Hello from a new guy

[Southman]

Gents! Just wanted to say hello and introduce myself: I bought my first xs400 about a week ago and I'm in love with it! It's an 81, clubman handle bars, custom fiberglass cafe seat, straight piped, cut down cafe racer wannabe. I'm still working on getting it full cafe but the process is long! Own a 97 XJ600s as well and previously rode an 06 R6. Been riding for about 6 years now and love spending as much time fixing a bike as I do riding it. recently attempted an iron butt challenge (as a personal whim) and only made it halfway before the bike decided it was done. Rode from Toledo OH to Wilmington DE. Was trying to go from DE to savannah, GA but the previous owner and I had not adjusted the carbs correctly to run with straight pipes. Fouled up my plugs and had to leave it in a friends garage. I have a compression issue: 145 in the right cylinder and 150 in the left. Also wanted to know of the slight rattle/tapping sound from under the tank is the product of an over tightened cam. Rebuilt one carb after it quit on me and hoping not too much else is wrong.
Do y'all's clutches engage really far out as well or is that just me?
Thanks!

 

[drewpy]

welcome!

what are the questions again?

 

[Southman]

Thanks!
Sorry they aren't really stated well there:
Is the rattling/tapping coming from the head an over tightened cam?
If I have bad piston rings that let oil slip into the chamber would that lead to enough carbon buildup on my valves to block one closed? Or am I not running a high enough octane?
Is my high compression acceptable? It's destroying the starter but I kick it more often...

 

[Southman]

Also, would changing my gearing increase top end performance or am I just sacrificing torque for no reason?

 

[drewpy]

Thanks!
Sorry they aren't really stated well there:
Is the rattling/tapping coming from the head an over tightened cam?

no, its normal

If I have bad piston rings that let oil slip into the chamber would that lead to enough carbon buildup on my valves to block one closed? Or am I not running a high enough octane?

you would have running issues and difficult starting along with high oil consumption, are you experiencing these?

Is my high compression acceptable? It's destroying the starter but I kick it more often...

compression is ok, ideally it would be 160

 

[drewpy]

Also, would changing my gearing increase top end performance or am I just sacrificing torque for no reason?

depends what gearing you have now!

 

[Southman]

I have 145 in the right cylinder and 150 in the left so theyre actually too low? I'm not positive on how high the consumption rate is yet but I know I am burning it off because there is no evidence of leaks anywhere. It's an absolute pain to start and yesterday it died running down the highway at 75mph.

 

[Southman]

Stock gearing

 

[Lou Ranger]

I have 145 in the right cylinder and 150 in the left so theyre actually too low? ...

Welcome to the forum. Attached are excerpts from the xs400 manuals (available on here). I think you must have a sohc, although I think the dohc came out in '81 so you should verify before ordering or adjusting anything.
Anyway, looks like you are right within spec after 31 years - not bad.

Also, would changing my gearing increase top end performance or am I just sacrificing torque for no reason?

I had fun with this when I got my bike. Not sure your bike will behave exactly like mine did, but I did some acceleration runs up a steep hill with stock gearing, then repeated the process after installing a bigger front sprocket. I was very pleased with the result , but whether you will be pleased will depend on what you mean by increasing top-end performance.
Anyway, if you like, you can read my comparisons here:

http://www.xs400.com/forum/showthread.php?t=7592&page=4​

Specifically the runs on a 16T and 17T are described in posts #68 and #75 respectively.
Best of luck!

 

[Southman]

Thanks Lou!! Saving me a lot of time and pain there. Based on your results I think I'll stick with the 16. I like the idea of lower rpms at cruise but since the differences in performance are so small there isn't too much need to swap out for a 17T.
Thanks!!

 

[Lou Ranger]

Thanks Lou!! Saving me a lot of time and pain there. Based on your results I think I'll stick with the 16. I like the idea of lower rpms at cruise but since the differences in performance are so small there isn't too much need to swap out for a 17T. Thanks!!

If you like the idea of lower rpms you should consider it. While the changes in performance are not noticeable, the loss of those 400 rpms at 55 really is. And even I managed to do it without breaking anything in less than half an hour

 

[drewpy]

it does make it less stressful on the body on longer runs