Bomb Shell venturis

[kitabel]

The M-53 is 1-1/2" throttle disc, so is the M-35. The M-53 already has a booster (no other does except MR), any other 1-1/2" model will need to use the DaVinci or make one yourself.
I found a bike with those cylinders on line using 1-1/4" M5 Linkerts (no reason given).
IMHO a pair of stock 1-1/4" M-51 or M-88 (much cheaper, easier to find) will do well with the obvious jetting adjustments. Was any JD engine equipped with 1-1/4" carburetors? You want to look at their main nozzles. Other than the float bowl orientation, the major difference between the OHV M5, M55 and the sidevalve M-51 etc. is a very different emulsion pattern in the nozzle, Palmer has pictures. The hole pattern is more or less related to the engine's VE: an OHV has power 500 RPM higher than a flathead, neither appears similar to a modified JDH.
AFAIK there never was a factory bombsight for the 1-1/4". My FDB Sport Scout Bonneville had a shop-made booster in its Chief Linkert (David Sarafan has it now) but I never saw another one.

I can't make out how the rear cylinder works. Are the rear cylinder cams reversed, or?

[aumick10]

I think the ports are 1 1/4", but i would have to confirm that.
I am aware of the bike with the twin M5's on it. I emailed him to ask some questions, but no reply. I may have to ring them.
There are aftermarket bombsites available for 1 1/4" and 1 1/2" carbs.
Do you need an extended main nozzle to use a bombsite?
The cylinders are the same as std ones, but the inlet castings on the cylinders have been seperated and move around. Still use std valve train.

[T. Cotten]

Just for clarity, Mick,..

Both Scheber and Linkert used 'nominal' sizes for their models.

The M53 series is a nominal 1½" Model M. Nothing measures that, but it has the 4-bolt manifold flange, and a 1 9/16" casting bore. 1½" Model venturi bores vary from 1 1/8" to 1 5/16".

M51, M5, and many others are the nominal 1¼" Model M. It has the large three-bolt manifold, and a 1 3/8" casting bore, accepting venturis with bores from 7/8" to 1 1/8". Once again you can hog one out as you please.

The 1" models had the small 3-screw manifold flange with a 1 13/16" casting bore, with venturis anywhere from 3/4" to 13/16" at least.

So its all about your inlet flanges for the cylinders. You can fudge and swap venturies widely!

....Cotten

[aumick10]

Thanks Tom, i have 3 bolt manifolds so that is one constraint i have with carby selection.
My concern is if i have to use a small venturi to maintain low speed response, i may impact the high speed air flow capacity.
I have Kitabel's "The Linkert Book", so looks like more homework yet,

[HDSmitty]

I just love "listening" to you so very knowledgeable gentlemen. So much to learn....so little time. Thank you all. Smitty

[T. Cotten]

Thanks Tom, i have 3 bolt manifolds so that is one constraint i have with carby selection.
My concern is if i have to use a small venturi to maintain low speed response, i may impact the high speed air flow capacity.
I have Kitabel's "The Linkert Book", so looks like more homework yet,

I've got it too, Mick!

(Although a very early edition..)

Its always a trade off:
With modern highways, big venturies help. With a sidehack (or a portly payload), you will want to be more conservative.

Your carbs don't really have to match as long as the venturies do. Synchronizing two carbs seems like the real trick!

...Cotten

[kitabel]

I can't remember: does the M-53 use the same nozzle as the M-53A? The big differences (engine size and booster vs. plain) argue for different.
Harley had a strong historic tendency to repeat the same component as many times as possible (accountants beat engineers every time) despite application differences, where Indian would employ a different nozzle for a change in "tune" (Bonneville vs. std.) as well as engine size.
H-D used the same main nozzle (27331-33) in every 1" and 1-1/4" carburetor for every 1933-58 flathead engine despite engine sizes of 45", 74" and 79", different compression ratios, intake port sizes, and a wide range of venturi sizes. I presume that it was a compromise for power, response and mileage in most of these.

[kitabel]

I saw some really "iffy" linkage on that running JDH.
If the carburetor bodies are not very close to parallel (not always possible) synchronizing the linkage will be a headache. Using the longest practical levers at the throttle shaft helps, because the disc rotation per inch of throttle pull is small. The cable should only attach after the merging of individual linkages.
I would prefer all mechanical (rod and heim) to cable, having many gray hair from my Bonneville, etc. where the angles and lengths seem especially prone to lose their adjustment.
I try to visualize linkage seen from above as a clock face with the throttle shaft as the center, and the take-off points as hours, using the same number on both and the same angle for their levers.
I have some thoughts on linkage on my site here: http://victorylibrary.com/mopar/log-2.htm

[aumick10]

I am with you on the geometry of linkages. Been there, etc.
I have balanced hundreds of carbies over the years, especially Bonnie's. When i was restoring air cooled Porsche's, i used a "snail" to balance those old P11 Solex carbs, usually after boring out the groves from the butterfly's. I have just put a second carby on my 4 valve Evo. There was no room for linkages, so i had to make twin cables.
There is plenty of room to get to cable adjusters on a JD, so i will probably make up a cable for this bike as well.

[T. Cotten]

I can't remember: does the M-53 use the same nozzle as the M-53A? The big differences (engine size and booster vs. plain) argue for different.....

I can't remember either, Kitabel!

Even though I took pics. The first shows an M53, quite worn at the spigot, compared to a common M74B on the right.
Last is a comparison of the M4 to an M53. (Sorry I forqot who to credit...)

HD wasn't afraid to ask L&L to make something new; For example, the M74 nozzle was different from the M74B, but found no where in my literature. That was just a couple of years prior to the M53 series.

Who's hoarding the K and Sport literature?

....Cotten

[ryan]

I have a M53 non bomb site, that is on the shelf, if anyone needs any information from it. Not sure how to help, but I will sure try.

[T. Cotten]

I have a M53 non bomb site, that is on the shelf, if anyone needs any information from it. Not sure how to help, but I will sure try.

Take it apart and explain the 'drool pit', and you will be declared a genius, and the angels will descend, Ryan!

Thanks in advance, but beware ever volunteering for anything...

....Cotten

[aumick10]

Does the drool pit have a hole going into the bowl?

[T. Cotten]

Does the drool pit have a hole going into the bowl?

At the very lowest apex of the endmill cut, Mick,...

Is a tiny hole to to the bowl headspace (or "head"), which is vented through a hole in the casting to atmosphere.

What on Earth were they thinking?

All History must be forensically resurrected, once it has been lost.

.....Cotten

[aumick10]

I assume the venturi comes to where your black marks are.
If it has an internally vented bowl, i could see it leaning out a slightly rich mixture, just of idle. I don't think it would be very effective though.
If it is an externally vented bowl, i don't see any use for it at all, as it would be sucking a lot of air from around the venturi.

My best guess.