250 to 350 conversion

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250 to 350 conversion

Postby Spikecat » Thu Feb 27, 2020 9:05 pm

Hi, has anyone done this, and was it worth the trouble, cheers
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Re: 250 to 350 conversion

Postby Wolfie » Thu Feb 27, 2020 10:23 pm

Yes and it's no trouble, just get the 350cyls, heads n pistons and bung them on your 250.. Nothing else needed..
Here's one I did earlier..

pic220.jpg


You will get a significant power boost but not to a full 350 spec, that gets expensive..
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Re: 250 to 350 conversion

Postby Spikecat » Thu Feb 27, 2020 11:16 pm

Thanks, sounds good , will give that a go soon.
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Re: 250 to 350 conversion

Postby Spikecat » Thu Feb 27, 2020 11:32 pm

Hi, is there enough of a power increase for a sprocket change, maybe a few less teeth. Thanks
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Re: 250 to 350 conversion

Postby Wolfie » Fri Feb 28, 2020 8:34 am

Oh hell yeah, if you're touring you can go as far as 400 sizes but it will wilt on inclines or a decent headwind.

I was on 15/38 for years but I started fiddling recently and cant remember what the back is now that the front is 16.

I have a table somewhere where I calculated all the ratios.
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Re: 250 to 350 conversion

Postby Neil the Don » Sun Mar 01, 2020 1:15 pm

Spikecat wrote:Hi, is there enough of a power increase for a sprocket change, maybe a few less teeth. Thanks

If you fit the 350 csrbs as well it should jump from about 26 as a kh250 up to around 45 hp as a 350.
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Re: 250 to 350 conversion

Postby SAM » Sun Mar 01, 2020 1:43 pm

My S2B has 46 rear sprocket. So just hits 90 on 8,500 perfect for most situations.
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Re: 250 to 350 conversion

Postby Wolfie » Sun Mar 01, 2020 4:06 pm

The Yellows are the Standard and option sprockets, and the pink are my S1 variations.. looks like I'm on 16/41 at the moment. That is way above anything other than grand touring and she gives in at around 6K RPM at the moment. I need some more fiddling,
She went on a Dyno a while back, he said that power is there apparently with a hole at around 6K right where I don't need it, once pushed past that it kicks in again and she will go to almost 11K.. What!!??


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Re: 250 to 350 conversion

Postby mraxl » Sun Mar 01, 2020 5:25 pm

Here is a good way to see the effects of gearing:
https://www.gearingcommander.com/
Select "Triples" as model. S3 will be the same as 250 for internal gearing.
A lot of answers are here: http://kawatriple.com/
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Re: 250 to 350 conversion

Postby scouse » Sun Mar 01, 2020 9:11 pm

This is not a rude question
How heavy are you?

This might affect what gearing you can use

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Re: 250 to 350 conversion

Postby Spikecat » Sun Mar 01, 2020 10:57 pm

Hi, I'm 12st 2lbs at the moment, I have a s1c, just wondering if the higgspeeds on it at the moment would be effected ,as they were designed for a 250, thanks
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Re: 250 to 350 conversion

Postby SAM » Mon Mar 02, 2020 10:04 am

Higgspeeds work very well on 350.mine had them. Performance improvement very noticeable.
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Re: 250 to 350 conversion

Postby robh1f » Mon Mar 09, 2020 9:53 pm

A mate of mine did it back in the day...….with 350 carbs on his KH250. That guy on the Suzy GT550 didn't know what was going on as we all took off from the lights.It was proper quick...…..but petrol consumption was silly :shock: :shock:
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Re: 250 to 350 conversion

Postby Treeman » Tue Mar 17, 2020 10:56 am

Don't bother with the carbs, as said above, the petrol consumption is silly. I got cought out twice thinking I had a problem with my bike, only to discover that I had run out of petrol (a full tank) at circa 45 miles :shock: I was a lot younger and faster in them days though :D
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Re: 250 to 350 conversion

Postby Wolfie » Tue Mar 17, 2020 11:11 am

I also got caught out several times after the conversion, the 350s were thirsty little buggers... although these days with my lighter throttle hand I seem to go for ever on Reserve..

Maybe my expectations have been tinted by having the H2..
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Re: 250 to 350 conversion

Postby MickTriple » Thu Mar 26, 2020 1:42 pm

Wolfie wrote:Yes and it's no trouble, just get the 350cyls, heads n pistons and bung them on your 250.. Nothing else needed..
Here's one I did earlier..

pic220.jpg


You will get a significant power boost but not to a full 350 spec, that gets expensive..


That is one handsome S1c ? , I did have one exactly the same colour for about 5 years in my youth (how did it survive). Did wonder why they didn't replicate those lovely upswept pipes on the H1 for example ,do look good in that picture
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