I have a 77 f100 with a 302. I have been having some problems with surging and off idle hesitation. I am not quite sure what is causing it and I have to get it smogged soon, so tonight i was tinkering and trying to figure out if I have a burnt valve or what is causing my hesitation and stumble. Tonight I ran the following tests i did a regular static compression test a running compression test which included a snap acceleration reading. The following are my findings

Cylinder 1 - Static 120 Dynamic 40 Snap 82
Cylinder 2 - Static 120 Dynamic 45 Snap 67
Cylinder 3 - Static 122 Dynamic 45 Snap 80
Cylinder 4 - Static 120 Dynamic 40 Snap 78
Cylinder 5 - Static 120 Dynamic 36 Snap 78
Cylinder 6 - Static 120 Dynamic 40 Snap 80
Cylinder 7 - Static 121 Dynamic 43 Snap 65
Cylinder 8 - Static 120 Dynamic 35 Snap 81

So it looks like I might have a problem with how my engine is taking in air in the number 2 and number 7 cylinder. Am I correct in my logic? Does any one think this could be a worn cam problem? valve issue? From the information that I have gathered am not quite sure what it could be. Does anyone have any suggestions?

Thanks!!!

 

Sounds more like a lean mixture from a misadjusted carb or a vacuum leak somewhere.

The compression is fine, so no burnt valves.

 

I agree with LXman..... That is a great motor.....

 

It also has a surge through the entire rpm range. With my stock motorcraft 2150 the problem is worse than with the 500 cfm holley, but the surge/gurgle is still there. I don't know what is causing it, but it doesn't matter how rich or lean my jets are, the surge is still there.

 

You need to put a vacuum gauge on the motor with enough hose to watch from the drivers seat and see what that tells you..... You might have a small vacuum leak somewhere..... You need to get on the Holley website and watch the carb tuning video after you look at the vacuum situation and see if you have the right power valve too.... With the guage you are looking for a steady needle.... If it moves around a lot look for a leak.

 

Awesome! I will definitely try that. I appreciate the help!

 

I wanted to let you know the videos are also on YouTube too.... Just search for Holley and the come up first.... Start with installation... there is a lot of good information on them.

 

You might have to do some searching for the vacuum leak... the last place to look after the rubber hoses and the vacuum bungs and ports around the intake and the carb.... is the carb to manifold gasket and intake manifold itself. the link below had a good write up about that: How to Find a Vacuum Leak - Smoking Out Vacuum Leaks - Popular Mechanics.....

Hopefully the carb tuning is all it takes.... but if you still have the same problems after looking over the carb, Last is to take a volt meter and put on terminal on the positive lead (big lug) on the back of the alternator and the other to the battery's negative terminal... and see if the voltage is fluctuating..... (it is a lot easier to do if you have a true voltmeter gage inside the vehicle.... because you can watch it driving and what you are looking for is the needle moving when you are at constant speed, or dropping under acceleration or jumping up after starting acceleration.... a good stock type OE alternator will be pretty much constant voltage after idle .... if the voltage is not constant especially when you are driving... its a sign the alternator is going bad.... more likely the voltage regulator inside the alternator unless it is externally regulated.... when then you just replace the regulator and keep the alternator.... Hope this helps....

 

So i tuned both the holley 4412 and the motorcraft 2150. I was able to get the truck running like a raped ape on the holley but the 2150 was a different story.

I think the 2150 is too lean and it also turns out that the venturi clulser has a cracked emulsion tube. I am having a hard time tracking down this part and I don't know if it will pass smog with the broken part in the carb.

Any leads on where i could track down a venturi cluster assembly for the 2150?

I've tried ebay, holley, and daytona carb, but holley and datona will not sell individual parts, just the whole carb, and if i'm going to spend that type of money i'm going to put it into something that breathes a little bit better.