We here at ARB Motorsports are building another Junior Sprint for our Daughter to race at Rockfish Speedway in Rockfish, NC. Since we’re basically building from the chassis up, we just had the rules meeting, the class is growing, and the first race being right around the corner we thought we would throw a post together to explain our process.
Hopefully someone finds it useful….
2018 was the first season of Junior Sprint racing at Rockfish. For us here at ARB Motorsports fielding two cars, this was a learning experience to say the least so I hope to save some time and frustration for others if you’re just getting started in the class. I did everything one could do wrong at least once at my poor children’s cars last year, so we learned a lot that I am now applying to our third car.
First a couple of helpful links:
Go-kart specific parts for the Predator 212:
270 parts:
There are always good deals on used parts at www.microracing.com or facebook mini-sprint classified pages as well.
Provided you have a good rolling chassis already, I will spend the bulk of this post on the go-kart specific portion of converting the 270 into a Junior Sprint. I’ll add the caveat that I get most of my 270 parts from Hyper because they are still in the 270 business, they have a ton of useful information for setups on their webpage, and they will help no matter the chassis manufacturer you are running. Not to take away from the Stallard rep at Speedway Motors but they don’t focus on the 270 stuff anymore.
I should state now that the parts and advice I’m giving is focused on a left hand drive chassis. That is what we run because I’d like to see my kids grow in to the 270’s eventually and it should save me buying and selling when the time comes. I already have the chassis.
Bill (Rockfish Speedway Owner https://rockfishdirt.com/ ) has some parts for motor plates, if you have access to a machine shop, or are just handy I’m assuming you have a motor plate or can get one built. Fairly simple construction but it should have slots to allow for minor adjustments (forward and back) to chain tension once everything is mounted.
Side View of Motor Plate (note the slotted bracket to allow forward or back movement to adjust chain tension):
Here is a screenshot of my initial purchase for components.
From www.ombwarehouse.com
From www.BMIkarts.com
OMB Warehouse didn’t have the ARC Racing plate so I went through BMI Karts.
The Predator 212 is available at Harbor Freight for usually $119 but most of the time they are discounted to $99. Keep an eye out for coupons or sales.
On that note, they seem to randomly carry either Hemi or non-Hemi Versions. We have both and don’t notice any difference in power or reliability but it’s your choice if they have both versions, or maybe you’re stuck with what they have.
The Hemi Part Number is: 60363
The Non-Hemi Part Number is: 60730
Article from OMB Warehouse, with pictures of the visible difference found here: https://ombwarehouse.zendesk.com/hc/en-us/articles/223139208-Hemi-or-non-what-do-I-have-which-is-better-
LESSONS LEARNED:
I run the #41 chain instead of the #35 chain. I find it more reliable and sturdy especially if things aren’t perfectly aligned. The downside to the #41 chain is if you want to mess around with the rear gear size, it isn’t as affordable and available as #35 chain sprockets. I did run a range of rear sprocket sizes from 54 tooth to 80 tooth in an effort to eek out more speed, but our average lap times never showed a marked change for the positive or negative.
Absolutely run a chain tensioner.
Buy extra belts for the torque converter, as well as extra bronze bushings. Spending the extra few dollars for quality on these will go a long way. The bronze bushing with clone torque converters is garbage compared to the quality brand one. They work, but I would say they don’t last.
If you aren’t going to relocate the stock fuel tank to somewhere else on the chassis, there is no need to buy the pulse fuel pump and ARC Racing plate with throttle linkage. The motors run just fine with the tank in the stock position.
If you do run the pulse fuel pump, you need to drill and tap a hole in the valve cover, thread in a NPT fitting, and run the hose from the NPT to the pulse fuel pump. I sealed around the threads on mine with JB Weld.
Non-Hemi Pulse Fitting Mod:
Hemi NPT Pulse Fitting Mod: (you can see the jackshaft setup for the drive sprocket fairly well in this picture)
Even if I was using the ARC Racing top plate because I moved my fuel tank elsewhere and needed the pulse fuel pump, I would not use the included throttle linkage. Take it off and just run your throttle cable from your pedal straight to the governor arm. This may not be as relevant if you remove the governor altogether but this will bypass the governor completely. (See Youtube link below)
I guess one last note: make sure things are lined up straight and square. Specifically the chain from the drive sprocket back to the driven sprocket.
Hope this helps a little. We’re always looking for sponsors 🙂
OTHER RESOURCES:
Amazon.com for digital tachometer with max RPM recall:
Transponder via PitStop USA which also has good prices on safety equipment.
Here are few more useful links since I didn’t make my own videos. There is a ton of stuff on Youtube:
Throttle cable install, governor bypass. Courtesy of Rather B welding on youtube:
https://www.youtube.com/watch?v=aQFgCTbI5w0
Torque Converter Install, courtesy of Red Beards Garage on Youtube:
https://www.youtube.com/watch?v=UK7EW9vcqSw
Comet TAV2 30 Series quality explanation, Courtesy of Studz Hardware and Powersports on Youtube:
https://www.youtube.com/watch?v=7Z1ZNJ531IU
ARC Racing and Pulse Fuel Pump install for Predator 212, Courtesy of ARC Racing on Youtube:
https://www.youtube.com/watch?v=CrSh_Hv6RgE
Support ARB Racing
All Donations go to support ARB Racing, Rockfish Speedway, and any charities or special events ARB Racing supports
$10.00
ARB Racing 