Author Topic: Which head to modify?(Opinions) Late model Alloy heads. (Dual carby conversion)  (Read 1123 times)

Offline bikerboy

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Somewhere on this forum is a picture of one of my twin carb heads. Its the big valve version with the manifold machined off then drilled and tapped to take the carbs.

I used some distance pieces from another bike (I wont mention the name in case it upsets Dutch) and it works a treat. I have to say tho its no better than the A7 head I have. This had the blt on manifold and I amde a manifold to fit twin carbs. Ported it a little, not much at all, I did have the valves cut out to take standard A10 valves. Both of them are using twin 30mm concentrics and despite tickover being a little bit difficult to get right they run extremely well.

Fuel consumption is about the same but accelaration is definitely better than my single carb version.

Online muskrat

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G'day Sluggo.
I've never put the Cafe on a dyno but from seat of the pants a single carb gives a lot more torque so good around town and off the lights.
My twin carb head is a  '54 A7SS with the edge of the combustion chamber chamfered to match the A10 bore. Super Rocket valves, 357 cam, 10.5:1 pistons and two 30mm Kehins. Not much happens till about 4500rpm.
If converting a single carb head to twin port be carefull not to break through into the two rear rockerbox holes.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline bikerboy

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This is one of mine

Offline duTch

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Quote
...I used some distance pieces from another bike (I wont mention the name in case it upsets Dutch) ............

 I don't care that much  *fight*.......mine's not exactly pure either   *smile*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline bikerboy

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Dutch

But my distance pieces are from a Tri.... no I had better not  ;)

Offline Listerjag

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Thanks for link, we live in Dunedin New Zealand, we are 120 miles north of Burt Munro's home town :-)
Attached is the result from the flow bench testing, number 2 was the original head from the 650 Super Rocket which had be lightly modified, mainly just around the seats. One of the other heads was one of those "special performance twin carb heads" offered to American owners.
 Hope that helps.
 If you work out how much air a 650 motor can pump, they all can handle it no problem.

Offline Sluggo

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Thank you, thats some verifiable base line numbers that will be helpful.  I will have to dig out my engine books, but I have a number of formulas and figures and see how it compares.  But that is an excellent reference and I am sure will be appreciated by many.
thanks again!
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