The Stovebolt Site Forums The Shop Area Engine Shop 235 Vacuum Leak?

yeah, i think my 235, in a '62 half-ton, has around 50 horsepower. uh, it was running great after setting the valves in july, or so, and then it slowly deteriorated in power to where i can't accelerate up hills. it's annoying. well, the timing is right, but i think there may be something wrong w/ the advance and/or vacuum, because, upon stepping on it, the distributor doesn't turn [physically advance....you know], and you can hear this distinct sucking sound, upon letting off the gas, from the floored position while cruising. anyways, i don't know what on earth to do, but it sure is getting on my nerves...any similar situations out there? advice, please...thanks a lot...-jeff

With your engin running and warmed up take a can of starting fluid and give short squirts of the fluid around the base of the carb and the intake to head area. If the engine boggs a little during one of the squirts of starting fluid you have found your leak
I would also check your point-gap (dwell), set it and check your timing AFTER you set the points.

Make sure your valves aren't too tight, or you won't have any compression.

hi, yeah, i did the starting fluid thing around the base of the carb, but not on the intake to head areas. so, you mean, by saying, if there's a leak there, the engine will "bogg" that it will sound like it wants to die, right?]

ps-my dad said it might also be the distributor mechanical advance weights? is there any way to test for that? he said the higher rpm's produce much less vacuum, which i don't understand, either, and that might be why the cap's not rotating at all [advancing, that is]. ok, thanks...

In a reciprocating engine the fuel mixture is naturally aspirated through the carburator then distributed to the combustion chambers via your intake manifold. As the engine speed increases with the throttle being opened more, the engine vacuum will decrease due to the stabilization of the engine's negative pressure with atmospheric pressure.

As a general rule of thumb, manifold pressure is an indication of how much power your engine is developing.

So take it from a Frenchman Junkyard Frog, what you've got to do is hook up a manifold pressure indicator that indicates in increments of inches of mercury in relation to a standard day at sea level (29.93" Hg.) and you're all set.

Big Lifter