1983 250 CR carb swap question

I have a 38mm Mikuni TMX that I was considering trying on my 83 250 CR in place of the stock round slide carb. Bike is used strictly for VMX.

Qs:
Does anyone have experience with this combination of bike/carb (recommendations for or against)?

Any suggestions on jetting or set up?

Thanks!

in my honest opinion i wouldnt..i believe the flat slide can be more finicky to tune, for little gain. i bought into the lectron hype and replaced a tmx on my 360. im so impressed with the throttle response and overall ease of tuning and the level at which you fine tune it have me strongly thinking of ordering one for my 88 250 to replace its roundslide, even though it runs and starts great. whats nice is they can machine them to any size spigot, bell, and length they sell you one that fits your stock booting/manifolds perfectly.
so no, if i were to go thru rejetting a previously ok running machine with a different carb, thats what it would be. but if you are very familiar with mikuni and have a bunch of jets, needles and needle jets or are willing to buy them im sure the tmx would provide a boost in bottom end and throttle response perhaps. i have a pretty good selection of those sorts of things, but i do not want to buy any more. lectrons have no jets to replace, just a metering rod. all jetting adjustments from top of carb, and its easy to access the carb by twisting in the boots.

Thanks for the advice, justintendo. The bike runs well now. So, I can always just put the stock carb back on. I do not have much in the way of TMX parts, jets, etc., but If I could find out some baseline settings for the TMX I might try it.

i wouldnt imagine they would be much different than what the vm is currently running...i would try using the main from the vm and going from there. pretty sure the tmx has a different needle tho..
one thing i was dealing with on my tmx was a bike with a powervalve, which complicates the jetting process..

If you install a UFO in the bottom of the round slide the mikuni round slide will act the same as a flat slide. The UFO removes the turbulence of the round slide. You need to rejet to smaller jets. Your engines response will be so much better overall. It's in one of my other posts about the UFO's.

Both the 84/85 CR250s have the flat side carbs ? Cant you use the baseline setting from them? Think the 85 engine manual is on here. I use it alot on my 84 CR

Bigbill: I am familiar with the UFO insert. I have one in my 83 KX250 VM carb. It did improve the the KX's throttle response, jetting was fat with it installed. Had to go down on pilot jet size by nearly half and main jet size by 1-2, but it does work well.

darren78787: I checked the carb specs on the 84/85 bikes. The parts list book shows a round slide Mikuni. Does your bike have TM on it?

The TMX is not legal for AHRMA racing, only the older style TM. The '84 CR250 came with a TM.

AHRMA: first they ban my 82-83 Kawi's for having disk brakes and now you tell me they don't like my "new" carb either. Thanks for the heads up on that one! Think I will leave the TMX on the bench and keep the VM on the bike.

Some flat slide carbs like the Lectron or the Mikuni TM are legal, but the TMX is a much newer design. Personally, other than the Lectron, I have not found any flat slide carb to be significantly better than a well jetted VM.

The Lectron looks interesting. I have no experience with it, or the TMX. I have experience with the flat slide PWK on a newer YZ, but that is an entirely different setup with a TPS and power jet. Might look into a Lectron for the Husky in the future.

It all depends on what year bike You are racing in VMX and when the Carb was introduced. In other words the Lectron came out in 1978 so its ok on any 78 or newer bike. No different for any other Carb, You just need to figure out when it came out and that's the oldest year of bike it can be run on. Keep in mind You can run anything from any year in Vintage just as long as You don't win. Its when You start winning that people start looking at what Your running.

I always thought the Lectron had been around since 75/76.
Powervalves on them came in 78/79.
Or am I wrong ?

Lectron carbs were first sold in '74 and in '75 you could get one OE on a Penton/KTM in place of the Bing, grouty is right that the power jet came around '78.