I have a 78 Cobra with a mildly built 302. We recently put a new ready to run mechanical advance MSD Pro Billet Distributor on it and tried to use a new Holley 770 CFM Street Avenger on it. The carb was too high for it which was making it run too rich. After the previous 650 cfm holley was put back on it the thing still has a back fire. It will idol fine but once it is given some throttle it fires a little from the exhaust. There is also a problem of every time I shift from P or N to D or the latter it stalls out. Kinda stumped. Need some help asap.
If you have too much cam, your vacuum will be low and thats what makes it tough to idle. I have a 600 Holley on my 302 with 66 - 289 heads and a edelbrock perfomer cam. I rejetted my Holley primary and secondarys. I took me about a year to get the right combination for my setup. I couldn't ask for it to run any better. I can do 20mph or 60 mph, nail the throttle and the engine instantly comes to life. No bog or hesitation at all.
I am assuming you didnt have the stumble before you changed distributor. With the mechanical advance you may have to put lighter springs in so it advances quicker.
I at last got the carb I need..I was way under. I got the new Holley ultra double pump 750 and it will peel the paint of the car now...If you are wondering what I have it in now it an forged eagle 347 kit with H beam rods and a main cap girdle , comp cam 35-522-8. intake 232 and exhaust 240 at .50 AFR 185 58 cc heads, with air gap intake....as you can see a 600 double pump was to small...must have messed up the math..lol
