STILL having ignition issues on my 5.0

Ohhhh I see. I was never 100% on how the cfm really worked...

 

Exactly...

The 670 I have on my 428 Cobra Jet was so lean it surged noticeably at slower cruse speeds(supposedly these are ready to run out of box, don't believe it... A friend with a 350 Chevy II had same issues)... I've increased front jets from 65 to 68 and it's better but still needs some tweaking...

The 600 on my Comet had the low speed stumble and I replaced the squirter(s) with the extended tube type mentioned in Summit video(robbed from old 2bbl, both are size 31)... With no other changes, that made a noticeable improvement...

My guess is with the 670 and small motor you may need to increase size, 35 was mentioned in video... Still give the cams a chance to help...

 

someone made the stement the other day that...CFM doesn't matter, just jet it to run...I was thinking if this was the case...all carbs would be 1000 CFM, just dial in what you need...

 

While that can work in a race engine, almost never does it perform satisfactory in a off idle street engine...

There's a reason so many different CFM carbs are available, bigger isn't necessary better...

For approx 25 years I ran a 600 cfm 390GT carb(factory is 735) on my 428 Fairlane only because it gave superior low speed operation... If I can't tune the 670 to my liking, it'll come off and the 600 will be back in place, does loose a little WOT power on the smaller carb but street manors rival a modern FI engine(at least when warmed up)...

 

see i wasn't sure how the CFM thing worked... now that i know it all makes sense now. so you guys suggest jetting the carb? primary and secondary? or just primary

 

I'd go up to 68 on the primaries as a start, along with pump cam tuning and maybe larger squirters, you can probably get it acceptable... In the end you may find a 670 is just too big, Holley does market a 570 cfm for small blocks...

BTW There are extended tube 35 squirters currently on ebay for a good price(around $16 shipped), search using lowest price..

BTW #2 my friend used a wide band o2 meter to determine 68 was optimum in front for part throttle cruse, I check back with him to see what he used in the rear...

 

okay thank you for all the info Krazy! i currently am running a 35 squirter and i am going to go to the local speedshop (yes i actually have a real speedshop by me lol) to get some jets. I'm going to get 2 and 4 sizes up to see which it likes best. I'm going to get it for the primary and secondary but I'm not gonna mess with the secondary till i dial i the primary. and Krazy please let me know if he gets back to you on secondary jetting that would be awesome. thanks so much!