Hey guys,
I have an 85' chevy 1 ton with a 350. The truck is a septic tank pumper and carries a 500 gal. tank on the platform.
I have been having issues with my vacuum. The way the system work is as follows:
A 1/2 hose is connected to the engine between the carb and the distributor cap right on top of the engine (in the center). This hose runs down under the cab and then up to the top of the tank on the back. The system has an on/off valve and an air valve.
80% of the septic tanks I pump will pump fine and fill the tank on the truck. Then every once in a while the vacuum sucks (not in a good way!...lol) it will only hold half of a tank full (about 250 gal.) and then it won't suck anymore. Anything that it does suck up will just make a quick sucking noise and drain back into the septic tank.
Is there any way I can tweak the engine into sucking more?
I thought it may be a firing problem and have replaced all my spark plugs and wires. It hasn't helped.
I've also replaced the PCV valve, but it doesn't help either!
Any ideas or opinions guys?
I know that the guy who owned her used to set her idle screw ahead a bit in the fall because he said she would pump better/ and faster on the colder days.
He also got new heads put on her last fall...maybe they altered the suction when doing the work?...possible?
Please help!
Thanks!
"Chevy Septic Guy"
1985 Chevrolet Custom Deluxe C30 (1 ton)