So ... I am having trouble getting my '68 F-100 running good. It has a '73 360 with a rebuilt stock motorcraft 2150 2barrel carb, electronic ignition, the jets are stock 54's, etc etc. nothing fancy. I have tried every imaginable adjustment on the idle screws, float setting and what not. I have not checked the vacuum yet cause I do not know the correct setting at idle. The timing is about 8-10 degrees.

When I say "running good" here is my problem ... It loves it when I'm on the throttle and it idles fine but you can smell the gas coming from the pipes when its sitting there idling (~850rpm). It WILL NOT just cruise down the road in 3rd gear or 4th gear (4spd granny trans). You can feel it "loading up" and then it backfires or detonates in the headers. And if I am on the throttle and I let off, it backfires and pops in 3rd gear.

I have taken the idle screws in to the point the motor starts to die .. backed them out .. messed with the throttle linkage .. but still it is begging for more air it seems. I am starting to think I might have a dead cylinder or something. I know I have a small header gasket leak but that shouldn't make it spit fuel out the pipes like this. Any advice is greatly appreciated!!!

 

My 70 360 runs around 17-18 on vacuum. My advice would be to get another carb and try it, just because you put a kit in a carb doesnt necessarily fix it. I bought a tomco remanned carb from the local auto parts store, set it and havent had a problem since.

 

mine was a remanned carb from Advanced auto. It wasnt a kit. my bad on the "rebuilt". I will try setting the vacuum to around there in the morning and see what comes of it. Thanks!

 

A decently tuned stock engine should be between 18-22hg and a steady needle.

How to Use and Interpret a Vacuum Gauge

Have a read and give the vac a shot. At idle an issue with basics will be obvious. Does the vac adv diaphram check out ok ? A backfire through the exh pipe and weak pull seems like vac/mech advance issues.

I'm leaning towards gummy distributor advance weights-plate etc.., weak, broken or loose spring.

 

what are your mixture screws set at ?

 

Great link Redman