New Engine breaks up around 1500 rpms

[mustang289]

I need some help troubleshooting this. Just finished installing a 5.0 in my 65. It is a stock 5.0 HO motor with edelbrock carb and intake. I have a professional products distributor and MSD coil.

Engine starts and runs fine. Timing is set to 10D BTDC and I am getting advance. However, in check advance I noticed the engine starts to bog and backfire a bit starting at 1500rpm. I am running the 5.0 HO firing order - 1-3-7-2-6-5-4-8.

This smells of distributor being install wrong, but I swear to all that is good that I had #1 at TDC and stabbed the distributor in the right location. I even marked it with a piece of tape.

I had a couple of ounces of bad gas in the tank and hoped that could be it, but I doubt it now.

Any thoughts on how to track this down?

[Franks68coupe]

Is it a carb backfire, or exhaust?

[mustang289]

It definitely seems more exhaust - some backfiring through the exhaust and a general rice krispie effect - snap, crackle, pop.

[Franks68coupe]

Double check your vaccuum lines, all intact, etc... Maybe try a little more advance?

[nbears747]

not trying to hyjack - I also have a similar issue... but on a non-HO motor. starts & idles fine, but sputters and misses as it's coming off of idle... I think it might be mismatched fuel pump / injectors? I too will try a little more advance.

[theman1990]

Are you counting the firing order COUNTER CLOCKWISE like you should?? Don't ask me how I know this issue....

[mustang289]

Yes - I am counting counterclockwise. I went back and found TDC on #1 and looked at my rotor and it was a little behind. I adjusted it and things seem to be better but my timing light now reads way off. I have one of those inductive timing lights where you can set the advance. Road trial was better but still some bogging. My timing light has me very confused.

[68RCodeConv]

How much vacuum advance are you getting? I don't like that the timing light reads way off. I would try a different light. Look at the mechanical weights and see if they are stuck.

[mustang289]

For sanity sake I found TDC on #1 and re-stabbed my distributor. Set initial timing at 10d.
I think I found my culprit...The stumble is only there with the vacuum advance hooked up. I have it hooked up to timed vacuum off the carb (triple checked this). The vacuum advance provides 10d of advance and it is all in before 15hg's of vacuum. My mechanical advance provides 21d of advance. Am I getting too much timing? Can I run a 5.0 HO without the vacuum advance? I can change my mechanical advance easy enough.

[mustang289]

I wanted to post my resolution to this. When my vacuum advance kicked in, the rotor would get out of phase and would either cross-fire or fire on the wrong distributor terminal. MSD has some articles on this and apparently it is a common issue with Mopars. That is why my timing light would read normal until I hooked up my vacuum advance.

Also, apparently this is not an easy fix. The professional products distributor did not come with the vacuum advance installed and I had to completely remove the shaft to install it and really work it to get it on. I am sure I horked things up doing that.

I dropped in my old distributor and it runs like a champ.

[ScottsGT]

And reading this makes me feel better that I didn't buy the PP FI system. Taiwan and all that other stuff.....