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justin49

Joined:

Apr 14

Posts: 3

justin49 says:

Sachs conversion help please

I was offered this Sachs Roadster 125 V2 for pennies. The original XV125 (Yammy Virago) engine, after a strip down and new seals fired up great.
So now, as I've come across an XV250 engine in good nick, and wondering about dropping it in to the 125. Considered all (I think), by comparing the full specs for the Roadster 125 V2 verses the Virago 250 V2, came up with the following, all being exactly the same for both bikes:

 Brakes - Single 260mm disc, 2 piston calipers, 130mm drum 

Chain size - 17.50mm, 10.16mm, 2.0mm, 1.42kg/100 links, 29.8KN 

Fork size - 41mm, with 120mm travel

 As well as the starter motor, exhaust system, rear spring size and travel also.

The frame on the Roadster 125 being considered way heavier (steel) than most believe needed for a 125. I thought that that might be a blessing, by having the extra strength needed to handle dropping a 250 in there? 

So, all the above said, is there anything I'm missing, that might make the conversion a total no no? Thanks, Justin.


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  • Posted 120 days ago (23 April 2014 15:43)

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kcmc

Joined:

Jan 08

Posts: 7382

kcmc says:

Sach 125-250 Yamaha Virago engine swap

Hi Justin49 and welcome to the site :smile

Should be not too many problems as there the same engine bar the bore and stroke, the 250cc engine maybe a couple of mm taller in the cylinders but probably won't cause too much of a problem, you may need to change the gearing by a tooth or so, and the jets in the carb if your using the 125cc carb?(think it's the same choke size but check anyway?). Good Luck

KCMC :tongue:

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justin49

Joined:

Apr 14

Posts: 3

justin49 says:

Sach 125-250 Yamaha Virago engine swap

Morning KCMC, many thanks for the welcome and reply with those points. Most appreciated mate.


As to clearance - yeah, there is at least 4-5mm to spare. So, should be fine.

And it looks like the carb models for both a 125 and 250 are identical - all are sold stating "for XV125/ XV250". And part numbers match too. So, I take it the choke size will obviously be the same?

Can I ask also what you think about the looms for both. As that's my only really grey area? 

Cheers,
Justin


 

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kcmc

Joined:

Jan 08

Posts: 7382

kcmc says:

Sach 125-250 Yamaha Virago engine swap

Hi again

All the engine electrical systems are the same on both engines,but as I thought the carb jetting is very different (if you could obtain the 250 carb it would make life a lot simpler)you will need to change the main jet-pilot jet-and main air jet if you use the 125cc carb I think the slide needles are the same as well as the needle jets are the same. When I said the choke side I wasn't meaning the starter choke which is a starter jet in this case, I was meaning the diameter of the carb intake bore, also as I thought the gearing would be two teeth less(rear sprocket) for the 250cc engine, unless you want better acceleration but it may over rev badly in top gear? being such a small engine. Good Luck


250cc jets

Main 155

Pilot 17.5

Main air 110

----------------------------------------------------------

125cc

Main 135

Pilot 12.5

Main air 77.5

------------------------------------------------------

So as you can see there is a vast difference

KCMC  :tongue:

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justin49

Joined:

Apr 14

Posts: 3

justin49 says:

Sach 125-250 Yamaha Virago engine swap

Brilliant. Thanks again KCMC. Invaluable info :biggrin: 

Another very "grey area" it seems for me :wink: 

Looking like an extra 100 quid, if go with a new 250 carb. 

I've learnt a fair bit over these last 18 months, and enjoyed every minute (well, almost). But, to be honest, I thinking best to go to a pro, if re-jetting will be any cheaper that is. Probably not, with time and labour. I'll be sure to pass on the most appreciated specs on that when I do find a workshop that might help.

Cheers,
Jus :biggrin:

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