67 250 backfire problem

====== ======

67 Chevy van w/250 manual tranny.

I think the 250 is circa 67 because the spark plugs it takes are AC 4 but has what appears to be electronic ignition from a late 70's model.

replaced all ignition components.

replaced the carb with a rebuilt Rochester. ( it did have a carter yf.)

now has bad hesitation and will backfire if you accelerate hard in neutral.

also stutters at WOT in neutral or while driving. timing is @ 8deg @ 800 rpm advances to 20ish @ 2300. vacuum is @ 20" at idle and falls to 0 for a few moments when accelerating from idle to WOT in neutral.

this also generates stuttering any ideas?

============ ============

Drive it ???

instead of try'n to blow it up in Neutral in the carport?

MarshMonster ~:~ ======== ========

actually i've driven it a number of miles while in an attempt to figure out what the problem is. however trying to drive and make any adjustments at the same time has proven to be very difficult...

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= *** Usenet.com - The #1 Usenet Newsgroup Service on The Planet! ***

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Re: "67 Chevy van w/250 manual tranny. I think the 250 is circa 67 because the spark plugs it takes are AC 4 but has what appears to be electronic ignition from a late 70's model. replaced all ignition components. replaced the carb with a rebuilt Rochester. it did have a carter yf. now has bad hesitation and will backfire if you accelerate hard in neutral. also stutters at WOT in neutral or while driving. timing is @ 8deg @ 800 rpm advances to 20ish @ 2300. vacuum is @ 20" at idle and falls to 0 for a few moments when accelerating from idle to WOT in neutral. this also generates stuttering any ideas?" ========================== Jerry,are you saying that the hesitation and backfiring started AFTER you replaced the carb and ignition components? That's what it sounds like,reading your post.If that is true I would start undoing your work piece at a time until you find the problem.It really does sound like a weak spark.Pull a plug and check what kind of spark you're getting.

Jerry, Are you backfiring thru the carb or the exhaust?

If you have an inductive timing light, go around to all the wires and make sure they are all firing- Plus, as Brian said, pull the plugs and make sure they are the correct ones- nice wet fuel soaked plugs indicate no sprk, possibly the wrong ones- check your wires- sometimes in an effort to remove the sp boots, the wires pull out from the plug boots, and just sticking them back in doesn't fix it.

Check your float levels/idle mixture, etc- if you have a vacuum guage it should be pretty easy to check proper mixture- lots of help here as to how.

When was the last time a valve job was done? bad valves, sticking lifters, etc are another reason for a backfire-

Good luck! Carl