RMX 250 barrel date?

[corndog]

Hi Guys

I have managed to secure a RMX250 barrel for a good price. the catch is that the bloke selling the barrel does not know what year RMX it came from (he had it as a spare barrel and never needed,dated it or used it). My RMX is a '99

I am planning to send this 2nd barrel and a 2nd hand head from a breakers to Eric Gorr for a replate and porting.

I know there are a few differences in the barrel between the different models of RMX, how can I date the barrel, and if it is from a earlier model will it be usable?

Cheers for any advice.

SC

 

[corndog]

Hi Guys

I figured out that it is a 89-92 barrel, I will now ask forward motion if this will fit my bike and go from there.

SC

 

[Yamadad]

It should be fine. I think the engines were the same from 89 to end of production. (I used to own a '93 and am familiar with the breed.)

 

[placelast]

It will fit everywhere except your existing pipe; you will need to change it ot the older model - oh, and the muffler too, because exhaust pipe-joint is larger in diameter, and the stinger (trailing end of the expansion chamber/pipe) is longer.
Maybe you can have a bell adapter for your existing pipe. Sorry.

There are generally three versions of the RMX barrel: '89-'92; '93-'95; and '96-'98 (and maybe the '99 non-USA version).

The latter two groups are completely interchangable although the last years have a slightly broader intake-side taper. The first group has the large exhaust port. The reason they made it smaller was to increase discharge velocity (scavenging?) for allegedly improved low end response. My son had a '90/me a '97, and his was fine, mine slightly more abrupt.

 

[corndog]

Cheers placelast,

The exhaust port is definilty bigger, I have acces to a lathe so machining an insert for the exhaust port/exhaust mating surface is no problem, but maybe I will sell the barrel and continue the search for a '93+ barrel, the powervalve is in great condition and the bore is reparible so it will be of use to someone.

 

[placelast]

I’ve a ’93 barrel on my ’97; ported by Eric for mo bottom. Funny thing is the first time I let out the clutch I was expecting the front wheel to reach for the sky! Talk about misconceptions in my own head. Instead it was a little thicker on the bottom and smoother into the mid; did not miss the over-rev one bit. I use this one for woods riding, but it works fine in open desert.

My ’97 barrel is ported by him for mo everywhere, and it is (ever-so-slightly) a bit snappier or pronounced into the mid though less of a ramp up than stock, and there’s more over-rev – a bonus for long and gradual uphill sand washes in the Mojave desert when forth is not enough and fifth is a bit of a gap fill.

I cannot decide which one is preferred as they are both improvements over stock, but not alarmingly so as that would defeat the purpose of the RMX to begin with. Either one needs your stock head for dome reshaping.