Yerf Dog Go-Kart Shocks Upgrade

The Yerf Dog 3206 & 3209 go-karts handle better than some other go-karts, but the shocks that came on my early production model were less than ideal.  The front and rear shocks did not allow much travel and the ride over rough terrain was pretty harsh.  Very bumpy conditions were not comfortable.  Obviously considering the relatively low cost of the go-kart, I did not expect the stock shocks to be perfect.  That's OK.  This just gives me room to try to make things better.  So, I began researching ways to try to improve the handling and comfort of my go-kart.     

REAR SHOCK UPGRADE

The first area I worked on was the rear suspension.  The stock rear shocks are 12" long (center to center of mounting holes) and they have VERY STIFF springs.  The rear suspension was not allowed to travel much with such stiff springs.  As a result, the ride over bumps was pretty harsh in back.  If you check to see the clearances between the rear swingarm/engine assembly and the frame, you can see why not a lot of suspension travel could be allowed in the stock setup.  Given enough deflection of the go-karts rear swingarm, there would be a collision between areas of the engine like the black plastic electrical box and the frame.  So, the stiff stock shocks were probably chosen in an attempt to minimize these collisions. 

I began thinking that a longer rear shock with softer springs would allow the rear suspension more travel and still provide some additional clearance to avoid the collisions.  I began searching for some used motorcycle shocks on eBay that might fit the requirements.  I was targeting shocks that were around 14" from eye to eye.  This length was just a gut feeling.  I didn't know what the perfect length would be.  I just figured this would give 2" more additional shock travel than the stock go-kart shocks.  I ended up buying a set of 87-88 Kawasaki KXF250 front shocks off eBay that were 14" long.  The KXF250 is a 4 wheeler quad.  The shocks cost me around $20each + shipping.  It turns out that these shocks worked really well - especially considering how much I paid for them.

It is very important that whatever shock is chosen be one that will bolt in to the go-kart.  There are a LOT of shocks out there that can be purchased.  Some are easier to use on the 3206/3209 go-karts than others.  Personally, I didn't want to have to weld on new shock mounts.  I felt that I should be able to find something that would just bolt on and improve the situation.  The shock mounts on the 3206 & 3209 go-karts are around 3/4" wide.  One of the reasons I went for the KXF250 shocks was because they had 3/4" mounting "bosses" on the top and bottom.  The mounting holes on the KXF250 where such that they worked with the stock 3/8" shock mounting bolts.  In the case of other shocks with larger mounting holes, it would be possible to drill out the shock mount holes on the go-kart to accept larger bolts, but another way is to get some bushings to adapt the larger shock eye hole to the stock 3/8" bolts.  Fortunately for me, the KXF250 shocks had mounting holes that were very close to 3/8" (probably a 10mm hole), and they worked fine with the stock 3/8" bolt size.  I just swapped the stock go-karts Grade 5 bolts with some better Grade 8's.

Because the longer shocks pushes the rear swingarm away from the go-kart frame more, I needed cut the zip ties for the wiring harness that goes along the back frame and then to the black electrical box on the engine.  The electrical harness then had enough slack to take up any movements of the go-karts rear swingarm.   I also cut the zip tie on the throttle cable and let the cable sit free because that worked better with the additional suspension travel in back. 

Here's a view of one of the KXF250 shocks mounted.

Go-Kart Rear Shock Upgrade - KXF250

The first time I took the go-kart out for a ride, I was very pleased with the results.  Just by changing the rear shocks (front shocks still stock), the ride on rough terrain was greatly improved!  The rear suspension now freely moved and soaked up the bumps.   The extra length of the shocks provided additional clearance between the frame and rear swingarm/engine assembly.  Even when I crawled up on the back rack and jumped up and down (200+lbs), I did not see the risk of any collisions.  Now, it may still be possible for a collision to occur if the go-kart is weighed down enough and hit hard (like landing from a big jump), but I did not see it as being a big risk on my go-kart.  Generally speaking, I'm not looking for jumps anyway!!  I just wanted to provide a better ride over rough terrain.  The KXF250 shocks have been successful in accomplishing what I set out to do.

Here's a rear view of the go-kart with the new shocks. 

Rear View with KXF250 Shocks

FRONT SHOCK UPGRADE (ATTEMPT)

I put "ATTEMPT" in there because this effort was not what I call successful... at least not in coming up with the final solution.  It was successful in helping me learn more about what is going on with the go-karts front suspension.  I now have a much greater appreciation of the task Yerf Dog had before them in designing the front suspension.  There are a LOT of different variable competing up front.  At first, I had a simplistic view that I just needed to bolt on some longer/softer shocks up front (like I did in the rear) and the situation would be improved.  Well, it is not that simple in the front...

I won't go into all the details because this attempt did not give me what I wanted.  If anything, in part, this is an example of what not to do! 

The stock shocks up front measure around 9.75" (eye to eye) and severely limit the amount of suspension travel.  At first, I thought that I would try to bolt some standard size 12" shocks up front.  It quickly became clear that that would be too long.  There are limitations on the length because of the the steering tie rod attachments to the spindles (and other factors that I learned about later).

So, I began searching for some shocks that were around 11".  Again, this was just a gut feeling for what I thought would work.  I finally found a set of shocks on eBay that I thought might work.  They were from an 80 Yamaha DT100 motorcycle (rear shocks).  Eye to eye length was around 11.4" but I thought they might work.  Well, in some ways they did work.  If I only drove straight ahead and never needed to turn the steering wheel, they would work great! 

I first bolted on the DT100 shocks and I already knew that the steering rack tie rods would not attach to the spindles.  I thought I could make this work easy enough with a spacer/adapter between the tie rod end and the spindle.  Well, the adapter did sort of work... I was able to get the front suspension set up so that I could bolt everything up and safely accept the additional travel of the longer shocks under all possible situations.  However, the biggest problem began to become very clear, very fast.  The go-karts steering geometry was all screwed up with the longer shocks and adapters I made.  In order to make everything bolt up, I needed to adjust the tie rod ends inward (shorter) and the combination of everything made for a bit more toe in than I wanted, but even worse was the steering was severely affected.  In the stock configuration, the front wheels turn unequally when the steering wheel is turned.  This results in one wheel sort of scrubbing/plowing and the turning radius is not very sharp.  After I added the longer shocks and adapters, this issue became much worse.  In fact, it was so bad that I did not even bother to drive the kart.  Just moving the go-kart around on the driveway was enough for me to see that this was NOT the solution! 

I now see that it would have been better to re-mount the steering rack lower using some sort of an adapter plate, instead of making the adapters between the tie rod ends and spindles.  It appears that relocating the go-karts rack would improve the steering geometry situation.  Even so, I am not sure that that alone is the best answer.  The  DT100 shock springs also seemed to be a little too soft (could bottom out easily), and the 11.4" seems too long given other constraints.  I only paid around $10 each for these shocks, so it's not a big loss if I don't use them long term.  My gut feeling is that around 11" would be a practical MAX shock length, and I can now see why Yerf Dog went with the 9.75" shocks.  Perhaps if people really want to do something different up front, but they don't want to do much work, then it might be easier to just look for a better quality shock for the front in around a 10" length.  For me, I plan to think about this some more.  For the time being, I might just bolt the stock shocks back on so I can drive it as is.  At least the ride is greatly improved with the rear shocks being upgraded.  That'll give me some more time to think about what I want to do up front.

So this "attempt" was not a total loss.  I learned more about how the front suspension works, and I now have a better idea of what I need to do to make things better.  Here's a picture of the front suspension with the DT100 shocks installed... note the adapters between spindles and tie rod ends...

Go Kart Front View with DT100 Shocks

UPDATE:  I spent many, many hours over the course of weeks and plenty of money experimenting with several different shock combinations on my Yerf Dog 3206 go-kart.  Most of my experiments are not documented here because they were unsuccessful attempts.  Many people probably would NOT want to hassle with all this.

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