I have two brand new 670s i am using. They seem to be jetted pretty lean out of the box. The one I had working well but it was pretty rich ran between 10-1 and 12-1 a/f ratio. Tried leaning it out for better mileage and just couldn't get rid of the off idle stumble even with some huge squirters. I think the 670 might be too much carb for the 302 i have it on.
Then I put another one on a 351 engine with giant ports. I got the jets setup pretty decent now but idle and off idle are just horrible no matter what I do to the damn thing.
So I haven't had much luck with these street avengers.
if it does good at WOT id leave the jets as they are and mess around with the squirter and idle circuit first.
