44t to a 36t rear sprocket, will not reach high rpms now

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CrownCruiser

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Jun 21, 2014
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So I couldn't find an answer to my problem on here, perhaps I'm not good
PHP:
at navigating forums. So I just swapped my 44t rear sprocket for a 36t. Before I was doing close to 40mph. I should be going a bit faster with the smaller sprocket but it doesn't seem to reach those high rpms like it used to. I have a dellorto 15/15 clone with a 65 jet and a voodoo expansion chamber pipe. I would add some pics but I cannot from my phone. I do have a few on my profile though. I have done many upgrades to the bike alone. Someone please help me out. Thanks and much appreciated.
 
crassius

crassius

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Sep 30, 2012
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sounds like you've geared yourself higher that the power of the motor can handle

I'd either skip breakfast & try again pulling less weight, or go to a 41 tooth. Otherwise, you may have to do serious work to make more power in the motor.
 
2door

2door

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Sep 15, 2008
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I concure and ask about your riding terrain. Are you having to climb hills?
Gearing higher will always bring your rpm down however it also reduces the torque available from a lower gear (bigger sprocket). The suggestion from crassius to go to a 41 sprocket is also a good one. 41 seems to be a good all round number for most bikes/riders and terrain. 36 is good if you're running a basically stock engine on flat ground but might be a bit high geared for your situation/conditions.

Tom
 
Henshooter

Henshooter

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Feb 10, 2014
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Yep I agree with both statements ,I run a 32 t and the noticeable difference in the high end is very noticeable ,I run on flat ground mainly and although I tow a trailer I do find the 32 to be a tad tall for a chinagirl ,I'd also recommend a 41 as it's a lot closer to middle ground
 
Venice Motor Bikes

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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I prefer to use 40T sprockets on all my bikes... I would only use a 36T on a bike with a highly modified engine that wouldn't need to climb any hills.

Also, I only use a 38T on my 8HP race bike because I think a 36T is a little too steep. ;)
 
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CrownCruiser

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Jun 21, 2014
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My terrian is really not all that hilly.I only weigh 150. And for torque I really didn't lose all that much since I have added a carb and expansion chamber. Also port matched intake and exhaust. Would possible upjetting make a difference? I have also thought about buying a different jug. Possibly a big bore kit. I don't need to pedal from a take off. I had a stock pocket bike and I put on a rear sprocket 13 teeth smaller and was able to get that thing going over 50mph, and that only had a 32cc engine.
 
crassius

crassius

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Sep 30, 2012
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still depends a bit on how many miles you have on it - these often don't get fast until 300-500 miles are on them
 
KCvale

KCvale

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Feb 28, 2010
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It's all about air flow. Crouch low, tuck your legs in when riding.
Heck put an aerodynamic front faring on like most motorcycles have.

Once you hit the high 30's air feels more like water to travel through, at 80 it feels like mud.

Your engine maybe could move you faster with that gear ratio if you cut the wind residence but for now you have lost the torque you had to get you to 40 against the wind to begin with.

Don't get me wrong here, I am a sit up and ride kinda guy, but if speed is what you are after it's pretty cheap if not free to just get more aerodynamic.

Or you could just get gears ;-}
 
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CrownCruiser

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Jun 21, 2014
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I ride this close to 300 miles a month and have had it for 4 months now. I've looked into a jack shaft kit but I don't want a deraliuer on my beach cruiser. Is there a way I could just up a tooth or two on the engine sprocket? And this bike ain't that wind resistant.
 
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Theon

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Jan 20, 2014
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To get the most from a 36t you likely need to lift where you max torque is in the revs.
You want a power band coming in around the 7000 RPM for example which will keep pushing the motor faster when yours is running out of steam.
It sounds to me as if you have good low down, this will need sacrificing.
By increasing port durations you will lift where your max power is.
Some put ramps on the piston, I prefer to lift the tansfers with base gasket and notch inlet skirt of the piston.
 
KCvale

KCvale

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Feb 28, 2010
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CrownCruiser said:
I've looked into a jack shaft kit but I don't want a deraliuer on my beach cruiser.
Click to expand...
I don't care for derailleurs either so I use an internal shifting hub like on this 5-speed when I can.



Just a thought for your next build as it's not clean or fun to pull a used engine out and retrofit it with the jackshaft system.
 
C

Citi-sporter

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Jun 16, 2014
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the whole thing about these engines is that they are fairly mild tuned, and low compression ratio in stock form. And adding a race carb and expansion chamber pipe just moved what low end torque you might have had up the RPM scale, not to mention shortened the engine's life some.

The 33 cc pocket bike is much smaller aerodynamically and will go faster, you have become a big air resistance when sitting nearly bolt upright on a full sized bicycle.
 
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