Paul thanks for the input. High rpm at this point about 3,500 and I'm not certain all the backfire is occurring upon deceleration, though that is the preponderant observation. I experimented with added back pressure after I read the plug which showed I'd been running running lean. I inserted a temporary baffle and just clamped it in place and it really helped. I then pulled the air cleaner and the backfire increased but not to the level experienced before inserting the make shift baffle. I'm running lean for sure with the straight pipe, so that's part of it.
I let things cool down and pulled the exhaust, the copper ring gasket showed the evidence of a leak where my shop built manifold had not uniformly compressed the gasket. It looks like I cut the steel flat ring a bit oversize and was pulling against the inside contour of the head just ahead of the exhaust port just a fraction before the gasket is engaged to form a 360 degree seal. I took great pains to ensure that the manifold components were welded true, but evidently misjudged the final fit up. A couple of minutes spent with the file on the offending steel ring and all looks looks good to go at the exhaust manifold.
One other item I need to spend some time on is making sure there are no leaks at the carb. Nothing obvious at this point, just need to make sure, because that also will lean a mixture
I'd like to report all runs smooth, but since the throttle cable decided to pull loose from the lead head in the throttle housing I'm kinda waiting on the new cable now, but have to think I'm closer to a solution than I was yesterday...progress. If I need to run richer jetting that's not bad, but I'd rather get all the buggers sorted first. Rick C.
