Newbie; 250 or 600 to learn best? Opinions?

Quote:

Originally posted by Russel Green # 734:
I don't know the difference between a YSR,NSR,TZ,GP... sorry for all the ?'s but I want to make an educated decision and I don't have an education... lol.

I didn't see anyone else answer it, and most people assume everyone knows all this stuff. Here you go:

GP: (Grand Prix) general description for a class of bikes that are mfg'd as race-only. Generally water-cooled 2-strokes in the 125 or 250cc size, significantly lighter than streetbikes. (125gp ~160 lbs I think compared to race-intended streetbikes which are all in the vicinity of 400 lbs, +/- 30). Honda's is called RS and Yamaha's TZ. Some confusion in that Honda's RS250 and Aprilia's RS250 are very different bikes. Honda's being a true GP and Aprilia's being a converted street-bike/simplified roadracer. 125's might be good learner bikes if you're willing to deal with the maintenance and there are obviously different thoughts on how serious it is. Also, there's the possibility of seizing a piston which I understand normally results in a crash. Can any of you GP guys respond to the likelihood and results of piston seizure (as well as how to avoid it, e.g. don't go too lean on air/fuel nor oil/fuel, proper piston replacement intervals...) I wouldn't have classed a 250GP bike as a beginner bike in any way, as it has about the same power as a 600cc 4-stroke but may also have a lightswitch powerband, depending on how fancy they've gotten with powervalves and such. Honda's site quotes the RS250R as 92 ps (~92 hp) with a "semi-dry weight of 101 kg" or ~220 lb.

125 and 250 GP bikes are in no way "minis". I think you have that, there's just been some confusion in the past. However, if you take a 125GP frame and put an 80-85cc motocross 2-stroke in it, that's the ticket for CMRA F4 and TMGP unlimited (fastest "mini" classes for each), though some say the "big wheel" bikes are not the best for TMGP's small tracks. Another debate. Those bikes are typically referred to by the chassis model letters and the displacement, e.g. TZ85 or RS80.

Yamaha YSR is the original mini. 50cc, air-cooled 2-stroke, 12" wheels, imported for only a few years around 1990, but hugely popular. Runs the bottom class in both organizations: CMRA F7; TMGP I forget the class name. Going price race-ready ballpark $1k. Negatives: might be a bit worn. Although now it's being challenged for the std. mini role by the...

Honda NSR50: water-cooled 50cc 2-stroke, 12" wheels. Rumor tells it is a much better out-of-the-crate mini but can't be bought for the dirt prices that YSRs are going for these days. There are newer and older ones. I think Emmitt Dibble is the brains and proponent on the NSR. Has a website somewhere with terrific write up on it. Emmitt? Ballpark price: I think they're going for $3k to maybe close to $4k for brand new? Benefits: ready to race without investing in any upgrades. Negatives: not the cheapest mini; 12"wheel small frame (like YSR) if you don't like that.

Motards: I have even less clue than the stuff I just acted like I knew. ;-)

CMRA's mini classes are F4-F7. Check the rulebook.

Disclaimer: I have never raced GP or minis, just been collecting some info in preparation for trying it out next year with my son. I'm sure the experts will correct any mistakes in this post. :p

Quote:

Can any of you GP guys respond to the likelihood and results of piston seizure (as well as how to avoid it, e.g. don't go too lean on air/fuel nor oil/fuel, proper piston replacement intervals...)

Yes, well, I, ahem, have a little experience here. It all depends on where the seizure occurs, but often it's entering a corner when you roll off the throttle and if you're leaned over on a water cooler and it sticks, well, be ready for some asphaltitis. The keys to prevention of seizures are proper jetting, proper octane rated gas for the compression, and proper ignition timing.

On the old RD stuff, air cooled, jetting was hard to nail down, often, and the friggin' ignition points would creep around causing imprecise timing. But, at least on the air cooled stuff, you could hear it coming. You learned to never take your fingers off the clutch, LOL.

With water coolers, if it does stick, you're just riding along concentrating on the track and BRRRAAAAP! OMG, now what? [img]/ubbthreads/images/%%GRAEMLIN_URL%%/eek.gif[/img] No time to clutch the thing. BUT, water cooled bikes are a lot easier to jet. With the GP stuff, RS125 Honda to be specific, friend and GP guru Eric Kancir gave me a chart to be used with a cheap "weather station" available from Radio Shack which reads temperature and BP. You'd just cross reference on the chart and it'd tell you what jet to use and by golly that chart was spot on most of the time! I came to rely on it and got to where I'd hardly ever do a plug cut it was so reliable.

However, the routine otherwise is go out jetted what you know is "fat" on the main jet, take a plug chop (run it up on the power in a high gear, chop throttle and ignition and clutch it at the same time, roll it in for the check. Then, you read the plug (an art form in itself which must be learned) to get an idea of where to go with the jet. First practice sessions are consumed with this routine, not good if you're a newb rider needing track time IMHO.

In the last six years since I came back to road racing, I've stuck a two stroke twice. Once was from improper ignition timing cause on assembling, I sorta forgot to set the timing. DOH! I paid for it with a slide out of T2 at TWS. I was full tilt right at the apex when it stuck, was on my butt with the bike on top of me in front of the whole pack off the start except for Tyler and Jay Deaton who were in front of me. I just KNEW I was going to get run over, LOL! That one, obviously, could have been avoided, was machanic's error.

The other was in Louisiana at No Problem Raceway, where I had the problem. The air is SUPER dense down there, enough to through that chart of Eric's off several jets cause it doesn't account for altitude, or the fact that you are BELOW sea level down there. It wasn't on the GP that I had the problem, though, but that poor KX80 again. Went out to do a plug check and didn't make it around far enough until it stuck. I wasn't mid corner that time, fortunately, and saved it with the clutch. Came in, went to a hardware store and bought some muratic acid (two stroke tuner's best friend), and even though the nickacil lining had a little hole in it above the exhaust port, still was able to race with a spare piston/rings I'd brought along. I wound up running THREE jets larger than I normally did in BOTH bikes that weekend.

An air density gauge is really a better way to go than Eric's chart, but they're expensive and you have to chart them, too. You're running blind until you work out with your notes as to what jet you were running on X day with X density and get enough data to go by.

Now then, another thing that can stick a GP that I just thought about is temperature. An RS125 can "cold seize" if it's not up to temperature before you go out on it. On a cold day, GP stuff has no thermostat. You control temp by how many strips of duck tape you put on the radiator. If you go out running 45 degrees, you're askin' for a seizure! You have to get up around 60 degrees, so your first couple of practice sessions on a cold day will be concerned with not only jetting, but engine temperature.

Are you beginning to get the idea why I think a newb rider needs to learn on a turn key bike, not a tuning intensive two stroke??????

Oh, yeah, another thing is proper PM. Never run a piston kit with more than 300 miles on it. Bad things can happen. Piston/rings/wrist pin/circlips should be changed out at 300 racing miles. Key here is good notes on your approximate mileage. Yamaha TZ manuals give run out limits and you can get 500 or so miles out of a stock TZ piston, or I used to. But, Honda only gives the mileage thing in their manual and you'd be advised to stick to the schedule. Cranks last 1300 miles and a big end failure can be almost as catastrophic as a piston seizure.

I think I may have found something. There is a TTR-125L here in my area. I need to call and find out the year. Ad says "Racing Pipe". They are asking $1250 OBO. Is this a good price? (i'll get back with the year). What upgrades would I need to do to take a stock TTR to race standerds? Can I run the stock wheels and just put racing rubber on them?

Run stock wheels with Bridgestone trail wings for rubber. Lower the front a bit in the triple clamps if you have a front end push problem.

Put a Works shock on it, proper springs for the application in the front and set sag. Maybe have someone look at the valving or just put heavier fork oil in it and don't worry about it.

New ones are like $2500 or $2600. That sounds like a good price.

Later, if you get all into it, you can get lots of go fast goodies for TTRs. They're not quite as popular as the XR100 aftermarket stuff, but they're gaining popularity. You can get a cam, put a carb on it, make it go real good. Don't go messing with displacement unless you wanna cheap. [img]/ubbthreads/images/%%GRAEMLIN_URL%%/laugh.gif[/img] Talk to Billy Wiese if you want motor work. His is quite strong. He built it for flat tracking, but occasionally brings it to Katy to play.

BTW, I've been playing with one of my XRs today, my flat tracker. It came set up for an oil cooler. I ebayed one for fifteen bucks and put it on today. Ain't pretty, but effective. No leaks, that's the main thing, LOL.

http://x11.putfile.com/11/30912392975.jpg