Ok ive been having a backfire through the carb, im gonna start from the beginning hoping that will give enough info to help figuring this out. on feb 16th my dad and i took it for a little drive and it drove great, for sitting for atleast 7 years. On on feb 18th i had put in new spark plugs and found out it was only running on 6 cylinder, #6 and #3 would not fire. on the 21 i did a carb rebuild. instead of rebuilding the point distributor i opted to put in an hei i also got new wires and put an msd coil in, i put that stuff in the engine on march 22nd. Through this time my dad and i would drive it and get on it pretty hard, it was fun to spin the tires, and drove great with no problems other than a rough idle. also we would lissen for pinging as we had put some cheap 87 octane gas in. around the end of march i was setting up a deal to get some rust repair but about a week before i took the car to the body shop i took it on about a 25 mile round trip to my dads friends house and again it drove great with no problems. It took about two months for the work to be done and in that time it sat only running when i needed to move it. now its july 22 and im driving to another shop to get some more work done and its just up the street so i pull out of my driveway and get on it and i get a backfire so i let of and drive regular the rest of the way not realy woring about it. About a week later its done and on my way home i do the same thing with the same results. Now im thinking about it, i start it to warm up the engine and then rev it from under the hood to open up the choke whenever im gonna work on it. One time i did my warm up procedure and it backfired and scared me so i reved it again and it backfired again. Through weeks of on and off messing with it and driving it i found it only backfires through the secondarys when they open. I also found i could get it to go full throttle with no backfires but it run worse then only on the primarys. i have driven it to everett and back about 3 times this summer, about 105is miles round trip, and it drove like a dream as long as i kept the secondarys closed. recently ive checked for a loose timing chain with the distributor cap off i spun the engine until the timing mark on the balancer was on the 0 degrees mark on the timing tab with tension on the dist then i spun the engine the oposite direction watching the dist rotor until it started movin. I then checked the balancer timing mark it had moved about 12 degrees, so now i know ive got twelve degrees of slop in my timing chain. Now i have put almost 1000 miles on it and within the last 100 miles the transmission has started hesitating between shifts and when it does the engine backfires. The shift hesitation has been getting worse with time and the low speed/ part throttle backfires seem to coinside with the tranny shift hesitation. I did swap that big tranny vacumn modulator with a little red stripe one my dad had and it didnt change a thing. Ok so now ive got transmission hesitating between shift with part throttle backfires that seem to coinside with that and the backfires that had developed earlier. Also today i drove it since its been sitting for a little while and the 1-2 shift started at about 20mph but it hesitated for about 5-10 seconds before getting into 2nd then the same thing for the 2-3 shift, on my way back home i got on the highway and it tried to shift but something wierd happend as i thought the engine died, i couldnt here it and i was not accelorating, i stayed on the throttle and it came back. So thats where im at i would apreciate any help with solving my backfire and shift problem. sorry for the long read.

 

I have tried changing the timing ive had it as high as about 14 initial but its at 7.5 right now i aslo run 92 octane gas with marvels mystery oil every time i fill up, its the highest octane gas around here.

 

Start by checking all vacuum lines as trans needs vacuum for proper shifts and backfire seems to be related.

 

The nylon teeth on the cam gear are probably worn out. Get a good roller chain and gears. Then set your timing. Be sure the HEI gets 12 volts all the time. If you are converting from points ignition, the yellow/black wire is 12 V when starting (it goes from the coil to the starter solenoid), but when the key is on "run", power goes through a resistor wire to the other lead in the spade lug on the coil reducing voltage and making the points last longer.

 

I have checked for vacumn leaks and i checked the line that goes to the transmission and it has vacumn. Could that metal vacumn line that goes from the engine to the trans have holes in it causing my problem? I have checked and the hei has 12volts while running.

 

You said in your first post you've got an HEI and an MSD coil?My HEI doesn't use a coil.Is this right?Just wondering.
railguy

 

Do the timing chain, it'll make all the difference in the world!
A $40 water pump will avoid doing it again later, since you've got it off.
I always do both together when one or the other is needed, to avoid twice the work.l
12 degrees @ the crank is very loose - if it breaks ya get bent valves or broken pistons!
Don't rev a motor cold - pistons haven't expanded yet!
Don't rev a motor and shut it off - raw gas washes the oil off the cylinder walls!

 

The coil for the HEI is in the top of the dist. cap.

 

From everything you've described, I would do the timing chain 1st. Both issues you are having could definitely be due to the timing chain jumping a couple of teeth.

 

Its been a while but my dad and i got the problem pretty much figured out. It turned out that the timing was too retarded at the factory setting, my dad advanced the timing until it ran good and reved without backfiring and when i test drove it it didnt backfire but now it pings. I thought maybe the balancer spun or something making the timing mark incorrect but we put it on tdc and the mark on the balancer was lined up with the 0 mark on the timing tab. When the initial timing is set to the factory setting it runs kinda weird and does the backfire deal but when its advanced to where it kicks back a little while starting it runs great, though it does ping.
I just wanted to let everyone know its going good i just gotta try to keep gas in it long enough to finnish tuning it.

 

You can either retard the timing by 1-2 degrees, or recurve your HEI dist. and use an adjustable vacuum advance module.

 

It still goes back to the timing chain. If you have to advance until it pings in order to run right you're just masking the underlying problem.