Chasing a vacuum leak

ptrmzr · Apr 6, 2014

Hi, I just rebuilt my 4300 (71 351 M) and I had it "flow benched" at the local carb shop. They said it all looked good, but when I re-installed it and ran it today there is a loud whistling coming from either in the carb or behind it.

I checked all the vacuum lines and snugged down the carb mounting bolts.

Any ideas?

Thanks?

wrshog · Apr 6, 2014

Hi, I just rebuilt my 4300 (71 351 M) and I had it "flow benched" at the local carb shop. They said it all looked good, but when I re-installed it and ran it today there is a loud whistling coming from either in the carb or behind it.

I checked all the vacuum lines and snugged down the carb mounting bolts.

Any ideas?

Thanks?

Try spraying some carb/choke cleaner on the vacuum lines and around the base of the carb. RPM will climb if you have a leak somewhere.

not2old · Apr 6, 2014

also check for split vacuum port plugs

droptop73 · Apr 6, 2014

Make sure you don't have any open vacuum ports. Look at the "tree" behind the carb.

Don C · Apr 6, 2014

PCV hose? Also make sure the gasket didn't get kinked or something is interfering with carb sitting flat.

You can use a piece of vacuum hose, hold one end to your ear and move the other end around to pinpoint the leak.

ptrmzr · Apr 6, 2014

Hey thanks everyone - this gives me lots of things to try!

Sent from my iPad using Tapatalk

caspianwendell · Apr 6, 2014

Any time you mess with older vacuum hoses it can cause a leak. Did you make sure to clean the intake mating surface (cannot have any leftover gasket material on the intake) also check power brake hose (if you have it)

Chasing a vacuum leak

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