Original/Stock CARBurator-Swapping of various DUKE-models
Posted: Tue Jul 13, 2010 5:49 am
____ Hey-there all good fellow-DUKErs,,
I decided to start this thread so that we'd have one on the intended subject with a topic-title which makes itself fairly-clear so as to more exactly indicate what kind of subject-matter ought be found within. _ (Hope this consideration starts a useful-trend, so that we all don't continue to make our seemingly unmarked 'Box-Of-Chocolates' any more extensive than it has already become!)
____ Anyhow, I recently received a PM which brought-up the subject of switching/swapping the various factory-original carbs (which came stock on various DUKE-models), over to DUKE-models which were never factory-equipped with same.
Since I may have more experience with such carb-swapping than most anyone else, I figure I ought to open a port to pass-on some of the related stuff I know (which may not yet have been independently learned of by others).
__ I've done so much carb-swapping between models, that it might be easier to make a list of all the possible match-ups, which I have NOT done...
At the extremes, I have never tried to put a 24mm-DeL.carb on a 450, nor a 30mm-Amal on a 200,, but otherwise, I've tried pretty-much any other match-up ya might think of.
____ To start this off, I'll bring-up what I'm recalling may be my very first unfactory-original carb-swap job.
Back in 1969, I had a 1965 250Scr. & also a 1966 350Sebring...
I then thought it peculiar that the 350 had such a smaller carb -(24mm) than the 250's -(27mm), and my primary interest at the time, was to improve the 350's power. _ So I swapped the two carbs between those two DUKE-models, and the first thing I noticed was that the 350 had become a bit harder to get started, while the 250 got notably easier !
Also, the throttle-response worsened for the 350, while the 250's improved.
On top of those changes, it seemed that the 250's performance as a 'scrambler' was actually improved more than was the 350's overall-power improved,,
all of which was unexpected.
__ While I could tell that the 350 had generally suffered a bit from the swap,, I could not really tell for certain if the top-end power of the 350 had actually been increased, as was expected. _ But I chose to leave the 27SSI-carb on the 350 anyhow, because I figured that it's mid-range & top-end power certainly had to have been increased, at least a little.
Conversely, the 250's top-end power must have been hurt at least a little, but I never really could tell for sure. _ Since in both cases at the time, the 'control' bike -(a small-valve Mk3, ridden by an equal-sized friend), was found to provide inconsistent comparison-results, seemingly due to how full the gas-tanks were, and varying wind-conditions plus even rider's choice of clothing ! - (In the real-world, it seems that The Specs do not always equate with actual-results.)
Still, there was little doubt that the 250's overall-performance had been fairly well improved for it's role as a 'scrambler' ! _ So it was forever left with that 24mm DeL.carb ! - (As I sold it in Spring of '72, and bought it again in 1980 (as a basket-case due to busted oil-pump), still with the same 24mm DeL.carb!)
And for both DUKEs overall, they both were deemed to be improved by that carb-swap, (even though the DUKE which was the UNintended-beneficiary of the swap, benefited most).
__ I never sold the Sebring ! _ (And by the following Spring, the cyl.heads of those same two DUKEs, were also swapped, (with the 250 then also getting a 80-thousandths oversize MC-piston)... But those details are another story, better placed within another thread.)
So that Sebring has gone through additional carb swapping...
It's next carb was a 28mm-Amal (from a 650-BSA), which seemed to be a better choice (overall) than the 27SSI but, it wasn't long after that when it was next replaced with a 27mm square-slide DeL.carb (from a Harly 350-Sprint), which much improved starting ! _ All three carbs were tried on the n-c 350 -(no longer fair to be called a 'Sebring', since it no longer had it's stock-head), during the same riding-season, in combo with the 250-Scrambler cyl.head.
My n-c350 was then compared to a stock Sebring (which I also still have), and both still stayed neck-&-neck until 3rd-gear was about half wound-out, at which point the larger carbed n-c350 (with 250SCR-head) would begin to pull away from the stock-Sebring.
I kept the last combo (with the Sprint carb) for the rest of that riding-season, and the following season I only switched the SCR-cyl.head for a 250Mk3 (small-valve) cyl.head. _ THEN, I had truely felt that I finally had a 350 which had reached my desired goal of a fast-350, as it was then running notably faster than any other stock 350-DUKE.
Then during the next following riding-season -(1972), my n-c350 got it's final set of engine-mods... a w-c (modified) piston, a large-valve Mk3-cyl.head, and a 29mm DeL.carb -(from my 450Mk3). _ Those changes made a very impressive increase in power ! ... Much more so over the previous-combo -(small-valve Mk3-head & 27mm carb), than that previous-combo had made over the stock-Sebring's ! _ I'll never forget about how my n-c350's power then became so strong (that after installing a new set of friction-disks), it then became very wheelie-prone whenever I grabbed some throttle (in 1st-gear with 49/15t gearing) ! - A scary-delight at the time !
Dukaddy-DUKE Cheers,
-Bob
I decided to start this thread so that we'd have one on the intended subject with a topic-title which makes itself fairly-clear so as to more exactly indicate what kind of subject-matter ought be found within. _ (Hope this consideration starts a useful-trend, so that we all don't continue to make our seemingly unmarked 'Box-Of-Chocolates' any more extensive than it has already become!)
____ Anyhow, I recently received a PM which brought-up the subject of switching/swapping the various factory-original carbs (which came stock on various DUKE-models), over to DUKE-models which were never factory-equipped with same.
Since I may have more experience with such carb-swapping than most anyone else, I figure I ought to open a port to pass-on some of the related stuff I know (which may not yet have been independently learned of by others).
__ I've done so much carb-swapping between models, that it might be easier to make a list of all the possible match-ups, which I have NOT done...
At the extremes, I have never tried to put a 24mm-DeL.carb on a 450, nor a 30mm-Amal on a 200,, but otherwise, I've tried pretty-much any other match-up ya might think of.
____ To start this off, I'll bring-up what I'm recalling may be my very first unfactory-original carb-swap job.
Back in 1969, I had a 1965 250Scr. & also a 1966 350Sebring...
I then thought it peculiar that the 350 had such a smaller carb -(24mm) than the 250's -(27mm), and my primary interest at the time, was to improve the 350's power. _ So I swapped the two carbs between those two DUKE-models, and the first thing I noticed was that the 350 had become a bit harder to get started, while the 250 got notably easier !
Also, the throttle-response worsened for the 350, while the 250's improved.
On top of those changes, it seemed that the 250's performance as a 'scrambler' was actually improved more than was the 350's overall-power improved,,
all of which was unexpected.
__ While I could tell that the 350 had generally suffered a bit from the swap,, I could not really tell for certain if the top-end power of the 350 had actually been increased, as was expected. _ But I chose to leave the 27SSI-carb on the 350 anyhow, because I figured that it's mid-range & top-end power certainly had to have been increased, at least a little.
Conversely, the 250's top-end power must have been hurt at least a little, but I never really could tell for sure. _ Since in both cases at the time, the 'control' bike -(a small-valve Mk3, ridden by an equal-sized friend), was found to provide inconsistent comparison-results, seemingly due to how full the gas-tanks were, and varying wind-conditions plus even rider's choice of clothing ! - (In the real-world, it seems that The Specs do not always equate with actual-results.)
Still, there was little doubt that the 250's overall-performance had been fairly well improved for it's role as a 'scrambler' ! _ So it was forever left with that 24mm DeL.carb ! - (As I sold it in Spring of '72, and bought it again in 1980 (as a basket-case due to busted oil-pump), still with the same 24mm DeL.carb!)
And for both DUKEs overall, they both were deemed to be improved by that carb-swap, (even though the DUKE which was the UNintended-beneficiary of the swap, benefited most).
__ I never sold the Sebring ! _ (And by the following Spring, the cyl.heads of those same two DUKEs, were also swapped, (with the 250 then also getting a 80-thousandths oversize MC-piston)... But those details are another story, better placed within another thread.)
So that Sebring has gone through additional carb swapping...
It's next carb was a 28mm-Amal (from a 650-BSA), which seemed to be a better choice (overall) than the 27SSI but, it wasn't long after that when it was next replaced with a 27mm square-slide DeL.carb (from a Harly 350-Sprint), which much improved starting ! _ All three carbs were tried on the n-c 350 -(no longer fair to be called a 'Sebring', since it no longer had it's stock-head), during the same riding-season, in combo with the 250-Scrambler cyl.head.
My n-c350 was then compared to a stock Sebring (which I also still have), and both still stayed neck-&-neck until 3rd-gear was about half wound-out, at which point the larger carbed n-c350 (with 250SCR-head) would begin to pull away from the stock-Sebring.
I kept the last combo (with the Sprint carb) for the rest of that riding-season, and the following season I only switched the SCR-cyl.head for a 250Mk3 (small-valve) cyl.head. _ THEN, I had truely felt that I finally had a 350 which had reached my desired goal of a fast-350, as it was then running notably faster than any other stock 350-DUKE.
Then during the next following riding-season -(1972), my n-c350 got it's final set of engine-mods... a w-c (modified) piston, a large-valve Mk3-cyl.head, and a 29mm DeL.carb -(from my 450Mk3). _ Those changes made a very impressive increase in power ! ... Much more so over the previous-combo -(small-valve Mk3-head & 27mm carb), than that previous-combo had made over the stock-Sebring's ! _ I'll never forget about how my n-c350's power then became so strong (that after installing a new set of friction-disks), it then became very wheelie-prone whenever I grabbed some throttle (in 1st-gear with 49/15t gearing) ! - A scary-delight at the time !
Dukaddy-DUKE Cheers,
-Bob