Home rebuilt 1920 has poor accel shot

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After rebuilding my 1920 I've noticed that immediately off idle when pressing the pedal The car slightly hesitates.

After checking the carb for vacuum leaks I noticed that when I hit the accelerator the pump shot is kind of weak. Weaker than before I rebuilt it. I didn't pull the lead plugs from the metering block just blew it out with carb cleaner and compressed air.

What could cause this issue ?

My thoughts:

Bad diaphragm (new)
Incorrect float level
Issue with checkball? I don't know how it functions
Clogged shot port ?
 
how do you correctly seat the check ball for the accel pump and the check weight?

You generally don't. Those 1920 metering blocks eventually hit the end of their useful life, usually due to "metal mould" corrosion, and once that happens usually they can't be dragged back to life. If it's a superficial fault power valve check ball retainer comes unstaked and falls out) it can be repaired easily enough, but beyond that generally not.

But you say your accel pump shot is weaker post-rebuild than pre-rebuild, which suggests you might be able to go back in there and fix it. I usually stretch the accelerator pump drive spring a bit before reinstalling it, and once or twice I've substituted a stronger spring (this is for '64-up 1920s with the spring-drive accel pump; it's a different deal on the '62-'63 cam-drive pumps).

Other ideas: make sure you got the right kit, of a good quality, that parts weren't defective (accel pump diaphragm/metering block gasket), that the accel pump is correctly adjusted by the book, ditto the float setting and other adjustments.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

@slantsixdan grace me with your presence[/QUOTE]
 
I disassembled the carb and found the problem. The accelerator pump diaphragm/gasket was slightly misaligned but still lining up with the screw holes. the misalignment caused a partial coverage of the port that the accelerator pump would pass fuel through.

I did drill out the two clean out plugs and clean the check weight and check ball. Then replaced the plugs with the supplied from the kit.

I made a little gasket shim to hold the gasket in the correct location while reassembling the metering block.

Accel pump now works excellent but unfortunately I now have a high idle. When hot.

So I'm assuming either when I replaced the plugs they are not fully sealed or whenI made the little shim for the gasket It is holding a metering block up so it's not fully against the diaphragm / gasket.

Good news is drivability is back. I think what I'm going to do is get some spare screws and cut the heads off. use them to align the gasket so I could drop the metering block into place without the silly little shim. Then reassemble after JB welding over the clean out plugs that were replaced.

I hate old carbs
 
Edit: another thought is that maybe now that I have it fully correct and clean that the curb and fast idle screws just needs to be adjusted? I did notice when assembling the car but they are fully in
 
if you give up IIRC I have a 1920 for ya...High idle when hot sounds like an adjustment, Maybe choke?
 
if you give up IIRC I have a 1920 for ya...High idle when hot sounds like an adjustment, Maybe choke?

Choke is functioning ok at the moment. I'll let you know if I go crazy ! I think it will settle out . It only has a high idle when in neutral/park. When in gear it seems perfectly fine. Automatic btw
 
sounds like a lean mixture problem. are you using manifold vacuum for distributor? what happens when you put your hand over the carb at idle (making it richer). Does it mellow out or die? Old carbs...yeah, they work great when new.
 
sounds like a lean mixture problem. are you using manifold vacuum for distributor? what happens when you put your hand over the carb at idle (making it richer). Does it mellow out or die? Old carbs...yeah, they work great when new.

Distributor gets vac from carb base port , direct feed.
I'll try the hand over it when I get it back from the alignment shop.

I couldn't kill the engine with the mixture screw turned all the way in with the limiter spring in place ....I could before .

I'll also check for vac leaks when it returns
 
If the mixture screws are all the way in, Im thinking the carb idle setting is too high exposing the fast idle circuit. try turning down the idle screw to stall it, then turn the mixture screw all the way in then out 1.5 turns start from there. Read #11 here:
Holley 1920 1 barrel tuning and adjusting
 
great, this was kinda of my assumption. i think they Previous owner had some issues and chose to just turn up the idle to avoid them. now that the carb is working better its exposed this again
 
Got the car back from alignment and it's driving great.
Took it on a 30-minute drive to get it nice and warmed up.
I adjusted the curb idle screw as it was definitely the cause of the high idle. It's much more reasonable now and I also adjusted the mixture screw to get it right by ear.

When I convert to HEI in a month or so I'll set the idle with a tach and vac .

Thx all
 
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