Struggling under load

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Matysik

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I am having a load problem with my slant six and need some help with diagnosis.

-Fresh valve adjustment
-Timing set to 10*
-No vacuum leaks
-Running temp idle set to 750 RPM
-Vacuum advance ran straight from dizzy to carb
-New plugs gapped correctly and sealing washers removed
-New cap and rotor
-New plug wires
-New fuel lines and clean tank with fresh gas

Now it will idle in park and neutral just fine but as soon as it is in a drive gear such as reverse, drive, etc. it bogs down terribly and picks up a rough idle.
 
My 69 slant did the same for 18 years, driving me crazy and trying many things (intake, head job, even new long block). After installing the maybe 4th Holley 1920 carb, it ran amazingly smooth. What carb do you have? I think mine ran lean at low rpm like when in drive.
 
You said "new fuel lines", does that include the fuel filter and fuel pump? It sounds like it's not getting enough gas at anything above an idle. If you keep your foot in the carb, does it still bog down?
 
yep filter and pump are also new. If you get on the gas its peppy right away, no lag at all. If I'm just sitting there in gear though its shaking the car apart.
 
Try lowering the idle speed 50 to 100 RPM and see if it gets better. The trans should pull only slightly at idle. Your tach may be off. Also try idle mixture 1/8 TO 1/4 turn either way and see what happens.
 
KitCarlson said:
Try lowering the idle speed 50 to 100 RPM and see if it gets better. The trans should pull only slightly at idle. Your tach may be off. Also try idle mixture 1/8 TO 1/4 turn either way and see what happens.
Click to expand...

All lowering the rpm is going to do is make it shake worse in gear at a stop, ask me how I know.
As for the tach being off my idle is set directly off of the plug wire with a digital tach, which at most can be 20 rpm off.
Idle mixture either way changes idle but no change in pull from being in gear.

Not sure if it will make a difference but it's worse in reverse.
 
Just more ideas:

Since it runs well when you accelerate it might not be the fuel related. Making changes there does not help. It may be the ignition. Are you running points or electronic?

It may be transmission, but not sure if it is possible. Not sure a torque converter can get tight like a clutch.

If it runs well when not stopped, that is a huge clue. Perhaps someone will have an idea about that. I assume the kick-down linkage adjustments are correct, not to interfere with curb idle setting. Does kick-down work correctly?

It is possible to have a bad engine to firewall ground that permits an engine to run when accelerating, and die when coasting, because it grounds via drive train under load.
 
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