My Rotax wont reach max RPM's??

jeremy freedman · Joined: 13 Nov 2011 Posts: 7

I just bought a brand new Intrepid kart and I'm having problems with getting it to reach top rpm. Ive tried different jets, we took the carb apart and tried everything else possible and it still wont run right. It has seen 14200 a couple of times but mostly stays in the 12300 to 13200 range. Any ideas what it could be?? thanks

Nick Weil · Posted: Wed Nov 30, 2011 9:27 pm Post subject:

1. Power valve improperly adjusted, not cleaned or just plain not holding together anymore. How many hours since you disassembled and reassembled the power valve?
2. Battery not charged constantly when off the track, or perhaps your battery has bad cell that only acts up at high RPM's. Do you religiously charge the kart as soon as you come off the track EVERY session?
3. Weak fuel pump or possible vacuum leak that prevents the fuel pump from providing maximum fuel at high RPM. How many hours since you rebuilt the fuel pump?
4. Exhaust pipe. How many hours since you rebuilt the pipe?

These are just a few things that come to mind.
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jeremy freedman · Joined: 13 Nov 2011 Posts: 7

this is a BRAND NEW kart with maybe 1 hour on it

Ray Chiappe · Posted: Wed Nov 30, 2011 10:01 pm Post subject:

What type of track are you running on? And what gear ratio?? I just raced at Infenion (the big track) and barely saw 13,000rpm. Didn't exspect more.

jeremy freedman · Joined: 13 Nov 2011 Posts: 7

the gearing is correct for track. it just seems like it wonts to go up but cant. some laps it will go higher than others but it seems like something is holding it back. i put a 160 jet in and it started popping so i jetted up and it seems too rich. plug showed to be rich so went back to 160. took it out today with 160 in and it didnt pop at all but it wouldnt go past 12300.

Nick Weil · Posted: Wed Nov 30, 2011 10:19 pm Post subject:

If the kart is brand new then I would assume you did a proper break-in. That would be 2-3 (10) minute sessions for a total of 20-30 minutes. From your description, you said you took it out for several sessions (or at least enough sessions to try 'different' jets) to me that implied at least 3-5 jet changes. Which is obviously not the case. Sounds to me like you haven't spent enough time with it trying different carb settings and different jetting if you only have 1 hour on it. And if you do have more than one hour on it that means the power valve 'could' have an issue or not be adjusted properly. How did you adjust your power valve after you did your 2-3 break-in sessions? What did you do with the spark Plug you used when you did your 2-3 break-in sessions?

A location would be real helpful. As well as what weather conditions. Seeing as how the weather and your altitude will ALWAYS determine jetting.
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Nick Weil
Authorized Rotax Service Center and Dealer since 2002
2004 Team USA Rotax Worlds Finals DD-2 Driver

Want to save money AND grow the economy? www.fairtax.org

jeremy freedman · Joined: 13 Nov 2011 Posts: 7

John Savage · Posted: Wed Nov 30, 2011 11:34 pm Post subject:

jeremy

Just get someone who knows the Rotax Max engine to take a look next you are at the track, I sure it will be something simple which can be sorted out quickly.
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al nunley · Joined: 13 Nov 2006 Posts: 3066

Never raced that engine, and there are a few things you’ve left out.
Air density for one, it can change from day to day, from morning to afternoon to evening and can have a big effect on mixture.
If you had an EGT you could tell a lot more about the mixture, rich or lean.
Fuel octane is something you might look into. High octane doesn’t mean more power, it means better for high compression engines where you would get detonation without it. I don’t think your engine is so high in compression that it needs high octane race gas.
Have you checked the compression pressure? Do you know what it should be? Compression is the Holy Grail.
You’re taking shots in the dark right now.
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Don Holmboe · Posted: Thu Dec 01, 2011 10:49 am Post subject:

Jeremy, your original post said that motor acheived 14,200RPM a couple of times. The jet you had installed then, barring huge change in air density, was correct. Continue your testing with that jet. Have you tried different, known to be good, battery? Even if power valve is adjusted properly it can still be hanging up when trying to open. Many 09 and newer motors have had valves that need special attention because of undo drag.
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Ihor Bilyy · Posted: Thu Dec 01, 2011 12:13 pm Post subject:

Can you reach 14000+ on a stand?
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tony zambos · Posted: Thu Dec 01, 2011 2:37 pm Post subject:

Jeremy, have no idea as to your expirence level but it seems that you're new to karting. If you are, welcome to the sport. It already seems that you have support at the track and good ideas to look into from the posts above. Relax.

On your engine, what were your water temps? For a plug on a 50 degree day, I'd would have kept the IW27 in as it would be the warmest.

Don't be fooled by tring to get every rev out of your engine. Your lap times when you hit 14.2 might not be as fast if you only turned 12.8 for a max. Also take a look at your chassis setup. You, the chassis and the engine are a package on the track. To go fast, all three have to be right.

Good luck
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ap kart racing
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Anthony Burke · Joined: 19 Mar 2011 Posts: 22

Jeremy, I'd be having a good look at the exhaust matting. If the engine's been popping, there's a better than average chance that the matting will be burnt out - which won't be helping your cause.
Do your class rules insist that you run a catchtank or similar on the carb breathers? If so, remove the breather lines from the carb and try again.
12,600ish is when the ignition timing changes. If the jetting and everything else aren't correct, you'll notice a significant lag in performance.
Recently had similar problems, engine would get to 12,600 easily and then needed another 2 seconds or so to reach 13,200 = frustrating

Larry Hayashigawa · Posted: Sat Dec 03, 2011 8:32 am Post subject:

Fuel?

Peter Zambos · Posted: Sat Dec 03, 2011 8:58 am Post subject: