Purchased 65 F100 when the truck was 6 yrs. old, installed (67) 289/302 shortly after and been tuning it myself since. Also, about 4-5 yrs. ago installed Duraspark II and it has been running fine. Just completed thorough tune about 100 mi's ago and at the time took compression test and all cyl. running 150 + - 10 psi. Replaced the dist. cap, rotor, plug wires (Ford Racing 9mm), and Autolite plugs gap @ .045. Yesterday drove about 40 mi's and it started running crappy, seemed as if too much back pressure, some popping out the exhaust. Been setting the timing at around 12-14 degrees BTC with vacuum line plugged and disconnected. Today reset timing but once I connected the vac line it started running cappy again. Been running the vac line off the base plate of 4V Holley all these years with no problem.

Have a basic understanding of what's involve in automotive tune up but this time I am really baffled. Not that familiar with the Duraspark II components and wonder if a faulty ignitor box, or dizzy could be the problem, if so, is there a way of testing or adjusting either, just seems it has to be connected to the tune up, it ran great before that, and problem came on all of a suddens. Any suggestions, comments appreciated. Thank you.

 

Dunno what to say, your gap seems a little bit much (I believe stock is .044, not much, but still different) and timing is advanced a bit much. (again, stock is 10*) Now if you have reasoning for this, that forget what i say, but id start from there, maybe your off a bit too much.

 

Appreciate the feedback. Seem to recall using Mustang II for the Duraspark II tuneup spec's. It's just that I have been using these settings for quite sometime and why I thought perhaps the symptoms, or problems may be connected to faulty ignitor box, or dizzy. Majority of the manuals I own are truck related but would not imagine there would be that much of a difference with the tuneup spec's; that being said, I agree the plug gap and timing seem off. I will see if I can find an appropricate manual and confirm the settings. Likely end up starting from scatch and pull the dizzy and all of the tune up parts and check for correct parts and settings while reassembling. Again, thank you.

 

Have you changed fuel lately? Were you running premium before and then went to regular?

Your initial timing sounds a little aggressive, but it depends on the curve. Use your timing light and rev it up until it doesn't advance any further and see what that shows for timing.

 

Doc, what's interesting is the truck was running on empty when I stopped at a unnamed brand gas station and filled up, did not go 10 mi's before it started acting up. Went with medium grade, which is not unusual for the truck, but as soon as the problem started I thought about the fuel but then set the notion aside. I may just siphon as much as possible and put it in my generator, although, it would be a sad commentary if power went out and unable to get the generator started. Hmmmm

I will take another check on the timing. Have a Truck manual and found a section that covers electronic distributors and found it interesting the timing can run anywhere from 10 to 14.5 degrees depending upon the p/n on the dizzy. Anyhow, think I will start at 12, and although it's probably not a good idea, take a gauge and see how many inches of vacuum it reads, and set it to between 17-22 then check the timing marks. The truck manual also has a section on testing the Duraspark box but seems like it may be little too hitech for me.

Appreciate the feedback, thank you!

 

Pour a can of B12 in the tank and drive the gas out of it. If there is any water in the gas, it will emulsify and go through the carb with the gasoline. Run it as empty as you can and then fill it with good premium. Then go from there.

 

First I will take a few min's and make sure the settings are reset and then add a can of the gas treatment. Thanks for the suggestion, it will certainly be less labor intensive a this juncture.

 

I'll go with the gas also. My 02 Chev truck and wifes 01 Honda Passport will run on anything. But I have 2 old Bronco's that will run right on Exxon only, no Shell, or anything else. People say there is no diff. but tell my Bronco's that.

 

Hope it's a fuel issue, spent the majority of the day with the initial tune up so hopefully the gas treatment will be a quik fix, not excited about a 'do over'. Still not certain, over the past 35 plus yrs. the engine has been in the truck it has pretty much run on any grade, or mixture of fuel that's available. However, for some unknown reason I had second thoughts when I pulled into the station. It's worth a try, may save some time and money. Thanx for the feedback.

 

Yes, I think that you need to eliminate the chance of bad fuel. In almost 2 million miles of driving, I have gotten no more than a couple of bad tanks of gas, but it happens.

 

Just finished resetting the timing at 12 degrees, and the vac gauge reads 18" and steady. It's seems there is minimal improvement but still rpm tends to fluctuate. At some point, will recheck the plug gap, currently at 045; if recall, book calls for .044. About ready to leave for the local hole in the wall auto part supplier, imagine there's a limited selection of gas treatment brands, just eager to see if there's any improvement. Thanks again for the feedback.