle is opened. I have had to oil the shaft on many a gummed up choke. They seem to get overlooked as far as routine maintenance.


Last the glowing exaust manifold if I am not mistaken is a sign of a lean condition. Maybe some trash in the carb has partially clogged the main jet.

 

Do you have rust/debris in your fuel lines, had a problem with hesitation and sluggishness for small amount of time, took off fuel filter and shook out the rust from gas tank, changed it now no problem, till i shake up more junk.

 

I'm sure I do have some rust among many other things in my fuel tank, but I've changed the fuel filter about 4 times in the past couple of months and have not noticed any thing I was able to shake out & no performance gain either. My carb is still under warranty, so I'm getting a new one in a couple of days. I'll see what that does. Still looking for an Offy intake & 4bbl carb to upgrade to. I've got a good Holley 600 cfm, but I think it's probably too much for the motor. Anybody want to trade a Holley 600 for a 390 or 450 cfm or an edelbrock 500 that's in good shape?

Another question.
I'm running true duels (no downpipe) from my EFI manifolds - 2" pipe to 2 cheap turbo mufflers & 2" the rest of the way out (no tips) & it sounds real good @ lower RPM's but @ higher RPM's sounds like a ricer. What's the best sounding exhaust setup for a 300 I6? Something not too loud, but a lower, deeper sound - Anything but the ricer sound. That's not the sound I was looking for when I decided to run EFI's & duels. Would it sound better with a Walker downpipe & single 2 1/2" pipe to a flowmaster then split to duels out of the muffler? I've noticed where that's a popular setup on other posts.



Thanks

 

OK, I replaced the carb with another reman (it was still under warranty) while I was at it went ahead and put on a new fuel filter installed new plugs & plug wires. Now it runs great, no hesitation or backfiring, good power, I'll see how the fuel mileage is in a few days. But I still have part of the original problem. Now the rear manifold glows a little after hard driving. The front looks fine. What could cause this to happen? Everything else seems to be good. Like I said it runs better than ever. I have not checked the timing yet. I don't have a gun, and I'm waiting on a friend of mine to bring his to me. Could being a little out of time cause it to run lean in only a few cylinders but still seem to have plenty of power & no hesitation. I'm ready to leave it alone for a while but I don't want to harm the engine any more than I have by running lean.

Thanks