Tuning a Rotax Max

[Bob Smith]

I just recently received a Rotax Max and was wondering if anybody knows how to tune it as far as the power valve on the rear of the engine and w/ the jetting.

Thanks

[Nick Weil]

Bob,
Welcome to the wonderful world of ROTAX.

First favor you can do yourself is to goto:
www.rmaxchallenge.com

There you will find a couple very important links to a lot of information. Go to the 'RMC NEWS' section and then click on the 'Max Tech' button. There you will find several monthly newsletters regarding how to 'tune' the MAX.

After racing 5 Rotax Max Challenge races I can tell you few of the critical things are:

1. Power Valve: When you are on track get cruising at 5,000 RPM. Then give the kart full throttle. At EXACTLY, and I mean EXACTLY 7,400 RPM you should feel the kart jump to life. This is one of the biggest gains you can get and it has to do with the ignition curves.

2. Be sure you are not running lean on your jets. If you hear any back firing or sputtering when the kart is under full throttle above 7,400 RPM chances are you are too lean. Fatten the jet one or two sizes and try again.

3. Never let completely off the throttle. There is a technical reason for this listed in one of the newletters, and I don't have the info directly in front of me, but the MAX will fall on it's face for a split second every time you get completely out of the throttle and then back in it.

Hope this info helps.


Nick

[Stephen Buckley]

Bob,
Again, welcome to the RotaxMax club. You won't regret it.

The key to RM (not counting chassis setup and driving ability) is carb tuning and gearing. It is critical for you to learn and understand the Dellorto carb (look at the various websites) and how to tune. I have over 500 laps of Rotax time and here's what I have found.

First of all, try to keep the motor clean. This can stop a lot of problems. Learn how to determine "adjusted altitude". Use the charts in the manual. They will get you into the ballpark. After you are comfortable with selecting a jet, try moving the jet needle clip. Oh, make sure you seal the exhaust cone. By the way, as sparkplugs go... while you are learning, don't spend the big bucks for sparkplugs. Buy a bunch of Autolite 2592's. They are solid copper core and are great. Say $4.00 each.... now smile. Let me know if you need anything else.
Take care.
Stephen

[Jon Andrews]

Jetting, jetting, jetting.....

Learn to read the plug, and don't be afraid to lean it down. That being said don't drop more than 2 jets at a time. I purchased jets from 175 to 155 (don't go higher than 175 it makes no difference and you will never need it).

As an example I raced on a day where the air quality was so so. I started at 172. It ran terrible, and stalled on the track (1st time this happened). I then tried a 168, ran Ok but wouldn't rev out above 12,200. To cut along story short I ended up at 160 for a main jet, and could have gone to 158 if I had not ran out of time. Bottom line is that with experience you will not waste time starting way off like this and start at maybe 162/165.

Also buy a humidity/temp/pressure gauge. I was lucky enough to pick up an Oregan Scientific weather station for $29 from an office max clearance sale (normally ~$180). You NEED to know what the RAD is to tune effectively.

Document your setups well. In the RMC there is very little time to play around with the motor jetting. You want to be able to concentrate on the chassis NOT the motor.

My 0.02c

[Randy Dye]

In light of an adjustable power valve, are any of you Max racers able to set up an Air Density baseline like we do in shifters which also use float bowl carbs? Are the Delorto jets flow rated or simply orifice sized?
Randy

[Stephen Buckley]

In light of an adjustable power valve, are any of you Max racers able to set up an Air Density baseline like we do in shifters which also use float bowl carbs? Are the Delorto jets flow rated or simply orifice sized?
Randy

Randy,
Yes, we do set a baseline. There are charts in the RM manual that show ballpark jetting with reference to altitude, in addition to a RAVE tuning chart. I believe that the jets are sized.
S

[perfonic]

Dellorto needles ,tubes and jets are all in metric sizes a 168 jet is 1.68mm .I use a B&G racing computer that calculates density altitude ,then I use one of the other programs in it to calculatre what jet or needle adjustment I have to make.Down in the Vancouver area the density altitude can be anywhere between 385ft to 1128ft jetting didnt change I run 162 jet K57 needle there,the first time I went to Quesnel I didnt have the computor and I only played with needle height my best lap time was 40:02.The next time I went with the computor my I found the density altitude was 3500ft in the morning and reached 4700ft by mid afternoon, by using the jetting program and knowing what my baseline down on the coast was,I needed a 155 jet and leaner needle settings . Put in 158 jet(lowest I had)and K27 needle set on the leanest setting had way more snap and acceleration my lap times went down to 39:33.
Ask Stephen I was a flying.

[Bob Smith]

Thanks for all this info on tuning the Rotax Max. I was recently at the track and I don't know why, but I kept going with bigger jets starting from a 168 then a 170 until I got to a 175. It seemed to run better but I was wondering why everyone else or those who replied have had so much success with leaning them down? Thanks

[Nick Weil]

Altitude, humidity, wind conditions, temperature, track conditions.

Every single one of these is part of a very complicated equation with the Rotax jets. If you have the right jet to compensate properly for all of these, your Rotax will REWARD you!



Nick