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Discussion Starter · #1 ·
As title I am going to undertake this conversion very shortly. I did find a thread originally going this site regarding someone attempting this conversion but am unable to find it now. I have motor,ECU, Header pipe and air box. A new drive train will also be purchased as the sprockets are different. From what I have read the conversion should be straight forward (No conversion is ever straight forward).

Has anyone completed this conversion that could highlight some issues I may encounter? Any help would be greatly appropriated before I start.

Thanks in advance:)
 

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Discussion Starter · #3 ·
Cheers thats the thread i read. No real info in here and im surprised theres nothing out there about converting the engines in these bikes? Is it because they are relatively new and parts are not readily available? As for being cost affective i did get my duke 125 pretty cheap so my calculations are coming in at £1000 cheaper than just binning the 125 and buying a 390. Perhaps as they age we will see some more conversions happening in the near future?
 

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I always remember a school friend of mine back in the very early '80 once fitted a Zundapp 175cc engine in a Yamaha 50 cc trial bike . We were all very impressed till the day he got stopped with most of us near our school :The police was then clamping down on all the suped up 50cc that were supposed only to do 40 km/h max speed .They had portable rolling benches to check the speed : Needless to say that he walked home that afternoon as the bike got confiscated . I shall admit that my Kreidler RS clocked 105 km/h on such bench and had to present it a week later " limited " to 40/h again .. The only way was to fit a 12mm Bing carb instead of the 21 mm , blocking up the exhaust with steel wool and limiting the throttle travel to 50% .

Just to say , these type of conversions maybe challenging projects but are economically unjustifiable , not to mention the illegality and total absence of insurance coverage on such vehicles in most countries .
 

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Discussion Starter · #5 ·
I always remember a school friend of mine back in the very early '80 once fitted a Zundapp 175cc engine in a Yamaha 50 cc trial bike . We were all very impressed till the day he got stopped with most of us near our school :The police was then clamping down on all the suped up 50cc that were supposed only to do 40 km/h max speed .They had portable rolling benches to check the speed : Needless to say that he walked home that afternoon as the bike got confiscated . I shall admit that my Kreidler RS clocked 105 km/h on such bench and had to present it a week later " limited " to 40/h again .. The only way was to fit a 12mm Bing carb instead of the 21 mm , blocking up the exhaust with steel wool and limiting the throttle travel to 50% .

Just to say , these type of conversions maybe challenging projects but are economically unjustifiable , not to mention the illegality and total absence of insurance coverage on such vehicles in most countries .
Costing is actually coming it at over £1000 cheaper than just selling the 125 and buying a 390. As for the legality of it. Its as easy as filling in the back of the log book with the new engine cc and away you go. All the DVLA are worried about is that your paying the right tax for the bike. As for insurance, motorcycle insurance are far more accomadating of modifactions than car insurance so dont forsee any problems there either. Just to clarify this conversion is not going to be slap a 390 engine in and ride it round illegaly. As soon as its running its going to be reclassified and done properly. I do like to tinker with things and this has my attention at the moment and to cap it all off when its finished i should be the owner of a one off 390 that will be staying with me for along time.?
 

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Hope it all works out fine for you , I ignored the simplicity of the legal / techical procedure for this in the UK . It somehow surprises me as I have close friends in the classic car trade in the UK , who in the early '90 entered classic Jag XK,s , Austin Healey's and Porsche 356 from California trough Belgium just because it gave them less complications for importing /MOT's . Once they had Belgian documents they took them to the UK .
 

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Discussion Starter · #7 ·
Thank you. I do believe importing is a whole new ball game. I was very surprised at the DVLA also i was expecting to have to take the bike to a vic test centre to check everything. But from information provided by .gov website it is just the tax class they are concerned about. Dont get me wrong things like this usually fall flat on thier face ? but i hoping i can do this in reasonable time? And im still expecting problems with converting and re class of the bike. Im one of those people who just gets something into my head and want to do it, with the lack of info out there on this im hoping if nothing else i can provide some accurate info on it, succeed or fail. Worst case i dosnt work and i change it all back and buy a 390 outright, ill then have a nice garage full of spares???
 

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I always remember a school friend of mine back in the very early '80 once fitted a Zundapp 175cc engine in a Yamaha 50 cc trial bike . We were all very impressed till the day he got stopped with most of us near our school :The police was then clamping down on all the suped up 50cc that were supposed only to do 40 km/h max speed .They had portable rolling benches to check the speed : Needless to say that he walked home that afternoon as the bike got confiscated . I shall admit that my Kreidler RS clocked 105 km/h on such bench and had to present it a week later " limited " to 40/h again .. The only way was to fit a 12mm Bing carb instead of the 21 mm , blocking up the exhaust with steel wool and limiting the throttle travel to 50% .

Just to say , these type of conversions maybe challenging projects but are economically unjustifiable , not to mention the illegality and total absence of insurance coverage on such vehicles in most countries .
A highly amusing anecdote :) , however I have never heard of such a thing in the UK and in this day and age the sort of roadside vehicle related enforcement the authorities seem to be mainly interested in is anything that just involves sitting in a van (and manning a speed gun or a ANPR computer to check road tax compliance). Although you of course still risk a 'pull' if doing something obviously illegal.

Homebuilt motorcycle hybrids have long been a reasonably common practice over here - back in the 80's there were plenty of 250 to 350 conversions (either a 350LC into the 250 frame or into an Suzi RG250 frame - the YammaGamma :) ) into the 90's and it was the turn of the GSXR7 / 11 - (the early 90s GSXR750s handled well but the 1100s didnt, so apparently slotting the 1100 motor in the 750 frame made a much better handling bike than Suzuki managed themselves :laugh: )

In short then, I very much doubt the OP will encounter any problems getting his bike either registered or insured. Some insurance companies probably wont want to know and he may pay a bit more than for a 'genuine' 390, although that may also be offset by the bike being not worth as much.

Best of luck with the conversion @Powell9539 and thanks for giving me an idea - I quite fancy owning an RC390 at some point and buying a ratty RC125 and converting it could be a cheap way in and make a nice little project.
 

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Thank you. I do believe importing is a whole new ball game. I was very surprised at the DVLA also i was expecting to have to take the bike to a vic test centre to check everything. But from information provided by .gov website it is just the tax class they are concerned about. Dont get me wrong things like this usually fall flat on thier face ? but i hoping i can do this in reasonable time? And im still expecting problems with converting and re class of the bike. Im one of those people who just gets something into my head and want to do it, with the lack of info out there on this im hoping if nothing else i can provide some accurate info on it, succeed or fail. Worst case i dosnt work and i change it all back and buy a 390 outright, ill then have a nice garage full of spares???
Go for it ! Physically it should be not that difficult ; after all the it was KTM who did it first by placing the 390 engine in the 125/200 frame . I just hope that it is not the wire harnesses and other electronic components that are going to complicate things for you .
 

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Good point about the harness - I would have thought he would be wanting the 390 one if he doesn't have it already - there's one on ebay now for £68
 
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Discussion Starter · #11 ·
Go for it ! Physically it should be not that difficult ; after all the it was KTM who did it first by placing the 390 engine in the 125/200 frame . I just hope that it is not the wire harnesses and other electronic components that are going to complicate things for you .
I Did think about the harness but have dismissed it for the moment. I may find i need it in which case there are afew knocking around on ebay but im going to take a chance on that aspect. I will know more very soon and update with a build thread as soon as i can.:)
 

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Discussion Starter · #12 ·
A highly amusing anecdote :) , however I have never heard of such a thing in the UK and in this day and age the sort of roadside vehicle related enforcement the authorities seem to be mainly interested in is anything that just involves sitting in a van (and manning a speed gun or a ANPR computer to check road tax compliance). Although you of course still risk a 'pull' if doing something obviously illegal.

Homebuilt motorcycle hybrids have long been a reasonably common practice over here - back in the 80's there were plenty of 250 to 350 conversions (either a 350LC into the 250 frame or into an Suzi RG250 frame - the YammaGamma :) ) into the 90's and it was the turn of the GSXR7 / 11 - (the early 90s GSXR750s handled well but the 1100s didnt, so apparently slotting the 1100 motor in the 750 frame made a much better handling bike than Suzuki managed themselves :laugh: )

In short then, I very much doubt the OP will encounter any problems getting his bike either registered or insured. Some insurance companies probably wont want to know and he may pay a bit more than for a 'genuine' 390, although that may also be offset by the bike being not worth as much.

Best of luck with the conversion @Powell9539 and thanks for giving me an idea - I quite fancy owning an RC390 at some point and buying a ratty RC125 and converting it could be a cheap way in and make a nice little project.
Thanks you. My duke 125 is alittle tatty aswell. had it very cheap compared to most for sale at the time. Had some fun on it on my CBT but now with a full license and time spent riding just wanted alittle more poke. When finished I'm hoping to use it as a summer commuter and it also holds sentimental value to me so even when the bigger bikes come along this will always be in my garage. I'm just hoping it will be straight forward but these things seldom are.:):)
 

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Thanks you. My duke 125 is alittle tatty aswell. had it very cheap compared to most for sale at the time. Had some fun on it on my CBT but now with a full license and time spent riding just wanted alittle more poke. When finished I'm hoping to use it as a summer commuter and it also holds sentimental value to me so even when the bigger bikes come along this will always be in my garage. I'm just hoping it will be straight forward but these things seldom are.:):)
sounds like you better sell the 390 motor and get a 200 one instead ;)
 

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I hope this project works out successfully. The software conversion, I believe, will be the most difficult challenge. It would be very useful to have a documented procedure for this conversion, which appears to stir a lot of interest.
 
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Discussion Starter · #15 ·
sounds like you better sell the 390 motor and get a 200 one instead ;)
I would of gone for the 200 motor but they are even harder to come by than the 390. The 390 motor i have is the only one i could find in the uk i pondered it for awhile before i took the plunge!? I did see one 200 motor but it was in a mess so left well alone and ive not seen any of the others bits for a 200 either. I think it would probably be a hard conversion purely on how rare the parts are unless you want to buy new?
 

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Discussion Starter · #16 ·
I hope this project works out successfully. The software conversion, I believe, will be the most difficult challenge. It would be very useful to have a documented procedure for this conversion, which appears to stir a lot of interest.
Hopefully no major problems will crop up but i doubt im that lucky??
 

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I would of gone for the 200 motor but they are even harder to come by than the 390. The 390 motor i have is the only one i could find in the uk i pondered it for awhile before i took the plunge!? I did see one 200 motor but it was in a mess so left well alone and ive not seen any of the others bits for a 200 either. I think it would probably be a hard conversion purely on how rare the parts are unless you want to buy new?
A 200 conversion probably would not have made economic sense - the 125s are worth more !

So a 390 it is (and a LOT more poke ;) )

Best of luck with the conversion, I'm sure many of us will watch with great interest and of course help where we can
 
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Discussion Starter · #18 ·
Some info on the wiring harness, both the 125 and 390 share the same harness according to the KTM parts catalogue (90111275000). So fingers cross the existing harness should be fine?
 

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Discussion Starter · #19 ·
May have jumped the gun on the last post. I have one of the early Duke 125s and it doesn't have ABS. Harnesses are now slightly different im hoping it is just the ABS system??


First image is the Duke 390 second image is 2011 Duke 125 harness
 

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