32mm Amals/750 vs. 850 Commando

JRC Engineering shows two different 32mm Amals on their website (one for the 750 Commando Combat and one for the 850 Commando). I'm told that the 850 version has a "spray tube." What is the advantage of the spray tube? I'm building a 1972 Combat (albeit with a decompression spacer and a .330" non-Combat cam). Which 32mm carb would make sense? Thanks, in advance, for your help.

Spray tube is unique to the 828. Use the 750 carbs, last time I mentioned fitting the standard cam to my Crazy combat there was dissention amongst the ranks ,so be forewarned.

I would have thought it is sensible to fit a milder cam to a combat for road use. It is not something I would do, however my road bikes usually ended up on a race circuit. When I had 650 Triumphs years ago I was always into hot-up. I gave up riding on public roads when I was 29 and went racing so I could survive and keep my licence. My idea of the perfect road bike is the BMW boxers, or the smaller Honda Gold Wing. I think commandos are unrealistic as road transport, however I love them.

All Amals we use have spray tubes that stick up in flow from the float bowl.
850's for some reason have their spray tubes notched or slotted to giver more easier quicker fuel flow spilling into air stream. Some like me do this to some degree on Combats get a bit more kix from lower throttle/rpm snap open response. Sure did not hurt when I tried it but might just stick in 850 correct version and be done with it or leave as if not broken.

Combats run fine as-is. I see no reason to detune it. I've run regular gas in a pinch and no pinging.

hobot said:

All Amals we use have spray tubes that stick up in flow from the float bowl..

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Isn't this to distinguish them from the 2 stroke versions of Amals.
Or rather, required for 4 stroke use, which sip fuel much more gently in the midrange....

The 750 ones are probably jetted slightly differently - to suit 750cc use ?

Combat run the best of any factory Commando, as easy to kick and idle and creep around on loose slopes on in wet stop and go traffic, just they have no saftety pop off valve to stop running up into destructive rpm in lower gears the pull is so good and more easy to get speeding tickets or enter turns faster than iso's can handle. Tend to be lighter and less- easier fork rake to fling around too.

Something about the 850's didn't suck fuel up as easy as 750's so most if not all had 2smoke type cut out spray tubes.

Remember that the later 850s with the 'cut' spray tube (just look down the carb with the top removed) will use the needle marked with 4 rings.
The 'flat top' spray tubes use the more common 2 ring needle.

I would think that with today's low octane street fuels, using either properly matched/jetted carb set would give equal performance.

Do yourself a favour and fit the JS flat slides. Much superior to Amals IMHO..

I ended up with a set of the 850 carbs for my late 72 non-combat 750. I went back to 220 main jets and switched the slides to #3 from the #3.5. It was running too lean at low throttle openings, seems okay with 220 at WOT. They have the stepped spray tubes and that doesn't seem to cause any problems.

acotrel said:

I would have thought it is sensible to fit a milder cam to a combat for road use. It is not something I would do, however my road bikes usually ended up on a race circuit. When I had 650 Triumphs years ago I was always into hot-up. I gave up riding on public roads when I was 29 and went racing so I could survive and keep my licence. My idea of the perfect road bike is the BMW boxers, or the smaller Honda Gold Wing. I think commandos are unrealistic as road transport, however I love them.

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Dude.....!
Buy a Combat Commando! ... Road bike ... really!... totally with in your means.... Roadster tank... Combat cam/10 to 1 compression... off the shelf..."C " stamped on the head. as it was in 1972 and then report back... New Amals ... new everything.... stock out of the box!. Please report back after you have done that much!
Then I will listen to your Methanol advances in racing.....
Cheers
CNN

Combats have Cream of the Crop engines to me too and work fine as any vintage race bike to creep slow in pits lanes or city parking lots idling and low throttle lugging with sooothing pitter patts of exht note, just have to restrain holding on to WOT for tickets and over reving as its so eager to do. My current factory Combat has #3 slides, 240 jets, needle in mid groove and v notched spray tubes, foe 1st "step" on starts, slow even idle and response to kick out rear on looser stuff to help steer and a few times in special places laid way over giv'er a throttle up to breaks loose as desired. Decent Combats should lift front toward the end of power band before shifts and can feel like slipping clutch noise and pull hesitiation it not feathering throttle on snick to 2nd. Alan there is also the uncanny disappearing act of a Commando just when the going gets good too. There is essentially no difference among Commando in normal operation but the 850 have more immediate pull sense to throttle snaps but then tapper off too soon while 750's tend to pull stronger longer even non Combats. Most reports of just putting standard cam in Combat w/o lowering its CR report detonation. I now don't think twice about putting in 87 octane in my Combats but to refrain from lugging hard in hi heat, as that's bad for any engine but no detectable ping dings.

acotrel said:

I would have thought it is sensible to fit a milder cam to a combat for road use. It is not something I would do, however my road bikes usually ended up on a race circuit. When I had 650 Triumphs years ago I was always into hot-up. I gave up riding on public roads when I was 29 and went racing so I could survive and keep my licence. My idea of the perfect road bike is the BMW boxers, or the smaller Honda Gold Wing. I think commandos are unrealistic as road transport, however I love them.

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Find a Laverda Jota, nothing better

Youre probably better to buy a 350 Matchless / A.J.S. & leave the Combat to the Real Men . :x

Serially ; Valve gear set up , decent spings , and somewhat more sophisticated carburation ( Mk II Amals , obviously :lol: 8) )
and if you dont ride much in town , the cars wont be to much of an obstical . though a decent brake'd counter that .

Obviously needs the ignition to work , too .

then all you need is a silk scarf , & a big grin .