Biturbo/Chain Adjuster Upgrades

[Scootmeister]

Here are two easy upgrades I just installed using old parts a fellow MB and Moped enthusiast gave me. The first is a Cam-style chain adjuster that simply goes between you drop out and your axle nut. You simply loosen the two axle nuts, twist the cam until your chain tightens to your liking, adjust the opposite side so your wheel is straight, and re-tighten the nuts. Without the adjusters my chain would loosen up no matter how much I tightened the axle nuts due to the engine torque in low gear. Now, there is no way for the axle to slide forward so the chain stays perfectly adjusted eliminating chain slap and excess wear caused by misalignment from the loose chain. The second upgrade is a Biturbo expansion chamber that comes with a 25 or 26 mm ID header pipe which will allow my reed valve engine to breathe a little deeper. The expansion chamber will accomodate several custom silencers. You will note from the photos I have not fabricated the silencer and/or stinger. I hacked and welded the header onto a steel manifold I made from 1 1/2" channel. I like these pipes because the steel is thick and doesn't perforate when I have my Lincoln welder on 105 amps using soft 7016 rods. I installed the pipe in a swept up angle to make the bike look like it's going faster. Attached is a photo of the old exhaust for comparison. Both upgrades took about 4 hours to install. I will report back on how the pipe works (and sounds).

 

[Scootmeister]

Here are photos of the final product. I used a B & S muffler and a piece of 57mm pipe to make a low resistence silencer that I pop riveted on the Biturbo. I noticed a significant boost in power, much quicker response and higher RPMs. I'll be tweaking the air/fuel ratio which is easy on this 16mm Walbro carb. All it takes is a twist on the high speed adjustment. A couple of plug chops should do it. BTW, the sound is great, not too loud but deep and rich, without the ringy dingy ping you get from some 2 strokes. One downfall is the extra torque blitzed first gear in my Shimano Nexus hub which has been flawless for 3 years of riding.

 

[Scootmeister]

Here are photos with the heat shield installed. The inside of my thigh is one place I definitely do not want burned! Sorry for the lousy photos but Tropical Storm Andria is bearing down on us and I can't go outside. The Whizzer in the background is not getting much use because I'm having so much fun with this bike.

 

[Scootmeister]

Something I learned from this project is the oil from premix will find the smallest escape route and make a mess. So I guess one of the keys to fabricating an exhaust for a 2 stroke is to eliminate all exit points in the system except the obvious one. My first silencer was connected to the Biturbo Expansion Chamber with pop rivets. The B & S muffler that was inserted into the silencer housing was also connected using pop rivets. Unfortunately, pop rivets do not provide a tight seal and oil eventually leaked onto the exhaust. I corrected the problem by using a one-piece silencer and connected it using a hose clamp instead of pop rivets. So far, so good, and it sound much better!