Holley 1920 Stumbles

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rp23g7

rp23g7

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Hey everyone carb questions

The 1970 Duster we just got has a slant with the Holley 1920. It has a stumble on acceleration but if you pump it a bit it will go, but it had a slight surge sometimes at a steady speed and you gave it a bit more gas.

I thought it may be the accelerator pump, so i got a rebuild kit and rebuilt it. It actually made it worse. Particularly when its nose down on a hill.

Before i rebuilt it, it would stumble, backing up our driveway, but give it a bit more gas and it would go, as well as accelerating from a stop.

Now it has become worse, it will die if you back up the driveway, and it will stumble and almost die, or it will die when accelerating.

i thought it may be a vacume leak, sprayed around but all seems ok. I am wondering if the float level is wrong.

If it stumbles on flat on acceleration, or when the car is nose down, that would be a float level thats too low right?

Hit gas, car uses all gas in float bowl since it is to low and dies? Or when its nose down, the gas is all in the front of the bowl causing the float to drop to far, not allowing the car enough gas to back up the hill?
 
i went back and measured the float level again, its 3/16 or pretty dang close. Went to start it again, drove it, still stumbles. not sure what to look for, the carb is "fairly" new, the records for the car show a new carb in 79, and a rebuild in 93. It does sound like the valves need adjusting but i dont see them causing this issue.

i squirted carb cleaner around, no vacume leaks, it idles ok, and goes dwn the road ok once it gets going, just has issues accelerating, wonder if the Acc pump in the kit was bad too
 
Check to make sure your distributor vacuum advance and its hose are in good shape (holds vacuum). Carburetor operation and repair manuals and links to training movies and carb repair/modification threads (including a lot of Holley 1920 material) are posted here for free download. Note that the 1920 has a lot of tiny blind passageways in its metering block; once these get full of powdery corrosion they cannot be cleaned out and the carburetor is well and truly Done. I have a new-in-box main metering block and, for that matter, a new-in-box (not "remanufactured") carburetor if you wind up in need -- send me a PM.

Other things worth mentioning: You say the carb is "fairly new", which suggests it is a "remanufactured" unit. These are almost always garbage that cannot be made to run right no matter how much time, money, and effort you spend trying. Also, improper valve adjustment can and will cause all kinds of driveability issues including stumble on acceleration. Use the valve adjustment procedure posted here. And tune-up parts and technique suggestions in this thread.
 
slantsixdan said:
Check to make sure your distributor vacuum advance and its hose are in good shape (holds vacuum). Carburetor operation and repair manuals and links to training movies and carb repair/modification threads (including a lot of Holley 1920 material) are posted here for free download. Note that the 1920 has a lot of tiny blind passageways in its metering block; once these get full of powdery corrosion they cannot be cleaned out and the carburetor is well and truly Done. I have a new-in-box main metering block and, for that matter, a new-in-box (not "remanufactured") carburetor if you wind up in need -- send me a PM.

Other things worth mentioning: You say the carb is "fairly new", which suggests it is a "remanufactured" unit. These are almost always garbage that cannot be made to run right no matter how much time, money, and effort you spend trying. Also, improper valve adjustment can and will cause all kinds of driveability issues including stumble on acceleration. Use the valve adjustment procedure posted here. And tune-up parts and technique suggestions in this thread.
Click to expand...

Thanks Dan, I will adjust the valves first, one lifter or two sounds pretty noisy, although my Scamp when I got it sounded horrible, but ran ok, Carb wasn't that bad inside, there was no difference in the bogging before and after the rebuild. Vacume lines ans such look ok, I will check the timing and see what messing with the mixture screw does.

What would you want for the new carb if it needs it?
 
Send me a PM on the carb -- both it and I are in Seattle, so local pickup would be possible. Check the vacuum advance by removing the vacuum advance hose from the carburetor and applying mouth suction, then capping it off with your tongue. The vacuum should hold til you remove your tongue from the end of the hose. If not, and the hose itself is good, then new vacuum advance (or new distributor -- got one of those, too -- and HEI upgrade ). If you do this test while pointing a timing light at the timing mark, you should be able to watch the vacuum advance work. If it doesn't, fix that. And what have you got base timing set to?
 
PM coming your way Dan, i didnt realize you were in seattle, we have proba bly met at a car show and not realized it. The vacuum advance seems fine, the car has a new distributer too, forgot when it was installed, the records for this car are amazing, she has stuff all the way back to 71. I havent checked the timing, i will tomorrow, gotta change oil, adjust valves, adjust brakes etc
 
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