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During the last reading of 11.5'' HG at 800rpm connected to ported vacuum, was the needle steady, or was it moving in any way, and did the engine idle smoothly ?
For info, Holley states connection to ported advance. Full manifold connection is no problem.
What is the current ignition timing set at, with no vacuum advance connected ?
When you get the chance, without making any other changes, run the engine once more, but this time connected to full manifold vacuum advance. Do the idle pms and vacuum reading increase ? (They should.)
Your vacuum readings at varying rpms are not helpful. One base setting for observation suffices, which in this case is 800rpms.
When you're driving at W.O.T. or climbing a hill, vacuum will drop, and if you are coasting down a hill, vacuum will be at maximum. I.E. Engine vacuum constantly changes as driving style changes.
Please check 440's comment about a dual pcv connection. I did not know that a 428 might have that. I simply assumed that it was Tee'd for an accessory. Sorry !
And it looks like in one pic your choke is not fully open. This might be why you can't idle down properly.
There should be zero vacuum on the ported vacuum fitting, which means that your throttle plates are too far open, which means you'll never get your idle down where you want with just the screw. Which is consistent with the choke being partially engaged and holding the throttle partly open on one of the high-idle cam steps.
Check that first, before pulling any more hair out over the idle speed.
And I'm guessing you know, which is why you're asking, but with a stock cam and proper tune your idle vacuum should be at least 18 or so, and even up to 21 on a good tight engine with a little more initial timing.
During the last reading of 11.5'' HG at 800rpm connected to ported vacuum, was the needle steady, or was it moving in any way, and did the engine idle smoothly ?
For info, Holley states connection to ported advance. Full manifold connection is no problem.
What is the current ignition timing set at, with no vacuum advance connected ?
When you get the chance, without making any other changes, run the engine once more, but this time connected to full manifold vacuum advance. Do the idle pms and vacuum reading increase ? (They should.)
Your vacuum readings at varying rpms are not helpful. One base setting for observation suffices, which in this case is 800rpms.
When you're driving at W.O.T. or climbing a hill, vacuum will drop, and if you are coasting down a hill, vacuum will be at maximum. I.E. Engine vacuum constantly changes as driving style changes.
Please check 440's comment about a dual pcv connection. I did not know that a 428 might have that. I simply assumed that it was Tee'd for an accessory. Sorry !
1800’. The needle was steady. I’m running premium gas with a little bit of octane boost now and it is idling pretty good other than not being able to really get under 800. I will check the choke today to make sure it is fully open
And it looks like in one pic your choke is not fully open. This might be why you can't idle down properly.
There should be zero vacuum on the ported vacuum fitting, which means that your throttle plates are too far open, which means you'll never get your idle down where you want with just the screw. Which is consistent with the choke being partially engaged and holding the throttle partly open on one of the high-idle cam steps.
Check that first, before pulling any more hair out over the idle speed.
And I'm guessing you know, which is why you're asking, but with a stock cam and proper tune your idle vacuum should be at least 18 or so, and even up to 21 on a good tight engine with a little more initial timing.
Good luck.
Paul
im getting 11.5 on gauge off ported vacuum at 800-900 and I thought it should be zero. So maybe this is where my problem is?
im getting 11.5 on gauge off ported vacuum at 800-900 and I thought it should be zero. So maybe this is where my problem is?
Yes it should be zero. Port of for the ported vacuum is just above the throttle plate. If the throttle is opened too far at idle this port will then be below the throttle blade and exposed to manifold vac. So the only way to drop the vacuum on the ported dist vacuum is to close the throttle more as ported vac port is starting to be exposed to manifold vac.
And what happens when you idle the engine down below 800 rpm does it stall or just get really lumpy.
And to verify you have the PCV hooked up correct?
At 1,800', your engine vacuum should be about 19'' with vacuum advance connected to full manifold vacuum, and about 16'' with vacuum advance connected to ported vacuum. Those of course would be lower if you have a radical cam installed.
The steady needle is reassuring.
12 degrees idle timing, with NO dizzy vacuum advance attached, is a good starting point.
Maybe I've misread you, but are you connecting the vacuum gauge to a full manifold port ?
The vacuum gauge measures 'engine vacuum', whereas ported vacuum and full manifold vacuum, in the context of attachment to the dizzy, is 'ignition timing vacuum'.
If the 11.5'' mentioned earlier was ported vacuum, then yes, not only should it read 0.00'' at idle, it is not giving an accurate 'engine vacuum' reading.
Please clarify which port is being used for vacuum gauge reading, and if it was indeed a ported vacuum connection, do it again with the gauge attached to a full manifold vacuum port.
This morning at operating temp. Gauge is not bouncing around
This is off or port where directions say to hook dizzy. Only other thing hooked up is pcv valve coming off front of carb. At idle between 800-900 rpm. This is off lower port beside pcv port that directions say is for “full manifold vacuum source”. At idle between 800-900 rpm.
I'd get that choke setting straight before proceeding further as it is going to throw everything else off. If you don't have your Holley's instructions, on youtube search Mike's Carburetors Choke and there should be a video to help you. When warm the plate should be fully open.
I'd get that choke setting straight before proceeding further as it is going to throw everything else off. If you don't have your Holley's instructions, on youtube search Mike's Carburetors Choke and there should be a video to help you. When warm the plate should be fully open.
I noticed plate was not going vertical today. Getting full voltage there
The choke has to have juice long enough to warm it up and fully open. if it still isn't opening all the way just adjust it until it does.
As said you shouldn't have vacuum on the ported fitting, if you do it's probably because your throttle is open more than it should be to make it idle. which can be for several reasons so again get your timing right it's the most important adjustment on the engine.
If you have any kind of performance cam that manifold vacuum is acceptable.
I noticed plate was not going vertical today. Getting full voltage there
You adjust it by turning it clockwise or counterclockwise. Get the engine warm. Loosen the three screws holding the choke. Turn the choke until the plate is fully open. It should have just a tad bit of resistance to move. Tighten the screws back down.
Choke is adjusted now
best vacuum i can get off bottom port of carb is 15.5 and that was by adjusting idle mixture screws. I think I may be down to timing right now because idle screw is backed all the way out and 800-900 is lowest rpm
