[F500] Tours and motors

[Eric D. Christensen]

I know it's tough when you're autocrossing to get much data... too
little run time and too much stuff to do when you're out there. But
try to pay attention to when it bogs in relation to cornering. If it
starts to bog about 4 or 5 seconds after a hard corner, it's probably
picking up air from the fuel cell.

Road racing it's easier to spot 'cause 4 or 5 seconds after a hard
corner you're cruising down a straight most of the time. In solo, of
course, 4 5seconds later is 3 turns down the course. :-)

The Rotax and the pumper carbs are VERY sensitive to air in the fuel
lines. It doesn't take much sloshing in the fuel cell to get the thing
to suck a bit of air or foam, which will cause a very noticeable
hesitation.

I assume you're running on light fuel load for solo (1 or 2 gallons).
You might try running a full tank to see if it still has a problem. If
not, then you've found it.

Fixing it is a little more difficult. I put a system in my Mk-8 with
an external surge tank, vented back to the cell, and 2 electric
pumps - one feeding the surge tank and the other drawing from the
bottom of the surge tank to feed the carbs. That totally eliminated
the problem, no matter how hard I tossed the car sideways.

One other remote possibility that hasn't been mentioned it the your
idle is so rich that coming off the gas fuel fouls the plugs. Try
leaning your idle screw out a 1/4 turn each run to see if it gets
better or worse.

And yes, you can run a WHOLE lot leaner than us road racers. I used to
jet my Mk-8 to 250-260 for solo. On the road course I'd run 310-320.
Note.. please don't blindly try to duplicate my jetting... it varies
quite a bit from car to car and track to track. You mileage may vary -
greatly!!!! EGTs, plug readings and piston crown readings are the only
way to properly jet a 2 stroke. You just have to test and see what
works.

Cheers-

-----
Eric D. Christensen    edc at proadmin.com
SCCA Formula 500       http://www.f500.org



> -----Original Message-----
> From: f500-admin at www.f500.org
> [mailto:f500-admin at www.f500.org]On Behalf
> Of Mike Quinn
> Sent: Tuesday, July 02, 2002 2:14 PM
> To: f500 at www.f500.org
> Subject: [F500] Tours and motors
>
>
> I got into the tour?  Great.  Now I've got a question.  My
> car (KBS Mk7,
> Rotax, Mikuni) has a problem "bogging down".  It starts and
> idles just fine,
> launches fine, but at times, at speed, when you hit that
> gas, the motor kind
> of chugs and darn near dies.  You take your foot off the
> gas and it returns
> to idle and if you work the throttle a little, it will
> finally go.  It seems
> to do it more when it's hot.  I'm new to the car, so please
> "dumb down" any
> advice.
>
> Gracias.
>
> Mike Quinn  #74FM
> NWOR-SCCA
>
> _______________________________________________
> F500 mailing list - F500 at www.f500.org
> To unsubscribe or change options please visit:
> http://www.f500.org/mailman/listinfo/f500
> *** Please, DO NOT send unsubscribe requests to the mailing
> list! ***
>