I know it's been recommended on here to run the vacuum off of the manifold versus a ported source. First of all, I tried to get a vacuum reading from my manifold source. When I hook the vacuum guage up, the car won't even idle. I have to keep the rpm's around 2,000 to keep it running. What does this mean if anything?
What are you disconnecting to hook up the vacuum gauge? There should be no difference in the way the car runs with the gauge hooked up to the manifold versus normal. It sounds like you are leaking through the gauge possibly.
Garnet Red 69/SS396/TH400/355 Posi Sold
'02 triple blk Vette Vert. now
94 HD Dyna Wideglide
you're probably unhooking the vacuum advance to hook it to your gauge, and the timing is too retarded to idle. Put a TEE in the line and hook up the gauge with the vacuum advance hooked up. Or if you have another manifold vacuum port, use that. You'll get a reading then. There are many opinions regarding vac/adv. Some engine combonations will not run well or won't perform the way you want them to using manifold vacuum. My car for example, will fall flat on it's face off idle with manifold vacuum hooked up. It idles smoother with the advanced timing but the total timing while cruising is too much for the engine combo i'm running. I set my total timing all in at 3000 rpm 32* and wind up with 12* initial which allows the engine to perform well from idle on up. I use ported vacuum (a maximum of 10*) a total of 42* to allow for better mileage and part throttle cruising response and it works well. I won't argue with anyone about the manifold versus ported vacuum opinions because it's pointless. your car may run well either way if the engine responds well to it. I have tried every combonation with my engine and have found that it runs best and responds best with ported vacuum. try it both ways and go with what works best.
Hope this helps
Guys, I posted the note from by bro-in-laws house. That's why it says 69CamaroDave. I hooked the guage directly to the manifold port. Although I still had the vacuum adv hooked up to the ported source. Was this my mistake? Should I unhook the vac adv from the ported source, then Tee that line into the manifold port?
Having your vac can hooked to a ported source won't do anything at idle. (your sure which is which?) If you put a TEE in line with the gauge at a manifold vacuum port, it will allow advance to keep the engine running while you read the gauge. Unplugging the vac/adv. while the engine is running will allow the timing to retard and depending on where you have base timing set can cause it to stall. This is tough to do (diagnosing this problem) on the computer. It might be a good idea to get somebody that can help you that understands this subject a little more? Timing can be a confusing subject even when you understand it, and much more confusing when you don't.
Thanks Jim. Just to make sure, the manifold source is on the manifold and the ported source is on the carb. Correct? I did unhook the line from the vacuum canister to the carb. I kept the hose connected to the canister, then Tee'd it to the manifold source and the vacuum guage. The engine still would not idle. Should I advance the timing any? Right now it's around 8 BTDC.
As you can tell, I'm trying to learn. So some of my questions might make you scratch your head. I appreciate your help and everyone elses help that I get on this board. I do recognize there are certain issues I should have a professional mechanic address.
Sorry for not getting back sooner. Some carbs have many vacuum sources. Usually the manifold vacuum ports are low and on the throttle plate which is at the bottom of the carb. Ported vacuum ports are usually above the throttle plates. It sounds like the gauge is leaking like Bob suggested in the earlier post. Eight degrees initial timing using a vacuum advance shouldn't be too much. Your vacuum can may be advancing your timing quite a bit. Check the timing without the vac adv connected. It should idle at 8 degrees without a problem. You may have to turn up the idle a little. Then connect the vac adv and recheck to see how much you have. Try this and post your findings. It's late here and I gotta go. I'll check tomorrow to see what you've found and try to help further.