[Eric Alexander]

The starter is prone to vibration breaking the electrical leads going to the bushings.  The design IMO is poorly engineered as the lead is soldered at a right angle to the way the bushing moves and that stresses the solder connection.  Its a fairly simple fix – starter rebuild kit is cost effective and it takes about 30 minutes.  Most guys racing will carry a back-up starter.

[Eric Alexander]

Just putting this out there:  the thing that makes Mooresville work so well is the 40-plus garages they have rented out.  Kart owners store and work on the karts there, and this make a great environment for consession karters to come to.  There’s always a racing kart lapping there and I find the guys who rent the consession karts really like watching those.

Like mentioned above, MMX runs 10 minute sessions, alternating between rentals and racing karts when both are looking for track time.  When there’s no consession karts, the track is open to kart owners.

Having the garages there makes things very convenient for kart owners and there’s always a kart owner or two there.  At tracks I’ve visited without garages – when I’ve had to transport my karts there –  I’ve typically been the only kart on track.  IMHO, having this type of day in and day out activity is the backbone for a successful track.  It brings new karters in, exposes them to racing karts, and creates a community around the drivers at the track.

[Eric Alexander]

Just wanted to follow-up here.  I found the 4hz GPS mode is only available in the 17.5 firmware for the camera.  I managed to find the firmware version and manually set the GPS record frequency to (4).

[Eric Alexander]

Bill,

I researched the same thing over the past six months.  What I came up with was a ContourGPS camera, my existing Mychron dash, and Dashware software.  The ContourGPS camera has built-in GPS that gives you accurate positioning, G-forces and speed.  Dashware allows you to load the video file from the ContourGPS and it automatically extracts the GPS data.  Dashware also allows you to create custom gauges easily to display the info.  Lastly it pulls in the Mychron data for revs and laptimes.

I picked up a second hand, like-new, ContourGPS on eBay for $100.00.  The Dashware software is only $50.00.  So it was really an affordable package.

Here’s a link to a video I created:  http://www.raceralex.com/video/MMX-2013-12-17-01_720P-LQ.wmv  It’s the lowest HD quality you can render using Dashware and is the actual video (not some YouTube compressed file).

Using Dashware I created a decent track map for GoPro motorplex and a MyChron3 gauge for the display.  For the price I think its pretty effective with anything I’ve seen.

 

[Eric Alexander]

Ted, the closest Rotax Service Center is Kartsport North America located at the GoPro Motorplex in Mooresville North Carolina.  They can breakdown, inspect, and reseal your engine and reissue a replacement passport.

[Eric Alexander]

So Walt, should the grease be applied between the piston and the back of the pad?

[Eric Alexander]

Thanks Tony.  I spoke with Dave Davis at CRG America and he said the 2000-up caliper will wear the pads a bit uneven.  The 2000-up system has dual calipers on the rotor, but only a single piston per pad – per caliper, so I don’t think its the pistons.  I’m going to mic the rotor next time I’m at the garage to see if possible the rotor has worn unevenly and may be contributing.

[Eric Alexander]

This will be interesting to watch considering the uproar early this season when the Leopard wasn’t competitive with the Rotax.

[Eric Alexander]

The new style clutch greatly improves reliability.  So much so that updating the clutch is a must do IMHO.

Updating is fairly simple and there are step by step instuctions from Rotax avaliable online. You will need a clutch puller for the flywheel and a torque wrench to match specs.

[Eric Alexander]

I bought my Rotax karts back in 2010 – a matching pair of 2005 CRG Kalifornia’s with same year engines.  The karts had been sitting up in NJ for a year or so.  I disassembled the karts and rebuilt them from the ground up.  I then couldn’t even get the engine’s to fire up.  LOL!  So, I started sorting the engines.  In the end, the 8-year old motors today fire-up nicely and perform smoothly on the track.  And my karting experience is far better as a result of all the hands-on time fixing and fine-tuning everything.  I was at the track yesterday and my biggest complaint was that I threw a chain.   =)

Good luck!

[Eric Alexander]

Battery-wise, as you probably know the Rotax is a total loss system.  The battery is used for all running electrical.  A bad battery can lead to misfiring and bogging.  When I was new to Rotax, I used non-spec batteries as they were far less expensive, and I had all sorts of issues with the engine missing and bogging coming out of corners.  Finally swapped to a YUSA Rotax-spec battery and the engines ran consistently well.

I had a fuel pump go bad once.  At first the symptom was the kart was simply running poorly.  As the issue progressed, the the kart would hardly run at all under load out on the track.  After trying everything else, the light-bulb went off and I checked the diaphragm.  It was fairly stretched from use.  I had about two seasons on that diaphragm.  Its such an easy thing to check and correct.  I now have a separate rebuilt fuel-pump on stand-by just in case, and I visually inspect them regularly.

I’m not running DD2 (I’ve got a pair of Seniors), but the principles are the same.  I do know the DD2 typically is jetted far richer than the non-DD2 Rotax engines.  In the beginning, I was taking my kart to a near-by track that didn’t have many pro karts there.  So I was basically all by myself.  From reading the forums, you’d think Rotax was basically Voodoo when it comes to jetting and carb set-up – lots of threads about problems.  And of course when you’re new to Rotax you’re not sure what is too rich or too lean.  But I have to say once you spend some time with it, it really is a very robust package.  These days I basically check the weather, run the data into a jetting program (like John Savage’s Jet Tech), install the specified jet and plug, and hit the track.

[Eric Alexander]

Mark, I’d go up a full jet size instead of float arms and needle clip changes.  If for no other reason to just see for sure if its too lean.  That said, from what I’ve experienced an engine too lean will miss on the top end and pop.  And since your’s is not, I can understand you trying the needle clip.  Also regarding the choke, when you apply it you essentially richen the mixture across the board.  Another reason to go up one main jet size.

When I had issues in the rev range you mentioned, it turned out to be battery related.  So you might look there if the main jet doesn’t solve it.

Other Rotax check points:  if the fuel pump diaphragm is old you might inspect/replace that and be sure all your fuel and vacuum hoses are tight and secured.  Sometimes air can be pulled into the fuel lines.  Or the pulse line can lessen the fuel pump’s capabilities.

Is your problem occurring all the time at that rev range?  Or perhaps just when exiting a corner in that rev range?

Something suspect is the 7-8k rpm mark.  That’s defiantly RAVE valve suspect range.  I know you said you checked it, but don’t 100% rule it out as you step through other areas if jetting doesn’t work.

Lastly, as John Savage would advise: if you can swap carbs with a known good one, you can then begin to backwards trouble shoot.  If you swap carbs and the problem still exists, I’d start looking at electrical.

 

[Eric Alexander]

So as you hit your braking marks, you brake hard.   As the turn-in begins, you begin to modulate the brake (trail brake).   As you approach the transition between braking and acceleration, you  can modulate the brake to the point of lock-up, which of course causes oversteer.  Simultaneously, apply some throttle which brings the rear back under control.  Using both pedals, you can ride the edge of this – controlling the rotation – until you roll completely off the brakes and roll onto the throttle as normal.

Now I don’t do this as a rule.  But there are corners in which I do this fairly regularly.  Hairpins for example.  And if making a pass I’m always ready to transition to this technique if needed.

[Eric Alexander]

What I sometimes do is use the brake to lock the rear and initiate the rotation (slide, oversteer, etc.) towards the apex while using throttle to stop or control the lock-up.  I think of it like yaw in an airplane – you’re literally controlling the yaw of the kart by balancing the brake and throttle pedals.  Having the throttle applied also raises the revs earlier.

I find the technique works better in some formulas than others.  Also, you have to be careful not to nullify the braking with the throttle.  Anytime you overlap throttle and brake you’re reducing the braking efficiency.

Also for the most part, oversteer is generally considered to be slower.  So the technique is best right just before the transition from braking to throttle.    So the rotation is happening right about this transition.  And by rotation, I mean the kart is physically rotating around its center point independent of the line you’re taking.

[Eric Alexander]

Interesting addition Ray.

Of course I think on the outset one must define threshold braking to clarify the difference to trail braking.

For me trail braking is the classic Skip Barber technique of trailing off the brakes gradually as turn-in begins.  This technique allows the driver to brake deeper into a corner and carry braking through the turn-in phase.

Threshold braking (I assume – I don’t use that term… although its a good as any to label the technique) is the use of throttle underneath braking to (1) control rotation more aggressively, and (2) keep the engine revs up at the point of transferring off of braking onto throttle.

Good topic, but I’ll hold off opinion until after we confirm this is what we’re discussing. ;-)

[Eric Alexander]

@ Paul:  By all means, this is an open discussion.

For me, the line driven is still on the edge.  The braking is hard and you should be near the limit at turn in.  I think that is what T.J. means early on in this thread when he says “you want to be fast in and fast out”.  In that graphic, you still want to be at the limit during the red and yellow portions of the line.   I think where you’re going be less at the limit of grip is under acceleration and track-out because you’ve lessened the arc – in theory.

But the real point is how to back the corner up to be faster on exit and thus carry that additional speed down the following straight.

Also, I think that embedded graphic might be over-exaggerating the line somewhat to show the concept.   I think the linked-to page has better theoretical graphics exploring the concept mathematically.  But personally, I find the math tough to digest and only like it because it explains what I feel I ‘m trying to do.

[Eric Alexander]

I’m going to try to explain this first with words, then I’ll point to a website that has some decent graphics and some geometrical calculations.

The basic premise in “Slow in-Fast out” is to back the corner up as far as track out is concerned.  The idea is while the corner itself can be taken faster using an ideal line, you’re going to sacrifice entry speed, turn-in sooner, push the “apex” later and essentially give yourself an more gradual track-out.  This enables you to get back on the throttle earlier (well before the apex), and accelerate faster, thus carrying more speed down the ensuing straight.

I find the turn-in point, depending on the actual corner geometry, may actually go deeper and more to the outside of the corner entry.  Instead of carrying speed to the actual corner apex, you brake a bit more slowing the kart down well before the actual apex.  This is the “Slow in” part.

You can see in the graphic above the arch is modified from the ideal line.  The ideal line would allow more speed to be carried into the corner, but less speed on exit.  You can also see how the apex is pushed somewhat later, but acceleration has begun well before the modified apex.  The track-out is more gradual allowing far greater acceleration.

Here’s a website with more info and some math.  LOL!

http://phors.locost7.info/phors17.htm

 

Also, it would be beneficial to point out this is best used on corners that empty onto long straights.  There are times when its best to be fast in- Slow out.  For example at the end of a long straight when the corner connects onto another corner (like an esse) or a small straight followed by another corner.  In this case, you may be better off carrying the speed you’ve got on the long straight deep into the corner and sacrificing exit speed.  Let the stopwatch be the judge.

[Eric Alexander]

Karting IMO is the most affordable form of motorsport there is.  That said, like all things in racing, your budget is what you chose to make it and there are guys spending big dollars to go kart racing.

I think a big factor in how affordable the sport is to you is how close you live to a track and what programs they run.  My karts are garaged at my local track, and the track runs events basically once a month (if not more).  So a race day is essentially a set of tires ($200), entry fees ($60-$100), and fuel & food.

Garaging the kart at your track is a big plus IMO.  Hauling the karts, while easy enough, increased my trackday expenses by over $100+.  Also the loading and unloading added time on both the front and back ends.  Now I drive a fuel efficient car to the track for $30.00 in gas, fire the karts up and go karting.  Just FYI.

A set of tires is $200.00.  You’ll want a new set for a race weekend to be ultra-competitive and managing tires is part of the sport.  But then those used sets are good for track days and practice.  And there are some guys who run sets for more than one race weekend and still have fun.  And some club events mandate tire set usage over time to lower costs.  Again, check with your local track and see what they offer.

I think maintenance costs are relatively inline with car costs considering the size of the kart (meaning its a lower operating cost than your 944).  But there are times when you’ll find yourself with sticker shock over some spare prices.  I guess that’s true for all motorsports.

OK, all that said, karting is a very pure motorsport experience.  75% of everything involving tuning and maintenance you can do yourself.  That makes it a very hands-on and personally rewarding experience.   And of course when on the track, the handling and power-to-weight ratio is unreal.  The speed and agility of the kart is a real rush.  The tire slip angles are wide and pushing the limit is forgiving –  although smooth is fast, of course.  But for someone like yourself, looking to push your focus, concentration, and be competitive, karting is very accessible.

You say you’re spending 10K annually for race your 944.  I spend half that as far as operational costs.  And that includes $2500 for the garage space.  That puts me at the track (not racing) about twice a month minimum – some months up to five times.  Race, say half a dozen times a year, and you’ll add $2000 to that figure – give or take.  So depending on how close your track is,  how much you head to the track – and whether you haul or garage your kart – your annual operational costs might be anywhere from $3000-$7000 for a budgeted karting effort.

[Eric Alexander]

Hey Jeff, I just noticed on eBay an auction for an older CRG frame that looks identical to the one you’re trying to fix.  Might want to hurry and take a look.  I searched “CRG Kart” and its newly listed.  Here’s the link but I’m not sure if its proper to link to the auction site from here.  FWIW, this is not my auction.  Just trying to help a fellow karter.

http://www.ebay.com/itm/Kart-CRG-Chassis-/261304403377?pt=LH_DefaultDomain_0&hash=item3cd6f4c5b1

[Eric Alexander]

The older clutch drum is larger in diameter and has six sizable holes in the front side.  The 09 and newer clutch is smaller and has a solid drum.

Inside, the actual old clutch has many parts including shoes, springs, support bracket, etc.  The 09 and newer clutch is a single machined peice.

[Eric Alexander]

Less money = more work. ;-)

[Eric Alexander]

Bob – Either you misunderstood the guy at GoPro Motorplex or he’s in the weeds.  You are correct that using that theory – and all things being mechanically perfect – he’d want the staggered tire on the LEFT side for that course.

Also as you most likely know by now, TJ is a great source for information.

Regarding tuning with air pressure:  I “once upon a time” scaled my kart to find it had a slight twist resulting in a higher diagonal weight.  At the time I thought I’d see what air pressure changes did to effect that.  I balanced the kart using air pressure, then went out – ran 10 laps or so – and blistered the rear that was on the heavy side.  Rookie mistake.  I’d never blistered a tire before, nor have I since.  But what I learned was use tire pressure to fine-tune the handling, not compensate for a mechanical imbalance.  Better to address the mechanical issues with mechanical solutions in order  to get your tires where you can fine-tune the handling.  In this case, measure the tire circumferences and match like-measured sets together.

I will say this, I’ve had very good results running different pressures left-right depending on the number and direction of turns.  At GoPro Motorplex, I start with .5 pound more cold pressure on the right (Bridgestone YLBs).

[Eric Alexander]

Good info there.  Thanks Nick!

For the record, there’s alot of vodoo written but the RAVE valve – “set it so many clicks”… etc.  From what little reading I’ve done, the design of the valve comes close enough to the piston that the 7500 rpm is critical to operation.  Open too soon and cylinder compression is lost before the 7500 rpm timing shift.  Open too late and the exhaust restriction reduces HP gains from the higher compression rate after the 7500 rpm timing shift.

[Eric Alexander]

I wanted to bump this back up and add to my findings..

First, once the RAVE valve fully opens the exhaust note does become more aggressive – more edgy sounding.  This sound can vary in volume based on the engines’s state of maintinance: exhaust matting, gaskets, etc.  But the note takes on a slightly harsher or shrill sound once the valve opens.

But here’s a few more questions for the experts:

1. Does the valve snap open when the pressure overcomes the spring rate?  Or is it a gradual opening over a few 100/1000 rpms?

2. Does the Rotax ignition programing actually change the timing at  <7500 rpm to allow the firing of the cylinder to occur as the piston draws even with the closed exhuast valve (on the down stroke)?

[Eric Alexander]

min. coolant temperature [°C / ° F] 45 / 113

Optimum coolant temperature [°C / ° F] 65 / 149

max. coolant temperature [°C / ° F] 85 / 185

I set my MyChron alarm to go off at 180° F.  Although that’s probably too high now that I think about it.

 

[Author]

Posts