Hello FTE,
I fear my mechanics have no idea what they are doing with my truck. I have been reading here a few months and just created an account today. Here is the situation I bought a 1978 F150, 4x4, 400M,auto trans a few months back. It ran and drove , just ran pretty rough. I replaced plugs, wires, cap, rotor, heater core, air filter and fuel filter. truck still ran rough. I identified and repaired a few leaky vacuum lines and it ran better but was still not right. I rebuilt the carb( first time to do this) and it ran a little worse so I took to an auto shop to tune it for me. I have had success with this shop for about a year with a 1988 Dodge Raider and our 2001 Toyota Sequoia. So the shop wanted to adjust timing and the dizzy was stuck and actually found out it was broken at base ( you could tell break was old by even discoloration of aluminum),so they replaced that and the melted ignition module (p/o told me the rosin I saw was from an old ignition module that went bad but had been replaced, he lied). My mechanic sent truck to another shop that supposedly has an awesome carb guy. Said carb guy adjusts as best as he can and says the problem is the timing is still off, not getting enough advance from dizzy adjustment. Maybe the timing chain/gears are old and have slack he says. Truck goes back to my shop and they do timing chain and gears and adjust timing to spec. Back to "carb guy's" shop for final adjustment and he rebuilds carb over again and installs aftermarket electric choke. I get the call that says "truck is done, its great, running real good" . I go to pick truck up, test drive it and it stalls under acceleration and pops likes its backfiring. It pops as though it is backfiring even when you rev it while in park. If you barely press the gas its more or less okay and you can even get it up to speed, at least up to 50 , didn't try higher. If you try to pass or accelerate from a stop it will start dying and sputter and pop pop pop when you back off throttle. I turned the truck right around and returned it to shop telling the mechanic all this. He drove it and was to look into today. BTW, the've had it a month to get this far. What could they be missing ?? I'm so pissed I cant even think straight to see into this. PLEASE HELP !!!

 

Many "mechanics " have never even seen a carb , except on a lawn mower . Most new guys are lost if they can not hook up a scan tool or lap top to a vehicle .
You need a second opinion . Find the old guy that has been around since dirt was invented , ask around at parts houses . See who they would recommend for your truck . Where are you located ? Someone close by , on this site , may be willing to help . Best of luck !

 

Yeah, I know. That's why they sent it off to the supposed "old as dirt guy" who knows what he is doing. I do appreciate the response though and I am ready to take it somewhere else at this point.

 

Go to the NC chapter , on here , and look around . You may find what you need .

 

try disconnecting the vacuum advance hose (and plug it) and let us know how it runs...

 

Looking in the NC chapter now. I'll try disconnecting the vacuum advance tomorrow. Shop still has the truck, if the don't make new headway by tomorrow I'm bringing it home.

 

Yes on shop for some help in your state FTE chapter.

 

Just from your description it sounds a little like the timing is off, like the distributor is "off a tooth". They will run but not very well, and the range of timing adjustment will be limited. If you want to test this theory without removal, move all plug wires over one iteration clockwise on the distributor cap. Then set timing. You may have to try it going the other direction (CCW) Be sure to mark the wires first.

The distributor won't care a whit what tower is #1 so long as the firing order is correct. It would be surprising that a shop wouldn't know this, or maybe they didn't want to risk other factors.

 

All good ideas, keep em coming ! I will update as soon as I know something tomorrow.

 

Agree timing sounds iffy, carb sounds iffy and maybe other problems. I can suggest step by step for you or your mechanic to get to the bottom of it... with easy things first.... starting with ignition:

1. Pull and inspect plugs... look for any that are off color or different
2. Go over every inch of vacum lines and replace if bad. Buy or borrow a factory manual to check routing.
3. Double check wires and firing order. Ford numbers cylinders differently than Chevy or MOPAR.
4. Check timing at idle with vacuum disconnected in the normal way and set to ~12 degrees advance
5. Check timing at speed with an advance light. With vacuum disconnected it should increase gradually to about 35 degrees at 3000 RPM (total mechanical advance)
6. Re-connect vacuum lines and drive it.
7. If all all above checks out and still not running right, run a compression test
8. If compression is reasonable, buy a professional reman carb. I used an Autoline from AZ and it has been fine.

Good luck!

 

Thanks for your input ! I forgot to mention that they did a compression test and they said the numbers are good.

 

If none of the above ideas work, try setting the timing without the vacuum advance. Set it at 27 degrees and take it for a spin.

 

Ok, so y'all were right about the timing. I went to the shop yesterday and timing was way off. They adjusted it to the point where the truck is drivable but still needs tuning. I took it home with me to try myself. I put my timing light on it and they had it at about 10 degrees and idle was too high( oh and they had left the distributor loose). I adjusted to 12 degrees, smoother and idle dropped to 750ish rpms. Still rough and raw gas smell is very strong. I am going to go through Chilton's tuning process and see what happens.

 

Raw gas smell could be carb tuning (idle mixture too rich) or non-functional evaporative emissions system (you're smelling gas vapors that should be trapped in the canister). If the smell is there whenever it's warm, even when it's been parked for a while and not running, it's probably the latter; if it's there just while the truck is running, more likely the former.

 

So instead of using the Chilton's manual tuning steps I just did it with my vacuum gauge. When I started tuning I only had 14" of manifold vacuum. When I finished adjusting air/fuel mixture and timing I ended up with 19" of vacuum and it runs MUCH better now. Now I'm going to change the plugs, they have to be fouled from running so dirty for a little while.