Another carb help...
 

So... I've got an Edelbrock 1406 that replaced the original QuadraJet ( I didn't do it, it came this way) I rebuilt the 1406...runs amazing, but I get significant rpm drop when I put it in gear (stalling) . Cold or hot it doesn't matter. What gives? I've done a complete tune up, plugs AcDelco R45ts (gapped to 45) new MSD 8mm wires(I know that means insulation) the HEI is a Delco and it is putting out about 15k volts on each lead and wire at the plug(zapped myself a few times testing... Ouch) timing is set to 12 dgrs advanced @ 800 rpm idle. Choke is electric and appears to be working/functional (choke flap is opening slowly as it warms)Vacuum gauge shows good vacuum hot or cold. My vacuum advance is connected to the vacuum port on the passenger side of the carb(swapping to driver's side port only increases in park idle speed) . I've sprayed carb cleaner on ever crack crevice and hose, I can't find a leak if there is one. Everything is set up per the Edelbrock set-up guide and everything I can find from the Google overlords. What am I missing?

Re: Another carb help...
 

Turn your idle down to 600 rpm.
Then check your timing.
At 800 rpm the mechanical timing might be kicking in,

Re: Another carb help...
 

Thank you, I will try that👍

Tried this morning... No go, still does the same thing.

Re: Another carb help...
 

Try it with the vacuum advance disconnected.

George

Re: Another carb help...
 

So at 600 rpm, what was your timing?

Re: Another carb help...
 

Did it have these symptoms before you rebuilt the Edelbrock?

is it the original cast iron manifold with a carb adapter, or is it a square bore intake manifold?

Where do you have the idle mixture screws set, and do they actually change the vacuum signal/idle speed when you run them in/out?

Re: Another carb help...
 

Those spread bore to square bore adapters are notorious for air/vacuum leaks.

Gary

Re: Another carb help...
 

Spray some carb cleaner around the base and listen for RPM changes when you hit the vac leak you have it will rev up. Jim

Re: Another carb help...
 

Timing did not change, 12 dgrs advanced.

Re: Another carb help...
 

Rpm goes up about 40-50rpm but other than that no change.

Re: Another carb help...
 

Original manifold with adapter, mixture screws set 1.5 turns "open" after screwing all the way in (snug, not torqued). Yes it starts to lean out if I turn the screws in about 1 full turn and it also starts to run rich/bog if I turn the mixture screws out more than 4 full turns. Vacuum does change significantly either way.

Re: Another carb help...
 

I've soaked the manifold/carb/ and anywhere I even think there could be a vacuum connection. No rpm changes... 😩

Re: Another carb help...
 

Not gonna lie, I'm leaning that direction... I just didn't want to spend the $$$ on an entire manifold, my wallet already looks as dry as the desert I live in 😅

Re: Another carb help...
 

I understand that the Edelbrock is a much easier carb to tune/rebuild... But I do have the original Quadrajet... Would it be worth my effort to rebuild? Assuming it is rebuildable...
Do they make an electronic choke "upgrade" for the Quadrajet?

Re: Another carb help...
 

I'm thinking you wouldn't get the idle speed down to 600 if there was a vac leak

Re: Another carb help...
 

you really want VA using manifold port, not the timed one. You may have to back down "initial", aka base, timing a few degrees as VA will add some at idle likely. You want 20-24 degrees with VA connected so if VA provides 12 degrees advance, set base at 8.

Fairly classic symptom of bog. die, without VA on manifold vac when put in gear (automatic) if that is what is happening. Eddy carbs are dead simple to tune, basically a Carter AFB

Timed port vac was a failed emission thing. Yeah I know the carb manual says use it, they basically have to. Just plg the timed port and use manifold vac for VA.

Now adjusting VA to come in and how much is a different discussion but the 411 above should resolve the stall issue when put in gear.

Vac leaks typically increase RPM so does not sound like that is happening

Re: Another carb help...
 

Don't get me wrong... It was struggling at 550rpm...and ran rough at 600...but it stayed running🤷

Re: Another carb help...
 

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*

Re: Another carb help...
 

When setting "initial timing" should my VA be connected or disconnected?

Re: Another carb help...
 

Sure, but IMLE, with even a tiny vacuum leak, the idle speed just won't drop below 1200, maybe 1k because it's still sucking air through the leak when the plates are closed.

What kind o' ignition are you running, btw

Re: Another carb help...
 

Initial timing should be with VA disconnected(and that hose plugged)

Re: Another carb help...
 

Stock ignition, aftermarket AcDelco HEI

Re: Another carb help...
 

I.... Am an idiot... Or just nieve... It is currently too late for me to futz with this anymore tonight (kids are sleeping and V-8 currently with straight pipes AIN'T quiet) thank you for the assistance, I'm pretty sure you guys figured it out and I just need to put in the work. I will report back tomorrow. Thanks again.

Re: Another carb help...
 

Here's my 2c. If you have vacuum assisted brakes, try it with that port (and any other vac. ports) on the carb plugged.If that's not it, you need to go back through that Edelbrock and check the idle circuit very carefully. Also, it would help if you answered Leftybass209's question; How did it run before you went through the carb? -BA

Re: Another carb help...
 

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.

Re: Another carb help...
 

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.

Re: Another carb help...
 

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.

Re: Another carb help...
 

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!

Re: Another carb help...
 

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

Re: Another carb help...
 

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.

Re: Another carb help...
 

What tool did you use to find tdc #1.

Re: Another carb help...
 

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.

Re: Another carb help...
 

The smoke detector ;-)

Re: Another carb help...
 

OP. Edelbrock makes a hard line that attaches to carb, specific to the 1406, and a AN fuel filter to that hard line and also an AN steel braided line to FP. You would need adapter fitting to AN of FP which several (Earls, Russell, etc) all make so you get rid of that soft hose and clamp on fuel filter...fire starter.

Regarding ported vs manifold vac...while some have their opinions on which to use, I and so many others have found manifold is better which allows VA to be "part" of idle applying advance. Ideally a combined sum of base + VA = 20-24. Yes VA goes away quick but mechanical takes over as you apply throttle. Yes it does involve setting up the VA itself (stop plate) and can involve adjusting advance curve or how soon mechanical comes in with lighter springs. Doing so though makes for a EXCELLANT running motor across the RPM band, idle, part throttle as well as WOT use.

If its just about putting around, use ported but MPG suffers and rich condition occurs especially in part throttle driving....which is at least 90% of street use driving.

Pics: Edelbrock fuel line setup I mentioned

Re: Another carb help...
 

If you're going to run vac advance on manifold vac, the vac canister will most likely need to be modified with a stop limiter; many vac cans add too much advance; this is especially true if you're running a higher initial timing.

You can use a hand vac gauge and customize a vac advance with a screw and a metal stopper to make sure it pulls exactly what you need. I slotted the stopper to make it slightly adjustable.

Re: Another carb help...
 

^^^^, yes. Unfortunately Crane does not make the adjustable VA and detent stop plate anymore. Homemade versions will work. I will say, doing so to really nail when and how much VA the can provides along with base timing and dizzy curve adjustments really make for a perfect tune on carb motors

Re: Another carb help...
 

Do you typically limit vacuum advance to 10-12 degrees?

On my last build, I used an off-the-shelf canister with about that much. I'll have to search for the number, but I got it at O-Reilly Auto Parts. Wish I would have bought a couple more!

Ah, just found these notes: My 82 C10 GM HEI has a Borg Warner canister, but I think it's the same part to fit a 75 Buick 350:
Part #: ECH VC1838 Line: Echlin Ignition
Also known by GM as AR12

Can't remember the vacuum specs though.

Turns out NAPA still has the Echlin P/N.

Re: Another carb help...
 

I have a document published by Lars Grimsrud and Duke Williams that shows the specs for (I think) all GM distributor vacuum advance units. One could pick and choose an advance unit based on that data.

Here you go- Lars' email address is in the first post. You can email Lars for that doc.

https://www.corvetteforum.com/forums...-and-duke.html

Re: Another carb help...
 

Yes.

Here is list of VA part #'s and spec authored by Lars, a 10-12 can be found

Re: Another carb help...
 

Here's the article by Lars. HEI canister listings and specs starting on page 5.

http://outintheshop.com/faq/Vac%20Adv%20Spec.pdf