Ironhead Backfire

[01rk]

I may have it fixed. I removed the Mikuni adapter, made a new gasket, stoned the mating surface of the S&S manifold, and put a very thin coat of gasket sealer on the mating surfaces, and bolted it up. The first run was way to rich lots of exhaust smoke with the needle clip down 2 notches, had to move it back one. adjusted the air mixture needle to 1 turn out and it runs good no popping back. Must have been an air leak, something I had not thought of. Thanks to Doc308 for the suggestion.

[sungod]

Originally Posted by 01rk

I may have it fixed. I removed the Mikuni adapter, made a new gasket, stoned the mating surface of the S&S manifold, and put a very thin coat of gasket sealer on the mating surfaces, and bolted it up. The first run was way to rich lots of exhaust smoke with the needle clip down 2 notches, had to move it back one. adjusted the air mixture needle to 1 turn out and it runs good no popping back. Must have been an air leak, something I had not thought of. Thanks to Doc308 for the suggestion.

When you get some miles on it let us know if the mileage goes up. PS make sure you add the support bar from the air cleaner to the tappet bolt. Good luck!
+1 Doc308

[Doc308]

Originally Posted by 01rk

I may have it fixed. I removed the Mikuni adapter, made a new gasket, stoned the mating surface of the S&S manifold, and put a very thin coat of gasket sealer on the mating surfaces, and bolted it up. The first run was way to rich lots of exhaust smoke with the needle clip down 2 notches, had to move it back one. adjusted the air mixture needle to 1 turn out and it runs good no popping back. Must have been an air leak, something I had not thought of. Thanks to Doc308 for the suggestion.

My pleasure, friend! So glad that this worked out for you. Check your plugs over the course of the next few rides to tweak the adjustments to perfection.

[73HEAD]

has the b got an air bleed ? if so where is it


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[sungod]

Originally Posted by 73HEAD

has the b got an air bleed ? if so where is it

That hole on the right side.

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[kitabel]

I haven't done this, but (if there's enough thickness at this point) you can thread the existing air correction hole and insert a carburetor jet to make it adjustable.
The common Holley 122-XX jet is ¼-32 NS.
The S&S 72-XX jet is 5∕16-24 NF.
Some Rochesters including Model B are ¼-28 NF.
In addition, Bill Jenkins suggested use of very fine wire draped through a jet (and looped around a screw &c. for retention) as a miniature metering rod.

[Ferrous Head]

73Head
Has the b got an air bleed ? If so where is it

You can see the air bleed in this pic. It's right next to the "B".




I drill and tap them to take an S&S main jet. If you want to correct the A/F transition from inter to main this is how you do it.

Others have suggested just drilling the hole larger or soldering it closed and then drilling. That's tedious to say the least.


.

[ryder rick]

The VM38 comes in many configurations. It has to have the right internal parts to work on your Ironhead.

For a sportster the correct designation is a VM38-9. The -9 has "branch's" jetting and slide.

[kitabel]

From the little he posted, he has some of the right VM38 parts, and won't tell any more.
the 6DP1 needle is almost the only choice.

The VM38-9's jetting is not always best, for example; :
1, restrictive exhaust system
2. anti-reversion
3. very hot cam
4. stroker (this is the expensive one: new slide, since 2.5 may be too rich due to higher vacuum, needs a 3.0)
You can also make intermediate needle clip positions (normally 5 notches, 1mm or .039" apart) to permit finer adjustments without removing the carb. A .020" thick × .250" OD washer may be installed below the clip and seated in the slide tower, moving the needle up (richer) by 1/2 step.
If the best needle position is either:
The top (full lean) notch, consider moving the needle jet size up 1 number, with the needle 1 notch lower, or
The bottom (full rich) notch, consider moving the needle jet size down 1 number, with the needle 1 notch higher

[sungod]

A 3.0 slide cost is about $30.