I have a 2002 Ford ranger, the truck has long travel suspension. big coilovers full cage etc... Its got a 400 SBC bored .040 over with 9.5:1 Kieth black pistons, solid roller lifter .570 lift cam 270 something duration, 1.6 ratio roller rockers, 6" skat rods, stock crank, Performer RPM edelbrock intake, 750 holley with vacuum secondaries, HEI ignition. Turbo 400 2WD transmission.


Engine is brand new


Whats going on is it falls on its face every time you give it more than half throttle from an idle. and it backfires out of the carb, when you drive it it does the same thing and itll almost die, but after it cuts out it runs awesome. I cant figure out why its doing it.


Carb has 66 main jets in it. 6.5 power valve. Ive played around with the plastic cam on the linkage, used anywhere from a 25 to a 40 on the squirter jet(the 40 jet helped it take throttle but driveability was worse)


Timing is set at 15 Degrees ignition and around 36 degrees total(ive subtracted and added and it doesn't seem to change the issue)
its got an HEI with brand new Pertronix 50,000v kit on it.


Im pretty sure its something with the carb, If someone could help shed some light I would really appreciate it!

 

Have you set the carb with a vacuum gauge?

Does it pull good vacuum at idle?

What do the plugs look like? Are they fouled or wet?

It sounds like either the timing is off or the valve train is not right.

I take it for granted that you are disconnecting and plugging the vacuum advance for the distributor when you are setting the timing.

What springs do you have in the distributor for the mechanical advance?

Sorry for all the questions it's just that the lack of response could be quite a few things and I am trying to help by asking some of the questions a mechanic could overlook.

 

I haven't set it with a vacuum gauge, i set the air screws at 1-1/2 turns.

I do have the vacuum advance disconnected and plugged.

I set the valve lash pretty loose to eliminate a tight valve being a problem ( I set them all at .020")

The pertronix kit I got came with 3 sets of springs and I used the silver springs which are the middle of the road springs.

All the spark plugs are dry and either really dark brown or black.

 

First I would set the valve lash. It is important that the valves are set properly so th engine can breathe correctly. You will need to find the spec sheet for the camshaft, the sheet will tell you the clearance for the intake and exhaust, as a rule the intake valves are set tighter than the exhaust.
This link will help:
Correct way to set valves on sbc w/ solid flat tappit camshaft? - Hot Rod Forum : Hotrodders Bulletin Board

To obtain a properly adjusted carb you will need to adjust it with a vacuum gauge to get the highest amount of vacuum possible at warm idle.

Here is a good link on how to set the carb with a vacuum gauge:
Setting Idle Mixture The Right Way


I fell that you are correct on the carb being out of adjustment but two or three items being out of specs can multiply the situation.

Oh almost forgot, the jets in the carb might be causing the engine to get a large amount of fuel dumped in at once, you could start with the smallest ones, set the carb with the vacuum gauge and see how it performs, if you are happy with the performance drive it a while then check your plugs to see if they look good if not change the jets and repeat the process until you get the desired effects.

 

I know the valve lash is supposed to be set at .016 and .018, I set them all at .020 because all the valve train is pretty much brand new and everything will wear in a little bit. I'd rather have them a hair loose than too tight

I'll get a vacuum gauge today and see what I can do, I'll try jetting it down too.
I know it's really rich on the bottom because when it's cold I just pump it twice and it fires up and idles fine even with no choke. The main jets are 66's but I'll have to check what the secondary jets are.

Thanks for the advice! I'll try using the guage on it and see where that gets me.