Pitster engine rebuild

After my track day with a Pitster, I decided to do a performance rebuild on my engine. I spoke with Vince at T-Bolt who spent some time answering my questions and giving his thoughts on what would be the best setup for my needs. I ended up ordering:

131cc big bore kit
Crower race cam
Kitaco inner rotor ignition kit
Kitaco super coil
Mikuni 26mm race carb & UNI filter
High flow intake
Ultima exhaust system
Billet oil cooler

I received the IRK, exhaust and coil first, so I'll install them first to get an idea of the difference that just these parts make. The rest of the parts should be here in less than a week.

 

Here is the test subject, along with a bundle of Bridgestone Battlax BT601fss tires. I also picked up another set of Pitster wheels so that I can try out different size or types of tires, or just have a spare set at the track.

 

Day 1:
Ok, the first day of work and the first set of problems. First, I went to install the new exhaust only to find that the mounting point on the silencer does not line up with the one on the subframe. I ended up pulling the subframe off, cutting off the mounting tab and then welding it where it needs to be for the new exhaust. I then sprayed the subframe in gloss black.

 

Next, I realized that I did not have the proper puller to remove the flywheel. I tried several different types of standard claw-type pullers, though I did not have any luck. My friend Alex had the proper puller, so I called it a day and picked up the puller on my way home.

 

Day 2:
I reinstalled the subframe and the new exhaust mounted up fine, though I did have to space it out quite a bit in order to get the center section to clear the subframe.

 

Using the proper puller, removing the flywheel was a snap. Once off, I removed the remaining stock stator components, coil and wiring.

 

The installation of the new components was really easy.

 

I went to install the new coil and realized that the supplied bracket uses too small of a bolt to attach to the stock coil bracket. I ended up drilling out the hole and recess in the aluminum bracket in order to use a larger (6mm) allen, instead of the supplied 5mm.

 

The last step was to hook up all the wiring, including a new kill switch (one wire, versus two). I kicked the bike over and it fired right up. I went to shut it off and got a nice shock from the switch. The new one wire switch is trying to ground the signal out through the base of the switch, though the handlebars do not seem to be supplying a good ground. I pulled the new kill switch off and reinstalled the old two wire one, simply attaching the second wire to a good ground point on the frame.

 

Finally, test ride time! The bike sounds much better (deeper and less raspy) and revs up much quicker. Riding it, there is a noticeable improvement in power and it continues to make power high up in the rpm band where the stock setup had dropped off. So far I am quite pleased with the new mods.

 

Day 3:
After disappearing for a week or so, UPS finally showed up with my remaining parts. Time to install the big bore kit, cam, carb, etc. Here is the stock setup coming apart.

 

I pulled the head apart to see what I could do with the ports. You can see not only how restricted the exhaust port is, but also how rich the bike was running.

 

Here are the ports after doing some smoothing and shaping work.

 

The exhaust port still seemed really restricted due to the massive guide that sticks out quite far into the port. Since the guide seems plenty long, I decided to cut it down and get it out of the path of the exhaust. I did not want to leave a large pocket in the port, so I left some of the guide sticking out and smoothed out the shape of the guide.

 

Here are a few pics during reassembly, showing the new oil cooler, 26mm carb and the TB intake.

 

Day 4:
The two bikes, one stock (knobbies) and one modified (slicks).

 

Here are some short video clips to show the difference in sound and the way they rev.

 

The modified bike is way, way faster now. It is nice to be able to ride the bikes back-to-back and really feel the difference. I still plan to play around with jetting, though the 131 pulls nice and hard throughout the powerband. Here I am, having some fun on the new bike!