Has this motor Ever pulled the same RPM's the other motor pulls? Or did it start after the backfire problems.

Chris

Did this issue start after you replaced the left side head gasket ? You had to pull the intake to replace the head gasket....MIGHT be an intake gasket on that side. I know it's a long shot...but spray some WD around the intake/head joint the next time you run it...you never know.

Do you have fuel psi gauges installed ? Wondering if the troubled side has a little too much psi and overpowering the needle and seat ?

Alternator charging well at idle on that motor ?

Distributor clamp and bolt clean on that motor ? Threads in intake ? Only way for distributors without ground wires to ground is thru the clamp grounding distributor body to intake manifold. if questionable try separate ground wire from dist body to ground lug.

Do these carbs have electric chokes ? If not grounding properly on this motor maybe choke staying closed or partially closed ?

Yes, they pulled the same rpm's when we had the air gap intakes on them before the blowers.

The problem was going on before the head gasket deal. Good point sprink, I've thought of that and looked closely at the gasket when we swapped the blowers and didn't see any signs of backfire, good idea on the wd40 though.

SB, we do have gauges installed and both sides are showing 7.5 psi at 4 grand. Haven't checked the alternator but its new (doesn't mean anything) I'll chec the distributor ground. Motors are manual choke held open all the time.

Something I thought of yesterday, back when we were having the msd ignition problems, we were trying anything. A friend of mine suggested gapping the plugs at like 045. Thats a good bit more than what it was or what the right motor is. I wonder if it's too wide and the ignition is putting out a weak spark across that gap. When I replaced the ignition parts saturday I noticed the rotor was fried. Maybe because the plug gaps are way too wide?

.045" should be okay but the norm is .035" with a close second amt of people setting at .040"

Yes, the larger the gap the more energy the coils/modules/boxes will put thru the entire system.

With the large cap HEI's If you have stronger coils and/or use ign boxes, the caps must use the low resistance MSD center button or they will literally melt and erode in very short use.

https://www.summitracing.com/parts/MSD-8412/

https://static.summitracing.com/glob...sd-8412_ml.jpg

Thanks SB. Good information.

Here's the old one..
http://i159.photobucket.com/albums/t...svfjtnhhq.jpeg

New one..
http://i159.photobucket.com/albums/t...pst0eu528r.png

Since all of the hard parts are in order and you're getting unburnt fuel passing through it seems like only the ignition is left.

Apparently a collapsed lifter can cause the valve to hang open and backfire through the carb. Just one more thing to look at.

We pulleded the distributor out and examined it. We went ahead and swapped the distributors. I checked continuity between the distributor and the block. Good continuity. We pulled the plugs out and gapped them to .035 like the other side. Nothing has helped. I've got some msd plug wires coming. That's the only part of the ignition we haven't swapped out. If that has no effect I'm not sure.

Also I sprayed wd40 around the intake at idle, no difference. And I feel pretty good that the intake gasket isn't leaking.

Double check the ground strap in the cap under the coil which goes to the center spade connector.
I have seen them left out before and cause all kinds of crazy problems.