Technical At wits end... early Chrysler Hemi tuning

Suggestion:

With the engine turned off, carefully turn each idle mixture control screw clockwise (in) until LIGHTLY seated, and record the number of turns (by doing this, you can return to this setting). Return the screws to your existing setting.

Start the engine, and get it up to normal operating temperature.

Turn the throttle positioner (curb idle) screw(s) clockwise to raise the idle RPM.

Now, using your recorded figures for the idle mixture control screws, start turning the idle mixture screws clockwise (in) 1/8 of a turn at a time, one carburetor at a time, then the other carburetor. It may be necessary to again raise the idle. So rear carb drivers side 1/8, rear carb passenger side 1/8, front carb drivers side 1/8, etc.

Where I THINK the engine will be happiest is with all four screws somewhere (all equal ) between 1/2 turn and 1 turn from bottomed. Set your final idle RPM, and go for a test.

Jon.

 

At the very beginning I am just idling along and I give it fuel, not even stomping on it, just a pretty normal acceleration and it cuts out almost entirely. It sounds like it stalls, but then after a second it picks up and takes fuel nicely (not the best video but it was hard to capture). Accel pumps seem to pump well, I even tried the longer stroke setting, which is why I was thinking timing initially. Had the distributor redone and advances checked (mechanical and vacuum) and carefully reset the timing. I checked TDC at one point, and if the harmonic balancer has slipped, it hasn't slipped much. So... I am now convinced it's fuel delivery. Anxious to try carbking's suggestions!

 

Do you think it may be TOO rich at tip in instead of lean??

 

I did buy a UniSyn... so I do plan to do some more investigating. Have not tried anything else yet.

 

Tinkering with this today. Feeling like the pump may need rebuilt again. Can you tell me if the Carter glass filter bowls should be kept full by the pump or if it's normal for it to be at 1/2 level or less while idling?
Thanks.

 

My 331 (bored 1/8" over to 354) has great off idle response with a single Holley 3-bbl. Like yours, that is WAY too much carb for my engine so I modified it accordingly. Not giving up my 3-bbl!! I installed a couple venturi reducers in the primaries so it flows like a 600cfm 4-bbl. Then I installed the strongest spring in the Holley parts pack on the vacuum secondaries. Finally put a micro switch on the secondary lever that lights an LED on the dash when they open. My cruiser rarely if ever opens the secondaries on normal driving. But they are there if needed!! Car drives responsively and great as effectively a 2-bbl.


Sure sounds like too much throttle is opening too soon on your setup. Bigger squirters would be a band-aid fix but the biggest problem is manifold pressure dropping too low to atomize any amount of fuel. Dual 4s are awesome for top end but easily overpower off-idle performance with too much throttle opening. Definitely look at progressive linkage options to keep that manifold vacuum up and talking to your carb throttle bores. This is one area of hot rodding where too much is truly too much.

And I always set my dist. advance with a vacuum gauge on the intake manifold. Takes all the witchcraft and unknown out of the equation. Just adjust idle screws and manifold vacuum 'til you have max vac at desired idle speed.

 

Thanks for the advice. I tried leaning out the idle mix a bit and went for a cruise and it was terrible. Stalling and hard starting. Ugh. After bad experiences like that we need some time apart!

Regarding the advance... you mean that you leave the vac advance connected and adjust the base timing while watching manifold vacuum?

 

By the video, sounds like accelerator pumps are late. Take the air cleaners off and open the throttle while looking down the carb throats at the acc pump shooters. When you move the butterfly's ANY AT ALL, even the smallest amount, fuel should be squirting . If you don't have fuel squirting when those butterfly's crack open, you will have a hesitation because it's sucking air and no fuel. When the engine has a load on it, it requires more fuel. JMO Lippy

 

No. Forgot to mention, disconnect vac advance when tuning like this.