After doing everything I could think of to get the Barth to run smooth at cruising speed, plugs, wires, cap, rotor, module, etc., I came across another guy with the same problem on another site. Many people suggested the vacuum advance as the culprit so yesterday I removed the 2 hose 1 steel tube setup and sure enough, all 4 connecting points were cracked open with age. Got some new tubing and put it all back together, and it really seems to be running better than ever. I didn't have time to get it out to the highway for a real test, but judging by how much better it runs I'm pretty hopeful. Just wish I hadn't destroyed one of my brand new turbo mufflers before I figured it out.

Good deal.
I was having a similar problem with my 86 F150 . Come to find out the vacuum advance line was on the wrong vacuum port on the carburetor .

What a relief!
good news

I found a list of vac advance specs. Looks like anywhere from 5-12 degrees were used. Most distributors had around 10 degrees of centrifugal advance also.

vac_advance.pdf (227 Kb, 120 downloads) vac advance specs

So at idle one must disconnect and plug the advance drive vacuum hose and set the timing to a desired advance. Reconnect the hose and check again, knowing the vacuum at idle one can determine the amount of actual vacuum advance generated. Is this a good check?

ok , it seems the Gremlins (some call it the "turd fairy") have attacked my truck . This morning my truck wouldn't start . It is acting like the timing is too far advanced or it jumped time . I'm at the Fire Station today , I'll have to diagnose it tomorrow .

Took her out for a test drive yesterday. Still missing and sputtering. Is it possible the advance is stuck or not working for some reason?

There's also centrifugal advance that gives the curve to the advance. The springs and weights can become frozen.

I remember reading a long time ago that there are a couple spark plug wires coming out of distributor that can’t be to close to each other or you could get a misfire by induction.

Dannyz, I bet you have already done this, but have you put in a new filter in the Rochester. Your problem sounds very much like gas starvation at speeds happens to Nose quite often.

After putting in the new vac hoses to the distributor, I ordered a new set of plug wires,[MTD $105], and installes them. Still ran crumby so I pulled the plugs to check them. All looked good, so I pulled the air box to see what I could see. The rubber cap on the other vac nipple had split open so I still wasn't getting vac to the distributor. Cut a new piece of line and glued a screw into the end of it and put it on the nipple. Then my buddy came over and checked the cables and said he found 3 that weren't on the plugs all the way, then he pulled the in-line fuel filter and blew a little crud out of it. Don't know if it was any one or a combination of these things but she started right up and runs great all the way through the power band. Already have the new muffler to replace the one that detonated in Georgia, but I have to bring it back to the shop to install it because they welded the entire exhaust system so it will have to be cut out and sleeved back in. Then I should be good to go.

quote:

Originally posted by ccctimtation:
There's also centrifugal advance that gives the curve to the advance. The springs and weights can become frozen.

"Money can't buy poverty"? Spend good cash on a airplane,boat or RV and quite likely you have bought yourself into poverty! I'm sure you herd something that before.