slight ignition problem

[tweet66]

Guys I need help. I just bought a 69 Falcon wagon, 2-barrel, auto, & points. I replaced the carb with a Demon Jr. 525cfm, dual plane manifold, MSD box, and Duraspark distributor (85 Mustang). Now I have a constant miss at all RPM's. I couldn't tell if it was there prior since it wouldn't run at idle at all . When I hook up the vacuum advance it's worse. Just revving it in park, no load, causes a huge miss-fire out the exhaust. Any ideas? I haven't changed the plugs yet, but the cap, rotor, and wires are new.

 

[2nd Mustang]

Regap spark plugs to .045 inches or there abouts, if you haven't already after installing an electronic ignition.

 

[tweet66]

still crappy

Okay, installed new plugs, gapped to .045, re-adjusted the carb since the secondary butterflies were open too much and I couldn't set a good idle and I still have the problem. I check the timing again and made sure I installed the distributor correctly. It doesn't miss as bad at idle but when i put it under load it falls on its face, missfiring and popping through the exhaust. Even out of gear when I rev it she'll pop and sputter. I'm running out of ideas here and wondering if the MSD box is bad.

 

[Ronstang]

Bypass the MSD bpx first and see if the problem goes away. If not go get a new condensor and intall it if you already did not.....sounds like this is your problem to me.

 

[tweet66]

no points

Ronstang, I thought about doing that but I've converted the distributor to a Duraspark unit at the same time, so there is no condensor and if I disconnect the box the only way I'll get it to run is to put in another box or a Duraspark ign. box.

 

[Ronstang]

Oops...sorry, i didn't see the Duraspark part in the original post.

 

[tweet66]

Alright I tried the Speed Demon carb from my Stang and the wagon still runs the same, good idle, barely any missfire, but under load I can't get past 15mph or she'll breakup and die. Which by the way is what I want to do to it since it has me sooo frustrated. I need this to drive daily and its not helping that I'm having this problem. Anyone with ant other ideas?

 

[2nd Mustang]

I think it's time for a vacuum gauge to help you do some troubleshooting. Either hook it up on a tee connection or temporarily on a manifold vacuum source:

http://www.centuryperformance.com/vacuum.asp

 

[2nd Mustang]

Oops forgot (sorry old age symptoms), but I don't know if you had mentioned if the engine was rebuilt or what. I once had an engine which after being rebuilt by a shop, wouldn't go past 40 mph, but would idle like a champ, turned out (after I had another shop tear it apart) the original shop used the wrong size crankshaft bearings. It also spewed a lot of oit out of the main seal. This doesn't seem like your problem, but just throwing ideas out.

 

[tweet66]

already did that

2nd, I used one when I first put it on and again when I re-adjusted the carb. She pulls a steady 20in of vacuum at idle, best adjustment, 17-18 at worst. I ran a compression test when I bought it. Every cylinder had at least 131(worst) to 143(best) lbs of pressure. The motor only has 47,809.xx miles (as of this afternoon ) and I have all the paper work to back it. I don't think there is an internal engine problem. I just can't firgure out where the problem is. Is there any way to test an MSD box or is that something the factory would have to do? I'm going to put the points distributor back in and see if that makes a difference or wire up a Durapark ignition box. somethings got to work. :damnit: :damnit:

 

[2nd Mustang]

You have more than adequate vacuum readings at idle, so it seems it's ignition related, but on the very outside chance, maybe the fuel filter or air filter? How new are the plug wires? Were they cut to fit, or a set already made up. I always keep one set of "cheap" new plug wires just for isolating trouble in plug wires. I had a factory (expensive) set go bad in less than a year. Good luck.

 

[tweet66]

another idea

Could the fuel pump be at fault? Without enough fuel off idle I would get the same problem, right? Driving it, it seems(feels) like its starving for fuel leading to the missfire . I know its anoying the crap out of me