Fuel Pressure specs for a Model J with Updraft carb???

Other than J487.I have had no experence with the updraft carburetor on a "J". J396,as it was when we worked on it and made a nuisance of ourselves on the streets here was a far more powerful car with the downdraft carburetor. We thought it possibly had high compression pistons but did only a half hearted examination.This was very high mileage engine and was eventually blown up by throwing a rod thru the side of the block.The owner was Melvin Clemans and he had let some shop try to tune it a bit.During that process,while trying to see 90MPH in seond gear and only getting 85,the rod either broke or the bearing failed. This car had 20 inch wheels on the rear and that slowed the speedometer a bit.The 90MPH was being attained but not showing on the speedometer and the guy working on it over wound it and then it went bang. This engine was later repaired and resides in a reproduction torpedo phaeton that I saw at Auburn some years ago.How well it runs,I don't know. The Packard bodied roadster that carried J396 now has J434 with updraft Schebler and I doubt if it does nearly as well as it once did. I am surprised to see as many of these cars still equipped with the Schebler updraft as there are.
Bill is right,if one of these engines were to be "blueprinted" and high compression pistons installed,I think possibly 700 HP might be possible.

One thing the J motor had was potential, like the old 392 Hemi. The Ab Jenkins record car had some carbs added, the compression upped a few points, and tuned to with an inch of its life it was putting out around 400 HP.

Built to 283 cu in/283 HP specs the J was probably a 700 HP engine. Just getting rid of the Shebler and going to a down draft carb was good for a sizeable HP increase.

I think you need to spend more time finding out why your needle valve isn't working and less time changing fuel pressure.

It would be interesting to see what the readng would be today with our better fuel and oil we now have. I wonder if anyone in RECENT years has dyno tested one on a rear wheel dyno to see what it could do. The old ads said 265HP @4250RPM and I would like to know what it is today.

Bob,

It was up to about 145hp when they panned away.

click here: www.jaylenosgarage.com/segment/r ... -the-dyno/

What was the output of the engine they dynoed?
There has been a lot of speculation about the true power output of these engines. With the low compession and fuels available in the early days of the "J",the fact they ran as well as they did said a lot for this design. At the time the "J"engine was being made,Lycoming was making an "L"head (flathead) engine of identical displacement and it was rated at about 100 HP. The efficient intake and exhaust system of the multi valve "J" engine at least doubled this and probaby even more than doubled it.
I think it was Don Vordermann writing in 1973 in the Automobile Quarterly who was probably right when he stated that "as delivered"the "J" probably didn't put out the advertised 265HP and that 245 to 250HP was
probably a more realistic figure. He also went on to say that the performance of these cars was far beyond the cars that were then offered to the luxury buyers of that day. I have personally compared the "J" to the Cadillac V8-V12-and V16 as well as the Packard "Super"8 and the 12 and it is hands down in favor of the Duesenberg by a wide margin.When warmed up as we did with SJ528 it was still yet another story.The 3.875 bore gave the engine about 450CID and the supercharger was not needed and could have been a liability if used on that particular modification. One thing for sure,it moved that heavy Brunn bodied car in a most satisfactory manner and did it with no real effort.

Thanks for all the reply's and suggestions. Using the regulator, I dialed the pressure down to 4 psi. It was an improvement, but still ran rich. So I cranked it down to 3 psi, and that seems to have solved the problem.

I noticed on a video on Jay Lemo's Garage that they Dyno'ed a Model J straight 8, and they had the fuel pressue set at 1.5 psi throughout the entire pull. Very interesting, maybe I will try that.

I always used the old AC AP11 pumps. Worked good wih any Duesenberg carb. You don/t need The big high pressure Holleys. Those thing put out like seven pounds of pressure. There is an aftrmarket needle assembly for those old carbs that will stop any fuel pressure. I think Brian Joseph has them.

Joel,

I wish you luck, but for what it's worth I had trouble with that one, and I tried two of them. I live near Summit Racing in Ohio and they were good about taking both back. I spent a little bit more $$ and got one mfd. for Holley that works fine. This one adjusts with an allen wrench and has a port for a guage.

I was looking at the posts from this past spring on this subject and the only "J" we ever had that had this type of carburetor J487.The rest had downdrafts.
Check the nuts holding the intake manifold onto the head.If they are not tight,an air leak can mess up the idle.
Check this on a cold engine. Also make sure the carburetor base screws are tight also. I had a Packard years ago that had a less than tight carburetor base and it idled poorly if at all

looks like the Duesey in this video has the same problem as mine. Check out the exhaust when he idles for a moment before pulling out onto the highway.

... 6eD0yiT3bs

The fuel pressure regulator showed up today, soon it will be installed and tested.

Thanks for all the replies!

I did go thru the carb last fall, I found a reprint of the full adjustment process on line. It seemes to work OK the first time I ran it after the carb was cleaned up and adjusted, but has not done so consistantly.

Since Mike's book says 3 psi, I am going to see if I can find an adjustible regulator to turn down the pressure a tad. The electric pump has an internal, non-adjustable pressure setting.


Edit: found one at Summit, I think I'll try it. www.summitracing.com/parts/MRG-9710/

I have AEA tune up charts for 1933,34,35 Duesenberg and they all call for 3lbs fuel pres. I know they don't all us Schebler carbs. I have a Schebler on my L-29 and it will NOT hold back 6 lbs pres. You should have 3 lbs at the carb. One of the problems with many ACD cars that run rich is to much fuel pres. People confuse pres. with volume. The Duesenberg needs lots of volume, thus the three fuel pumps and large dia. fuel lines, but not lots of pres.
CORDially Mike

If you can get a copy of the[i:2x1xv0md] Dyke's [/i:2x1xv0md][i:2x1xv0md]Automobile Encyclopedia for Automobiles [/i:2x1xv0md]supplement for carburetors, there is an excellent diagram and procedure for adjustment of the Schebler Model S duplex. This write up is reprinted nearly entirely in the L-29 service manual.
That should be a good start to getting the carburetor properly adjusted.

Del.

Del.

I put a guage on it tonight and the pump is putting out 6 PSI. Is that to much for the old Schebler updraft carb?

I think most mechanical pumps run from 4 to 7 lbs. for standard carb . engines. Do you have a pressure gauge on the line? Even stetups with electric pumps and injecters have their limits. A truck I owned had 90 lbs after the regulator, caused all havoc with the o2 sensor and computer. Was an easy fix with just a new regulator. Good luck

Hi, what is the minimum and maximum allowable fuel pressure, measured at the inlet to the carb. This car has an aftermarket electric fuel pump, and the factory mechanical pump has been bypassed. It seems to flood at idle, and on deceleration. I was thinking maybe the electric pump is set at too high of a pressure, and is pushing gas past the needle and seat. Thanks, Joel