Iirc with my 17/34, I’m revving about 4100 @ 60mph. This is with aftermarket tach and Speedo so I don’t know the true accuracy.
It is not unlikely that aftermarket instruments are more accurate than oem mechanical/ magnetic instruments. Many years ago, I replaced the mechanical speedo on my Ducati Monster, and installed an electronic tachometer in its place. Then I fitted an electronic bicycle speedometer with an inductive pickup. For this speedo, you could enter wheel circumference in mm. That front wheel had around 2000 mm circumference, so the setting would have a max error of 0.05 %. Which is pretty good, I would say. After the initial programming, I checked the calibration, using the odometer function over a 10 km distance, going by the official "mile markers" (steel poles every 0.5 km). Then I altered the circumference setting accordingly, and did another test run. So I am confident that the bicycle speedo was as accurate as can be. While mechanical speedometers often read 5 to 10 percent optimistic ...
That's the beauty of a 277, 5500 is a nice cruising rpm on the highway if you need it to keep up with traffic.
Is your re-phased XS a 700, 750 or larger? What brand pistons?
I have 2 277 engines, the one in the bike now is all stock. The other one has a megacycle cam and used to be 700 with je pistons. Now it is 707 with cruzinimage pistons. The 707 is going back in when I get a rainy afternoon.
Ok, just wondering what to expect from a re-phased 750 with regards to vibrations
The je pistons were the heaviest and may have been the smoothest with them. Should be pretty good with 750.
They're supposed to be that.
Sounds like it behaves like my bike when it was stock.
I believe that should be true if running as the manufacturer intended.
Online dictionary gave me Lollygagging - spending time aimlessly. Thank you for teaching me another wonderful Americanism.
Yesterday, I employed my XS650SK. It has 17/33 sprockets. My speedometer is unsteady in the needle. 4000 rpm is about 65 mph. 3500 is about 58, so I positively drive it faster. Here’s the big deal. The XS650SK doesn’t have high amplitude vibrations. It’s smooth everywhere! So, something isn’t right with the XS650SH. Perhaps the easiest troubleshooting is to just swap the carburetors between the bikes. Now that I felt that much difference between the bikes, I’m not going to be able to live with it.
Has the balance factor changed between these models? Different pistons, rods, crankshaft? Sounds odd if not.Yesterday, I employed my XS650SK. It has 17/33 sprockets. My speedometer is unsteady in the needle. 4000 rpm is about 65 mph. 3500 is about 58, so I positively drive it faster. Here’s the big deal. The XS650SK doesn’t have high amplitude vibrations. It’s smooth everywhere! So, something isn’t right with the XS650SH. Perhaps the easiest troubleshooting is to just swap the carburetors between the bikes. Now that I felt that much difference between the bikes, I’m not going to be able to live with it.
I'd try carb sync, fresh plugs and fresh plug caps first... one at a time to see which, if any makes a difference. Valve clearances 'tween cylinders can have an affect too, though much smaller. Off the top of my head that's stuff I'd try before swapping carbs.
Could be a difference in tune: little carb synch or combustion differences....... My bet though would be on crankshaft balance or runnout being different between the two bikes.
With a spec. crank Runnout of .002", it leaves a lot of room for variance
I gotta say, the SK is silk smooth compared to the SH in the 4000 to 4800 range. I can’t do 5000+ test easily on the SK because the speed is so high. I need lots of room and no traffic.Could be a difference in tune: little carb synch or combustion differences....... My bet though would be on crankshaft balance or runnout being different between the two bikes.
