So I'm working on this 79 New Yorker. 360 magnum with a factory Holley 2 barrel. The car had a significant vacuum leak and hardly ran. The carb was junk. The customer got me a carb off rock. Put it on Friday and ran pretty good. Put my vacuum gauge on it and it was pulling about 17 inches. Not bad....figured it was fixed. Start it up yesterday and it's back to a massive vacuum leak. I cannot find any external leak. Plugged up and pinched off every vacuum hose. Sprayed carb cleaner everywhere. It's gotta be internal to the carb The old carb was so bad the engine hardly ran. With this carb, at least the engine runs. Would debris in the fuel clog something up internally? I put a new fuel filter in and purged the line. I just can't seem to figure this out. I wish j could put this carb on another engine to rule it out. Any suggestions? advice? Im at a loss here
Clogged idle circuits will cause symptom similar to vac leak. Pull apart carb and make sure every little orifice is clear. Blow out with compressed air and reassemble
Did you compare them really carefully before r+r-ing? Rebuilt carbs often have the wrong base plate, air horns or whatever. You checked the base gaskets carefully?
You can Also use the old timers trick Jason . Suck on the carb . Start it up and rev it up to about 2500 or so and choke off the venturi With your hand and when it almost stalls out remove your hand and feather the throttle . Do this about 3 times and see what you turn up with . Its worked numerous times for me .
Pull the oil fill cap and place your hand over it. The intake gasket could be leaking. I can't answer why it would be temporarily fixed though.
In answer to Frank's question- yep, they are identical. Same number and everything. Im gonna try the "suck it through" trick today if it ever stops raining. And if thst doesn't work, I'll reluctantly take the carb apart and blow it out
If the carburetor came from Rockauto, it's probably re-manufactured. You know how re-builders like cliff Ruggles feel about re-manufactured carburetors. Take the original over to Allstate.
What are the symptoms that cause you to say “massive vacuum leak”? Is it just an idle problem? Have you tried propane enrichment or closing the choke blade a bit to richen it up? Does this engine use an EGR valve?
I should say it's lean as F. If I choke it out, the idle goes way up and the AFR goes down to a reasonable 13 to 1. It does have an egr. But it doesn't seem to be leaking
Have you tried adjusting the idle mixture? Does it run OK at cruise or WOT? Can you check to see whether the EGR valve is sticking open? If you road tested the car with the new carb, maybe the EGR valve opened and is stuck open now??
Seems crazy that two carbs in a row would have such similar issue? Maybe there is some kind of small crack or hard to see leak in the intake? Just for people who may not be aware (not Jason) Rebuilt carbs often are not properly setup for particular applications. They may require adjustment/bending of linkages and tuning. Or rebuilding LOL.
I seem to rememer EGR valves didn't come into play until around '73 or so by the OEM's. I could be wrong BUT maybe that's NOT a '70 manifold??? Tom T.
If it ran decently with the new carb & then started to running like crap again, sure seems like the carb is the problem.
