I have a Diamond T cabover with the original Hercules engine in it and the weird thing is that I want to leave it in there, not hot rod it. Anyway, I have it running OK, but not like I really want it to. Because of the cabover and the floor panels, it uses a Zenith up draft carb. I am looking for other options for a carb. I have converted the truck to 12v neg ground already, but I would like to keep the mods to things that could be put back to stock if I wanted to. I would be willing to make an adapter but I am not sure what would be better if anything than what is on it. I really want to get it to the point that I can just walk out to it and fire it up and go without all the song and dance it takes now. Have any of you found a favorite carb to put in place of an up draft? Would a side draft carb be worth looking into? Pertinent info: it is an inline 6 flathead, app 250 cid. Thanks for the help, Jason
How much room is there to the side? Three sidedrafts or EFI are about all I can think of unless you want to go propane or CNG where mixer orientation does not matter.
Just gotta ask: What song & dance do you have to do everytime you want to fire it up and go? Seems like Diamond T didn't build it requiring such. Isn't it fixable?
There were a lot of updraft carbs built but they were for machines like welders, forklift trucks, and airplanes. None were designed for a lot of throttle movement since most are single venturi types. An old Winfield or Linkert side draft or two would be real cool with a custom built log manifold but they are hard to find now days. Stromberg, Carter, & Marvel Shebler all made them as well as Zenith/Bendix. You'll need to design the carb jetting & venturi size for the cubic inch displacement of your old Herc motor.
I don't know how much room you have, but you might be able to make a U-turn and mount a downdraft low. Apart from that, you might be able to find a Fish, with an adjustable bowl, or reorient an SU bowl to make it an updraft.
Lots of trucks, passenger cars, race cars, etc. were built to utilize updraft carbs. There are lots of different designs out there. The original probably is one of the very best carbs you can use. C.O.E. (cab over engine) trucks as late as the mid-1960's reliably used updraft carburetors, because of clearance issues. Starting issues may simply be a matter of using correct procedure. When starting cold, ALWAYS use the choke. Zenith used a vacuum type accelerator pump on updrafts (if an accelerator pump were deemed necessary). Vacuum pumps will NOT function until the engine starts and produces vacuum. Pumping the footfeed on a vehicle with a vacuum type accelerator pump results only in exercising one's ankle. If the compression, and spark are good, and the Zenith is functioning normally, no song and dance should be necessary. Jon.
Thanks for the replies guys. As far as the procedure to keep it running, it is a dance to keep the gas pedaled and the choke in the right spot and grinding the gears, trying to stop etc. Makes for no fun in traffic. I know it will be better but I am not pleased with how cold blooded the thing is, it seems that the choke is the key to keeping it running. I have had the carb apart in the past and I do not think that it has a acc pump at all. On everything else I have I can give it a squirt of gas, where this one I cannot. Why I brought it up yesterday was that I had to drive it to the new shop app 12 miles away and it was quite a trip. I thought that I had been fighting wiring on it, so I ran all new to just the basic needs and it fired up great, went around the block nicely and as soon as I tried to turn onto the main road it died and didn't want to go. It would restart immediately with the choke fully closed, but as soon as I cracked it open at all, it would die, nothing over an idle. I was not able to give it any throttle at all. Also to note it does have an electric pump on it. I pulled the line off and turned the pump on and it moved fuel so I put it back on after a tap or two on the carb with a wrench, then it fired up with the choke open and ran great for 20 min of driving and then it started acting up again. I did not get to work on it yet, but I am guessing that the carb has some junk in it. Now that I have had some time to think about it and I am not stuck on the side of the road, it is probably better to fix what is on it. It could be as simple as it picked up some trash. I had a new fuel filter on it, but I will still have to see once I take it apart. I just thought of it too, I do not know how much pressure the pump is putting out, it was on it when I got the truck, I should put a guage on it and confirm. As far as room, there is app 5" between the carb and the frame now, the gen and starter are on that side too, below the carb. I was just trying to come up with some ideas and see if there was something that is much much better since I have not messed with one of these on anything else. Again, thanks for the thoughts Jason
SOME of the older engines have symmetrical intake manifolds which may be turned upside down and then a downdraft carburetor installed (assuming one has the proper hood clearance). POSSIBLY, a new intake manifold could be fabricated. If you go with side draft carbs, due to what is available, you will need at least 2 for an engine the size of yours. A pair of Carter YH's from a Dearborn marine engine could probably be recalibrated to work. Fabrication of an adapter (U-tube) that would accept a downdraft carburetor sitting below the current manifold would be worse than the existing carb as it would still in essence be an updraft plus you would have introduced additional resistance requiring higher vacuum to pull the fuel into the engine. Personally, I would fix the current problem (whatever it happens to be). I would start with: (A) compression test (B) complete ignition test (C) complete fuel delivery system test, including fuel filter (D) if all of the above is good, I would then rebuild the carburetor. Jon.
Tapping on the carb probably loosened the needle of the seat to let fuel in the carb. You may want to check & see if the needle is hanging up. I have that problem on my Gibson tractor with a Stromberg updraft.
They used the same engine in the standard trucks with a downdraft carb, so if i had the room I could use that manifold set, but I don't want to modify the doghouse/cover on it. There is not any room to go up at all. I also took another peek at it this afternoon and there is less room between the carb and frame than I had thought, closer to 2.5". I too am thinking that either there is junk in the carb or the needle/float is hanging up. If I recall everything in it was brass or cast iron, it may have some oxidation etc in it. I will try to keep this updated when I get to it.
I have not had a chance to do much to the truck other than run it in and out of the shop when I need to get material in, but Thursday I went to back it out and short story is the electric fuel pump quit. May have been part of my problem. SO, my question is what pressure should these carbs run at? I will put a holly blue or red on it that I have on the shelf and a regulator, but where should I set it? Is 5 psi too much? Jason
I have a Gray Marine engine with twin updraft Zenith Carbs. I have never tried to start the engine but I think it will run. The engine came out of a old wooden speed boat. I don't have a clue who made the engine, it's a flathead 6 cylinder that might have been made in 1940. Someone told me it was a Chysler, now I am thinking it might be a Continental. The Zenith carbs on it are not frozen, they are made out of cast iron.
I'm thinkin updraft carbs were mostly gravity flo fed. My Gibson is as were model A's. The gas tanks on those were higher than the carb. I think chevy had a vacuum tank. I would imagine the pressure should be very low, maybe a 1# or less at least that is where I would start & increase upwards from there.
Check with any John Deere restorers, the 55 combine used a Herc engine. I don't know the cubes on them. I used one on my Lincoln welder. Lee
When your fuel pressure is sorted out, you can decide if a new carb is needed. There are still some available updraft carbs. Buy one from an engine of about the same size as yours. If you need an updraft carb, get the aluminum zenith used in forklifts I am using one on a 2.5 liter chevy engine It must be choked but starts instantly every time. They work so well, there is no reason to convert to updraft from these simple inexpensive ($5) carbs.
If you're having the problems you describe, it's not due to the inherent design of updraft carbs. I've got hundreds of hours on tractors, cars, trucks (including Diamond Ts) and boats with updraft carbs. When they're right, they all started immediately, took throttle evenly and pulled to redline. Get the carb remanufactured (not just a kit) by someone who knows how. Then you'll know it it's right and the problems will be somewhere else. jack vines
Hey...Check your fuel flow! The gas we are getting today is rotting out neoprene, painted surfaces, (springs & hardware inside carburetors & fuel pumps; imagine what it's doing to your sediment bowl, fuel filter, etc.) As well as the old Diamond Ts ran with those updrafts, the problem likely is in the liquid corn you're introducing into the ancient appliances. Check there, from the tank forward, replacing any and all flexible hoses!
I have been fighting fires at the shop, so almost forgot I even posted this. Anyway, I am confident that I will be keeping the carb that is on it. I have a brand new tank but have not made the mounts for it yet. I want to get that mounted and run new lines, pump, filter. I have ran new wiring on the basic needs, so that I know that is as it should be, I want to get the fuel supply new before I clean/fix the carb. I think that it had a pump of some sort on it factory, I do not know where they would have mounted a gravity feed tank on this truck. It had an elect pump on it when I got it, no idea as to age now that I think about it. Anyway, I'll start low and maybe bump up the pressure if it acts like it needs more as I drive it.
i have a old forklift with a chrysler industrial 230 flathead 6 and i always have to mess with the updraft carburetor what a pain would like to convert to propane!
I was told that a forklift zenith carburetor would not work well on a car. I'm glad I tried it anyway as it starts well and runs well. I did not think such a simple carburetor could work that easily. Don't give up on an updraft carburetor.
First choice, have Carbking rebuild it or go over it yourself. But be sure valve adjustment and ignition are good first. Second choice, convert to EFI. Some adapting required. A throttle body doesn't care what position it is in. You would have to drill the intake manifold and weld in bungs for the injectors. Look up Megasquirt for home made EFI ideas.
Ford model A Zenith carbs work great. If it will fit they can handle 50 horsepower.. Lots of good parts and info available.
>>>It would restart immediately with the choke fully closed, but as soon as I cracked it open at all, it would die, nothing over an idle.>>> Seems like a big air leak to me. Jack E/NJ
Chryslers in the 30's used them CM6 etc What about a Throttle body injection conversion [I'm sure injectors would work upside down] There are conversion kits that use GM TBI's Here's one for a slant 6 [they also do one for a 258 jeep engine] http://www.affordable-fuel-injection.com/product/mopar-tbi-complete-system/#_form_13
Model A is 200 cu in, Diamond T Hercules six is about 500 cu in. 5 pounds is awful high. 2 pounds at the carb would be more like it.
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