kart carb jetting

[RobbieNelson]

Nate/Jason,

Care to share jetting knowledge? I know Nate had some sort of spreadsheet and was using a relative air density gauge. I think Jason has a gauge but I'm not sure of his method of selection. I've been doing some research. My info is posted on eKartingnews.com: http://ekartingnews.com/viewtopic.php?t=76954

Basically I've found a way to calculate air density from temperature, barometric pressure and humidity (dew point). I've also found that the flow rate through an orifice or pipe (like a jet) is directly proportional to the fourth power of the diameter of the orifice or pipe.

Oh yeah, check it out...

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[Jason V]

right now I am looking at the plug to keep the main jet in check and slowly tuning the mid range of the carb by feel... I plan to change imulsion tube stlye (longer tubes to hold back fuel longer) and meetering needle next year.... anyhow with my Dellorto Carb tuning the part throttle portion of the mixture is very important.. using EGT or RAD won't help much. I plan to buy the software package sold by John Savage a poster on the linked thread.. BTW I have learned the most by looking at the plug vs my air density gauge.

[Jason V]

Just watched the video... good stuff. One thing you missed as far as tuning the rear axle stiffness is the length of the rear hubs and the overall width one has the kart set too... longer hubs stiffen the axle... narrowner track also stiffens the axle. Right now I run medium hubs and 53 to 54 inch rear track..(I plan to try long hubs next year) I run the front hubs to about 80% of their widest setting...(wider takes away a little grip but increases the weight jacking effect of the karts geometry) Oh and ICCs do have expensive parts but are as easy or easier to work on than the honda. I would still only recomend an ICC for autocross if the driver in question is over 200 pounds due to the rules for minimum weight.

There is just sooooo much you can tune on these things... front and rear track, steering akerman, front toe, camber, and castor... rear track, axle stiffness, hubs (short,med,long) tire pressures all round, adding or taking away extra seat struts, seat position (to change f/r and l/r weight balance, front and rear ride heigth, some kart have an adjustable wheel base (mine does not), brake balance f to r, adding or taking away front and rear "sway bars", and some karts also have a removeable 4th rail by the seat....

Not sure what the others are up to but for next year I plan to get longer rear hubs, a Mychron Gauge, some new imulsion tubes and jets for the carb....I plan a change in approach to carb tuning in order better suit the carb to autocross and my size (er weight)... I am also looking at trailers.... the Van is going away and a new to me GTI is now my "tow" vehicle!!

See everyone in January

[RobbieNelson]

Glad you enjoyed the video. I did it to answer questions that I had up to this point. Trying to help newbies while I'm still in the category. After a year, I may have forgotten that I didn't know how you started the engine. I'm sure I missed lots of stuff, but I just wanted to cover the basics.

Winter plans:
top end tear down and inspection
- cylinder is sleaved as I was informed by the seller; cylinder in good shape
- moly coated piston?
- new head; mine was in rough shape. $62 new from Fastech Racing
- piston top showed that I've been running rich
- port work to the case
- reed cage in good shape

carb tear down and inspection
- everything was nice and clean
- floats were empty as they should be

exhaust
- weld small crack (done)
- install EGT bung (done)
- new o-rings (done)

New parts:
- Mychron4 2T with data-key (installed already)
- MG green tires (from MG)
- kart cover (ebay)
- cylinder head ($62 Fastech Racing)
- number plate for rear (MRP motorsports)
- rear stiffening bar (MRP motorsports)
- brake rebuild kits (MRP motorsports)
- brake bleeder (~$60 Fastech Racing)
- missing main jets for my Keihin PWM carb
- chain guard

I've spent most of my time learning how to tune the carb. The last thing I want to do is blow the engine up and have the expense of a rebuild. I plan to just learn how to drive it and make minor adjustments. I need to tune the nut behind the wheel. I also plan to purchase a kart for the kids in March. We'll likely be traveling to other regions that have the "pilot program" (kids 5-7yrs).

[Jason V]

Let me know when you mount those tires.. I have a tool that will help alot. it uses a sort of scissor action to slip the tire on or off the rim..... even with the right tools it is not easy.