3810
 

hooking up vacuum gauge on L-79 with the holley 3810. Seems distributor is connected to the full vacuum port on the side of the carb. Is this correct ? Engine dies with vac gauge hooked up there and distributor line plugged...Thanks....

Don't know if full vacuum is correct, but it's better than ported vacuum for the vacuum advance. The engine should run better and cooler with full time vacuum. The engine shouldn't die when you disconnect the vac adv hose---The idle speed will always drop, but it shouldn't die unless the idle speed is set too low, or the base timing is way too late.


RON

You're correct in assuming that the advance can is connected to the manifold vacuum (full time) on your Holley List 3810. If you're idle speed is setup around 750RPM with the advance connected to the full time vacuum, when you disconnect the advance can and hook up your vacuum gauge, your RPM's can drop considerably (200 RPM or more)...this is typical and normal. It is sometimes hard for a L79 to run at such low RPM and stalling will occur...there is nothing wrong with whats going on. You may have to feather your throttle linkage a bit, with the vac disconnected from the can, in order to attain a RPM that the engine can tolerate. My L79 wants to stall when I check my vac reading (which is 15" @ 585RPM). What all are you attempting to accomplish?

3810
 

Check vac gauge reading..
Engine running rough..
New plugs, cap,rotor, wires...

Did it run rough prior to all the changes? What did the old plugs look like, the cap, the points, etc?

3810
 

Yes it did.
The old parts looked good...

This is one of those "where to begin". I would put a plastic "T" in your vacuum line between the carb base and the vac canister and then hook the vac gauge up to the third leg of the "T". This way you won't loose the initial vac advance, the car should idle at a higher RPM and then you can observe the vac readings as you delve further into whatever it is that's making your car run rough. Read the attached article for some helpful advice/information.

https://www.motor.com/magazine-summa...-vacuum-gauge/

3810
 

Will install a tee next. Thanks for the info....

It helps to verify your vacuum port. Pretty easy to identify a full vacuum port. I just use a thin metal wire in the port nipple and see if it comes out in the throat of the carb. Full vac port comes out below the throttle plate. Ported vacuum comes out above the throttle plate. Some carbs have ports that just go to chambers within the carb. Sometimes it helps to take the carb off and verify each vacuum port as either full or ported vacuum. Also I use WD40 with the long red applicator to see where the different vac ports may come out.
I think its more fun than work and this way you can nail which port is which instead of guessing.

Hope this helps.