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Problems with speed


ArranCole11
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So, I’m pretty new to this and am not entirely sure what to do, I have a zontes monster 125cc which is struggling to reach even 50, which can be quite dangerous on a 50 road, there is a chance it has something to do with the fuel as I think my uncle mentioned something about putting g-fuel in or something similar to sort of clean the fuel out if you will, any help is greatly appreciated.

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Many 125s run out of steam on open roads because the engine doesn't have a huge amount of torque. As speed increases so does wind resistance - you double your speed and quadruple the wind resistance so it's an exponential loss of capacity.


In many cases 125s are over-geared which means that when you get fast enough to engage top gear the engine doesn't have the torque needed to hold that gear at speed. A common trick is to fit a smaller front cog - just one tooth less is usual.


I had the same on my VanVan, it would accelerate to 50, then I'd go into 6th and it would slow down until I had to drop a gear, rev it up to 50 again and just repeat the whole process. Fitting a smaller front cog meant it could hold 6th and cruise at a steady 60 - 65. It hit the rev limiter at 70 but since it could never get that fast with the original cog the theoretical reduction of top speed wasn't a real life problem.


Having said that you do need to make sure everything is working as it should. A fuel additive may help clean the fuel system if it's gummed up but usually most fuel sold in the UK has additives in it already. Virtually all the petrol sold in the UK comes from the same source with tankers having several compartments for different outlets - ie your Tesco and Asda petrol is the same as BP and Shell - the only difference is the additives in each compartment. Your basic unleaded is fine for the engine as it won't have a management system that will notice putting higher grade fuel into it.


The big factor on smaller bikes is wind resistance - to put it politely, a more bulky rider will generate much more wind resistance than a slimmer one.

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The big factor on smaller bikes is wind resistance - to put it politely, a more bulky rider will generate much more wind resistance than a slimmer one.

 

Indeed, just yesterday I rode home with [mention]Magpie84[/mention] and we hit a bit of NSL, I accelerated up to 60 only to have her giggling behind me because despite pinning the throttle the headwind was pushing her back again.


(Clearly she needs to tuck in a bit :lol: )

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[mention]SometimesSansEngine[/mention] Had to read that a couple of times because at first I thought you were calling your wife bulky! I thought he’s going to be in trouble for that comment!



My 125 is happy up to 65 and can manage 70 but not uphill or in stronger winds! Like someone else here said it’s the length of time they take to reach those speeds that causes the difficulty with other drivers.

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@SometimesSansEngine Had to read that a couple of times because at first I thought you were calling your wife bulky! I thought he’s going to be in trouble for that comment!



My 125 is happy up to 65 and can manage 70 but not uphill or in stronger winds! Like someone else here said it’s the length of time they take to reach those speeds that causes the difficulty with other drivers.

 

She'll tell you herself, she's six foot 1 on a Yammy 125, bulky or not her head is in the wind some :lol:

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Have you actually Googled to see what the claimed top speed is for this bike ? I have , and I have drawn a blank . I did , however, get directed back to a review of the bike on this forum which might be well worth a read . It seems as if 50 mph might be all you can expect so if you are struggling to reach even this then a top end service and an air filter change might be a good idea. https://www.themotorbikeforum.co.uk/viewtopic.php?f=84&t=61212

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