Rotax Problem at the Start.

Mike Robertson · Posted: Sat Jul 27, 2002 3:07 pm Post subject: Rotax Problem at the Start.

We hare having problem getting off the line at the start of the race. We start with a rolling formation, but when the green flag flies, we lose several positions before the Kart gets going. We've tried low gear ratios. But these don't work either. Once we get going, we run real good.

Any ideas?

Matt France · Joined: 21 Jun 2002 Posts: 106

are you bogging in the corners too?

You might want to try changing the jetting in the carb.

Nick Weil · Posted: Sat Jul 27, 2002 7:42 pm Post subject: Rotax Problem at the Start.

Mike,

Have Jr. do some practice starts and make very close note if the RPM's seem to die out at any given point. I have seen similar problems lately and may be able to offer some guidance...

Nick Weil

Mike Robertson · Posted: Sat Jul 27, 2002 8:31 pm Post subject: Rotax Problem at the Start.

Thanks Nick. He even has trouble when he starts from a stop. Is there something in the low end that can be adjusted?

Jeff Edwards · Joined: 10 Sep 2001 Posts: 193

My experience is with road racing and standing starts, so may or may not be applicable.... but we have lots of practice with awful starts, due to the gearing we need.

When the flag falls, the tendency is to floor it, but this can be very wrong in a Max. Have him try to feed the fuel just part way, then gradually more as the speed picks up, to keep from flooding it.

Maybe you can find a practice day (mid-week?) where you can throw a green flag for him, timing through the first half lap. Let him test different throttle positions. It takes a lot of strength to not let your adrenaline take over.

This is most likely the problem, but your jetting, especially the low speed jetting (needle) can also be a factor.

Jeff Edwards

Nick Weil · Posted: Sun Jul 28, 2002 8:46 am Post subject: Rotax Problem at the Start.

Mike,
I need for him to tell us if there is a specific point in RPM that it seems to stutter. If not, you may need to work with your idle screw and/or your air mixture screw. The Main jet is ONLY for top end and would not solve the problem you are experiencing most likely. Call me if you get some more specifics...

Nick

Mike Robertson · Posted: Sun Jul 28, 2002 8:03 pm Post subject: Rotax Problem at the Start.

I'm going to take him out this week and we'll practice some starts. I'll check on the RPM's and also try the different throtle possitions and report back.

Glenn Holland · Posted: Sun Jul 28, 2002 8:48 pm Post subject: Rotax Problem at the Start.

Is he mashing the throttle? The Rotax is sensitive to throttle appliciation.

adrian ward · Joined: 17 Jul 2002 Posts: 7

The Needle position stage of the carb is what is controlling your power at a rolling start, try lowering the needle(eg

osition 1 vs 2)which will allow less fuel into the engine. Also ride the brake to keep load on the engine, then at the drop of the green, release the brake and feed throttle slowly. All this works for me everytime!

Shannon Schmidt · Posted: Mon Jul 29, 2002 6:29 am Post subject: Rotax Problem at the Start.

Mike...I woould agree witht the post just above this one. I do this technique and I have been lucky enough to have never lost a spot on a start and usually pick one up!

Chuck Groat · Joined: 04 Apr 2002 Posts: 60 Location: Salt Lake City, UT

Mike/Nick - I have the same issue and the stutter/bobble occurs at approx 6,000 RPM. The kart is great out of the corners after racing starts so I wouldn't change the needle settings, but RPM never dips that low when racing. I will roll on to the throttle and not "mash the gas", but still have the bobble around 6,000.

Rob Martin · Posted: Wed Jul 31, 2002 8:53 pm Post subject: Rotax Problem at the Start.

Don't forget that the Rotax Max has a flat spot on the power curve typically around 7500RPM. Depending on the adjustment of the exhaust valve and jetting this flat-spot can be shifted higher or lower. Gear selection can also exaggerate or highlight this problem.

What is the max RPM you are obtaining?

Is yours a series 1 or series 2 FR125 motor? There are subtle differences in the carburation.

Chad Stapleton · Joined: 19 Jul 2001 Posts: 4403

quote:
Originally posted by Rob Martin:
Is yours a series 1 or series 2 FR125 motor? There are subtle differences in the carburation.

I don't think any series 1 (pre 2000) motors were imported to the US , were they ??

Rob Martin · Posted: Thu Aug 01, 2002 9:57 am Post subject: Rotax Problem at the Start.

Chad,
You may be correct about the likelyhood of having a series 1 motor in the US but I try not to take anything for granted when troubleshooting a problem.

You guys down-under have been running the Rotax motors a lot longer, so I appreciate your comments.

Do you have any good Rotax part sources who wouldn't mind shipping to the US?

Chad Stapleton · Joined: 19 Jul 2001 Posts: 4403

Rob,
one of the best "international" sources for Rotax (and most other kart parts) is "Dartford Karting" in the UK :- www.solokarts.co.uk.
+44 1322 222645
+44 1322 288966 - fax
They carry a huge range of all spares at the lowest price. Orders can be phone/faxed thro' , pay on visa etc, world wide service.
Example:- new nikasil barrel 160 pnd UK (=$250 US)
The prices in Australia are sometimes lower, but few kart shops are set up for international service.