Question about carb setup '73 MK2 850

Tornado

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You mentioned moving to the stepped spray tubes? I think these are press fit into bodies with no standard way to change them out.
 

NIX

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Yes, Andover sells them separately, so they should be removable somehow.
 

NIX

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...you can use carbs with the flat top spray tubes and 2 ID needles on an 850 (long story) but it isn't the original 850 specification.
2 groove is standard '750' but that doesn't mean the 2 groove needle and flat top spray tube doesn't work on an 850 (again long story) and my 850 Mk3 works fine with that combination (932/300 & 301 carbs and '3' slides).
I like to hear the long stories, or maybe some interesting fragments of them.
 

L.A.B.

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I like to hear the long stories, or maybe some interesting fragments of them.

The reason for the stepped spay tube (and 4-ring needle) was to pass an acceleration test with mutes fitted.
You can read about it here:

I believe Bob Rowley has been a member of this forum for a while.
 
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NIX

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There aren't any to "check" on the standard carbs - they are built into the carb. That's one of the important improvements in premier carbs- removable pilot jets.
Hope in that case that they are all the same...
 

NIX

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Is this feature a severe restriction? Never saw it in any other filters of the old type.

2521772793.jpg
 

L.A.B.

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Is this feature a severe restriction?
I don't believe there's any evidence that it causes a restriction but it is supposed to reduce intake noise.

Although listed as "060902 Front Plate 750 Air Cleaner" it would appear that type of front plate was also fitted to some 850s.

 
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It was part of an initial attempt at noise reduction. Hard to see how it could have any negative effect on airflow when you consider that at WOT a stock 850 Commando engine needs less than 100 CFM to produce full power. I saw a calculation in one of the mags many years ago showing that the OEM Ham Can can provide several hundred CFM.
 
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Main jets usually don't matter much as long as they are slightly too rich. Needles and needle jets are much more important. The slide cutaway is usually 3mm on most bikes. It only affects the first one-third of the throttle opening. If the cutaway is greater than a number 3, you might need more choke on cold mornings.
If you get your needles and needle jets right for best performance, your carburation will probably be more weather dependent. So most guys probably run their motors slightly too rich. With petrol, if you move the clips on the needles one notch, that is a very big difference. It is probably the main reason that fuel injection systems give better performance.
 

NIX

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So far I cleaned the L301 (spare) and R300 (on the bike when I bought it) bodies and ground down the parts that could interfere, sanded the bowls and connecting surfaces of bodies and manifolds, put 260 mains in them, poked the pilot jets and sprayed them, so at least they are not clogged. I adjusted the float heigts, got the chrome 3 slides and 2-grooved needles (middle position). Now I need to mount them, make the slides open at the same moment, put back the filter and house with that horrible plumbing and after checking valve lash see what happens when try to fire the bike up....
Should be better than with different slides (3 and 3.5) and different spray tubes (stepped and flat). That set should never been sold as a matching pair to the PO.

Still thinking of buying an extra 4-groove needle and some anodised 3.5 slides for the L35 (was on the bike and hardly worn) and R36 (old replaced one) bodies and mount the rest on them.
 
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NIX

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Just to come back on this one more time: I took another look at the boxes in which the old carbs were put. This is what was sold as a pair:

7097923809.jpg


As you can see it was an L36 and an R300. Even the slides and mains are different on the boxes already. In them were the old L36 and R35. But without mains and with chromed #3 slides. Noo needles. But in the carb stuff stash that came with the bike I only found a new 2-groove needle and a new 4-groove needle, so I guess the new carbs were had their needles replaced right away with the old 2-groove needles. In the new carbs on the bike were a chrome #3.5 slide in the L36 and an alu #3 in the R300. Both had old used 2 groove needles and 220 mains.

The PO told me the old carbs were worn and hardly adjustable. If I look at what came with the bike in parts, The old L36 and R35 must have had 260 mains, but #3 chrome slides and 2 groove needles, that should have been #3.5 slides and 4-groove needles. No idea why they had completely wrong slides and needles, but I guess it made them hard (if not impossible) to adjust. The problem however is that these complete carbs were replaced by a non-matcing set that was also set up with wrong parts and the alu slide already starting to stick.

I also found a loose small tickler knob. That was probably replaced by a bigger one on the R300. The spare L301 still has the small one.
 

L.A.B.

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06-3516 and 06-3517 don't match the specifications marked on the boxes (which are correct for /36 and /300).
According to AN those numbers are for 932/19 & /20 which were 750 Combat carbs (although not the original 932/19 & /20 carb numbers in the parts book Edit: the reason being 06-3516 & 06-3517 were the float bowl drain plug and extended tickler carbs introduced from serial 208628 during '72).

"06.3516
CARB L/H 932/20 230 JET"

"06.3517
CARB R/H 932/19 230 JET"
 
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NIX

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Yes, this supplier (don't know yet which one it was) should be ashamed of himself. I found one bowl without drain in my stash and it will remain in the stash. But I sanded it anyway and adjusted float height for pratising it.
 

MichaelB

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Yes, this supplier (don't know yet which one it was) should be ashamed of himself. I found one bowl without drain in my stash and it will remain in the stash. But I sanded it anyway and adjusted float height for pratising it.

Supplier?? Not sure who that supplier was but I've seen plenty of incorrect stuff on E-Bay.
And usually not at very good prices.
E-bay is a dumping ground for umatched/odd pieces of all types.
Definitely, 'Caveat Emptor.'
 
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