50 MPH truck

[wildcard]

My 71 has an I6 300. At 50 mph it starts missing bad and running like crap. At an idle and up to 50 it runs perfect. No misses or hesitation at all. It started this a month or so back when the cam gear on the dizzy broke. Has a new dizzy and gear. Timing has been set by light and by ear. I've even tried advancing and retarding the timing just a bit. Checked point gap a dozen times. If I try to go any faster, it sounds like it could start backfiring any second so I back off. Any advice or ideas will be apprecited.

[bb429power]

Is your condenser wire loose?

[Dragon]

Toss out the ear and set the idle timing at 10 degrees with a light, look at the total advance at 3000 rpm on the wheel with the light. Should be up around 38 degrees. I have been tuning for 40 years and no way can I set the timing by ear. If I could I would save a lot of time.

[wildcard]

I'll give it a shot. The reason for the ear was because, after the new dizzy was put in, it ran worse by light. I can have my GRANDdaughter run the RPMs up and set it and get it to smooth out enough to get to 50 mph.
And I'll check the condenser wire this evening.

[Ranchero50]

I'd also put some suction on the vacuum advance hose and see if the diaphram is blown. Been there...

Jamie

[Dragon]

Your timing wheel could have slipped if it got worse by light.

[michael69]

Is your condenser wire loose?

I had same trouble and after checking everything I could, found my condenser wire almost broke into and that curried the problem.

[Dragon]

I got rid of my points and lived happily ever after.

[wildcard]

OK, first off, this morning it ran fairly decent at 60 mph. Don't know if the cooler air had anything to do with or not. This evening I pulled the dist. cap and was poking around and the wide strip that wraps around in a horseshoe shape could be lifted up and down and would come apart. I didn't figure that was good. So I went and got new points and condenser. I checked the timing and it still wouldn't run right so (sorry Dragon) I tuned it by ear. Took it out and ran it to 70 mph and it ran fine. So I really can't say for sure what it was but i really appreciate all the suggestions. I know they put me on the right track to find it.

[Dragon]

The points base fell apart if I read you right. It is attached to a pivot at one end and the vacuum advance at the other.

[wildcard]

Don't know if it's the base. It's just the thin copper metal strip. If I still have it I'll try to get a pic of it. And it wasn't broke, it just pops out of a slot. Hard to explain.

[Dragon]

hmmm

[Skifu]

When I was a mechanic at the CSMS shop ,Fl Natl.Guard,I ran into a dodge 318 army truck with a crack in the dist.cap,it ran fine untill you stepped on the gas pedal,
it took a while to figure out,because the cap looked fine,but thats all it was.If you babied it up to 50,it was ok,the second you applied any hard throttle,it would miss bad.

[bb429power]

Is your condenser wire loose?

I had same trouble and after checking everything I could, found my condenser wire almost broke into and that curried the problem.

Yeah, well try going through all the things possible to do with the timing (not including the timing chain) while at the high school drags and trying to get it done so you can run it. The event only happens 2 times a year and a night or two before the race, the timing started going bad. That wasn't a good experience and I'm sure you know what I mean, Its the only thing that you wont think of when the timing is out of whack like that. IT SUCKS!!! And it just HAD to happen the night before. Whoever designed points, we salute you not.

[cdeal28078]

Those early points type 318's were bad about cracking the caps. Mom had a Fury III that would bust a cap about every 3 months until pop finally rebuilt the distributor.
Sounds too me like the points were the problem. Give yourself a break and try some electronic ignition. You'll love it
clint