305 backfires through the carb under accel since swapping it

[Don Nicholson]

I pulled the 305 out of my '84 K10 and stuck it and the SM465 attached to it into my '86 K5. Other than burning some oil and not having a ton of HP, it ran great in the K10, but since I've put it in the K5 it's not doing so great.

Under accel it backfires bad out of the carb. I've got ~17" of vacuum and can't find a leak. I've tried with and without a fuel regulator in line. I've tried anywhere from 8-18 degrees of initial timing (without the vacuum advance hooked up). I've tried running it with and without the vacuum advance connected. It all does the same. I've adjusted my carb as best as I can using a gauge (Edlebrock 4bbl). I also had the Holley 4bbl that was originally on it and it did the same thing.

I've seen a couple of posts that say it may be a wiped cam, but this engine ran great before, so I don't see why it would have all of the sudden killed a cam.

Any suggestions? Ideas?

 

[Don Nicholson]

I was thinking maybe the transmission isn’t kicking down causing the engine not to rev enough to burn the extra gas with throttle acceleration

 

[Big Chip]

I had a problem with the 305 in my 86 C1500 backfiring through the carb. I found out a rocker had come off the pushrod. I don't remember but I would assume it was an exhaust valve. Of course I only found this stuff out after I bought a 350 and a pile of parts and pulled the 305 out.

 

[Pender1]

Ok guys, I set it to about 9 degrees and checked my plug wires again. The timing made it a little happier, but it's still backfiring. I'm starting to wonder if it's a problem with the distributor itself.

 

[Pender1]

I was thinking maybe the transmission isn’t kicking down causing the engine not to rev enough to burn the extra gas with throttle acceleration

It's a manual.

 

[Pender1]

I had a problem with the 305 in my 86 C1500 backfiring through the carb. I found out a rocker had come off the pushrod. I don't remember but I would assume it was an exhaust valve. Of course I only found this stuff out after I bought a 350 and a pile of parts and pulled the 305 out.

It's worth pulling the valve covers just to check I guess.

 

[Snoots]

The power valve situation isn't so bad anymore. Lots of power valves have taken a good backfire and lived to tell about it.

I'm glad you didn't have my luck with power valves then.
Another thing that comes to mind...I had a backfiring problem in a 326 engine and found that a pushrod had worn out the rocker arm (where they meet). I replaced the rocker arm and cleaned out the pushrod and that fixed it. Not sure why it wore out because the pushrod wasn't clogged and oil was flowing thru it.