changing sprockets

For posterity...

I was reading through this thread and noticed that several fellow Canadians mentioned having 36 tooth rear sprockets on their Specials and one Canadian mentioned that 34 was standard.

My Canadian 1980 XS650SG owner's manual states that the XS650G and XS650SG has a 36/17 ratio.

For whatever reason it appears that the standard is different for the Canadian models.

Also as one would expect with the larger sprocket the original chain has 106 links rather than the "standard" 104.

mike
 
Last edited:
LanarkXS said:
- - - My Canadian 1980 XS650SG owner's manual states that the XS650G and XS650SG has a 36/17 ratio. - - -
Click to expand...

Hi Mike,
I bought my '84 Heritage Special new in Winnipeg and it came with 17/36 sprockets and although I don't remember what the owner's manual said my Clymer's says 17/34 is stock.
After my first highway ride I wondered WTF has this thing got sidecar gearing?
Swapped to 18/32 (had to carve the rubber facing off the inner chainguard)
Upgraded to o-ring chain (had to discard the inner chainguard)
Swapped to 17/33 (18/32 felt a tad high and I'd noticed the notches the chain had gnawed in the shifter shaft)
Swapped to 17/38 when I attached the sidecar. (a tad too low)
Finally back to the 17/36 the bike came with.
 
fredintoon said:
Hi Mike,
I bought my '84 Heritage Special new in Winnipeg and it came with 17/36 sprockets and although I don't remember what the owner's manual said my Clymer's says 17/34 is stock.
After my first highway ride I wondered WTF has this thing got sidecar gearing?
Swapped to 18/32 (had to carve the rubber facing off the inner chainguard)
Upgraded to o-ring chain (had to discard the inner chainguard)
Swapped to 17/33 (18/32 felt a tad high and I'd noticed the notches the chain had gnawed in the shifter shaft)
Swapped to 17/38 when I attached the sidecar. (a tad too low)
Finally back to the 17/36 the bike came with.
Click to expand...
I just switched to 17/33 but I am waiting for the new chain to arrive so I can try it.
 
Here is an Excel spreadsheet that will yield RPM vs MPH for all combinations of gears, sprockets and tire sizes. Ir uses rolling distance instead of tire diameter. Rolling distance is the distance that the bike rolls forward for one revolution of the rear wheel.

RPM vs MPH
 
Hi you all.. okay.. been reading through this thread and havent wuite found the answer, so her it goes.

Im having a 750 bigbore with 520 chain and 17/34 sprockets. Its equipped with Dellorto PHF36 pumper carbs and been dyno tested and runs great.

The issue im facing is when riding through town at rpm around 1500-3000 the engine kind of stumble/stutter.

Im thinking two things.. The engine had been dyno tested and carb jetted for high performance and the thought of driving around town and jetted it for that purpose were left out of the scope.

The other thing would be the sprocket size, so... what would be recomended sprocket wise to eliminate the above issues.

Im living in flat lands and also a lot of the driving would be city drive, with stop/start and between red lights.. would a 17/30 help with this?
 
have you tried cleaning the carbs? Might just be as simple as a clogged jet.
 
Well, kind of think it would be last resort, as the carbs are all new only has 300km on them so far. Could be a solution of course.. And one I would look into, so thanks for the suggestion.
 
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vsop-dk said:
Hi you all.. okay.. been reading through this thread and havent wuite found the answer, so her it goes.

Im having a 750 bigbore with 520 chain and 17/34 sprockets. Its equipped with Dellorto PHF36 pumper carbs and been dyno tested and runs great.

The issue im facing is when riding through town at rpm around 1500-3000 the engine kind of stumble/stutter.

Im thinking two things.. The engine had been dyno tested and carb jetted for high performance and the thought of driving around town and jetted it for that purpose were left out of the scope.

The other thing would be the sprocket size, so... what would be recomended sprocket wise to eliminate the above issues.

Im living in flat lands and also a lot of the driving would be city drive, with stop/start and between red lights.. would a 17/30 help with this?
Click to expand...

No a 17/30 would be worse.A 17/30 is at its best out driving high speed expressways. That ratio would be poor when doing a lot of city driving (slow acceleration) . For city driving with lots of red lights, you should go with 17/36, which will give real snappy acceleration, and a high fun factor.

I used a 17/36 for a year, and it was just great for low speed around town driving. Not so good for high speed operation, because the rpm's are higher than need be.
 
Ok, thanks for clearifying that.. ;) Right now its 17/34 and with the Pumper Crabs acceleration is already extreme.. So can almost imagine how a 17/36 would feel like. :eek:

Ill have to look into the carb tuning I guess.. Its been dyno tested with these carbs, so my guess would be that its more of a carb thing than a sprocket thing if I were to go for the 36 solution.

How much more rpm would you get on highways?
 
i think you are going in the right direction. stutter / breaking up is almost always a timing or carb issue. since you had it on a dyno i'd assume the timing is right on so it might be time to crack open those carbs ad have a look. Did the carbs come before or after the 750 kit? Might just need to bump up the main jets.
 
Ill might have to move it to another thread ;) but the engine came with the carbs and the engine and carbs were dynoed together..
 
no matter how many miles are on them they get clogged. No idea how but they do. I used to know nothing about carbs now I can take them apart and reassemble with my eyes closed.
 
vsop-dk said:
Ok, thanks for clearifying that.. ;) Right now its 17/34 and with the Pumper Crabs acceleration is already extreme.. So can almost imagine how a 17/36 would feel like. :eek:

Ill have to look into the carb tuning I guess.. Its been dyno tested with these carbs, so my guess would be that its more of a carb thing than a sprocket thing if I were to go for the 36 solution.

How much more rpm would you get on highways?
Click to expand...

Most lads always wish for more power, faster acceleration etc.. from their bikes. Your complaint is that you have too much power/acceleration:shrug:

To calculate rpm..............use Pamcopete's spreadsheet in post #84.

Your carb's are not plugged up with only 300 kms, unless your fuel tank is full of loose rust.

Make sure you're not driving around town in too high of a gear, i.e. lugging the engine might seem like stumbling.
 
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haha, trust me, this engine is a rocket and has plenty of power.. the real issue is that its not running silky while at low rpm ;) thanks both for chipping in :bike:
 
The dyno testing probably just sorted the mains and high speed/RPM running. You probably still need to do some low speed circuit tuning. I would start with pilots one size larger or smaller, take your pick. The results of that one change should tell you which direction you need to go (richer or leaner).
 
5twins said:
The dyno testing probably just sorted the mains and high speed/RPM running. You probably still need to do some low speed circuit tuning. I would start with pilots one size larger or smaller, take your pick. The results of that one change should tell you which direction you need to go (richer or leaner).
Click to expand...


Good idea, I'll look into that aswell. Thanks guys as always much help.
 

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