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-   -   Ironhead Best Carb for an Ironhead? (

11B40 23rd July 2021 17:37

Naaaa....There were no heroin users in drag racing. Now US made pharmaceutical grade cross tops ? Oh Yeah. You'd drive to Guatemala if no one stopped you.

They were looking at a bunch of busted K model cases to send to HD for new Sportster cases.

Ferrous Head 23rd July 2021 23:05

Back to the carbs. (Though I'm sure this thread wasn't meant to be about them)
I don't think HD put a bad carb on any Ironhead. They all worked very well for their intended application at the time.
Even though Harley built down to a price their ignition systems, fuel systems and frame were all up to the task. It really was brakes and suspension that let them down.

Once you start modifying the engine, especially if you make it bigger, then you need to consider changing. That's why S&S got started. Drag racers needed something better.

It's a shame road racers didn't dominate the race scene in America as it did in the rest of the world. Then the Sporty might have grown wings on the street as well.

brucstoudt 23rd July 2021 23:11


Originally Posted by thefrenchowl (Post 5906551)

i've seen these pictures here before but i just noticed the 1960 XLCH style paint scheme on the ''turnip eater'' gas tank.this was said to be a 1957 motor. looking at the oil tank i would tend to agree.

Ferrous Head 23rd July 2021 23:38

I think a lot of people fail to understand the basics. This leads them into trying to put a bigger carb on a stock displacement engine.
If you use a carb that can flow much more than your engine requires performance will suffer. At lower rpms it will not have sufficient velocity in the port to work correctly.
And ther is a simple formula for calculating the required air flow.

"If we want to calculate the CFM (Cubic Feet per Minute) for a 4 cycle motor we can multiply the cubic inch displacement of the engine by the maximum rpm (Revolutions Per Minute) and divide the result by 3456. Then we multiply the results by the volumetric efficiency of the motor"

You'll note that the efficiency factor can be increased but it doesn't have that big an effect overall. So, unless you increase the displacement there's not much point in going bigger than the stock carb. And they work quite well.

If you run the numbers on a stock 900 engine you get to 100 CFM.

I can't remember what the big L's flow but the Super B's (from memory) run like 170 with a velocity stack.

So if you are looking at changing the carb on your Ironhead the first parameter you need is your required air flow. Find a carb that best meets that. Not too small, not too big.

Ferrous Head 23rd July 2021 23:52

i've seen these pictures here before but i just noticed the 1960 XLCH style paint scheme on the ''turnip eater'' gas tank.this was said to be a 1957 motor. looking at the oil tank i would tend to agree.

One of the problems with working out just what is what with race bikes is that it so often depends on a time frame. Race bikes evolve (generally) over time and different parts are substituted. You need dated pictures to know what your looking at if your trying to work out what was what.

I could be wrong but I know many of my engines in the past had to have case changes for one reason or another. Many of my race engines don't carry an engine number. Or have something like 57XL7777 stamped into them.

I used every new engine case I could lay my hands on. But they have pretty much dried up now. Aluminum fatigues with heat cycles and vibrations. So, the "newer" the better for engine expected to perform beyond the norm.

iNSaNeSHaNe 24th July 2021 03:16

I've gone back and forth with different carbs on my daily transpo stroker.
I had a round slide Micy an SU and a super B and now a CV and I tend to like it best.
AS for cases I have had the bossings come loose in 4 so far on this particular engine and blew out the back end twice.
It never ends when it comes to having fun ..

DR DICK 24th July 2021 03:33

respectably gentlemen there has been one no commenting that there are two different side bowl s&s carbs.

im not talking about throat size. im talking about fuel/air circuitry.

whats being shown here isnt an L series its an 'early'.
L and early are not the same.

the early departed from the dc linkert in ways very important to hi perf guys then.

and probly still.

that said the L (L for late) series reverted to something much closer to a enlarged copy of the dc linkert. actually that was better for 90% of street guys. it was less finicky then the early.
on this site is a post detailing the history sand cast s&s carbs. i wrote it.

the earlies didnt draw low speed fuel and more importantly air bleed thru the main well as the dc linkert did. but the L series DID. any one who need to go from zero to top speed will appreciate this seperation.

in the earlies this separation of circuits opened the door tuning for exotic fuels that didnt act like gasoline at all.

that was a selling point to what: maybe 100 guys.
to wit i havent seen 4 digit single letter carbs: prove me wrong.

the 3 letter L series addressed what the street guy needed.
thats why you see serials in the 2000's.

further more the L series main jet was in the float bowl area.
pull the bowl and change jet. easy peasy.

for earlies the main jet wasnt in the bowl like the linkert or the L.
it was in the main well.

that meant you needed to basically remove the carb to rejet.

you will see a 1" spacer s&s supplied as an accessory.
though many view this as a performance part, at the time it allowed access to the main well as it was moved outward past the mag cap.

lets get to fuel "main jet".
there is none.

bottom line anyone comparing an e carb (f or g) to an L series ----- you guys take it from here.

Ferrous Head 24th July 2021 04:15

I've never owned an "F" version of these things.

I'm not sure if there are internal things I should be aware of.

With Amals, there are gas and alcohol versions. You can't use the gas versions for alcohol as they have internal passages that simply aren't big enough.

With the Super B's, it easy. Just drill and tap the float bowl and run the alcohol needle/seat.

I am asking because I wanted to run either an MGAL or a GBL on my 58 Stroker engine.
But I have been toying with the idea of running it on Methanol instead of gas.

And parts for these are getting very thin on the ground. Not sure I can find inters to suit.

Not racing this engine. It's just for fun. But I often have spare Methanol which I just can't use in my lawnmower.

11B40 24th July 2021 06:52

It was an 17/8" GAL Mine had two things, the main jet which was inside with the float, 4 screws and the bowl comes off w/float and the main jet is sitting right there. Then there was an emulsion tube it had a long brass pipe extending down into the throat of the carb body. It came with a wire full of various main jets and several different emulsion tubes. As I mentioned before, when I first put it on the '66 900, it had a huge flat spot right off idle. I phoned George at his house and asked him if he could help. He asked for the serial number of the carb which I gave him. He told me to hold on while he checked something. He came back on and said that they had drilled the air bleed holes a bit too far back on the early carbs. He said to take the butterfly out and file a 45 degree cut at the top front of the butterfly and that would fix it. I thanked him and thought sure pal!! Anyway it took about 5 minutes to file that brass butterfly and put it back in. It literally ran perfectly after that, not a hint of flat spot, just smooth response. I was amazed. It basically opened up the air bleed hole a little earlier.

thefrenchowl 24th July 2021 12:12

Thanks DD for clarifying stuff,

But to be fair to your readers, and you said it yourself, the Early is so rare, nobody's ever seen it in the flesh, never mind dismantling it to check the inners.
The choke was an afterthought, but unlike on the DC, with no provision whatsoever for an air filter...

As I see it, the Early was purely a nitro carb with no need for all these compromises/trade off/ancillaries we call decent iddle and intermediate running!!!

One would open the throttle and it went bezerk, one would shut it and the engine would die!!!

So obviously, when the time came that fellas wanted that carb on their daily ride, it had to be "civilised" a lot, hence the L and later M variants...

As for moding a G to an F, it can be done, I started it on my XLRTT and we finished the job together with Richard...


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