A friend of mine has a '77 Celica GT with a carbureted 20R and 5spd.
I went with her when she bought the car and test drove it with her. At the time, it was running just fine, but now it has developed a backfire through the intake side under hard throttle, acceleration or under load. This doesn't happen durring shifting or deceleration, so I don't think it has anything to do with the air pump or anti-backfire valve system.
I timed the engine with the distributor that was in it, but another friend of hers replaced it, because it was believed to be the wrong distributor, possibly from another R motor or A motor? I didn't look at it that closely. I'm not even sure if the A 4cyl motors in Tercels will swap distributors?
Anyway, the engine now has the correct electronic dist. that it should have and appearantly, the problem has progressed even worse. I haven't taken a look at the car, but I spoke with the owner last night and she told me that it was worse.
I plan on checking the distributor rotor placement against true TDC (pull #1 plug, check for compression, etc.), and retiming it myself, but I'm beginnning to think that the backfiring issue may be unrelated to the distributor and could be developing a valve issue. Possibly lash or valve seat related.
I wanted to ask you folks if there were any common causes for this condition with the 20R. Thanks!