Do I need a new carb?

I want to see if this is a carb issue, before I pull it off and rebuild/replace or whatever.

I have a 1974 302 in a 1968 ford bronco.

I have done a lot of fixin on it, and am having some issues now that I got it back up running.

engine sat for 20+ years. Got it back running. No smoke, all plugs look great (30,000 miles on rebuild).

However, still having issues on throttle response. I want to see if all this stems just from an old carb

So if I am at a standstill and slowly rev the engine, it will smoothly rev (perhaps a little bit of hesitation or whatever, but still revs just fine) However, if I attempt to stab the throttle from an idle it almost dies and then will kind of pick up at rev like normal.

If I rev it several times in a row it seems to rev better.

I know my little fuel jets are pushing fuel properly, so that is not the issue.

Also, when under load (Such as in 4 low coming up a steep grassy hill in 1st) the engine will kind of gain and loose power (as if I was giving it varying amounts of throttle).

Would this stem from just a bad carb? or are there other issues here?

Carb is a holly 600 (1850) vac secondarys.

Sounds like either or both the accelerator pump and power valve aren’t working. Rebuild the carb.


After checking the timing, vacuum and distributor advance mechanisms. so many options. The accelerator pump sounds good to check, sure I could look on the interweb, but what is a power valve?

I’m in agreement with Tester and the power valve is a vacuum operated valve in the carburetor float chamber that meters additional fuel under a heavy load and is prone to failure with age. The rubber diaphragm gives up.

Yeah, It backfired a lot when I was timing it, so I prob busted something in there.

I know the accelerator pump is working however.

If it backfired while timing it, you might check the timing chain. Did you know they used plastic teeth on the cam gears on these engines?


Well, I had it 30 deg or more off time, so I think that was the problem. it didn’t really backfire, more just the engine recoiling on the compression or something.
Did not know that they had plastic gears in there.

Is the distributor the 1968 model or the 1974 model? Do you have access to a dwell meter or a DVOM with a dwell function? Have you checked for vacuum leaks at the carburetor base? How many vacuum ports are on the distributor? Will the engine hold a steady vacuum of 18 in at idle?

I think it is the 74 dist. It has two ports on the dist. It runs teribble with ported vac on the outer port, and pretty ok with the ported to the closer in port.
I have my own mulitmeter, volt tester, if that is what you mean.
I don’t have a working vac gauge, but I do know that it has a lot of vac, as I can take off the cap on what used to be a trans kick down (I think the intake came off an auto trans car) and the idle will come up, but it will not miss or anything.
It may have a leak on the base plate, as they have two spacers on it and I noticed a little bit of fluid leaking out between them when I flooded it out trying to start it again.

Remove the carburetor and inspect the spacers and gaskets. What type intake is on there? What are the spacers? If the original intake and carburetor were on the 74 engine an EGR spacer would be installed. And as for timing, remove all the vacuum hoses and move the distributor to where it runs the fastest/smoothest and snug the bolt down temporarily.

Stock looking 4 bbl intake. Spacers look like the st spacers (I think they were trying to make a ‘high rise’ intake by stacking them).
I will have to inspect and change those gaskets. Think that would be the best time to rebuild? or do one thing at a time or?
Yep, I did that for timing, as well as checked it with a light. 6 deg btdc was where it is.