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digitalstartz 01-05-2020 02:57 PM

Timing - Vacuum - Correct settings
91 GW. 360 with a freshly rebuilt 2150. All new vacuum lines, (EGR is new but disconnected because my CTO is shot). Air pumps removed. Manifold vacuum is great. Starts great, hesitates on throttle when cold, and will stall. My first thought was accelerator pump, but I just rebuild the carb. I’ve got the carb well set, I think, and I started looking into timing. New ignition module and coil.

The vacuum advance is connected to ported by PO. Timing sticker says 600rpm timing should be 17 deg. Mine is at 15. Lots of strings recommend a 5-10 degree at idle.

What’s the best setting for timing? (I’m at sea level). Could it be my cold hesitation/stalling problem?

babywag 01-05-2020 03:22 PM

stock low altitude is 10 - 15 may be slightly high for stocker.

i would look @ choke setting(s) if it's only when cold.
fast idle working? choke pulloff working?
with a carb even if perfect adjustment it needs a minute or a few to warm up before driving.

don't know your skill/experience level but many folks have never seen/driven a carb'd engine. They think you can just turn the key and go like EFI vehicles.

digitalstartz 01-05-2020 03:43 PM

I’m not the highest level expert, but started in my early teens rebuilding Quadrajets. My 73 vette Holley a few times. The 2150 I have done twice. But I’m not the best “carb adjuster”. I used this write up to adjust it all last time:

I will check it again for sure.

Is the vacuum advance on ported only ok?

babywag 01-05-2020 05:35 PM

only difference between ported/manifold is @ idle.
above idle they are the same.
on ported = no vacuum timing advance @ idle
on manifold vacuum = the vacuum advance will be full amount.
personally i prefer them on manifold but opinions vary

661warwagon 01-06-2020 09:04 PM

I just set mine to 10 runs like a champ

Dave Jeeper 01-08-2020 06:24 PM

17 +/-2 degrees on the sticker is for high altitude. The EGR is different on the high altitude cars, not sure about the rest of the emission components. Have you checked your plugs and gapped them to .035"? If you are at sea level the gap is 9 degrees I think. Add 1 or 2 degrees for each thousand feet above sea level to the timing. Make sure that your cap and rotor are in good shape and that all of the ignition wires are clipped in place on the cap and plugs.

A vacuum leak will cause rough running. The vacuum control on the vacuum canister can be a hidden leak as can the vacuum to the brake booster. The brake booster vacuum hose can have a leak from rubbing ont he valve cover, the grommet at the booster can leak or the booster can have an internal leak.

Also the spacer under the carb can crack or be mounted loose and the carb hold down bolts can loosen causing a vacuum leak. You can try removing all of the vacuum lines from the vacuum ports and capping off all vacuum ports on the manifold and try idling and giving it gas in the driveway to see if it runs better. Don't try driving it with the vacuum disconnected from the brake booster or you may not be able to stop it.

If it idles and revs smoother with the vacuum ports plugged, then add them back one at a time and retest the idle and reving to see which vacuum line is causing the problem.

Bob Barry 03-29-2020 12:35 PM

I would confirm that the vacuum lines are run correctly, and that the accelerator-pump is moving freely. If that mechanism is binding on the throttle-shaft boss, it can cause erratic off-the-line performance.

I just documented the rebuilding of the vacuum system on my 1987 J-20's vacuum system in three videos here: 9wHC0pdSJ

The third one is where I go in depth with the spark-advance harness, using the phrase "Non-Linear Relay Valve" an inordinate number of times:

Make sure what's on your engine is routed correctly (mine wasn't, as you can see in the video), and check the accelerator-pump operation. I bet it's one of those two things.

letank 04-02-2020 12:11 PM

a slight miss off idle can be related to a slight leak at the charcoal canister vent hose to the carb, the cap that is labelled do not open, there is a rubber diaphragm mounted on a spring... yes the diaphragm will crack after 30 years... most of the time people break the nipple... when they try to remove the small hose... we can live with a small miss... we live without airbag...

nograin 04-03-2020 04:02 PM

I was going to answer but the OP hasn't been back since mid January...

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