Carb selection and difference

[NiteOwl]

Please indicate if I am making a wrong assumption or with any thoughts.

My engine: 42 EL & the M74B Linkert Carb

Research says:
M35 1941-1947 Harley E,EL, 1941-1947 F,FL (1 1/8" Venturi)(12deg disc angle)(slot width .020")
M74B (early 408 casting) L-1951 (15/16" Venturi)(9deg disc angle)(slot width .0155")
M74B (late 418 casting ) 1952-1965 Harley F,FL")(15/16" Venturi)(9deg disc angle)(slot width .0155")

Question:
What

1. I am assuming that its hands-down I would lean to the M35 for authenticity and model correctness. ?
2. What do the differences of venturi size, slot width, and disc angle, mean in the operation and performance of these carburetors?
3. My present M74 bowl does not have a drain screw, I know I can run the bowl dry when I expect extended down time, but, is it common to drill and install a drain screw or is there a sound reason why some have them and some do not?

[Sargehere]

The M74B is Panhead, '52 and later, as you discovered. The correct carb is the M35 for a Knuck of that vintage, replacing the M5 that was on the first Knuckles. The no-drain float bowl preceded the ones with a drain, late-'30s. A judging team would write "incorrect carburetor" on your judging sheet and take off points under "engine."

That's one of the basic requirements, and easy to check, the numbers right on top of the carburetor, in plain view.

[Rubone]

While the M74B will work on your bike it would be too much for a 61" engine to make good use of. The venturi size affects total air flow as well as the speed of the incoming flow. The slot width and disc angle affect the fuel feed in the idle and just off idle positions. An M35 is an adjustable high speed jet model, and M74B is a fixed high speed. You can change the venturi in the M74B but the other factors you cannot do much with. M35 carbs are pretty common. you will be better off with one as far as tuning your bike.
Robbie

[NiteOwl]

Thank you very mush Robbie, that makes total sense.

I see there are 3 models of the M35

• M35 1941-1947 Harley E,EL, 1941-1947 F,FL
• M35T 1948 Harley E,EL, 1948 F,FL
• M35TP 1948 Harley E,EL, 1948 F,FL

Not certain what the differences are, as I can't yet find any specs.
I would assume that using the incorrect year model is a loss of a point ?

[c.o.]

Bob,

If you're looking for points, then the M35 would be the magic carb. I hadn't thought of the M74B with a 61 inch engine. That Robbie fella is a very handy guy to have around!

[NiteOwl]

Grin. He is indeed !

I am having a ball, learning something every day !

[T. Cotten]

Folks,

Please note that the M-25 for 1940 E and EL models used a 1 5/16" venturi.

My experience with the larger M74 series upon 61" machines was always delightful.

My M74 (no B) on my standard bore '37 got better fuel (and oil) mileage pulling a hack on the interstate to D-port and back than My '65 Police Special with the same hack.

A 68" '39 I built for a customer jumped like the proverbial scalded dog with an M74B, but installing an M35 for a new owner noticeably tamed its advantage on the highway.

The DLX/L&L design is wonderfully adjustable for a wide range of motors, when all other things are in order.

....Cotten

[c.o.]

That's some interesting findings Cotten. I'm gonna tuck that info away for a day when I may have a 61 inch machine at my disposal!

[upsrod]

Here is one to watch.
http://www.ebay.com/itm/VINTAGE-HARL...sories&vxp=mtr

[Robert Luland]

Or you can buy this M35 from me for $500.00. Rebuilt 2/11/10. Real cad plating and all disk screws, lock washers and bowl locating pins are stainless steel. It will be at Oley. If ya want the extra kick just install one of Wildenes's sleeper kits which basicly makes it a M74B internaly. Bob L

[NiteOwl]

Thank you all for comments and suggestions, this gives me the needed information I was looking for.

[T. Cotten]

Bob!

I'm not going to critique the carb,
but please put the top of the LS liftlever spring in place so I can stop gritting my teeth.

....Cotten