ok, heres my deal, have an 1985 12a fb with emmissions eliminated, hollow cat. Finally got it idleling at 800 smooth, but whenever I press my brake it drops to 500 and slowly get back up to 800rpm's ofcourse, it revs smooth until it hits 3500 on the tach it sputs and then smooth till 6500. I guess my true question is, Why are the RPM's dropping when I step on brake coming to a stop light or (stop sign) causing it to shut down??? All vacuum lines have been replaced. Are there other vacuum lines I may have missed??? Thanks.

 

check the hose from brake booster to intake manifold. spray carb cleaner to vacuum lines (capped or not), one hose at a time. if idle changes, then you found the leak

 

I wonder if a bad check valve (in the vacuum line to the brake booster) could cause this?

 

a check valve just prevents fluid from getting from the booster. I havent seen them go bad but again, I tend to clean the check valves every 6mos to ensure its not clogged/corroded.

 

Actually, I was referring to the check valve in the vacuum line. This is intended to hold vacuum in the booster, and not letting it "flow" back into the motor during low vacuum phases.

 

where would that check valve be located exactly what color is it cause I have changed all those vacuum lines. Thanks for helping me out with my smoke situation on the other thread kentetsu.

 

ok, I figured to upload two pics the first one is showing vacuum line from brake booster on firewall from passenger side connected to another vacuum line, the gas tank canister thing was eliminated by someone before me so that vacuum line is connected to the brake booster line, not sure if this is right but if someone could help me figure out if thats correct or show some pics of the canister eliminated and what to do with vacuum line, thanks.

On second pic I dont know what this is and what it does, wonder if I could eliminate it with a straight vac line, it sits on passenger side on NIKKI Carb. this is probably unrelated to this thread but as I was taking picture realized that for a while been trying to figure out what it is, could someone tell me what the heck this is and what it do? Thanks again.

 

the brake booster check valve is usually right on or near the booster where the line goes into. normally a 90 degree elbow type thing. If its bad it can cause this problem. You can tell if its bad by pulling it out and blowing thru it. If you can blow thru both ways its bad. If its good then theres a chance your booster has a leaking diapham and the whole booster with need to be replaced or rebuilt. Typically when the booster leaks it will have a loud hissing noise coming from it when running tho...


The green thing there is either a check valve or a device which restricts the flow of vacuum in one direction or "delay valve" used to create a slowed release of vacuum to an actuator(usually for anti bacfire valves or decel valves on carburetors)

 

thanks on my way to check the valve now that its sunny here, thanks.