Another carb help...

[tim_mc]

The mention that it will idle, but drop RPM when put in gear AND aftermarket GM HEI caught my attention. I had a very similar issue which was an aftermarket GM HEI that wound up causing my problem: Truck had an occasional backfire or load up when driving. It progressively got worse to where it would start OK, but would die when put into gear. It would idle and rev OK, but ran badly under a load, or when stopping at a stoplight. I had to put it in neutral a few times to keep it from dying at intersections. Later it would lean out and backfire after it warmed up and eventually would not restart when warm.

Replacing the GM HEI coil and module with Davis Unified Ignition parts did the trick. No issues since June 2021. Coil and module are relatively cheap & easy to replace if you at least want to eliminate them as a possible culprit.

Also, I compared a stock HEI module out with a Davis module - what a difference in performance, especially acceleration.

[72SB]

Originally Posted by Kalums

So... I should disconnect from the carb and connect the VA to the manifold?

I went back and read you post again... And literally walked out to the truck to try this... When I have the VA plugged into the carb (timed port?) it runs rough (like I need new motor mounts... Which I have in the garage) at 12 dgrs advanced (manually set by me using a digital timing light) but if I turn my distributor ever so slightly til it is about 20 dgrs advanced it speeds up my rpms AND runs smoother. I can then turn down my idle to 800 rpm and it only drops to 650-675 when I put it in gear, still a drop but no stalling ...... My light bulb just came on... Was I manually retarding my timing? Too much?? Was I the "malfunction" *face palm*

No, you use the manifold vac port on carb, lower one on DS. The one slightly higher on the front, PS, is timed. The fact you advanced timing manually shows you want VA on manifold, so you get the additional timing ON TOP of your base (8-10 degrees)

Set your base back to around 8-10 without VA and the vac port on carb plugged. Then with VA connected to the manifold vac port on carb adjust idle RPM as needed

if you don't have it you can download owners manual for the 1406. and yes again it will say to use the timed vac port....its an emission thing, don't do it. It will however have all the tune and trouble shooting steps if you need them.

I am assuming your timing marks are right and the carb otherwise is in good working condition, To me, your issue was and is no VA at idle because you used the timed vac port.

[Dashman]

Timed port vacuum is NOT a failed emission thing. That's a myth, fallacy, propaganda... The fact is that manifold vacuum drops when the throttle is increased, and timed port does not. It was an improvement to simply fill in the drop in timing, just for a moment, until the mechanical timing caught up. The only time a person needs to recurve a distributor's timing advance is when it's a performance engine or race vehicle.

I believe that Geezer#99 probably has it right. There's a mismatch in the balancer and timing tab. Find top dead center of the #1 cylinder, and verify where the timing mark on the balancer is with respect to the timing tab.

I experienced a similar situation when the distributor gear bushing was wearing out, so that's something else to inspect. You may also want to verify the fuel inlet needle and seat, the fuel pressure, and the fuel filter. I had fuel leak at my fuel filter and temporarily ran my engine without the fuel filter, forgot about it, and dealt with near stalling while in gear. When I installed a new fuel filter to cure the leak and when the engine dropped RPM while in gear, the engine idle stayed smooth. It could also be a float level too high. Good luck!

[Rust_never_sleeps]

Thunderhead289 on Youtube has good videos on timing, carb tuning, and how they work together. I like this one, but it feels like drinking from a firehose at times:

https://www.youtube.com/watch?v=Ort2Gk7Lvuk

His stuff is usually about Holey, but I think Edelbrick works comparably

[Kalums]

Originally Posted by geezer#99

That there tells you one thing!
Your timing marks aren’t accurate.
Either the mark on the balancer is wrong or the timing tab is wrong or a combination of both.
You need to find true top dead centre on #1 cylinder to see where your timing tab/balancer marks are at.

Found TDC by pulling plug on #1 and manually turning crank( the balancer is dead on the little plate is off by 12 dgrs). With the VA disconnected (and plug# 1 reattached) I timed it to 8 dgrs advanced... It didn't really like it so I went to 12 dgrs... Then my fuel line from the pump to the carb started leaking AND the carb backfired.... (see photo) now I've melted the cable on the bottom of the carb (not the throttle cable connected to the gas pedal, the one on the bottom next to the return spring). Today... I'm done fiddling with it and am very glad nothing else happened. Unfortunately not my first gas fire (first in this vehicle) but it still sucks. On a good note it was running fine before the leak and subsequent fire. I think I'm going to eliminate the fuel filter by the carb and just run a line from the hard line to carb.

[geezer#99]

What tool did you use to find tdc #1.

[Dashman]

If you found that TDC was 12 degrees on the tab, then you were actually setting the timing to 0 degrees. You had a backfire through the intake because your timing is off, either early or late. I believe your timing is still too late. You could find the correct balancer or timing tab, or you could use a white marker pen to mark a new zero line on the balancer. Set it TDC at 12 degrees like you did before, and mark the balancer at 0 degrees. If you set the new zero mark to 12 degrees on the timing tab, you'll probably be just right.

Like Geezer#99 wrote, you need to physically determine TDC through the spark plug hole. I have used one of these:
https://www.summitracing.com/parts/c...iABEgI6ePD_BwE

You can find a video or instructions on how to do it.

In regards to your fuel filter, sometimes they are made for 5/16" hose and they will leak with 3/8" hose.

Transmission kick down cable. Cut the burnt plastic off of it, and see if it is still funcitonal.