Further carb issues on my 1940 248

Last year I made a Frankencarb by using the air horn and choke assy from a WD0 448S carb on my 440S carb. This was because my original 440S air horn was missing many of the choke linkage parts and someone had adapted it to a manual choke. I acquired a 448S and was able to make the switch to get auto choke function back. Well I finally got a another 440S and using the linkages from that I was able to put my old air horn back on and de-Franken the carb.

So I made the swap and put it back on today and it seems to be running much worse! :mad: Runs terrible when cold and not great warm - I seem to have lost 2+ inches of merc on the vacuum. The only things I changed besides the air horn was a small adjustment on the tang that lifts the metering rod assy (I used the right gauge for this) and lowered the bowl level back to 3/16" (my mech had raised it to 1/10" to get better high speed performance). Other than that the carb is the same as before. I guess I need to look for a vacuum leak somewhere. Could a warped air horn assy be causing this? I do have another air horn to try if I think I need it.

Cheers, Dave

Dave - the two areas I would check first would be to see if the starter switch has a vacuum issue, or if one of the gaskets on the idle circuit has split.

Jon.

Dave - the two areas I would check first would be to see if the starter switch has a vacuum issue, or if one of the gaskets on the idle circuit has split.

Jon.

I think your car should have a 474S carb which according to the books I have was the carb used in late 1939 and the 1940 248 cars.

The 440S and the 419S are 1939 carbs. From what I have always read, the 1939 used all three cars. I've never found that one worked any better than the other. My yellow car is a very early '39 and it has a good working 419S. The blue car has a 474S and the green car has a 440S. Of the three I like the 419S the best. I would suggest you just get a new carb and start over.

Jon: Yeah, looks like I have to take it off again. I have an electric vac pump so hopefully I can rig it up for some bench testing to see what is happening.

Earl: Actually, 440S is correct for my engine serial number. I am about 1500 below where the 474S starts at 3976130. I have a second 440S that is in the process of an thorough cleaning and overhaul (doesn't seem to have been used much but it sat on a shelf somewhere for a loooooong time - lots of white powder from surface oxidation). Another option would be to give in and get a WCD since this is a driver anyways.

Cheers, Dave

Jon: Yeah, looks like I have to take it off again. I have an electric vac pump so hopefully I can rig it up for some bench testing to see what is happening.

Earl: Actually, 440S is correct for my engine serial number. I am about 1500 below where the 474S starts at 3976130. I have a second 440S that is in the process of an thorough cleaning and overhaul (doesn't seem to have been used much but it sat on a shelf somewhere for a loooooong time - lots of white powder from surface oxidation). Another option would be to give in and get a WCD since this is a driver anyways.

Cheers, Dave

My Carter information shows the 474S for 1939 and 1940. I ran a 474S on my blue sedan for years until Ethanol destroyed the Bill Hirsh 1980s vintage stuff in the tank. I tried a 474S on the convertible and it didn't play, so I switched to a 440S. The convertible sedan has always had a 419S and has always run great. <shrug> It's like a well...................too deep to figure out why Buick kept switching them around. On different cars one has run as well or as bad as the other.

Do you know what the difference between the 3 are ?? What was the variations ??

Danny

419S used anti-percolate valves that were removable and adjustable. 440S and 474S has them sealed. 474S used different choke linkage arrangement. Take a look at the attachment for part number differences.

Carter WDO Sheets All001.pdf

Cheers, Dave

Also this one for what was used when.

Carter WDO Cover 001.pdf

First of all, I found a real mechanic. I also read the literature. Yes you are right, 419s was early '39, 440s was late '39 and early '40, 474s was late '40. However, the 474s works best on a '39. Only difference I noted is that the 474s is not quite as tall, which gives a slight slant to the air cleaner top and yes the linkage had to be moved a little. Okay here is what I think is wrong with your carb, based on my own experience. You have a vacuum leak somewhere; likely in the pile of gaskets under your carb. That was where mine was. There is a tool (machine) called a "smoker" that can absolutely identify any vacuum leak, and most good shops have one. If you find a vacuum leak, fix that first. Then you will probably find, like I did, that the carb is all messed up from various people trying to fix it while there was a vacuum leak. After the vacuum leak was fixed, the 440s carb was loading up so bad the car was choking on gas. Other mechanics had tried to fix a carb that wasn't broken. We just changed the carb, changed the linkage and my 474s carb, rebuilt by Daytona that I had wanted to use for my car, worked just like it was supposed to. Waalaaa

A simple check for intake leaks is to spray WD-40 (or starter fluid) around the intake gaskets with the engine idling.

A vacuum leak will cause the engine to speed up when it can take in the WD-40 and burn it as extra fuel.

Earl: I am thinking you are spot on about the vac leak. I took off the carb and am going thru it again. I am checking some of the vac circuits within the carb with a bench vac pump that I have. The ball for the start switch seats nicely and stays sealed against almost 30 inches of mercury so that is not the issue. Other vac circuits test good with the carb disassembled, final tests once the reassembly is complete.

After looking at the quality of the carb gaskets that I put in it 2 years ago against what I just got from the Carb Shop in MO I saw that the Carb Shop's kit quality was far superior and decided to put that kit into my carb rather than in the backup 440S (kudos to Jon at the Carb Shop, BTW). Also he included the small idle gaskets and I still was using the ones from God knows when so that should help as well.

So I am using his jets as well and am setting everything back to baseline. On checking my air horn it appears it may be warped, the backup 440S air horn has much less "rock" on the flat surface so I will likely put that in instead. I have sealed the "gasket pile" against the manifold with red RTV and plan on sealing around the sides as well. I have been assembling the carb with a very light coating of Permatex Permashield (that stuff is expensive but good anywhere gas or ethanol is involved) on the gaskets to make sure of good tight seals.

Does anyone know of the tightening spec for the carb holddown nuts? I want it tight but obviously not so tight as to damage the threads or break the studs.

Mark: Yes, I will try that when I put it back on, hopefully in a week or so when it warms up a bit.

Cheers, Dave

In addition to being warped on the bottom my gasket pile had a break-out of material between the two holes at the bottom where they fit against the intake manifold.

Update: As I said above, I put in the Carb Shop kit and was very careful on reassembly. Besides the gaskets, I also put in new jets and accel pump. The pump I was using was way too long and now I realize that this totally messes up the metering rod adjustment - I did not understand how interdependent they are. So I did the pump readjustment and then went back and adjusted the metering rod tang. Reassembled all and put it back on today - I made sure to seal the edge of the gasket pile with red RTV and used a light coat of Permatex #2 on the carb gasket itself. I torqued the carb bolts to about 8 lbs and made sure I had the accel linkage adjusted correctly for full swing.

Result: much better. Choked idle much smoother, fairly nice idle when warm, got most of my missing 2 inches of vacuum back. Still not silky smooth as I would like but I can live with it for now. I took it out. It popped back on me a few times at first but seemed to settle out. I drove into town to get some gas and then took it out on our local interstate for a quick run. Was able to run about 50 mph and I floored it there and it felt like there was more left (couldn't run any faster due to our heavy rush hour traffic here).

I will do a few more tests (exhaust gas anal, etc) but I think I have gone about as far as I can with this carb other than more adjustments. I have another WD0 but it is pretty filthy and will take some work to get it back online. So I think I will go ahead and put a kit into the WCD 663S I picked up off of flea bay. I did a fit check on it today and it goes on like a glove. I need a heat tube but I can cobble something up from copper tubing. Also if I want to keep the hand throttle control I have to do something there as well, but I will take my time - at least I have it running reliably now.

Cheers, Dave

Dave - would suggest using steel tubing for the heat tube. Copper will dissipate the heat so quickly the choke may not function as desired.

Jon.

Dave,

I used a short section of steel brake line for my heat tube.

Mike in snowy Colorado

A simple check for intake leaks is to spray WD-40 (or starter fluid) around the intake gaskets with the engine idling.

A vacuum leak will cause the engine to speed up when it can take in the WD-40 and burn it as extra fuel.

Jon, Mike: OK, I will do that. NAPA carries some short premade pieces and I can custom fit one of those.

Larry: Cool idea. No paraffin residue like with WD40. Maybe a little dangerous?

Cheers, Dave

Just on the choke tube, many years ago I tested the time it took for the choke to shut off with the insulation shield on the tube and without the insulation shielding.

I can't remember the exact differences in times but I remember that it was definitely better to have it on.

Danny