What is the significance of "R35" carb stamping?

Status
Not open for further replies.

jimbo

VIP MEMBER
Joined
Sep 25, 2004
Messages
1,970
Country flag
What is the significance of the "R35" carb stamping on a MK11 850 ? Roy Bacons book mentions the carbs, stamped R56 and R36 will have bigger mains , why is that? Different cams or higher compression?
 
jimbo said:
What is the significance of the "R35" carb stamping on a MK11 850 ? Roy Bacons book mentions the carbs, stamped R56 and R36 will have bigger mains


(932) R35 and L36?
"Will have bigger mains" than what, exactly? What are you comparing 35 &36 with?

jimbo said:
why is that? Different cams or higher compression?

R35 & L36 would be the standard spec. carbs for an 850 Mk2.

260 mains
.106 needle jet
3.5 slide
928/104 needle
928/107 spray tube
 
MK2A had smaller mains due to black cap silencers, also the black plastic air filter too but my MK2A has peashooters fitted and needed 260 mains to run full throttle so I doubt the air filter is contributing much in the way of difference to how the engine runs.
 
according bacons book there are three different main jets for 850's; 260,230 and 220. :?
 
When I was buying Roy Bacon's books in the 70's and early 80's they were known for quite a few inaccuracies. I would ignore most of what is in there for restoration purposes.
 
"R" refers to right hand side carb, tickler on the right side. The number is only AMAL reference to how the unit was set up....slide cutaway, jetting, needle...etc. All of this is changeable and the number is only significant to configuration at AMAL for specific purchase requirement at the motorcycle manufacturer. I don't have a copy, but have see reference lists from AMAL that decipher the number codes and application. I would think Roy Bacon used this in his Restoration series of books.
 
jimbo said:
according bacons book there are three different main jets for 850's; 260,230 and 220. :?

260, 850 Mk1 (Amal 932/29 &30).
230, Mk1A and maybe also early Mk2A according to Bacon. (932/31 & 32).
260, Mk2 (932/35 & 36).
220*/230*, Mk2A and Mk3 (932/33 & 34).

*This can vary depending on the source of the information. For instance, the Mk3 parts book lists the main jet as "220", but it's "230" in the Mk3 manual.
 
L.A.B. said:
*This can vary depending on the source of the information. For instance, the Mk3 parts book lists the main jet as "220", but it's "230" in the Mk3 manual.


220 and 230 main jets are only one size apart in the world of Amal, after all.
Not exactly life changing stuff.
A true fanatic could well change between them for hot days and cold nights riding.

But Amals (and other makers) one-size-suits-all approach means you would barely pick the difference in performance and engine temps by not so changing them.

You can buy little variable-main-jet thingies for monoblocs and sidefloat carbs, for riders who insist on having it just right.
Can tweak them on the fly even.
Not sure I have seen them for concentrics, so maybe it really doesn't matter...
 
According to Burlen's/Amal's own list, the Mk3 carbs were 932/42 & 43, with "200" main jets, however as far as I'm aware, the standard Mk3 carbs were 932/33 & 34. :?
 
+1 Rohan
When setting up my race bike motor initially with the 32mm Premiers, standard Vv's and manifolds,it would take a big step of 2 or 3 jet sizes to get any significant changes to plug colours and or dyno out puts especially in the WOT positions.
It is 0.0015" difference from one size to another across the orifice diameter.
Regards Mike
 
but a range of 220 to 260? there must have been a difference in the bikes to use those jets. Exhaust?
 
jimbo said:
but a range of 220 to 260? there must have been a difference in the bikes to use those jets. Exhaust?

As kommando said, above.

kommando said:
MK2A had smaller mains due to black cap silencers, also the black plastic air filter

(Also Mk1A and Mk3).
 
Status
Not open for further replies.
Back
Top