Ironhead twin carbs on a iron head

[chevelle]

Carb size depends what you are looking for.
When calculating throat size on my 77 CI XR, for all out HP throat size was something like 52mm per cyl.
Seems outrageous, but individual runner engines require more carb.
I'm not looking for topend power, I don't rev over 6000, I have run dual 40mm cv's and 38mm mikunis.
I don't recommend the cv's for individual runner applications.
Although they work fine after 2000 rpm, I found the vacuum slides did not work well at lower rpm's.


There's more details below.
Here's a link to my Sputhe XR:
http://xlforum.net/vbportal/forums/s....php?t=1151857

Dyno thread:
http://xlforum.net/vbportal/forums/s....php?t=1194750

[brucstoudt]

ferrous head,does that sidehack racer have a,reverser? [im looking at the clutch release area on the cam cover]

[thefrenchowl]

Cut down engine, it's got an AMC/Norton/Matchless/AJS gearbox...

[Ferrous Head]

He's running a non unit construction gearbox. Yup, heard me right. Bruce cut off the gearbox section of the engine, welded it up and added a TT Industries gearbox. It gives him the option of running 5 or 6 speed gearboxes plus those gearboxes will handle over 160HP with no problems whatsoever. Of course for $6,000 you want a pretty good gearbox.

The new Amals inlcude a MK2 Smoothbore version ()What Bruce is running) and they do an alcohol conversion. Sizing carbs isn't that hard, it's actually understanding (or admitting to) the kind of use your engine REALLY sees. If your going to run it on the street about the worst thing you can do is over-carburate. Makes the bike hard to start and hard to ride. Not what your after on the street. I have 2 different carbs for my Ducati, a 36 and a 38mm Amal. The 36 is for the shorter twisty tracks and the 38 is for places like Phillip Island or Eastern Creek with very long fast sections. But if I was riding it on the street it would go down to 32mm.

[RGT]

stock xr runs 36mm, for a hot setup I would think some flat side mikuni 38's, though I hate the way they look(I have one on my other bike)

[Ferrous Head]

Here's a quick way to do it. Just add cash.

http://www.ebay.com/itm/Harley-Panst...a83373&vxp=mtr

[waza]

Have you considered Del Ortos, as run on the older bevel Drive Ducati? They are available (new) in 32 to 40mm at bevelheaven. Mine (shown) were 32's that I bored to 36.5mm. What's nice is they run an accelerator pump and come in R & L versions

[waiteitei]

have ordered 2 36mm mikunis

thanks for the wealth of infromation

[ryder rick]

Originally Posted by brucstoudt

before the thing will even run,you need to change the cam timing,on the rear cylinder,because the intake and exhaust valve locations ,are now reversed. its not a,simple swap.normally 2,front heads are used.

A rear cylinder head reversed on the front puts the valves in the same order.
The rocker box can easily be turned around so the pushrods stay on the right side.
One carb on each side, right side facing forward, left side facing back.

[waza]

Originally Posted by ryder rick

A rear cylinder head reversed on the front puts the valves in the same order.
The rocker box can easily be turned around so the pushrods stay on the right side.
One carb on each side, right side facing forward, left side facing back.

good to know, anyone have any pictures of this set up?