Looking for Rotax 125 advice

[PT Cruiser]

I just purchased a used Rotax kart (2005 Margay Brava 1.4) to use as a practice tool. Had it out for the first time last weekend at the North Texas Kartway (1 hour north of Dallas), and based on that experience have a couple of questions. Since I know a couple of guys who post on the team juicy site have some experience with Rotax karts (Paging John Pew, Paging John Pew), I was wondering if somewhat might be able to provide some answers --or at least some helpful hints.

Question 1: I lasted all of 30 laps --i.e. about 20 minutes, before I had to quit due to Rib pain. I already have a RibTech, so I was disappointed that I wasn't able to last longer. Does this sort of thing become less of a problem after one has run the kart a few times (i.e. does the body condition itself over time, or does one just learn how to drive the kart more smoothly)? If not, is there anything one can do to the Kart's seat to mitigate the problem? Any gym exercises that build up muscles in the right places?

Question 2: When exiting corners, the engine would hesitate for a few ticks before accelerating strongly. Is there a driving technique one can use to keep the engine in its power band in slow corners --such as leaving the gas on a bit even during braking and corner entry-- such that this hesitation doesn't occur at corner exit? Alternately, does this mean I don't have the engine tuned properly? Either way, it seems like this lag would be a real killer during a race if the other guy has a way to avoid it on corner exit.

Question 3: Also while cornering, it felt like the rear of the kart was alternately hooking up and then breaking loose on many of the slower corners -- almost crabing sideways at times. Tended to happen from appex to track out. I'm guessing this was due to the fact that I was unable to keep the cornering forces high enough in mid-corner to keep the inside rear wheel of the kart off the track. Since Karts don't have differentials, I presume that having both rear wheels solidly in contact with the track during cornering leads to rather evil handling effects. Are there any driving techniques to deal with this? Chassis setup changes? Or is my analysis of what is going on completely off base?

Thanks in advance for your input!!

[dalyduo]

RJ Valentine, the owner of F1 Boston has a Kart service business that would know the answer to your questions.

RJV Enterprises, LLC
135 Wood Road., Braintree, MA 0218
781.843.0100
Toll Free: 877.GO-SSC-01
Fax: 781.356.2245
www.ssceast.com

I believe Jon Miller has or had a Rotax kart but not absolutely sure.

I'd check out www.ssceast.com. and give them a toll free call first though.

My 2 cents

[jp56]

I’ll give you my two cents, but the karting kids probably can help you the most.
The rib problem is common and depends on the track. I can drive Moroso all day, but Opa Locka in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-comffice:smarttags" /><st1:place w:st="on"><st1:City w:st="on">Miami</st1:City></st1:place> I only last an hour. I separated my ribs in <st1:City w:st="on"><st1:place w:st="on">Miami</st1:place></st1:City> just from the G’s on the track. A good fitting seat helps and a strong core body does too. You will condition your body somewhat just by karting. Keep your ab’s tight in the corners and don’t let your body flop around. When I start flopping around, I take a break.
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Rotax is all about rolling speed. If you make a mistake and over slow or over drive a corner and slide too much, you’ve had it. This part is very good training. The centrifugal clutch is the challenge. It takes a second for it to spool up. When I used to drive Rotax, I would anticipate the throttle application and apply it early to get the clutch spooled up. Using gas and brake can develop bad habits for car racing. Just be aware of that. Sometimes the lag can be an improper jet in the carb. I don’t know much about this. I just tell my mechanic and he works his magic.
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I’m not quite sure what you mean in your last question. There is a real talent to getting the set up correct in a kart. Sometimes it defies logic as it’s not the same as you would do for a car. I tell my mechanic what it’s doing or not doing and he fixes it. If it’s hopping on two wheels in the corners, you have too much grip. Plus it’s tough on your ribs. Experiment with the set-up. Sorry I can't be of more help.
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[AZRCD]

Originally Posted by PT Cruiser

Question 2: When exiting corners, the engine would hesitate for a few ticks before accelerating strongly. Is there a driving technique one can use to keep the engine in its power band in slow corners --such as leaving the gas on a bit even during braking and corner entry-- such that this hesitation doesn't occur at corner exit? Alternately, does this mean I don't have the engine tuned properly? Either way, it seems like this lag would be a real killer during a race if the other guy has a way to avoid it on corner exit.

Easy answer and for doing always: Put your foot down early, you have to time it because you want to be flat while still in the corner, but still not on pipe. Most including I do this by going to the gas while still on the breaks. keep on the brakes deep into the corner (this is big advantage of the rear break.) This may depending on other factors help with q 3.
The more complicated answer is the jetting. The carts are very sensitive to the humidity and you need to get the jetting right. Makes friends with somone who has the sensor and software on their laptop.

[Matt]

Is the lag like a sputter or more like turbo lag? If it's a sputter, it could be jetting. If it feels like a turbo kicking in, it's the power valve doing its job. It's been so long since I've run a Rotax, but I believe the power valve opens up around 7,000 rpm.

[Yarab]

I have been doing Rotax for a few years. My tips
Get maxjet software for jetting. It is amazing what effect weather has. Also, Make sure the packing in your pipe is changed every 8 hrs
My kart was bogging down and I tried everything and it turned out to be the packing. Make sure you clean the power valve after every use. Unfortunately I can't find John's mechanic up here in y-town, So I have towrench everything.

Ron Yarab

[Matt]

Ah yes, packing the pipe. Not sure I ever did that (which might explain a few things!). Looking back, I'm remembering all the small routine maintenance bits I had to do between each session -- tighten & lube the chain, lube the bearings, plus all the times I cleaned the carb, fuel filter, and power valve. Still beats shifter maintenance!

[PT Cruiser]

Thanks to everyone for all of the advice.

I suspect that my lag coming off corners was mostly due to poor jetting, since the engine did sputter a bit before accelerating briskly. I took a flyer on what jetting to use, and I suspect I ended up too rich for prevailing weather conditions. I knew the jetting was off because the motor would only rev to 12K rather than 14K, but I didn't consider that it might also be the reason why the engine was stumbling on the exit of many of the slower corners. Sounds like the jetting weather station and software is a good investment, so as to avoid all of the trial and error involved in getting the jetting right on any given day. It hadn't occurred to me that humidity as well as temperature would play a role in jetting decisions, although when I think about the role that moisture plays in determining atmospheric pressure, it makes perfect sense.

I have to admit, I was in such a state of sensory overload my first time out with the kart --on a new track to boot-- that I simply didn't notice the transition to the power valve. I'll have to pay more attention to this on my next outing.

Ron -- Like you, I'm stuck doing all my own maintenance. A pain in the neck, even if the Karts are relatively simple mechanically. Sure adds to one's appreciation of the SBRS's arrive and drive deal.

Back on the topic of rib injury, does anyone have advice on how to tell when it is safe to go karting again? I would like to go out for another test session this weekend, but 1.5 weeks after my first outing, I still have some rib pain if I put pressure in the wrong place. It's better than it was a week ago, but still sore enough such that I'm dubious about my ability to run more than a few laps. I don't know whether it's better to wait until the rib area is completely pain free before heading back to the track --which I'm guessing will take at least a couple of more weeks-- or whether the only way to build up tolerance over time is to push the envelope a bit, and return to the track before the effects of the previous outing are completely gone. Of course, my fear is, that if I try the latter approach, I will just exacerbate the original injury, and put myself out of karting action for a solid 3 months. If anyone can offer suggestions on how to make this judgement, based on their own experience, it would be appreciated.

[jp56]

Speaking from experience, ribs take a long time to heal depending of course on the extent of the injury. I separated mine and it took a couple of months before I went karting again. That was two years ago and they have not bothered me since. I don't kart at Opa Locka, Miami anymore. Moroso is much kinder to the old ribs. Get a good rib protector, a good fitting seat, and strengthen those core body muscles. Unfortunately, time is the best way to heal them.

[Matt]

It normally didn't take so long for my ribs to feel better if they were bruised. I did break a rib at Jacksonville, which took weeks to heal. If it's painful to sneeze, cough, or laugh, you've certainly done more than just bruise 'em!

[Yarab]

HEY, THEY'RE ONLY RIBS.
IT'S NOT LIKE IT'S A LIVER OR PANCREAS
THE FASTER YOU GO THE LESS THEY WILL HURT

RON YARAB

[KevinH]

I do a little Rotax running at OVRP when I am not at LRP with Skippy. The ribs can be a real issue but I make sure I am very snug in the seat. I barely fit in with my rib protector. This has seemed to calm them down and I never really feel discomfort when riding, the next day can be a different story though.

As to the lag in the corners most of the other members have said what I would, get on the gas earlier. You might try faster cornering speeds as well. It is amazing how much grip karts have and are usually underestimated. Braking is pretty squirrely but once you are set in the corner the g-forces that are sustainable are tremendous. At the track
I go to I can keep it in the power-band everywhere but two 100-120 degree turns. The only thing is it is physically abusive to keep up that kind of pace. I can usually only do a handful of laps at that speed before my concentration lapses and then I start making mistakes. My hat goes off to those kids that can do that all day long competitively!

[PT Cruiser]

Well, at my second ROTAX practice session, my ribs held up just fine . . . but only because my clutch expired after only ten minutes of running. Turns out the nut that holds the chain sproket to the clutch housing had come off, which of course leaves the kart with no drive whatsoever. Wasn't hard to fix, except I needed to buy an impact wrench to get the clutch opened up in the first place. I guess the guy who owned the kart before me didn't bother to use lock-tite or some similar goop to help hold the nut in question in place.

Hopefully, I'll learn how to avoid these little mechanical gremlins relatively quickly. 4 hours of towing/kart preparation for ten minutes of seat time is not exactly my idea of a good return on investment, timewise!!

[Matt]

Here's a link to a Rotax-specific message board on the Ekarting News website. You can find vendors and a wealth of knowledge there to help with anything Rotax! http://www.ekartingnews.com/viewforum.php?f=18