Curse of the 1920?

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TylerW

TylerW

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Hey all:

My 1973 Valiant has 49,000 verified miles on it, and still possesses it's original 1920 carb complete with functioning idle dashpot(it's a manual trans).

I'm 99 percent sure it's never been off the car based on the thickness of grunge on it and the original owner saying it hadn't. The ears on the float bowl are unbent too, lol.

It's doing something weird:

It starts easily with the automatic choke, idles down in steps as it warms and idles fine after the choke comes off. However, if you switch off the engine, let it sit about 15-20 minutes, you can't get it started without holding the pedal part of the way down.

Once it starts, it will not idle. It chugs down and sounds like it loses a couple cylinders, then quits. Next day, it starts right up.The choke is WIDE OPEN during this episode, so no need to even mention the choke.I did adjust the valves, only had to loosen a few.

So, does this sound like something familiar with one of these?

I'll end with saying that I dislike these carbs. I know some people profess to love them, but I've seen a lot more that didn't run right than I ever have that did. On top of that there are two major potential leak points right over a hot manifold. On top of THAT, there no more floats to be had and the metering block can't be cleaned all the way. Why does anyone want to fool with one of these things?

Thanks for reading.
 
Just had to deal with a lot of fun with these carbs not that long ago. My biggest gripe with these is the really really really stupid float bowl design making it an easy leak point.

Holding the gas pedal down a bit is actually the suggested warm starting method for these engines. I forget where I found the Mopar brochure that had cartoon depictions showing this. The fact that it wont idle is another matter though. Check for vacuum leaks first then five it a proper deep clean and see if that fixes anything.

If you're really done with the 1920 (as I was before I figured out my problem) talk to slantsixdan about getting a new old stock Carter BBS. I'm not a fan of carbs to begin with so I told my wife that the next time her carb starts acting up I'm converting her car to fuel injection. Its a big job with a good amount of fabrication, but I find that stuff fun and we'll get all of the benefits of EFI.
 
havensole said:
Just had to deal with a lot of fun with these carbs not that long ago. My biggest gripe with these is the really really really stupid float bowl design making it an easy leak point.

Holding the gas pedal down a bit is actually the suggested warm starting method for these engines. I forget where I found the Mopar brochure that had cartoon depictions showing this. The fact that it wont idle is another matter though. Check for vacuum leaks first then five it a proper deep clean and see if that fixes anything.

If you're really done with the 1920 (as I was before I figured out my problem) talk to slantsixdan about getting a new old stock Carter BBS. I'm not a fan of carbs to begin with so I told my wife that the next time her carb starts acting up I'm converting her car to fuel injection. Its a big job with a good amount of fabrication, but I find that stuff fun and we'll get all of the benefits of EFI.
Click to expand...

Thanks for the reply. I was following your problems too...I hope you are out of the woods.

This only happens when the carb is hot, so I think it's either got a crack inside it somewhere that opens when the metal expands or there's a seal that went bad somewhere inside it.

I'll probably overhaul it just for S&G but my plan is to run another kind of carb.
 
805 thinks like I do. high fuel level for some reason. Either bad float, bad needle seat or both. rebuild will solve it. That cartoon had a cartoon lady leg with high heal in it right? I remember seeing that. Even my Mazda with a New NOS carb cranks 2 times before it starts when warm. When cold choked, it lights off immediantly and I can see the fuel level in that one, its always right at the line. There is also a "FABO FSM" by our slant guru slantsixdan that has a fuel line reroute away from the hot exhaust to help vapor lock. EFI baby! Im on it.....
 
Thanks for the replies.

What I can't understand is why it can sit and run at hot idle for 20 minutes and never miss a beat. If I start it back up within just a few minutes it runs ok. 15-20 minutes and it's a whole different story.

I'm starting to wonder if this could actually be an ignition problem or a vacuum problem. If the float is sinking or anything else is causing the float bowl to fill too high then there's going to be gas coming out somewhere it shouldn't and it's just not doing that. I looked down the carb with a light and it's not dripping inside at all.

I've only driven it once because it isn't tagged, and it didn't run good then. Started and idled fine, but it had a huge stumble in it once you were rolling in the gears and lugged it down.

I'll look into this further and report back.
 
TylerW said:
Thanks for the replies.

What I can't understand is why it can sit and run at hot idle for 20 minutes and never miss a beat. If I start it back up within just a few minutes it runs ok. 15-20 minutes and it's a whole different story.

I'm starting to wonder if this could actually be an ignition problem or a vacuum problem. If the float is sinking or anything else is causing the float bowl to fill too high then there's going to be gas coming out somewhere it shouldn't and it's just not doing that. I looked down the carb with a light and it's not dripping inside at all.

I've only driven it once because it isn't tagged, and it didn't run good then. Started and idled fine, but it had a huge stumble in it once you were rolling in the gears and lugged it down.

I'll look into this further and report back.
Click to expand...

if its not coming out the booster then its not a high fuel issue. and as i said the brain gets clogged your gonna have to try another if you cant blow and clean your current one...

you need to pull the carb down and start over as i think your PV circuit is plugged/malfunctioning

tear it down, clean everything.

set the idle bleed to .035" (head side of the carb)

blow out all the passages and make sure you can get light thru all the passages on the body.

also good idea to install a 57 jet, best mpg and power jet for a stocker.

P.S. before you pull the carb take a flashlight to the base plate spacer and see how much it shining between the spacer gasket and carb base.
 
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