carb for 57" strokert

[fillibuster]

A 57" stroker (chief wheels) is in my shop. Belonged to a deceased good friend; now his son owns it, and he is worthy and as dedicated to its preservation as one could expect from a young, gainfully employed parent of two kids. I have "adopted" the bike's maintenance chore that got extended somewhat, and the low-budget hot rod had many loose nuts and bolts, poor on brake works, shot wheel bearings, loose neck bearings, and the carb screws were loose (which explained the full choke starting). I started it yesterday, ballsy bark and cackle!

But I've never in the 24 years I've been acquainted with this machine been proud of its carburetor. I don't think the "M-BONN" with 1 1/8" venturi and bored out lower 2 holes in the main nozzle has been the right "recipe" for this engine, even considering that it has aggressive cams (valve durations overlap). I'm not sure what it ran besides that Bonn carb, but I think it's too difficult to tune, especially for more conservative riding. ... I don't expect "sonny" to hot-dog it until we rebuild the lower end and a few other areas. So, I expect to replace the bonn with either a scout M-41 linker, or a chief 344 with (?) probably a 1 1/16" venturi, perhaps 1", ...... heck! I don't know!

I know this: I wish to consult an expert, or one who has experience with which to advise me.
Anyone out there that can steer me into the right direction?
Gonna check virtual library first, but I'd like to see discussion here, too.

[T. Cotten]

Filibuster!

A Bonne nozzle has all holes the same size.
Larger holes at the bottom sounds like a standard nozzle.

My approach is to return everything to spec before I condemn it, and that doesn't happen often.

I start at the manifold; Have you bubble-tested?

....Cotten

[fillibuster]

Filibuster!

A Bonne nozzle has all holes the same size.
Larger holes at the bottom sounds like a standard nozzle.

My approach is to return everything to spec before I condemn it, and that doesn't happen often.

I start at the manifold; Have you bubble-tested?

....Cotten

Hi Tom, I was hoping you would answer.
I've not made the plate with air attachment for the manifold. I've use the butane bottle on my chief in the past, but haven't got the stroker sustained running long enough to try that. Perhaps my prejudice against the Bonn is short-changing my results, but I feel it's out of proportion to expect its venturi to draft a proper mix with less volume (57" vs 74") than a chief. We're not putting it on the race track. ..... But I'll be "bubbling" on Monday, scout's honor, okay?

Are you saying the Bonn main nozzle has all holes of the small diameter that you would see on the upper end of the std nozzle? That would allow only a leaner mix than std, then, wouldn't it? I have a few of those nozzles, and I have a few 1 1/16" venturi's.

What was spec'd for the stroker scout, and on what basis were these things "engineered", IF ANY?

Back when I was in the army I tried a 74" carb on my hd-45, ran like crap til I turned the pwr needle all the way in. Back to the stock carb for the cure.

Last question for this post: got a "linkers-for-dummies" book? Something that might teach me a little rule-of-thumb?

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I did look through an older "subject index" compiled by Doug Strange, and carburetors are discussed in several of our mags from earlier years, '85 and prior, before I was a member. ....virtual library doesn't have them yet, do they?

[T. Cotten]

Filibuster!

A standard nozzle is second from the right, and a Bonne is on the far right.
nozzls.jpg
I doubt anything was "spec'd"" for a "stroker scout", although a Bonne kit would be first choice of course.

The size of the venturi only determines the RPM range where the machine is most comfortable.
A poor choice, if there is such a thing, should still not prevent tuning.

.....Cotten

[fillibuster]

Filibuster!

A standard nozzle is second from the right, and a Bonne is on the far right.
[ATTACH=CONFIG]13636[/ATTACH]
I doubt anything was "spec'd"" for a "stroker scout", although a Bonne kit would be first choice of course.

The size of the venturi only determines the RPM range where the machine is most comfortable.
A poor choice, if there is such a thing, should still not prevent tuning.

.....Cotten

thx Tom!
Interesting. How about the far left, what are they?
and yes, the Bonn I have has a std chief nozzle. So what characteristics would be at play here?
geez, that sounds like a can of worms

[T. Cotten]

Filibuster!

The three on the left are various Milwaukee OHV models.

....Cotten
PS: Does it still have the unique 1" venturi?
Undoubtedly you will choose larger.

[fillibuster]

Filibuster!

The three on the left are various Milwaukee OHV models.

....Cotten
PS: Does it still have the unique 1" venturi?
Undoubtedly you will choose larger.

No, the venturi in the Bonne is 1 1/8".
I had believed that this was out of proportion, going from Scout's std for 45" being 15/16" venturi, Chief's 74" std 1 1/16", and that 57" would be 1" (if you do the math it isn't far from that). The bike will be on the street ridden conservatively 95% of its running time. There just ain't enough Harleys to give it competition for the other 5%!! ... otherwise, yeah, it needs the Bonne cams and carb once in a blue harley moon, ya know!
Sunday it smoothed out and ran strong at power, and idled fairly well too. Patience!

[T. Cotten]

Filibuster!

Sorry about the1" venturi question, but I had too many browser tabs for different forums open at a time!

As far as the 'proportion' of venturi diameter to displacement, it has other variables: how heavy is the payload, how much of its time does it spend at highway speeds, etc.
For example, Milwaukie used 7/8" for their heavy Servicars, but 1 1/16" for their civilian solos, even though both were the same displacement.

Bigger is often better for today's traffic conditions, unless you are unusually large payload....

.....Cotten