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3-Bolt 1 1/4" Linkert Carbs

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dalaymond

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Post Thu Jun 23, 2011 7:53 am

3-Bolt 1 1/4" Linkert Carbs

Since a 3-Bolt 1 1/4" Linkert Carb was also used on '36-'39 Knucklehead's, Big Twin Flathead's, Indian Chief's and Bonneville's, and Crocker's, wouldn't one still be a good choice for a carb for a 45" Flathead hotrod project or stroker project ?
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RUBONE

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Post Thu Jun 23, 2011 4:58 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

Didn't you answer your own question? :mrgreen:
Robbie
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dalaymond

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Post Mon Jun 27, 2011 8:35 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Hopefully, I have answered my on question, since no one offered any sort of discussion. :)

I've used an aftermarket adjustable main jet, 1 1/8" venturi, and nozzle, all intended for an Indian Bonneville Chief.

Hopefully, this will improve the performance of my M88 at least a little.

Thanks.
Last edited by dalaymond on Tue Jun 28, 2011 8:05 am, edited 1 time in total.
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Mr. Big

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Post Mon Jun 27, 2011 3:43 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

New here but always up for a Linkert discussion. The M88's bowl is internally vented which is why the OEM venturi has a notch at the bottom leading edge. I've never seen an 1-1/8" venturi that is notched. I believe all the other 3 bolt Linkerts (HD models) are externally vented so that venturi would work for them. Might could notch it to make it work but others here would know better about that mod.
Last edited by Mr. Big on Mon Jun 27, 2011 5:07 pm, edited 1 time in total.
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Kurt

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Post Mon Jun 27, 2011 4:48 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

Dal,

Make sure you plug the jet hole on your M88 if you're using an adjustable needle.

Kurt
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Cotten

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Post Mon Jun 27, 2011 7:02 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

Mr. Big wrote:New here but always up for a Linkert discussion. The M88's bowl is internally vented which is why the OEM venturi has a notch at the bottom leading edge. I've never seen an 1-1/8" venturi that is notched. I believe all the other 3 bolt Linkerts (HD models) are externally vented so that venturi would work for them. Might could notch it to make it work but others here would know better about that mod.

Mr. Big!

As Dal posted, the "notched"1 1/8" venturi was spec for all Indian Bonneville models.

Off-topic, but one enigma about the Indian Bonneville models is that the carb bodies and carb venturies were listed in the 1940 parts listings, however no such Scheblers have surfaced in the "fossil record".
Linkerts, with proper Bonne specs, are commonly accepted to first appear upon Indians for the '41 production year.

Dal!

It is anybody's guess as to how the Indian Bonne nozzle will perform.
It varys only from the "performance" H-D M75 nozzle (not shown in Palmer's) by a larger center bore, and less charge volume for accelleration.

These things are extremely forgiving (otherwise I would be pushing a broom), the variables are infinite, and without a dyno with an unusually gifted operator, the results damn subjective.

My only extreme experience with incorrect nozzles was when a Chief would quickly overheat at highway speeds with an M51 (1/16"), whereas bolting on an M344 (1/16") cured it, with no other variables changed.

The major difference between the two models would be the nozzles; The standard (non-Bonne) Chief's has a large hole at the bottom, then a slightly smaller, then three small holes. The H-D Flatty nozzle has only four holes, all small. (Curiously, it is also used in the tiny Indian 741.)

Since both Models 51 and 344 were designed for 74" Flatties, one must assume that there is truly enough other differences in the motors to require radically different metering at the nozzle.

So Dal, my question would be:
Just how radical is your motor? More radical than a ULH?

...Cotten
Side note:
One other difference between Indian and H-D models was the "titted" idle bleed well cap.
My best guess is that it was perhaps just a "bubblebuster", but plumes of soot upon it suggest it affects flow and mixing in other ways.
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Mr. Big

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Post Mon Jun 27, 2011 8:00 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

Dang, I need to change my granny glasses. All I saw was M88 and missed the Bonne reference for the venturi. I know enough about HD Linkerts to be dangerous and less than zero about Injun Linkerts.....

Interesting note about the M51 and the M344. Wouldn't the larger air bleeds on the bottom of the 344 nozzle create a leaner top end and thus more heat? Or am I assbackwards.......????
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dalaymond

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Post Tue Jun 28, 2011 7:10 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Mr. Big wrote:New here but always up for a Linkert discussion. The M88's bowl is internally vented which is why the OEM venturi has a notch at the bottom leading edge. I've never seen an 1-1/8" venturi that is notched. I believe all the other 3 bolt Linkerts (HD models) are externally vented so that venturi would work for them. Might could notch it to make it work but others here would know better about that mod.


Thanks, Mr. Big. It already has a notch in it, as it is intended for an Indian.
Last edited by dalaymond on Tue Jun 28, 2011 7:12 am, edited 1 time in total.
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dalaymond

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Post Tue Jun 28, 2011 7:12 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Kurt wrote:Dal,

Make sure you plug the jet hole on your M88 if you're using an adjustable needle.

Kurt


Thanks, Kurt. I have it plugged off.
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dalaymond

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Post Tue Jun 28, 2011 7:28 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Thanks, Cotten.

Right now, my 45 is built basically to a 1939 WLDR spec.

It has # 5 aluminum heads milled down to # 6 aluminum head specs, a BTFH intake manifold and nipples, modified M88 carb with stock style air breather, KNS intake cams, stock exhaust pipes (with the short turned out WR exhaust pipe tip) . It also has K-Model intake valves and the porting has been smoothed up a bit. Also, I running a 34-tooth engine sproket.

If I can't tell any difference in the power, then I'm going to stroke it to the Indian Chief stroke spec offered by T&O, which basically stokes the 45 to 52.5 inches.
Last edited by dalaymond on Wed Jun 29, 2011 7:07 am, edited 3 times in total.
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dalaymond

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Post Tue Jun 28, 2011 7:47 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Cotten wrote:My only extreme experience with incorrect nozzles was when a Chief would quickly overheat at highway speeds with an M51 (1/16"), whereas bolting on an M344 (1/16") cured it, with no other variables changed.
The major difference between the two models would be the nozzles; The standard (non-Bonne) Chief's has a large hole at the bottom, then a slightly smaller, then three small holes. The H-D Flatty nozzle has only four holes, all small. (Curiously, it is also used in the tiny Indian 741.)
Since both Models 51 and 344 were designed for 74" Flatties, one must assume that there is truly enough other differences in the motors to require radically different metering at the nozzle.


Cotten,

Just curious, would the fact that one carb was internally vented and the other externally vented, would that have made any difference?
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Mr. Big

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Post Tue Jun 28, 2011 9:10 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Yep, swing and a miss on that venturi. But I'm curious as well about the difference between the bowl venting and why would Linkert go to the trouble to make them both ways....
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RUBONE

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Post Tue Jun 28, 2011 5:04 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

The M88 was internally vented to prevent debris from getting in the bowl vent (it was thought it would be used in a desert environment initially!). Why Indian used it I do not know but I suspect similar reasons, to control the quality of the air entering the vent. H-D being the cost conscious company they were likely opted for the cheapest option that works, and external vents were likely cheaper!
Cotten,
Would the speed of the intake air into the vent change the pressure in the bowl at any given time?
Just my thoughts
Robbie
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Cotten

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Post Tue Jun 28, 2011 5:49 pm

Re: 3-Bolt 1 1/4" Linkert Carbs

Folks,

Let's not confuse the nozzle vent with the bowl vent!

Schebler introduced the internal nozzle vent with the early DLX models.
They retained the design through '40 for Indian models, the last of their motorcycle production.

Side nozzle vents didn't appear until H-D switched to Linkerts, and returned to internal vents apparently only because of military specifications.
Perhaps they thought the internal venting was hindered by the airflow over it, possibly causing a vacuum, but it seems unlikely.

The size of the sidevents varied only slightly, with the exception of the M35TP where it was severely restricted, and raised upon a casting boss.
H-D immediately returned to a wide open side vent.

Mr. Palmer declared that a carb outfitted with both a side vent and a throat vent will run lean throughout the range.
I have found no evidence of that, and I suspect it has to do with modern manifold sealing and testing techniques .
And the nozzle vent should have no effect on low-speed operation at all.

The vent will only pass as much air as the vacuum upon the nozzle demands, and an extra hole cannot add more.

Basically, the annullar groove around the venturies' circumference is a 'plenum' that supplies air uniformly to the very top of the nozzle body (below the spigot). Nonetheless, I believe the Military 741 manual cites indexing the nozzle's holes to the internal vent.
This is the only reference to indexing that I know, and it is only for good luck that I alway index side vent models to their vent. (With M74 and later, there there are four sides of the nozzle!)

Mr. Big asked: "Wouldn't the larger air bleeds on the bottom of the 344 nozzle create a leaner top end and thus more heat?"
Alas, but for lack of a glass carburetor, I can only conjure about what goes on in the nozzle well.
We know from the Armored School Handbook that the nozzle void is expelled upon rapid accelleration.
Schebler's diagrams show the void totally evacuated at high speed. Thus it is the total area of all holes in the nozzle that meter air into the flow of fuel up the bore.

So if we presume that slowing allows the void to refill from the bottom up, we must consider the situation where there is another burst of acceleration before the vacuum has subsided enough to allow the level to fill the entire void.
Or if intermediate speeds keep the level low in the void, we must consider the size of the holes to meter appropriately at various speeds. Of the dozen or so nozzels used in vintage motorcycles, the standard Indian nozzle is the only one where there are grossly different hole sizes. (Bombsite nozzles did add tiny ones at the top, otherwise all have symmetrical holes.)

Simple pieces of plumbing, aint they.

....Cotten
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dalaymond

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Post Wed Jun 29, 2011 7:08 am

Re: 3-Bolt 1 1/4" Linkert Carbs

Thanks, Cotten.

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