What is the correct barrel and head combo?
On my '93 '21 SE, I have SP(L2) barrel with an R head on the rear(top) cylinder and an R(H2) barrel with an R head on front(bottom) cylinder.
Is that combo ok? Or should it be sp head with sp barrel and r head with r barrel.
I tend to jet both the same but for some reason I always get some pitting on the top of the piston on the rear cylinder. And when it seize up it's always the rear cylinder that's dinged up.I've never had any problems with the front cylinder.
The only mods on the bike is wire splice, 3 holes in airbox, and JHA over-rev chambers.

The correct combination, as I think you probably already suspect really, is an R barrel + R head or SE/SP barrel + SE/SP head.

If you want to play safe, use an SE/SP "L" barrel with an R "H" head, but it's not an ideal situation and can mess up the jetting due to the low compression.

"Pitting" in the piston is generally a sign of detonation caused by either high compression or lean mixture.
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

The rear cylinder that I tend to have problems with does have the 'safe' combo with the L barrel and H head. That's what was on it when I got the bike.
With that low compression setup, jetting it the same as the standard compression(H barrel and H head) on the front cylinder. I shouldn't have a problem with the jetting on the rear cylinder being too lean correct? Or am I completely off?
Sorry don't mean for this to be about jetting specifically. Just would like to know the general relationship between compression ratio and jetting size.

Can overly rich setup cause detonation as well?

An overly rich setup won't detonate, it'll just foul it's spark plug and not run.

Andy's right and lower compression is "safe", however, just the markings on the barrel/head are no guarantee of setup, my heads have been machined for instance as have any barrels that've been replated.

Stock squish for an NSR is around 1.2mm, you can measure this when the engine is assembled by poking a piece of solder into the plug hole (make sure you get it right to the outer edge, then turn the engine over on the kickstart and squash the solder between the piston and head, the resulting squashed end of the bit of solder is the squish band thickness measurement. 1.2mm is stock, 1mm is R barrels, SP heads and requires some careful setup to run on the road, much less is unsuitable for pump fuel.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread

Thanks for the reply fellas.