Ironhead Rebuilding and Tuning a S&S GBL carburetor

[rocketnorton]

my ol pan shovel
aka 1952 honda shadow

ran b and later, l on it

[Chuckthebeatertruck]

And, here's the HD spec sheet for boring out your own Linkert DC.




Note that the "bore" of the carb is only taken out to 1.5" with slightly larger inlet and outlet . . .then go back and think about the Bernoulli Principle.

Yet, even with a subtle opening up of the bore the performance increase noted in the magazine article is pretty hard to deny!

Imagine what happens at 1.75 with some hot cams to boot :-)

Hence why these carbs work so very well with stock to small size strokers. They are very flexible.

Note also the lengths of the exhausts given if on XLR pipes. Remember what I wrote about adding spacers or cones when the bike tells you -- what if you could also easily change the length of the exhuast?



TGIF

[thefrenchowl]

I like H-D race instructions!!! They let you believe it's all so easy!!!

Fitting the 9X disc (from the much bigger K/KH Linkert M53) means you have to bore the Linkert DC throttle body... Which sadly means boring through the intermediate chamber and use some kind of new screw shaped like this to restore the 4 intermediate holes...



Remoddeling the tapers away from the OEM casting as per above drg also allows one to make a reverse body to allow a twin carb application and end up with the float chambers on either side:



Patrick

[DR DICK]

Originally Posted by CHOPTOP37

i need to brussh up on gal info now that i have one...thanks

as you see im not on here to often anymore.


i did get your magneto message.


as far as L or early series follow along this thread.

--------------------------------------------------------

about a decade ago on this forum choptop and i had conversation. it was about two bikes.
both the same subject.
1) "i built a stroker"
2) "then i built a bigbore stroker".
his mechanical skills an insights are top of class.
the builds were solid. make no mistake i know what a solid build is.


he actually investigated my claims of how precise hd located crankcase features. my experience was h-d was real good making interchangeable parts. he was astonished that his tests matched my predictions. a bond was cemented.



but he had the classic issues,
my 74" is hard to start. it runs "ok" but not great.
my 89" starts ok but isnt what it should be compared to the 74". and the 74 kinda sucks.


we worked thru all that on keybords. (voice recognition was infantile back then).

anyhow between both of us we got those bikes to run.

we did it here on this forum.


i cant find those threads any more. to lose that wealth of info??? probly me - i just cant find it.
-------------------------


Anyhow where I'm going with all of this is that I told Chuck just to get an L series. Put that on your bike then you will realize how good a carburetor could be.

So he did he went out and bought an L series. bolted up and "what a piece of junk" .

thats what this thread speaks to.

pay attn:
1st you build. lots of things to coordinate. lots of ideas to intergrate. plans has come together. build is done. result is dismal.


when i was there: someone with more always seemed to see my struggles. wouldnt give me much more than hot spark on a cold day.


"how many sparks do you need you piss away"?
me standing. there right foot on popsicle, left foot on pavement------------------


moving on to practical stuff.
i feel this thread has some connection to our externally adjustable linkert float video. to shine a light on what happens intrinsically in the idle (kick start) rpm bad

[DR DICK]

Originally Posted by mrmom9r

The B's run better on the 1 7/8" manifold anyway.

The 1 7/8" carbs run better on a 2 1/4" manifold .

These comments assume you actually need more airflow.

this is correct.

using bigger mani on smaller carb is a real thing. h-d did it with the linkert.


anyone with enuff s&s expeirance figured this out by trial and error.


cbt: we discussed this at waseon couple seasons past.

[Ferrous Head]

Sorry, I might be confusing some people. (I'm old, what can I say ?)

For me there are two "types" of tuning.

One is "final tuning" (fine tuning ?). This is done to "dial" in the components you have selected to build your engine. This is the intersection between theory and the real world.
This is getting the A/F ratio to as close a flat line as possible. This is altering ignition timing and observing the differences. For some people this is "fiddling at the edges".

For me, this is almost always done on a dyno. Partly because these changes may not be felt by "seat of the pants" experiences. 98% of volumetric efficiency is great but I'm always shooting for 110%.

The other tuning is really design.

The first step in tuning is how you design your engine. If your serious about it you decide what the engine has to do before you take the first step. An engine built for drag racing is not suitable for LSR attempts or sand racing. Much as we would like one engine to do everything there are different conditions that change depending on requirements.

HD built stock engines that perform their stated goals. If you seriously modify the design all bets are off. If you change the physical dimensions o the engine it is in effect a new engine design.

It's possible to use strokes from 3.1" to 5 " (Maybe a tad more ?). You can actually build over square engines. Picking the stroke length is part of your tuning. Your "tuning" for particular characteristics of the engine.

To cut to the chase, if your building for maximum power you select components that met those goals. We've known how to establish the "correct" length and diameter of exhaust pipes for decades. (maybe 8 ?). It's just physics.

If you have established the rpm that you want to produce maximum power, and that's just one number, then you simply do the math. The same is true for the inlet tract.

If you pick the same pm number for both tracts the engine will make maximum power at the one rpm and that one rpm only. In effect your taking as much power from underneath the entire power curve and concentrating it at one point, one rpm.

That's what I attempt to do when building a race engine.

If I "tune" for 6000 rpm it doesn't matter to me that the engine does at 3000 rpm. It will run like a dog there. Well, comparatively like a dog. But my race engines spend most of their life above 4000 rpm.

Here's a caveat. Serious race engine aren't that good to ride on thee street. You really want a broader spread of power and most of it to be made at lower rpm's.

Sorry about the long rant, I'm old.

[Ferrous Head]

i cant find those threads any more. to lose that wealth of info??? probly me - i just cant find it.

Unfortunately, this often happens with us all.

What's needed is an author to pull ALL of this information together in one book. The stickies are OK but you often have to search trough many pages to find just the bit your looking for.

I've just had a ride shock, discovering I appear to have lost all of my paper documentation for the last 10 years in one fell swoop. I would cry but I'm just too old for that.

Clanahan (? spelling - I'm old) wrote one on Ironhead engines many years ago. Not perfect by any means but at least it was strictly Ironheads and it was aimed at making more power.

We really need a more up to date, more concise, more inclusive version of that book.

Then, when I lose my info I can recover a lot just by buying another copy.

[mct496]

20220813_001425 by Michael Tochterman, on Flickr

s&s intakes L to R 1 3\4 1 7\8 2 1\4

[mct496]

20220813_001927 by Michael Tochterman, on Flickr

20220813_001946 by Michael Tochterman, on Flickr

20220813_002001 by Michael Tochterman, on Flickr

20220813_002024 by Michael Tochterman, on Flickr

mgl base drilled to fit the bowl vent of a super B

20220813_002424 by Michael Tochterman, on Flickr

20220813_002450 by Michael Tochterman, on Flickr

[thefrenchowl]

Thanks Michael for these shots...

I still wonder what the gas flow thinks on the 2" 1/4 on accelerating so quick/fast in the manifold from big carb bore to more or less std port diameter!!!

I'm certainly not a big bore or race expert, but looking at XR750 manifolds tells me the Sportster inlet tracks would benefit from longer length and smaller carbs.

Probably why the DC Linkert, the smallest of them all, has my vote as the best Sportster street carburettor...

Patrick