Hello all! I've got a 1978 f250 with a transplanted 72ish lincoln motor. It used to run like a champ, but for the past two months it's ability to run good has slowly been declining. I have a pointless ignition system with an edelbrock 750 carb. When it started to decline it still ran great but started to ping. I've been running 91 octane so i ruled fuel grade out, but if I retarded the timing at all it would miss like crazy and bog. I have constantly been switching the vacuum advance from ported to non ported and adjusted the timing all over the place and I still haven't got the thing to run good. I bought a new cap and rotor today and after tinkering with it it ran really good for about ten minutes and now its missing and bogging like crazy. any help would be very appreciated! thanks !

 

Sounds to me like it's your timing chain. Try taking the cap off of the dizzy and rotate the engine by hand and see how much play is in the unit. If you can move the crankshaft more than a few degrees before the rotor starts to turn, it's likely to be your problem.

 

I would check your camshaft timing. The gears and the chain wear and stretch over use. The gears usually installed by the factory, aluminum with plastic teeth, were soft, designed to eliminate noises. The plastic teeth break off, and the aluminum wears down, retarding the camshaft timing.

The chain accumulates all this wear. The following is an easy check to determine the amount of slack, slop or wear, in your timing chain.

It is not necessary to remove any components as long as you can see the timing marks clearly. It can be done with one person, but a second person can be helpful if the distributor cannot be easily seen while turning the crankshaft from the front of the engine. This test cannot tell if a chain has jumped; it can, however, tell you if there is enough slop in the chain to have let it jumped.

Tools: Breaker Bar with socket to fit the front crankshaft bolt

1. Mark the TDC or 0 mark on the damper clearly. Ensure the rest of the timing marks can be clearly seen; clean them if necessary. You may find it useful to scrape a little chalk over them to highlight them.
2. Remove the distributor cap and place it out of the way. You must be able to see the rotor while turning the engine with the breaker bar. It usually is not necessary to remove the spark plugs, but some high compression engines may require it to get an accurate reading.
3. Turn the engine in its normal rotational direction until the TDC or 0 mark is lined up with the pointer.
4. IMPORTANT: Do NOT turn the crank backwards just to line it up. Doing so will give erroneous results. You MUST rotate the crank in ONE direction only. If you overshoot, just go around again. This is where it may be helpful to remove the plugs.
5. Once the TDC and 0 marks are lined up and while watching the rotor, rotate the crank in the opposite direction. When the rotor begins to turn, STOP. It may help to have a helper push against the rotor's direction of rotation. (Remember, it will be going backwards at this point.) They can feel it begin to move more accurately than you can see it begin to move.
6. Note the value of the timing mark the pointer is indicating. It will be BTC, because you went in reverse of normal rotation.
7. This value is the amount of slop your timing chain has in degrees of rotation. Anything less than 10 is safe, but normal driving performance begins to fall off after 5.
8. If you have anything over 25, STOP driving that motor and get the chain and gears replaced! I have seen motors run with up to 45 degrees - but I wouldn't risk it myself.

 

Wow, I have never seen one go to 45 degs and not skip the chain, that was one lucky person. The rest of the info is dead on.
But to add to that if your chain is not way off check for a vacumn leak also, something like a carb base gasket etc those can cause you major problems.

 

That one with 45 degrees off wasn't a 385, it was an FE. Ran terrible, and once it shut down after jumping the chain, it wouldn't start.
Only found out it was at 45 by checking it before I replaced it.
I think it tapped the valves too, because it never did run right after that, but my friend didn't want to tear it down.

 

AirSmitty, are you having any backfire issues? Thru the exhaust or thru the carb? I had HUGE vac leak on mine when I forgot (oooppps) to plug an extra hole when I changed my intake. I learned from some of the guys here to take another look at things. Sure enough! Hiding back under my carb was a big ol vac port, just suckin in air. It did everything but run. My poor truck deserves better than me sometimes...

 

i have a 460 that was missing one time turned out the intake gasket was leaking sucking air check your's with eng running and spray carb cleaner around the intake ports to the head if it speeds up it's leaking.

 

Bad brake booster will make one miss and run like crap. I just bought a truck real cheap because of that reason. Put a pair of vice grips on the hose and it smoothed right out.