Jetting Question For Modified '84 250R

[Kev250R]

Hey guys, here's a problem which I've been chasing for the past couple of years and now I'm ready to find a permanent solution.

The victim is my '84 250R running a 0.40 bored engine, larger Keihn carb, ported and polished cylinder, Wiseco piston and only runs on 100 octane racing fuel.

My problem is I'm pretty sure it's running lean at lower altitudes. It runs awesome at ~4,000 feet (Hungry Valley) but down low (sea level) like Ocotillo Wells it starts surging and seems to run hot (I've checked, I don't believe there to be any air leaks).

So I think it's a jetting problem. Currently I *think* it's running a 130 main jet (does that sound right?) Next week I'm going to Oceano dunes (Pismo) for four days and since that's sea level I'd like to get this whole jetting thing sorted-out ahead of time.

It's been a while since I've done any work on this ATC that's why I'm a bit fuzzy on the details, it doesn't help that the trike isn't where I'm at but I'll have some time over the weekend to do some wrenching on it.

So my question is what sort of changes should I make to the jetting? Also what sort of changes should I make to the clip? I know all of this will be dependent on doing a plug-chop but if I could just get it close then I'll take a handful of jets with me so I can fine-tune it once I get there.

Any advice would be appreciated :)

--Kevin

[ATCnut]

Per most honda manuals I have seen, they recommend that you change the main jet by two sizes when riding over 5000 ft. If your trike runs good at 4000 ft with whatever main jet is in it, I would put two sizes bigger in at sea level and see how it runs. If a 130 is in there now then go 132, 135. The stock 350X main jet is a 138, and I thougth that the 250R was bigger. I do not think you can expect the same jetting to work at sea level and at 4000 ft. I know my 350X won't.

After you get the main jet dialed in, then you have the needle clip to play with

[Mr. Richard]

kev i think that you are on the right track ,, i don't ride over about 1500' ... but i know that a couple of jet sizes will save alot of $$$$ ... my 250 is jetted to sea level now ,and in the mornings on the dunes when its cold and damp she runs a little fat (rich) so i know that i could go a jet size smaller but in the warm afternoon it runs great (just a shade fat ) so i can live with it cause it does not foul plugs ,,,,, and it will live alot longer like that,,

if it was me i would go 4 sizes larger and see if it is real fat,,, ,, but the main will do nothing for you from zero to half throttle where most of your cruzing is done,,, there is a jetting chart on the board somewhere,,study it while riding in your mind it will help you to figure out where your throttle positions are and what needs to be changed,,,, there are more than 4 throttle positions too ,,,,make a mental note when riding where that throttle was and how it feels,,, it will help jetting a two stroke is easy if you listen to what the motor is telling you,,,, pinging ,lugging ,run on ,detination ,lean ,rich ,,,,,, of course i have been around 2 strokes for 35 years too,,,,

[BIG BAD RED]

i have been arount 2 strokes for 2 weeks tops...they suck...no....i kinda like the powerband....i like more low end power tho

[Kev250R]

Thanks for the replies guys! I'll try going up three or four jet sizes, I'd definitely rather be rich then lean as well. I'll also be bringing a few with me "just in case."

I actually don't mind having to re-jet each time I (drastically) change altitudes, just want to make sure I come-up with a set-up which won't toast my engine (BTDT) :rolleyes:

Two strokes really don't deserve the bad rap some people have given them. I've ridden and wrenched on both and when it comes to all around reliability and drivability a four stroke is hard to beat, but when you want to make power fast and (relatively) cheap then it's hard to beat a two stroke.

Thanks for the feedback! :)

--Kevin