My 420cc Mods Blog

A little about me:

My name is Charlie, I am sort of a “Jack of all trades, Master of none” kinda guy.  I am starting this blog, because over the last couple of years, I have started to get into go karts.

I am NOT a go kart racer, by any stretch.  I just like go karts.  I buy, trade, sell, fix mostly just “fun” karts.  My main baby is a Carter 2910TH (trail hunter), but more on that later.  Future posts will include the mods that I have done to this kart so far, and my first hand opinions of them.  Hopefully, you find this entertaining and possibly informative.

It seems to me that there is not a ton of information readily available on the 420cc clones.  I have a 420cc clone installed on my Carter, and will be modifying, piece by piece, and testing the results, in the future.  There will also be some other smaller, “fun” go kart stuff strewn in here and there.

My Baby ….

A Carter 2910TH (trail hunter) was my starting platform for this build.  Unfortunately, I didn’t start this blog when I first got the kart, so I will try to bring you up to speed, so far.  In stock form, the kart was fun, and was capable of handling some trails, even with two adults on it.  I did find, however, it was a little lacking in some areas … So the modding begins.  One of the very first things I noticed was the lack of fenders and driving this through any puddles would instantly get you very muddy and drenched.  So the very first mod was to make the fenders.  The whole kart was built from a pretty thick walled tubing, so me, being the kind of guy I am, and wanting to do as much as possible by myself (without spending a ton of money) figured using gas pipe from Lowes would be a great idea.  I bent up some pipe to make some very basic fender frames.  I then used a thin sheet of fiberglass riveted to the pipes to complete them.  Problem #1, SOLVED!!

Problem 2 was the lack of ground clearance.  I tend to like to take the kart out in the woods, in the quad trails (which can be quite rocky and rough) the kart came equipped with 16×6.5 x8 tires on the front and 18×9.5×8 tires in the rear.  I also noticed problem #3 around this time.  It seems with two adults on the kart, the front suspension was way too soft and would lower almost HALF of the total suspension travel (decreasing my ground clearance even more!)  So, the next order of business, which to me seemed to be the easiest way to gain more ground clearance, was to get larger tires.  I installed 22x11x8 on the rear, and 20x x8 in the front.  This gave me the ground clearance I wanted and with only a 2″ difference front to rear it also gave me a lot less rake.  The next order of business was to stiffen up the front suspension.  From the factory it came equipped with a single shock on either side and the stepped type preload adjustment on the spring.  The easiest and fastest (and cheapest!) way to accomplish this was to simply add another pair of shocks.  I purchased a duplicate pair from BMI and went about installing them.  Again … I like to keep things simple so I just removed the front shocks from their mounts and installed one on either side of the mount with much longer (grade 8) bolts.  Quick and dirty, but effective!  Now, with two adults on the kart, it will not sag at all and can easily roll over a cinderblock!  Plenty of ground clearance, for my needs.  Problems 2 & 3 SOLVED!!

The next problem in line (due to my new found ground clearance and larger tires) was the EXTREME LACK of power!  I searched the internet for the HIGHEST horsepower, single cylinder I could find.  I wound up with 420cc Clone, rated at 16hp.  I ordered the motor from Caroll Stream.  At the time, it did not have a lot of other specs for this particular engine, but at 16hp for under $400 shipped to my door, it was worth a try!  Upon receiving the motor and attempting to install it, I ran into Problem # 4.  The factory motor mount plate for the stock 10hp, was MUCH to narrow for this “big block” and the engine cover would not clear the 60t sprocket.  Being overly anxious I fabbed up a quick and dirty motor mount by bolting up a couple of pieces of 1×1 box steel to the stock motor mount and drilled new holes in the 1×1 to bolt the wider engine to.  This allowed me to mount the motor with the height I needed to clear the axle sprocket.  I had to purchase a new comet 40 series driver, because the old one was frozen to the stock 10hp and despite my best efforts to remove it, it simply would NOT BUDGE, and I wound up destroying it.  I ordered a couple of new belts, because the length was slightly different, due to my taller “motor mounts”, and having to slide the jackshaft assembly much further back simply due to the size of the engine.  OK, now the motor is installed … and my first impressions were good.  I got back some of that lost torque due to the tire size.  Problem #4 SOLVED … or so I thought.

I drove the kart around like this for quite a while, but was plagued with belt alignment issues, due to the motor constantly getting cocked on my crappy “motor mounts”.  I knew the mounts would eventually get to be an  issue, but at the time, it was a quick and easy way to at least test the motor.  Looking back, I definitely should have taken the time to make a better mount.  Around this time, my factory brakes (Carter used two 5″ band brakes on this model) wore down to nil.  I then ordered two new drums and two new bands.  When they arrived I learned very quickly how much of a pain in the ass it is to take the rear axle out to this kart.  As I am sure it had NEVER been removed before, pretty much everything was frozen (of course).  I could not get everything loose enough to slide the axle out either side of the kart.  Again, I took the quick and easy way out because I am just that patient to install my new parts.  So, the easiest way out was to actually grind the openings in the bottom of the bearing hanger plates until they were just large enough for the 1″ axle could drop right out of the kart.  This made it much easier to free up all the frozen stuff.  I also noticed that the axle bearings were in rough shape, so I replaced them while I was installing the brakes.  I adjusted the brakes and went for a ride.  To my amazement, they weren’t much better than the brakes I removed!  I was guessing that the brake problem was due to the huge tires I installed.  Too much rotating mass!  To test this theory, I replaced all the tires with 16x8x7 tires all the way around (I had them hanging around from another kart I have).  Turns out, I was right!  With the smaller tires, it easily locked up at full speed, even on pavement!  More on the brakes later.

After getting used to the 16hp, I soon needed … MORE POWER!!  I was happy with the speed (at this point anyway) but wanted more low end power … Problem # 6.  So, back to the internet, looking for a larger sprocket than the stock 60t.  A good friend of mine (Shawn) found me a nice 70t #40 sprocket for a 1″ axle.  I had to send it out to a machine shop to get the axle hole enlarged to a little over an inch, and bolt holes put in it to match my sprocket flange.  I noticed a big difference in low end power right away.  The kart accelerated MUCH BETTER, even in the dirt, or grass, or mud, etc.  It did, however, lose a little top end speed.  Which brings us to …

Problem # 7 … Lack of top end speed!  Being new to small engines, I again, sought the advice of my buddy Shawn.  I decided the easiest way (again, I like easy, even if it is not necessarily right … ) was to by pass the governor, so we could get more RPMs out of the motor, and hence … MORE SPEED!  (Before any of you jump on me, for “by passing” the governor, I know that it is not the “right way” to do this, but I am only in testing mode, damnit!  Eventually when I disassemble this motor (for more goodies) I will completely remove the governor).  Shawn came by my house and explained to me how these governors work, and then proceeded to bend me up a piece of linkage in place of the governor spring.  After he finished, I took it for a test run, and WOW, what  a difference.  I am pretty sure I gained back my lost speed, and then some!

The next step I decided to see if I could make this thing breathe a little better on the cheap, so … a homemade header was in order.  Back to Lowes.  I bought a handicap grab bar that was approximately 1.25″ in diameter x 24″ long and (BONUS …) made out of stainless steel with round, welded flanges on the ends!  I cut a 45 degree angle in the pipe (to approximately 16″ long) and cut down the round flange to the shape of the exhaust gasket.  Like a dumbass, I slotted the bolt holes, one of which was right under the 90 degree bend (in the pipe).  Again … Back to Lowes.  The problem was that due to the bigger diameter of this pipe, I no longer had enough clearance for a regular bolt head or nut, even if I used studs.  My fix?  Allen head bolts!  One bolt went in with no problems, the bolt under the bend, I could get started but could not fit the allen wrench in, as the pipe was in the way (too tight of a bend!) so, I broke out a page from the old “Yankee Ingenuity” book and cut an allen wrench (10mm, I believe) to approximately 3/8ths of an inch long.  This allowed me to get the piece in the bolt and tighten it with a thinner, ground down, 10mm wrench.  I wrapped the header with 2″ header wrap and then with stainless steel wire over the wrap in a chriscross fashion.  Next, I painted the wrap with flat black gas grill paint to keep it all glued together (and hopefully, withstand the heat).  I was pretty happy with myself, because it looked cool and made the motor a little more snappy (although a bit louder).

I decided I still needed … MORE POWER, and was running into another problem.  I have found, that when off roading (and bouncing around a lot), I would get an intermittent bog that would last a second or two and then go away.   It took me a while, but after talking with Shawn, I found out that more than likely, bouncing around was wreaking havoc with the float bowl in my carb.  Sooner or later, the float would probably just break off, and leave me stranded out in the woods.  This, I could NOT HAVE!  Shawn to the rescue!!  He is MUCH more knowledgeable then I am, and he told me the cure for my carb problem would be to get rid of the stock carb all together and purchase a Tillotson carb.  This would cure the bogging problems, and has an added bonus of … yay … MORE POWER!  Gotta love that!  He ordered me the right carb, for my application, with a matching intake manifold, fuel pump, throttle linkage bracket and air filter adapter.  When the presents came in, I installed them (it was fairly straight forward), and tested it out.  I was a bit disappointed at first, because I had a pretty good lack to power mid range.  I played with it for over an hour, and got it better, but not as good as I feel it should have been.  I get back on the phone with Shawn, who promptly corrected my tuning methods.  Turns out, you can’t tune these like a regular carb.  After his words of wisdom … back to the kart, and VIOLA! no more bogs, and noticeably snappier, with a noticeable jump in power through all RPMs!  I still haven’t installed the fuel pump yet.  I can’t wait!

The engine finally ripped right through my crappy motor mounts, and I decided … enough is enough!  The next step is to remove the motor and make a real motor mount.  While I am at it, (and the motor is off) I will be doing a serious brake upgrade.  It will include TWO 8″ hydraulic discs, with accompanying calipers and master cylinder.  If that doesn’t stop me …

I will be uploading pics of everything (and possibly video too) and part numbers, links, etc for those interested.  Future mods will include  a bigger (8.5″ diameter from 7.5″) driven on the torque converter.  I am looking into a longer than stock aluminum connecting rod, short skirt piston with a higher wrist pin to accommodate the longer rod.   Slight cam for more torque, and beefier valve springs.  Following that will be an aluminum fly wheel, with the ring gear for electric start.  And hopefully a better header.  I already have a 4.5 gallon aftermarket fuel tank that I will be putting on it as well.

Stay tuned …

  1. November 14, 2012 at 14:44

    Great article. I too am into go karts (racing them) We recently got into the 420cc engine too and we love it! It is so much nicer than 2-stoke or the other 4-stokes that you have to pull start. We love having the ability to just unload, turn an key and make a few laps!

  2. August 21, 2013 at 02:23

    hey! i was wondering if you had a diagram of the engine plate you ended up with? id like to do this to mine i also have a carter just like yours but i still have the roll cage on it

    • August 31, 2013 at 09:46

      sorry…i do not have an actual diagram. but….it’s easy….i used a piece of plexiglass and just marked out the holes {using the actual engine} and then drilled the holes in the plexi ….then transferred it to the steel.

  3. Zac
    October 10, 2013 at 21:43

    What model carb fit the 420cc?

    • October 11, 2013 at 04:57

      It is a tillotson carb
      I needed the intake manifold also
      Both part numbers and links are on the parts info page

  4. Jason
    February 12, 2014 at 22:01

    Can you tell me all of the mods you did to the motor to upgrade the carb , intake exc. such as part names and part numbers if you have them please

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