426HEMI idle speed adjustment

[charge69]

Hello,  I need to know something simple but frustrating for me. The service manual indicates you adjust the idle to 750 Rpms after warming up the engine and THEN adjust the idle mixture screws for max rpm with them initially open 1 to 2 turns.

Simple enough but do you set the idle speed with both carbs or just the back (4621s) carb? I can adjust idle speed using both as they both have an idle speed screw on them but only the back carb has the Idle mixture screws. The front one has just factory block-off plates there and no adjustment is possible.
Is the idle speed set with just the back carb or both? Do I just set the idle with the back carb and make sure the idle-speed screw for the front carb is just touching the carb?

I can effect the idle speed with either screw, front carb or back carb, and it is a little frustrating. Until they were rebuilt, I really did not know the front carb had an idle circuit as the idle mixture screw plates are blocked off and no adjustment is possible!

HEMI guys, help me out here, please!

Carl

P.S.  this is a 1969 factory carb set-up  Rear 4619S   Front 4621S

[Scaregrabber]

I always set the front one to close completely and do the speed and mixture on the back one with that setup. If it won't idle nicely at that point you will have to dig out the plugs on the front carb and set those screws as well, most likely you won't have to though.

Sheldon

[charge69]

Thanks for the reply. That is what I went ahead and did to it but, it doesn't want to idle when in gear. It will idle fine after it is warmed up but it acts a little fussy on initial start-up and will not idle by itself until really warmed up. After it is warmed up, it idles fine but still acts like it is flooding when starting up!

These old original AFB's are giving me a hard time even though they have been rebuilt and gone over with a fine-toothed comb.  I suspect this crappy ethanol-laced pump gas might be part of the problem but I will just have to keep trying. I will not let this get to me! Guess I will have to get off my azz and get 5 gallons of racing fuel to lace this pump gas with or, maybe, some 100 octane low-lead avgas!

[Scaregrabber]

Where I live I have to jet them up about 5% - 10% to get them to run right on this garbage fuel. Hemis are a bit cold blooded anyway but if yours is lean during regular driving I would jet it up a shiver and see if that helps your idle as well.
I also like to run about 18 initial timing with 34 total, I assume you have a stockish cam?

Sheldon

[charge69]

Hi,  sorry it took so long to answer.

My cam is a Comp Cams Hydraulic Roller Kit with custom cut pushrods and it is hotter than stock. It is still very streetable as it will settle down to a nice lumpy idle at about 850 to 900 rpms. Even with this heat down here right now (98* outside when I was trying to adjust it) it is a cold-natured engine with no heat risers and TTi headers on it. However, it does have almost .595 lift and dynoed out at 588hp at 6500 rpm. I have custom JE 11 to 1 pistons in it also that gives a true 10.96 to 1 compression.

It is possible the floats are set too high but I do not think so. I do not have a vacuum gauge handy here at my house but my friend does and it needs to have one put on it to adjust the idle mixture screws.  I will keep trying to get it right.  It is just an ornery beast right now!

[Scaregrabber]

Were these carbs on it when it was dynoed? What fuel did they use when it was dynoed?
What stall convertor does it have? Mind you if it will idle at 850-900 the stock convertor should work.

Anyway, the next step is to see where your initial advance is, check where it is set at before doing anything else. Then set it to 20 and set your idle speed screws on the carbs to something reasonable in neutral and then see if it will idle in gear. If it will then you will have to limit your total advance to 34 with the 20 initial, install a Mopar light and a Mr. Gasket lite advance spring in the distributor and you'll be close on your setup.

If it still dies in gear then we need a vacuum reading with it idling in neutral, so you can change the step up rod springs with 4 matched ones (Edelbrock sells them in packages, you'll need two packages of course) that are rated lower than your vacuum reading at idle. The idea of this is to stop the step up rods from fluctuating from cruise to power mode at idle.


My guess from a few thousand miles away is that 1) you don't have enough initial advance for it to idle correctly, 2) the step-up springs are allowing the metering rods to fluctuate between power and cruise mode, 3) well that"s enough for now.

Sheldon

[charge69]

Thanks for all this info.

My converter is he one that came with the car and factory stock.  I wish I had changed to a higher stall speed converter now but, with the engine in the Charger and TTi headers and X-Pipe exhaust, it would be a real headache to change the convertor.  Probably as easy to pull the engine (from the bottom) than try to change it in the Charger.

Dynoed on pump gas (93 octane w/ethanol blend)

Same carbs as dyno run

When carbs were rebuilt, I do not know if the step up rod springs were changed. That sounds like a plausible problem as it runs fine for a while AFTER it warms up just sitting there. It also has a hotter cam than stock (Comp Cams Hyd Roller). It acts up and floods after driving it a little and you come to a stop. Really acts like it is flooding out then.  It will start right back up but runs as if it is trying to flood out at idle. You can get it to run by giving it the gas to around 2500 to 3500 rpms (estimated) and it cleans up and runs smoothly.

I run a MSD Digital 6 ignition and I am thinking the initial advance is already set at around 20* and I know the total is set to 35* by 3000rpms right now. No vacuum advance.  Digital 6 ignitions have the ability to retard the spark to close to TDC on start-up and automatically put 20* advance on the engine at 750 rpms and above. Mine is set this way and working right.

I will investigate your suggestions and get back to you,  Thanks again for the help.

[Scaregrabber]

Good info:
Lets check the advance at idle for sure.
Then check vacuum at idle in neutral.
One other thing that it could be is too much fuel pressure, does it have a fuel pressure regulator? if it doesn't have a regulator, what fuel pump are you using?

Thanks
Sheldon

[charge69]

No pressure regulator, just a new stock Hemi fuel pump with the return line hooked up. New pump rod was put in during assembly (bronze tip per requirements.) I don't think t could be too much fuel pressure but, I will check this out also.

It will be a few days before I can get over to my friends home to check all this out,  I will post my results!

Thanks again