41 T Sprocket to 32 T?

Okay guys I just got into motorized bicycles about 3 months ago. I saw a local add on craigslist for 100 bucks for a complete 80 cc 2 stroke chinese motor kit so I decided to pick it up local. I put it on my 1972 Schwinn 10 speed 27" racing road bike (weighs in at 18 pounds with nothing on it). Once everything was on the bike and tuned right I put new brake pads on,a headlight,a tail light,new seat, straight handle bars (helps me lean over some on the bike to go faster), and new brake cables because the old ones were on the verge of snapping. So anyway I'm only 16 years old and I am 5'10 and about 125 pounds so I took it riding for a bit and I could get up to about 38 mph top speed on a flat and I had my friend in his car behind me to check the speed but at the speed the rpm was very high and the vibrations were very uncomfortable being as light as I am. So what I have done so far for upgrades is a new cone style air filter, new iridium spark plug,new fuel line, new fuel on off valve, new fuel filter, made the stock exhaust a little more free flowing with some simple modifications which helped, and I got rid of the crappy chain tensioner and just shortened the chain to the proper tension and use a master link which worked great. So far it runs good and I have a comfortable cruising speed of about 25-30 mph any faster than that and its pretty rough. Now to cut to the chase sorry for all the typing here guys... My main goal since I live in the middle of memphis which is a large city is to achieve a nice cruising speed of right at 35-40 mph range would be great and have the RPMS relatively low well atleast 1.5k-2k below redline would be great. Anyone think that swapping from the current 41 T sprocket to a 32 T would be worth it and would it help me reach that goal? I've basically already done the little tune ups already and the sprocket is last on my list. Everyones input would be greatly appreciated.

Thanks!

TheJimGuy said:

First, Put the chain tensioner back on. The chain will stretch (break in) over time, dramatically so in the first number of rides. After all the break in of the chain is done, if you want to remove the tensioner, that's fine.
Would recommend the tensioner with the bearing, and upgrade to the 415 or the 41 chain vice the "kit chain". At the MINIMUM, upgrade to a good motocross chain.
For speed at lower RPM's, look into a "shift kit" from Sick Bike Parts (http://www.sickbikeparts.com/catalog/index.php?cPath=21). This allows you to run YOUR gears from the motor.
Careful on those Memphis streets, we are not always seen.
Grew up 30 miles north of you. Now in Jacksonville FL on the beach. Less humidity, better bikini's.

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Can do on the tensioner how many miles should I let it break in? As for the shifter kit will the standard one do fine for me? Looks like a great idea and I definitely am considering it but I am strapped for cash so I may just get the $25 32 T sprocket from ebay for now and wait until my birthday in july for the shifter kit. Also what kind of chain do I have now with the kit? I know its bigger than a standard bicycle chain.. Is it 415?

Anyone else?

TheJimGuy said:

After a few weeks of good riding, you will notice that you no longer need to adjust the tensioner. The 1/4 to a 1/2 inch of chain flex doesn't change from one riding day to another. That is how many miles. Some of us ride hard and fast, some of us are more the "get there eventually" type, I cannot give you actual number of miles. The chain will let you know.

If your chain looks like a slightly smaller motorcycle chain, you most likely have a 415. This is GOOD. In short: if the chain looks markedly bigger than a standard bicycle chain, you are good to go.

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Sweet! So what are your thoughts on going from the 41 T to the 32? In theroy wouldn't I gain about 8-9 mph on my top end speed? I know I would lose torque but I don't think its to much of an issue being that it is mostly flat in memphis and I'm a super light weight at only 125. The shifter kit will have to wait.

Rocky_Motor said:

Go for the 32 sprocket. Careful about the tensioner, it has a habit of falling into the spokes of your rear wheel and ruining your day. I personally don't use it. Got rid of it after first 10 miles. The chain did stretch quite a bit though.
You may need to pedal a bit more with a 32 tooth but I doubt it'd be too bad.

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Thanks for the input! I had the tensioner do the same thing and it pissed me off. I've already gone a good 100 miles on the bike already with the motor. I bet a 32 tooth sprocket will make me haul ass over the 41 tooth. Man would it be nice to cruise at almost 40 mph. I think if I do some good performance upgrades and tune it real nice I should easily achieve 50 mph top speed but my weight and small frame helps out some lol The shifter kit is something I am definitely going to get in the future because it looks nice as ****.

Rocky_Motor said:

If you're already so close to 40 with 41tooth then 50 on a 32 tooth and an expansion chamber tuned for high RPM should be no problem. The exhaust is as much a part of the 2 stroke engine as the compression is. Back pressure is key. Look at the one at sickbikeparts who have the shift kit. Oh and you'll need the more expensive HD one with a 66cc motor or you'll end up breaking the jackshaft.

You may look into buying thatsdax.com's RT carb. I have it, works wonderfully. You'll need to jet it correctly. Unless you're perfectly happy with your current carb. There's a lot you can do with these engines. My only gripe is that at a certain point you may ask yourself if buying a morini motor would be more worthwhile. Except they're no longer made so it's getting hard to get them


I haven't used a shift kit, but I hear it's a love or hate situation. Some people can't get the hang of changing the gears or find it cumbersome. If you can remember to shift to a low gear when you come to stop you should have no problem.

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I think I'm not gonna work about the shift kit if I like the way the 32 tooth sprocket works out. As for the carb I'd like to stick with the stock one if possible. Only issue I am having now is the bike will not idle properly do you know what could be the cause of this? I've tried adjusting the idle screw and still no luck. Other than that bike runs great. And 50 mph would be sick! I could right the streets with ease.