I am having some issues with my '78 F150 4x4 with recently built 400 backed by 4 speed tranny. I just hooked up my vacuum line to my distributor as it was missing since I've had the truck. Now the truck runs worse than ever. It feels like it is hesitating under slight load in every gear. It kind of lunges or lurks/jerks a bit. Wide open throttle while accelerating seems fine. It's hard for me to tell if it is pinging as I cannot hear a clear ping, but it does sound like a faint backfiring when I let off the gas. I set timing per the instructions someone posted on here by vacuum gauge. Cannot remember the site I used, but seemed pretty simple. I had good vacuum around 19 psi when I was done adjusting. Idle is fine. On my highway run, I was excited. My RPM's at 70 had dropped from 2800 to 2400 so I was happy to see better fuel economy. However, after my second highway trip, the RPM's went back to the previous numbers. I hooked the vacuum line up to the port manifold of my Edelbrock (passenger side). It was plugged during the timing. It almost feels like maybe a vacuum leak. The hose I used was 7/32. Is this the right size? Seems a bit loose on the fittings. Could it be leaking from around the lines? Any suggestions? I do not have a timing light yet so I cannot check that. I just switched it from port side to manifold side but have not had a chance to see if this helps. Thanks for your help.

 

First things first get a timing light with an adjustable advance there around 50.00.

I dont have a clue how your suppose to time by a vacuum gauge never tried it and never will, The timing needs to be set *6-*8 before top dead center at idol with the vacuum line disconnected and plugged then run it up to 2300RPM's and set that to somewhere in the range of *28 to *32 BTDC if you get more then that there is a small allen screw inside the dizzy vac can adjust that until you get close to that, Running with out a vac advance is fine I have done it and do it now on my 78 460CJ with bad fuel and for mine with 10.5-1 compression you just cant run that much advance,As long as its close to *25 mechanical advance its fine.

If you ping the engine too much it will destroy itself, Set lower is better then a new motor,Yes it wont have full out power but it wont end up in the oil pan aether,Unless less your made of cash and can afford $4.00 a gallon premium fuel.

I know it will be cut and paste quoted "you cant do that" I wont argue the point its up to the operator on how you want to proceed.

 

Read the following article, reread it multiple times if necessary, it's an excellent primer on tuning your ignition

FORDMUSCLE webmagazine: Timing is Everything - Distributor Curving for Maximum Power

 

x2 on the timing light.

Read the article Montana told you about - it's very good.

The vacuum line is 5/32" so you have a vacuum leak now - change that and check all other vacuum lines for cracks, ETC. Go back to the ported vacuum on your carb. Do you have the EGR hooked up?

Mark

 

Thanks for the line size. I bought a timing light today. Hope to play with it this weekend. I did switch back to ported. Ran crappy on manifold side. I do not have EGR hooked up. I did a timing adjustment by feel and has definitely helped. I think I was advanced too far. No more bucking. Hopefully with the light I will get the most out of her.

 

Very good article, I enjoyed reading it!!