Check Valve and Engine Performance

[showman]

Saw someone post that they heard a hissing noise on there 84 and ended up replacing their brake booster check valve which they said really improved engine performance.

Does that make any sense?

When I disconnect mine, the idle goes way up.

Thanks!

 

[Rex S]

Any booster leak will cause a lean condition as they draw vac from the intake manifold. Replacing a leaky (to atmosphere) check valve would correct the lean mix.

 

[Schrade]

Saw someone post that they heard a hissing noise on there 84 and ended up replacing their brake booster check valve which they said really improved engine performance.

Does that make any sense?

When I disconnect mine, the idle goes way up.

Thanks!

Makes sense only if the hissing was a vacuum leak.

Idle should go up when the vacuum line is disconnected. Then it should go down, and up, and down, like a Duncan yo-yo. Vacuum leak will make a lawnmower with a carb, or a brand new car on the lot, lope idle.

Any booster leak will cause a lean condition

Only for a moment. Then the computer will ADD fuel for the rpm increase, bog down, stall, TAKE AWAY FUEL, idle up, go lean again, and repeat the cycle.

Carbed motor works the same way, except the fuel draw is mechanical coming through the carb, instead of the computer adding fuel for the rpms.

This is why vacuum leak causes loping idle.