So I took my car to the track the other night and I was parked in staging waiting for my turn to make a test pass. When I was called up next to make my pass I began to crank the motor to start it and kaboom.....backfires and a ball of fire spit out threw the carb and the carb stayed lit like a candle. I quickly shut off the fuel and ign and floored it and cranked the motor hoping for it to suck the flame into the manifold and disperse it.. Well it didnt. My damn starter wasnt cranking fast enough. Probably because I was running a stock LS1 starter on this 12.5:1 ratio, lol. So I was forced to disperse my halon since my hood is zuesed on and it would have taken my 2-3 min to get all the damn zues pins undone. So....with that said.. I replaced the starter with a MSD high torque LS starter. handles 18:1, 3.5 hp motor. It turns the motor over about 350-400 RPM...very impressed.. however it still is backfiring...not seen a Hiroshima yet but I am concerned. What happens if I go to the track and it does the same **** again? Here is what I am doing to start it up. Hit the fuel pump to make sure my carb has full fuel jackets. Pump it once, then kill the pump. Turn on the box, and crank. Sometimes it fires right up with no throttle but more times then not it just cranks and cranks, so I give it a little throttle and then sometimes it fires up and sometimes it just cranks and cranks and then it backfires out the tail pipe. I have a pic of my timing curve. Here are my specs. Possibly a bad cam and crank sensor? I dont think that would be a problem since the motor runs great once it starts. Just a thought. any help or ideas would be great......please....before you post think about this....I dont need lecture on the timing curve being crazy or that it isnt tuned right or the cam isnt right or the motor or any of that stuff. I need honest advice. This cam idles best at 36*. I have played with it all over the place and thats where it responds best at. There is a little lag after initial throttle but I think thats because this cam is just really really big.
This post is about a bad backfire issue and I dont want this thread being 5 pages long and we all end up talking about the tires I am using as being the problem...get where I am coming from? I have seen lots of threads take that direction and the original question not even being answered...thanks again guys..

GM 6.0 block .030 over to a 408 12.5:1
Callie dragon slayer crank,
Compstar rods, Ati super dampner,
Cam - .744/.766 .288/.306 115LSA Solid Roller
1/2 pushrods, jesel shaft mount rockers, Triple spring seat pressure 350 psi closed, 850 psi open, Trick flow custom 245 intake runner 255 cc exhaust runner, titanium vavles
Super vic intake, quick fuel 1050RQ series jetted appropriately for 12.8 AFR at WOT, front jets are 84 rear are 88. It came at 88, 96
Float levels are both right in the center.
Aeromotive A1000 pump with low press aeromotive return style regulator
MSD 6LS ignition controller box with MSD ignition coils......I have been running these coils for about 4 years now and I had it when it was EFI and had no problems even spraying up to a 350 shot on it. Plug reads were good.
ARE dry sump 4 stage oil system
MSD high torque starter
NGK br-7 non projected tip plugs for NA application gapped at .33-.35
I think that sums it all up

 

Why so much timing at idle? Or did I miss something while scanning thru? My carbed ls was backfiring untill the engine warmed up, but it was about 48 out today so I just put it off as its cold out.

Edit: just noticed your cam likes that much idle timing. What was the temp out?

 

Classic symptoms of a bad cam sensor. According to the MSD site if the cam sensor is bad or even completely unplugged then you have a 50-50 chance of the motor starting up correctly each time you turn the key. The other half the time the timing will be 180 out causing back fires.

But IMO that is way too much timing at cranking speed. That could be contributing to the problem and is probably the reason why your starter was being overworked. Try setting it down to under 15 to 20 degrees at crank (500 RPM) then go ahead and ramp it back up at 1000-1500 RPM. That is the beauty of the MSD software.

With my car I find it better to not touch the throttle until after I am cranking it. If it doesn't catch right away then start pumping the gas.