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Old 11-27-2013, 04:58 PM
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mapbike mapbike is offline
Motorized Bicycle Elite Member
Join Date: Mar 2010
Location: Central Texas
Posts: 5,379
Default Re: what did you do to your motorized bicycle today?

Well, the verdict is in on an issue I was having with my latest build.

I pulled off the newly made up expansion exhaust and put the home built pipe that has the large cylinder shape lawnmower muffler brazed to it and a 5/8" hole drilled through the diverter plate that is in center of muffler, I took my bike for a ride and GPS checked the top speed before removing the expansion pipe and I got a flat land top speed of 37.5mph and 40.0mph running down a small hill.

After putting my old made up exhaust back on I,m @ 43.0 mph on the flat..... seems that the RT carb may have actually reduced my top speed by 2 mph on the flat compared to the NT carb I ran on the bike when it would scream up to 45 mph on the flat, I'm not changing back though because the RT dellorto clone is much more responsive and I can tell that most of the low to midrange gains I have seen were do to the RT carb and not the expansion pipe, there were low to mid gains with expansion exhaust but I can just barely tell any difference in acceleration and that difference is only on the low low end once I'm at around 20 mph it revs up about the same now and hit top speed quickly.

I also pulled my clutch cover, removed the pucks and sprayed the pressure plate off good with carb cleaner and then took my pucks and sanded them down just enough to remove the glaze so they would grip good again, they had been slipping so bad I could hardly get the bike started but now they hold solid.

Conclusion, I have lost top speed on my bikes every time I've put an expansion exhaust on them, probably due to the header pipe not being big enough (shrug), but I have found on my bikes that if I just make up a simple free flowing exhaust they do the best all the way around for mid and top speed power and rpms, I have one more expansion pipe that has a much larger inlet than what I've been toying with and I plan to make a 7/8" or 1" header pipe for it and try it on my Western Flyer build, if I don't get the results I'm looking for I'm probably done fooling with expansion chamber exhaust on my china girl engines, just not seeing any benefit to them on my bikes so far other than they are quieter and they help the basically stock engines in the low to midrange and are way better than the kit exhaust in there stock form, in my experiments so far I have lost top speed on every expansion pipe set up I've used on my bikes but I'm hoping I can get one together next time that I'll be happy with, if not then I'll just build what I know works the best for me and throw the expansion pipes in the junk!

Next mod on the Moon Doggie bike is gonna be a 32T rear sprocket, seems I have plenty of power to pull it and that will get me at 40mph cruise at lower rpms.

By the way, the SBP expansion exhaust is excellent on stock to mildly modified engines, low mid and upper power are increased over what the stock pipe will allow the engine to do, I still run the SBP exhaust on my Karaoke Huffy and I'm satisfied with it on that engine because it is so unbalanced that at 32-34 mph that is as fast as it is comfortable to ride and the pipe lets it breathe great from start up all the way up to that speed, just wanted to add this part because for stock to slightly modified engines and those looking to cruise in the 35 +or- MPH range the SBP pipe works great.

I dont always ride WOT, but when I do..I do my best to keep the rubber side down..Ride safely my friends!

Last edited by mapbike; 11-27-2013 at 05:52 PM. Reason: bad spelling on Galaxy phone...LOL
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