2 Strokes Down Under

Thank OldJohnno for reminding me, I've gathered various RZ carbs, and some have a black coating on the carb slides. I hadn't seen this coating on a carb before, and the local carb spares supplier (Ian Williams Tuning, a karting supplier) hadn't seen it either, thought it was something someone had applied to take up clearance or as a performance aid. It feels a bit "teflonny".
Anyone got any ideas?
Looks original to me.

OEM. Teflon i think.

Mikuni flat slide stuff - TM, TMX, HSR etc - is hard anodised black, maybe this is something similar. It's quite possibly original; the OEMS carbs were often specced differently to the aftermarket carbs of the same type.

I liked the old VMs with the chromed brass slides - smooth as silk.

A bit off-topic but I tested some carbs a few weeks ago and found that a 38mm TMX flowed practically the same (211 vs 218cfm @ 1.5"hg) as the old 40mm VM. I still think the VM is hard to beat as an all-rounder.

What ever the coating is it never lasts for long. My beloved Dellorto's use annodised and chromed slides

Delirtos? What ae they on?

I can't comment on the nature of the black OEM slide coatings (e.g. Mikuni TM etc.), but see my reply to the piston coatings topic (viewtopic.php?f=22&t=2083). Although I've never had it done to a carb slide, I believe that the HPC DF1 coating is suitable. As the coating attracts oil, it should (theoretically) prevent the slide from sticking.

Regards,
James

AFAIR, the black coated slides were introduced for the 2nd series/`85 model RZ's,
& for sure - it is def' not the same material as on flat slides..

I've had a bunch of 'em, both as they came on original bikes, & as spare parts..
& the RZ coating seems soft-wearing/matt-finish compared to the F-S's..

VM cylindrical slide carbs will flow more smoothly if you radius-fill the underside of the slide, with fuel-proof expoxy..
..or fancy 'UFO' stuffers, if you like to spend..
( same applies to flat slides, but they need less fillin' around the needle orifice)..

The improved venturi-effect is shown by having to go down in pilot jet sizing, & in superior throttle response/fuel economy..

To put the historical timeline together, my bikes are 83/84 and an 85, the carbs I've looked at are early RZ ones, not powerjet carbs. One set is from a Canadian 350.
For me this is curiosity, I'm not practically concerned unless I have to replace parts due to wear, but the variability is curious.
Interesting how many different ways a slide can be treated.

Lots of aftermarket stuff these days for Banshee ATV's & the like BRG...

See here for some Mikuni carb CFM flow comparos.. http://www.aaenperformance.com/snow_carb.asp

I have found that certain Polaris snowmobile applications use common Mikuni brass..
.. but retail them quite a bit less pricey than bike parts generally go for..

ie, SLP performance in the US sells 'Polaris' Mikuni needle jets for $US 4.99 & needles for $US 1.99 each..