New Engine for Smallkat

The 1990's Japanese market GSX250SSN (GJ76A) and GSX400SSN (GK77A)
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Smallkat
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New Engine for Smallkat

Post by Smallkat » Sat Jun 29, 2024 4:46 pm

I've been pondering over the carb issues with Smallkat and also it's relatively lowly torque. I'm thinking about putting in a 2005 Bandit 650 engine and electrics. 2005 is the last year before ABS, which I think may complicate matters.

I know people have put other engines in, but I can't find any details. Can someone point me in the right direction?
GSX250SS Tinykat (gone, but the hole in my wallet not forgotten)
GSX400SS Smallkat
GT250 X7
GT200 X5
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Re: New Engine for Smallkat

Post by fossie » Sat Jun 29, 2024 7:55 pm

Harry Hawkins in Cumbria is probably the best/ closest ...I think he's on OSS or something not here anymore .
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Re: New Engine for Smallkat

Post by Uncle Bob » Sun Jun 30, 2024 9:39 am

fossie wrote:
Sat Jun 29, 2024 7:55 pm
Harry Hawkins in Cumbria is probably the best/ closest ...I think he's on OSS or something not here anymore .
Smallkat should know Harry from the VJMC Furness section... if not he can contact him there.
I have heard of a couple of conversions but they used bigger cc engines, personally I think if you do go that route then a 600 would be a good size. I remember one of the issues was the petrol tap and it fouling things.

Still not sure why the LiteTek O ring kits haven't sorted it for you (with correct float height) - worked fine on mine and Pookie's 250. I think mine pulls well. First startup after winter sleep was a little longer, but since then it just starts on the button. The new starter and Li-ion battery I think have helped that as well.
I have put a set of LiteTek O rings in my 250 as well which started fine when I first put the carbs back on but then haven't ever tried since (must get back to it some day).

I forget what issues you are still having?

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Re: New Engine for Smallkat

Post by Smallkat » Mon Jul 01, 2024 11:07 am

I only know Martin Crooks in the Furness VJMC group, but I will try and make contact with Harry.

Starting isn't too bad now. If it's been standing a while, I drain the bowls and then it seems to start after a bit of churning. Now the main problem is that when it gets hot it's very unstable fuelling wise in the 1500-3000 RPM zone.

I was going to completely restore it this winter anyway, so I may as well sort the engine out too. I thought of the GSF650 as the engine is black, they are plentiful, relatively cheap and hopefully the engine height won't cause too many problems.

Anyway, I've got time to think about it, while I try to sort out my GT200 X5 which has carb problems!
GSX250SS Tinykat (gone, but the hole in my wallet not forgotten)
GSX400SS Smallkat
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GT200 X5
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Re: New Engine for Smallkat

Post by Uncle Bob » Mon Jul 01, 2024 12:50 pm

Smallkat wrote:
Mon Jul 01, 2024 11:07 am
Anyway, I've got time to think about it, while I try to sort out my GT200 X5 which has carb problems!
What is the issue with the X5? Based on your X7 I assume it's stock airbox and exhausts, so really just stock jets and away you go...?

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Re: New Engine for Smallkat

Post by Smallkat » Mon Jul 01, 2024 8:45 pm

Yes, you would think that, wouldn't you? but I've tried two sets of carbs, both dismantled and cleaned twice in my ultrasonic bath. Same thing, only run under 3000 rpm with the starter circuit on. Everything is stock.

I've borrowed a set of 'known good' carbs from a fellow VJMC member, but same problem. I'm going to give those an U/S bath and try again. If no luck, I'm thinking the crank seals have gone. I didn't build this engine, it was re-built by the previous owner.
GSX250SS Tinykat (gone, but the hole in my wallet not forgotten)
GSX400SS Smallkat
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GT200 X5
BMW R1250R
VFR750FT

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Re: New Engine for Smallkat

Post by Uncle Bob » Tue Jul 02, 2024 1:03 pm

From what you are saying it doesn't sound like carbs. The X5 I had, I paid a top price for at the time as it was supposedly fully restored including engine. However it didn't run correctly and when I pulled the top end off from the carbon you could see that it hadn't been touched in years, and also had 1 proper X5 piston and 1 replacement A100 piston. Due to that I striped it all down and the middle seal was shot. I complained to the dealer and did get most of the cost of a recon crank, pistons and rebore but I had to do all the work for free.
You could try a leak down test if you have the equipment.
Other things it could be is CDI, possibly coils, blocked exhausts, or someone trying a porting job without the knowledge!

The joys of a 2 stroke - I think of them as female - Expensive and temperamental!

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Re: New Engine for Smallkat

Post by johnD » Tue Jul 02, 2024 7:14 pm

A very guilty Hi Smallkat.........

I promised you the bits for your GS550 carbs ages ago, but life well and truly got in my way. If you Email me your address, I'll post them up to you. You will need some new needle valves as I used these on another of my builds.
I left mine in the corner under a cover while wrestling with boxes of very rusty bits that eventually turned into a very presentable motorcycle, at least two months or more. It just....... starts. No melodramas involved.
As to fitting a Bandit engine, the 600's are a heavy lump, two valve per cylinder, pretty anaemic, actually.
Plus arguing with exhausts, getting carbs to fit into the limited space, whatever rewiring will be necessary, not, in my opinion, really worth the time, money and effort. These 400's are a far more modern engine, I'm only reluctantly getting round to, eventually, sorta, putting mine on the market. And only that because I've sourced a modern 600 so not putting the rare as hens teeth Kat through my riding wringer. I am staking what little reputation I have on stating that the BS32's transform the Kat from sulky to dependable and I never had an argument with its general performance given its not a 1000cc snarling monster.
I'll send you my telephone number with them so we can talk through the process.
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Re: New Engine for Smallkat

Post by Smallkat » Tue Jul 02, 2024 7:39 pm

John, don't worry about it. I don't even know how the years go by without even starting any of my projects! Last few months have been bad for us as a family so haven't got much done anyway. Just spent a lot of time thinking about things!

I'll PM you my address. I guess I should try the carbs first, before I do something drastic. I appreciate all your help so far.
GSX250SS Tinykat (gone, but the hole in my wallet not forgotten)
GSX400SS Smallkat
GT250 X7
GT200 X5
BMW R1250R
VFR750FT

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