I can't seem to leave well enough alone! Wasn't really satisfied with my Chinagal's performance, so I swapped out my enduro-style expansion chamber for a dirt-bike style wrap-around. First I tried an expensive KZ65 replica that was big, expensive, and extremely well made. Unfortunately, the angles did not work on my configuration and the mounting flange didn't line up. To say I was disappointed would be an understatement, but I sucked it up and ordered a cheaper pipe from China, and I could not be happier with it. The installation was easy and even though the belly is smaller, it noticeably increased my output. I like the way the pipe is designed in two pieces for ease of installation and ease of adjustment. I had to raise the support slot slightly where it bolts to the clutch cover, but that was simple compared to most exhaust modifications I've done in the past. I added an extension to the outlet pipe to keep it from blowing oil up my bloomers! Removing the left side pipe cleared the way for a recoil starter. Kick starting works well, but it puts a pretty good strain on the clutch and the rest of the drive train like the SBP freewheel and chains. Any suggestions on the best recoil? I tried one several years ago and it lasted about a month. Hopefully, they are better now.
Shanghai Scrambler
- Thread starter wrenching4fun
- Start date
Woops! Had my front fender installed upside down. Here is correction. She purrs at 40 in 6th gear. 7th is like overdrive, it holds cruising speed, but has no juice. Shifting makes it ride like a small motorcycle without engine break when downshifting. I've already worn out the rear tire, will re-shoe with Schwalbes.
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Hi Mossy. Actually, it's a Miaowa brand pipe from Amazon. At 38 bucks it's a blooming bargain given the quality! The spring-tight joint allows slight changes in the installment angle to compensate for variations in the way the engine is mounted. Plus, the inside diameter of the stinger is exactly 7/8" so standard handle bar stock slides in perfectly to extend the outlet. Some have reported that the pipe is loud and add a silencer, but I like it as is and the power boost is definitely helpful on these low output engines.
Ok... I like the design... And price... A 5/8" stinger halfway through the belly and 1" U bend t to 7/8" piece about 25" or so to 3/4's of the belly of the expansion chamber to the face of the piston... I could chop it up and make something out of it that would run out of it... I'm going to get one and play with it..
I have three of that type of pipe, watch the weld where the rear mount connects to the pipe, I've added silencers to all and couldn't be happier. The pipe is designed wrong according to the experts and lacks sufficient back pressure, i made my silencer with a smaller stinger that makes them all run better and keeps the neighborhood happy too.
I've noticed that most pipes have the diameter of the inlet and outlet mixed up... Working on 2 strokes for 40 years I've noticed a few things... The old chainsaw mods would use a piece of rectangle stock cut at just the right length for top end only... The Enduro bikes in the early 70's had the pipes with long headers and the expansion chambers to the rear for bottom end no top... The dirt bikes had fat pipes with the expansion up front for top end... Moped pipes are the best of both worlds built for mid range loosing some bottom and top for it... Saws and mopeds use 4stroke carbs for a level power curve and dirt bikes use 2stroke carbs like a mikuni/OkO for a power band... The thing about 2 strokes is you can make them act differently depending on the setup... But knowing what does what and why will help get it to do what you want.... Same engine just configure different and the port timing is something also... Gearing... Short or long stroke... It's important to plan your build and leave room for trial and error... A Winnebago and a muscle car have the same engine block... Very little else
I thought about adding a silencer, but sort of like the jagged purr while riding. Have read the stinger should be 60% of header diameter, but most pipe builders are driven by price point and use the same tubing on both. Adding the handle bar stock reduced the I.D. of the stinger to about 70% which is close. Might add an aluminum sleeve in the stinger to reduce further. Thanks for the warning on the mounting strap, Greg, will keep an eye on it. I'm relying on gearing more than HP to push me as fast as I want to go on a bicycle. Call me cautious, but 40 MPH on 2" wide tires is all the thrill I need at this point.
Okay, I get it. A scrambler should have scrambler bars on it. Replaced the bighorn bars with these. At the same time, I re-jiggered the exhaust with a heat shield from a Yamaha XT500 and threw on some Schwalbe Magic Mary's front and back. Am thinking this build is through until something breaks.
Even though Chinagirls are simple engines, they sometimes offer curious surprises. When I set mine up, the stock intake placed the carb too close to the downpost to remove the filter. When I replaced the stock intake with a longer one that extends the carb back and away from the downpost, the engine ran noticeably stronger. Is it possible the longer distance between the carb and the compression chamber effected the timing? Maybe the longer distance enhances atomization of the fuel air mixture, optimizing combustion. Total advantage-better access to the carb and air cleaner and improved performance. All-in-all, a good two hours in the skunkworks.
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There’s a thread somewhere on this, I believe it was by Jaguar who did a lot of experimenting with performance upgrades.
Great article, that points out exactly what I experienced. Turns out my extension is right in the middle of the optimal range at 8.5 inches. That, plus the added 1mm or so in increased inside diameter over the stock intake probably explains the increase in torque at low revs. It pulls noticeably harder. It's an easy hack that everyone should try for fun. Thanks for digging up the study, Greg. If I was as smart as the author I'd probably have this thing breaking the sound barrier!
I did some work on pipes several years ago, Dave, a former member and I found the same improvement with a 14" head pipe. I think that's covered by that book as well.
I get the same low end improvement with an expansion chamber and a silence as I did with the homemade pipe, the chamber looks much better too.
I agree, a chamber makes a huge difference on a 2-stroke. Here's the chamber and silencer I threw together. I like the way it sweeps down and out of the way. I had a heat shield on the pipe but took it off because it looked bulky. This chamber is a cheapie, but it's better than the stock pipes and it's easy to fit in my weird setup. I have to use a beefed-up rear wheel stand to kickstart because of the freewheel on the cassette and since my engine has a lot of compression I really have to lean into it. CDI box, rectifier, and wiring terminal are protected from weather by the black key box. I've only ridden the Schwalbes a few miles, but so far I like them a lot. They have deep tread, but are surprisingly quiet and smooth. I have a vintage Raleigh frame that's calling out for some attention. I have a 142 F I was thinking about throwing on it, but thinking maybe I'll pick up a 5 horse flathead Briggs and tie it to a shift kit. What do you think?
I know it has been a while for this thread. I am looking to get a rear wheel stand for my bike. I found many shipped from over seas. They cost around 80 dollars. The ones showing location in USA are 120 dollars there about. Any suggestion on what is good that is in USA so I get it sooner? Oh not looking to sit on bike with stand down, but it does weight about 130 lbs so it has to be strong. Was not sure if my center stand is too low with the legs not high enough for the off road trail riding, I have the CA Green Sticker for OHV so that is where it is run.