'80 Special FD vs. '82 XJ FD

[XJkid]

I have a buddy member who rides an '80 Special. I told him I run 4k rpm @65 mph and get 42 mpg. He said his takes 5k to get 65 mph. He did not say what his mpg is, but from the look on his face, it wasn't near 42. My question is this: would installing an '82 FD on an '80 bring the rpm's down for him? I have an extra FD I will give him if it does.

[DGXSER]

The stock FD on the XJ and the XS were all the same. That component was nto chnaged throughout the models or years, with the exception of the paint scheme.

Take a look at the back of the FD on your XJ though, See if you see YJ7 as the first three in a model number on it. You may well have an XS750 FD installed on your XJ.

[XJkid]

The only # I could find was 2H701. Whazzat?

[DGXSER]

That would be the stock FD, 2H7 being the same number as the 78 E models started with.

Now, the other possibility is the speedo being off substantially as to the RPM difference. I know on one of mine I noticed it was almost ten MPH off. When I was supposedly doing 70 in a 65 I was about blowing past everything.

As to the milage, well, these beast do have a habit of drinking heavily if your right hand is jumpy. So if your friends riding style is more aggressive, he would find his mpg lower. I know you can find threads on here discussing MPG and find it range from low 30s to low 40s. I rode about 90 miles with a fellow XSive once where we both filled up before leaving, he ran out of fuel about half way there. He had a fuel issue and tried to re-gap his plugs to compensate. He corrected the plug gap and made the return trip with fuel to spare.

[Poprock]

Front tire size can "adjust" a speedo. Running a 110/90/19 Metzeler, my speedo is about 1 mph slow (checked by GPS) @ 60, so it's close enough to dead-on. With a 100/90/19 Dunlop it was about 5 mph fast at cruising speeds. I like the 110 tire. No clearance problems noted.

[TopCatGr58]

Hey XJKid,

Your friend needs to check his clutch for slippage, that could also cause higher rpms and loss of mileage. Have him ride it in 5th gear at 60mph and crank the throttle wide open and see if the rpms rise without the bike speeding up or increasing mph. Aside from the clutch adjustment at the engine, his springs may be sprung/weak. Also is he using full synth vs. dino oil, that can also contribute to slippage with a weak clutch!

T.C.

[XJkid]

I'll query him on those points. What about the trans/middle drive. Are they the same from '80 to '82?

[DGXSER]

Everythign about the drive train is pretty much identical on all model/year of XS-XJ. Yes, there were some engine changes as to cams and pistons and the YICS system, internal to the engine. The ignition system was modified in later years to use 3 ohm coils. But they should all pretty much bolt right up and provide the same performance from the level of speed at RPM and or MPG.