Board index Flathead Power-Technical Questions, Answers, and Suggestions Indians back to the old carb topic

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Post Mon Feb 19, 2007 6:25 am

Posts: 3158
Location: Central Illinois, USA
Just for clarity:

The only Indian nozzels with only four holes were used in the tiny 741 and 841. Sport Scouts always had five, even when they used Scheblers. Going smaller will compromise accelleration, as the nozzel acts like a "pump".

"English brass" (high ferrous content?) floats are made in India, and weigh three times as much as original cork or "Armstrong" issues.
"Good" brass floats for Linkerts are more than "rare": it is impossible to construct one of original buoyancy from brass and solder.

I wish someone would tell me (for certain) what the tit on the idle bleed plug was for.


Post Mon Feb 19, 2007 10:50 am

I'm not sure which Indian nozzle would be best for a stroked motor. They all had more effort put into their development than the generic -33 H-D side-valve nozzle used on all 1-1/4" carbs regardless of engine size or tune.
What nozzles do you have as donors?
57" is about the size where a 4-bolt will actually add power even though it can't bolt up and the transition from the throttle disc to the Scout manifold must be gradual. If I were doing this I'd try an M53 M61B.

Post Thu Feb 22, 2007 3:36 am

Posts: 202
Location: Middle England UK
By 4 hole nozzle I meant the one in the M21.I think the bonneville 74" used 1-16th venturi so the M21 in good condition will get the bike up off it's knees and running and he can take it from there.As it's Steve's first Linkert he's not got a bag of nozzles to choose from.He can always enlarge holes if needed.

From your pics I'm even more sure that body is gun metal not alloy as stated by seller.What is it?

Post Thu Feb 22, 2007 6:45 am

Posts: 3158
Location: Central Illinois, USA
Bonne venturies were 1 1/8"

Standard Indian nozzels average a #36 bore, and it is stepped; Bonne's average a #28 bore; just drilling out the side holes will not always approximate an original. Nor is the volume of void outside of the holes the same, which is the charge of emulsion ejected upon rapid accelleration.

The entire catalog of Indian nozzels in under production by Fickau Prototypes, including those specific to only Sport Scouts.


Post Thu Mar 15, 2007 6:58 pm

Posts: 108
Location: San Diego
SIMPLE PERFORMANCE DESIGN EQUATIONS: (from Harry Ricardo as published in “How to Build Hot Rods and Race Them” by John Christy, pages 130-135)

Intake Airflow speed criteria: Ricardo found “good” volumetric efficiency at 130-160 fps, 140-150 fps best
(flow rates greater than 160 fps indicate a restriction to power at attempted rpm)

Sg = V x rpm
dxd x 4630

rpm = engine speed at peak performance;
Sg = speed of airflow in feet / sec;
V = volume of one cylinder in cc (assumes one cylinder drawing)[ci x 16.387=cc];
d = port diameter in inches;
4630 is a conversion factor for this combo of metric/US units

You can check port sizes, manifold sizes, and carb size for one or two cyls, RPMs, etc

According to "Motorcycle Engineering" by Phil Irving, pg 269, "...maximum torque is usually obtained at a nominal mean air velocity of 300 ft./sec. through the choke". (Irving elsewhere opines that flatty's torque peak is usually 3500 rpm)


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