pmr2000

Trying to chase down a potential vacuum leak on my stock 75 coupe, 4 speed, L48-350 with Rochester 4 barrel. I changed the choke thermo a recently so may have disturbed or cracked a line. I hear a hissing with air cleaner off that was never present in the past, not running as well as prior.

See attached, when I take the line off this tarnished piece I am pointing to (rear vacuum break # 7 in diagram I was provided) idle increases. Other lines don't appear to make any change.

Any suggestions?

Thanks.

terry82

spray starting fluid around carb and see if the rpm changes.check all vac lines.

biackbenz

I'm joining the no such thing as a "small" vacuum leak. That is just a short line from carb to choke pull off. Just fix it. IMHO.

pmr2000

If I take the rear vacuum break side of that line off (where I am pointing to in pic) rpm goes up. Other end removed does not appear to change rpm. Does that mean that vacuum break piece is clogged or not working?

I'd like to replace all the vacuum lines, are there any I should cap off?

I don't have a functioning air pump, no cat on the car.

pmr2000

Update:

I have started replacing all the vacuum lines, did some last weekend including the rear vacuum brake. I also capped off open ports that are on my air pump with no belt, unknown if it functions.

Will replace the remaining vacuum lines next weekend.

So far running better, the exhaust leak type sound when getting off the gas between shifts is almost gone.

Perhaps that sound is more of a rich running, backfire from the vacuum line issues?

Buccaneer

If you are fighting a vacuum leak, here is a very simple, but effective leak detector that does work. I have one very similar to this and found two leaks in about 45 seconds. It comes in handy when dealing with hard to find vacuum leaks.

https://www.ebay.com/itm/EVAP-Smoke-...4AAOSwzgBY0cxJ

pmr2000

Thanks, I think I got the vacuum leak fixed, while I am making the effort figured I'd replace all the hoses, and cap off open or unneeded ports.

I capped the 2 lines coming out of back of air pump they were open, no belt on air pump.

Does anyone have any suggestions for what can or should be capped off? Engine is stock L-48 with cats removed, air pump non-functioning.

Will any help performance?