Home Forums Autocross / Solo 2 JA kart w/WF slow off the line

This topic contains 9 replies, has 3 voices, and was last updated by  Alan Sheidler 5 years, 5 months ago.

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  • #4924

    Kevin
    Participant

    Greetings –

    I’ve got an issue with a JA kart being slow off the line (at Pro launches in particular) – it seems to have a good motor, rebuilt by Kart City last year, and it runs just fine once he gets rolling.  But at the Packwood pro, his 60′ times were terrible (.5 off the only other JA kart there per-side, and the difference got pretty large by 200′, and .1 slower than the JB kart that was present).  It’s slow enough off the line at normal non-Pro courses to affect his times there, too – almost sounds like it’s bogging for the first 200′ or so, then picks up and goes.  I’m trying to figure out if this is purely a gearing issue, or if there might be a problem with the clutch, or if I simply have the thing jetted incorrectly.  Gearing-wise, it had a 16/69 setup at the pro.  The other JA kart seemed (I didn’t sit there and count the teeth) to have a much larger axle gear, but on ours I think if I went shorter he’d spend more time on the rev limiter (which I’ve been trying to avoid).  The gearing seems OK once he gets going.  Clutch-wise, he has a tendency to brake torque it before the launch, maybe that’s heating it up enough that it’s grabbing at a lower RPM than it should for the orange springs?  And I’m not really experienced enough with jetting these things to know, but the main jet seems fine (plug always looks OK, doesn’t seem crazy rich, and again, runs great once he gets going).  I’ve been playing with the needle and idle mixture screw without really changing the bogging behavior.

    It’s not as much of an issue at normal autocrosses, except when he overdrives into tight corners, gets sideways and nearly parks it and has to pull out of it (he’s over-exuberant a lot of the time, and is aware that he needs to chill that out a bit), but it seems like I’m doing something wrong with the setup.  He is a bit heavy (35# more than the minimum), but I wouldn’t think that’s nearly enough of a difference to account for the differential to 200′ we were seeing at the pro.

    Thanks in advance for any advice/tips.

  • #4927

    Scott Boito
    Participant

    Hi Kevin,

    I’ll share our recent experience as it seems relevant. My son’s JB WF is essentially brand new and rebuilt (twice, unfortunately) by Eric Nelson at 7th Gear. The motor is strong, but Kieran was having exactly the issue you describe: terible launches and terrible recovery from slides and sharp turns. Gearing didn’t matter and we tried several different ones. Importantly he experienced the same things when he briefly drove a loaner motor while his was being rebuilt. The only common piece between the two motors? The brand new clutch. That’s foreshadowing.

    After a few events where he wasn’t improving, I decided that a track day was in order to get us both back in the swing of driving fast. It worked wonders for two reasons: we got more seat time that one day than we’d had for the previous year combined, and his clutch finally came in. My guess is that either the shoes had to be scrubbed some or the drum needed to be heat-treated as we did at the track. The result? Kieran went out and was faster than all of the JB and JA kids at Summer Nats and finished the Champ Tour paxed 13th out of 213, his best finish in a National event ever by a long shot. His launches at the Pro were great and his clutch didn’t falter all weekend. He said it was a dramatic change for the Pro and we were able to gear him all the way down to 17/65 for the Tour.

    So my hypothesis, right or wrong, is that autocross doesn’t allow the clutch drum to heat up enough for a proper break-in/coating. The answer for us was a track day to allow that to happen. Alternatives might be to sand down the clutch shoes a little to get to the good material and/or rough up the inside of the drum to make material transfer or heat-treatment to more readily take place.

    I was almost ready to ditch this motor and head back to the KT100 (and would have if we’d still had them around). Kieran was not having fun until this change and constantly asked about going back. Now he’s VERY happy with the motor and we’ll work on weight-balancing the kart better now that I know we’ll have it for several more years.

    Good luck!

    Scott

  • #4951

    Kevin
    Participant

    Wow – thanks a ton for the response.  Makes sense, since I couldn’t imagine that the jetting (or the gearing) was *that* far off.  I have a buddy who’s into snowmobiles that pointed out that he’s had similar issues with those when the clutch wasn’t quite right, so I’ll focus on that for the time being.  Thanks again!

  • #5367

    Alan Sheidler
    Participant

    I’m happy that Scott was able to get Kieran’s problem solved.  And, the clutch was where I was going to suggest looking as well, when I heard of the issue with slow launches and spin recoveries.

    The clutch we got with our WF had Yellow springs.  I bought another clutch without checking what was in it, only because it was CHEAP.  Since we run the sprocket inboard, I took the unit apart and swapped the direction of the pucks, noting that it had orange springs, which are supposed to be the stiffest?

    Colin immediately noticed the improvement in launches, and it got better as the clutch wore in.  Yes, we also did several track days for him and brother Connor.  I’d suggest reading up on the expected engagement RPM for the various springs.  If the clutch is engaging shortly off idle, and/or locking well before the designated engine speed, then there is an issue.

    FWIW, the only time we experienced the issue both of you described was when an outrageous gear was selected for an event in Oscoda.  Colin was in charge of choosing his own gears, and I let him put the 56 rear on (16 or 17 front, I forget…) although I knew it was not going to work.  Was it slow to get going?  Ouch!  Tight corners meant it took way too long to get up to speed again.  After the event, we devised a method of checking for his actual top speed capability with a run down the long taxiway.  67 mph when the limiter kicked in.  After that, I handed him a calculator and had him first estimate his actual top speed potential, based on course design, then choose the gear based on what we knew the other one could achieve.  That is when the wins began.  Good times……

  • #5511

    Kevin
    Participant

    Thanks Alan – yeah, the current clutch is the orange springs (I was under the possibly-mistaken impression that I had to have those, since that’s “how the motor is delivered” – although maybe you can order a WF motor with other colors?).

    So last week, I noticed that the original clutch that came on the motor did have the hub reversed (and appeared to have non-orange springs, although they were hard to identify), and this kart has seemed to have this issue since we bought it.  I did buy a new clutch before getting the motor rebuilt, however – and last Friday remembered that, when I got this motor back from rebuilding, the clutch came back inboard – at the time I just turned it back around without disassembling it, so my working theory was that maybe this was a side effect of reversing the hub (notwithstanding the number of people who seem to do it that way out of preference).  I took it apart last Saturday, and no – the hub direction was the right configuration for outboard, but there was an oddly sized thin (very thin, like feeler gauge stock) washer/shim that was “sort of” underneath the snap ring that keeps the sprocket in the drum.  The ID of this thing was large enough that only some of it would be located under the snap ring at any one time – so suddenly my theory converted to “perhaps the drum is initially misaligned relative to the shoes, due to this shim/washer thing?”  I couldn’t even find this shim on the diagrams on Noram’s site, so I removed it…   This seemed to help, although not completely – and I noted that the outboard-direction half of the shoes had slipped a lot.  This was clear from the amount of material built up in the grooves.  So I’ve got a new clutch coming, we’ll be careful breaking it in, and see if that helps.

     

  • #5528

    Scott Boito
    Participant

    Sounds like that washer is the shield for the needle bearing piece of the assembly (officially named the thrust bearing).  Check out the exploded view here: http://www.noramclutch.com/go-kart-clutch/premier/titan-sp2.html

     

  • #5529

    Alan Sheidler
    Participant

    Kevin,

    Do you have to run the clutch with the drive sprocket “outboard” in order to clear the chassis properly?  From what I have seen since we got our WF many years ago, the general consensus is that running it “inboard” places considerably less strain on the crank and drive-side bearing.

  • #5616

    Kevin
    Participant

    Sounds like that washer is the shield for the needle bearing piece of the assembly (officially named the thrust bearing). Check out the exploded view here: http://www.noramclutch.com/go-kart-clutch/premier/titan-sp2.html

    That was the drawing I was going by – if you’re talking about the thrust washer, that’s not it.  This piece had a large enough ID (and was much thinner than the thrust washer) to almost slip past the spiral snap ring holding the sprocket to the drum, and didn’t really have the right dimensions to locate any particular part of the assembly.

  • #5617

    Kevin
    Participant

    Kevin, Do you have to run the clutch with the drive sprocket “outboard” in order to clear the chassis properly? From what I have seen since we got our WF many years ago, the general consensus is that running it “inboard” places considerably less strain on the crank and drive-side bearing.

    I’ve heard that – to do that on this kart, I’d have to remove some of the unused (currently) middle axle bearing bracket.  That would be easy to do, though – I might try that when the new clutch arrives.

  • #6633

    Alan Sheidler
    Participant

    Another option might be to reconsider what is being used as an engine mount.  Many of them are fixed laterally, with the only adjustment being fore and aft along the frame rails.

    The one we began with and still use is flat, and allows side-to side adjustment as well.  That came in handy when getting the proper  clearance.  The frame we have was designed as primarily for outer right drive (such as the 2-cycles, KT-100, etc) where the rear sprocket is inside the RR wheel.  Mouting the WF was not all that tough, though.

    The Gold chassis does not have the 3rd bearing hanger.  I thought only the frames built for higher power engines used those?  That must be some beefy frame you have there.  Are you sure it is for a kid?  ;-)

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