March 6, 2015 at 1:49 pm #43526
I just received the upgrade kit today for the junior. Is the expectation to run this “as is” out of the box? Took the carb apart and I see 4gr floats, 130 main, 60 outer pilot, 45 inner and a 60 start jet. The 130 seems pretty far off as we typically run 152 or 155 (in Houston area). Not fully versed in the overall carb changes and don’t want to stick a motor. Anyone else fire one of these up yet?
March 6, 2015 at 2:20 pm #43528
The new carbs do run with a much smaller jet i know the DD2 motors ran around that 132 jet and DD2 typically runs a higher jet then junior
March 6, 2015 at 2:42 pm #43529
I think the DD2 comes stock with a 145, and micro, mini, jnr, snr all come with a 130. I wouldn’t worry about sticking that motor with the 130, if anything, I’d imagine you will want some leaner jets. We have to forget everything we’ve learned about the vhsb 34; the new carb has completely new internals and the jetting will be very different. Supposedly the tuning window is much wider with the new carb and nailing the perfect jet isn’t nearly important.
March 8, 2015 at 3:43 pm #43603
Agree, we just put together a couple new EVO Jr. complete engine packages and took the carbs apart to see what they came with. Needle is different, floats are now 4.0 gr and came jetted at 130 which we are guessing may actually be a tad rich.
All in all, really impressed with the changes and upgrades that Rotax has provided. The only thing that didn’t give us a ” warm and fuzzy” was the new pipe mount. We actually drilled another hole and added a spring to get it to sit and secure properly. If anyone has the answer to getting the pipe to sit properly with the springs included, please upload a picture to the forum, I am sure others will appreciate it. Thanks, and feel free to reach out to us if you have any questions or need assistance. george V. @ ApexKartSports
Rotax Service Center
March 10, 2015 at 8:17 am #43732
I have heard Junior running a 116 and senior on a 118. That comes from a south african article that has had the evo engines for a little while.
April 7, 2015 at 6:42 am #45599
Used 115, 118, 120, 122 and 125 jets over a two day period last weekend both testing and racing. Weather conditions were pretty stable with a 10 to 15 degree total change in temps (track at sea level, 60 – 75 degree temps). No discernible performance gains or losses when changing jets. We maintained what we perceived as best jetting using plug color because the driver couldn’t notice a difference, even when we new we were too rich, he said it felt great. Zero bog. The new carb appears to meet objectives set out by Rotax for Junior Rotax. Now that doesn’t appear to be the case with Micro Max from what I witnessed.
April 7, 2015 at 7:57 am #45617
Scottie, might I ask what you did see with the micro max, going to upgrade soon and have limited testing time.
April 8, 2015 at 10:17 am #45707
Steve, I was out this weekend with Scottie and agree with his assessment on the Jr jetting. Once the jetting was resolved, the upgrade was roughly 0.5 second faster than the old setup. We even dropped 2 teeth on the Prevo while maintaining the same max rpm as our old setup.
We also race Micro but I really think Rotax may have dropped the ball with this group. The lowest jet commonly available is a 115 and the EVO upgrades will not run with that jet… a leaner jet is required. One racer in the group running an Evo engine was able to get a 112 and run it. He was as much as 1 second faster than any of the other competitors in the Micro class. Until this event, the top drivers in this class ran within a tenth of each other.
My other issue with the Micro is that the faster EVO setup is now legal to run as of March 30 but is not available to everyone. Even those who were lucky enough to receive their upgrades are screwed unless they can source the non-standard jet sizes below 115.
As a tuner for a Junior and a Micro, I definitely have a love/hate opinion on the new EVO’s at this point. Hopefully that will change in the coming weeks.
April 8, 2015 at 11:21 am #45711
For micromax, you are not limited anymore to the supplied jet kit of 115, 118, 120 etc., you can use rotax jets from their next kit down, which starts at a 100. You cannot use any jets that are not in the rotax jet sizes though so don’t go buy a 94 from delorto and use it, you will get a DQ. I ordered two of the smaller jet kits from rotax last week and already got them.
April 10, 2015 at 12:01 pm #45834
We tried a 122 in our micro and still have a lot of bog (came from 130). We’ve changed the clip to 1, the plug to a 31, nothing so far eliminates it. We have a 115 jet waiting for us tomorrow (race day), so hope to try it in first practice and see how it works. Our times are staying relatively stable as we’ve been experimenting, but zero increase in performance that we can detect. It seems a little more robust at the low end, but still seems to bog down on exit. Contrast that with someone who used a full Evo at the first race (he knew it was not legal yet), but that kid flew by us on the main straight a couple weeks back. So looks like its going to be a rough weekend. (the cynic in me is trying very hard not to think that Rotax just shoved out a handful of update kits that really don’t do much, knowing we’d be forced to go buy a full motor if we want to keep up) Trying real hard.
April 13, 2015 at 9:37 am #45960
I think you are probably still way too rich. and going to the cold plug when you are very rich will make it worse. a hotter plug like an IW24 may have worked better. There some an interesting turn of events for the micro class at our track. Ill will post a report on the upgrade thread I started.
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