So I just swapped over to the Victor Jr. manifold along with some 1.6 rockers. I figured I would need to jet the carb some more but I drove it anyways. I would get an occassional "lean" backfire when I nailed it, but not too bad, and the plugs were a tad on the white side. So I increased the jets by 3 sizes (74 to 77, and 81 to 84) and now it backfires more. What could be causing this? Would a blown power valve do this? Thanks.

 

timing issues?

 

Timing should be good...16 degrees base, 37 degrees total.

 

backfiring out exhaust or the carb? if its comming out of the carb ur to lean...exhaust means ur to rich

 

It's coming from the carb. When I nailed it last night, in first gear around 4000 RPM, I got three consecutive pops (backfires) straight from the carb. I was afraid 77 and 84 might be too rich, but I'm not so sure now.

 

You increasing the rocker size means your valves are open slightly long due to the increase in the distance they now travel. Try retarding your timing a few degrees, you maybe experiencing a lean condition cause your valve overlap has also changed and you are loosing fuel out the exhaust valve, so if the timing change doesn't fix it try to increase your jet size a few more.

 

I retarded the timing back 2 or 3 degrees and it didn't help at all. The plugs are tan with a hint of white, not a serious lean condition. I'm probably going to switch back to my Performer RPM manifold, so maybe the motor will like this manifold a little more.