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davidsquaredson

tuned jet200 gearing recommendations

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Hi, my Jet has: GT200 barrel & head, 28mm Delly, BGM clubman. I changed front sprocket to 16 tooth. It pulls like a train through to 3rd gear, say about 85-90 kmph, then I get into 4th gear and the revs drop. Acceleration continues but noticably slower. I top out about 115 - 120 kmph but it takes a while to get to that. The engine feel like it still has power beyond that, that I am running out of gearing.  I'm wondering is it better that I try a 17 tooth front gear, or switching the crown wheel to a 47 tooth, or to put in a Li150 gear box.  

I've also got a PM tuning expansion chamber sitting on the shelf that I will try at some point, but not until I figure out the gearing to make use of the few additional HP.

Thanks in advance

David

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Go back to stock gearing. The SX200/TV175/JET200 gear box with 15/46 is one of the best combos out there. That slow acceleration in 4th is an indicator of too tall of gearing.  

What do you mean by GT200 barrel, is it a TV200 top end? If that's the case, with the big carb and clubman you need to really go back to stock gearing. 

Google "lambretta gear box calculator". Good stuff. 

 

 

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its a Gran Tourismo 200 kit. Should give me something like 23 HP with my carb/exhaust. It has a ton of torque. I beat sports cars off the start when I forget how old I am. 

Indeed my 4th is too tall, but I thought I needed to go up in front sprocket? 

Here is the table: Cambridge Lambertta    

 

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Your top end should make plenty of go. Maybe the pipe is not ideal for the rest of the motor?

 

Use this for gearing. 

 

https://avantone.wordpress.com/

 

I don’t agree with Cambridge on their opinion of the sx box. In my experience the ratios are ideal and the only issue is that the small front makes for a hard life on the clutch. At the end of the day it will come down to how you ride of course. Personally, for all around riding I like to aim for a 4.8 or so final drive ratio (sx200 with 15/46). 

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Yep, I agree. The SX/TV/Jet Gearbox is one of my absolute favorites. I would also agree to go back to the 15/46. Your 1-3 will be a touch shorter but your 4th will become much more usable.

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I kinda would think with that setup it should pull fine in 4th gear and an extra tooth on the front sprocket.

 

what is your jetting set at? How is your bottom end performance before half throttle? What type of air filter?

 

also 120 kph is pretty quick on a scoot, 74.4mph, i would say that is better than most.

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I did a lot of reading on UK forums about this kit. The BGM clubman is indeed restricting it. I have a 28mm dellorto and breath sweet filter. I'm going to put on a PM Evo pipe and see what happens. It will move the power band up a bit. If I still don't like 4th, I'll go back to a 15 tooth front. 

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On 2/19/2018 at 6:06 PM, davidsquaredson said:

I beat sports cars off the start when I forget how old I am.  

 

Only reason you a beating sports cars is because you have told them it is a race.

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On 2/22/2018 at 3:33 PM, nickthekorean said:

also 120 kph is pretty quick on a scoot, 74.4mph, i would say that is better than most.

Better than most what? A $700 top end should get you better than 75mph.

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