Hi performance XR75

[35elsinore]

Need some feed back on my new project. As a lover of everthing honda, a XR75 impressed me at the coffs harber national. After much thought of building a pre 75 fourstroke for 2012 nationals I have decided to fit a K1 XR75 engine into a 73 cr125 frame. I guess this has been done before but myself have never heard of anyone doing it. The thing I need help with is getting the most out of the 75 engine to compete with the bigger bore bikes. The XR75 at coffs harbour went very well so if anyone knows this gentleman and maybe a contact number it would be much appreciated. Would love to have any feed back eg: im wasting my time etc. or any info on suppliers for go fast bits.
Thanks Troy

[Freakshow]

Did it have an Sl125 barrel.

[Viper79]

Here's some pics of one in progress on the VCM website.

http://vcmweb.ning.com/photo/albums/xr75-engine-progress

[John Orchard]

Didn't FMF do it in the 70's with a bored & stroked engine out to 110cc ?

[Viper79]

I started to do my XR a few years ago and it got shelved, more important projects to do.
The go back then was to have a SL 125 sleeve put into the XR cylinder, have the engine cases machined to accept the bigger sleeve and you have to have the con rod machined to take a 14mm gudgeon pin and you fitted I think a Kawasaki GT550  piston (I still have all the parts to do it somewhere) you need to have the head O ringed as well.  From memory a guy called Glenn Stayley in the Sevill area in Melbourne does them..   

[EML]

What do you weigh mate, under 50kgs one hopes on a wee thing like that.

[jimg1au]

ask steve gall his was very fast back in the day
jim

[35elsinore]

Thanks for the feed back, just what I was hoping to get. EML, 79kg light haha. I love riding my 125s an know how much more fun they are to ride compared to my 250. This was my train of thought with this project. The corner speed you can keep compared to 70% of the field being heavy XL350s hopefully will compensate for the lack of power. Viper79 are you interested in selling any of your mothballed project. Cheers Troy

[xrBarf]

G-day there Troy, yeah that was my XR75 at the Coffs Harbour Nats a few years back. It was a pity i smashed my knee up a little in the second race as i was planning on knocking a few noses out of joint by beating the big bikes. Oh well ! Yep the little things a rocketship that took a few lunched motors to get it absolutely bullet proof. Has had a bit of history in the VCMR a few years back taking out the 4 stroke All powers title for a few years running and yes it did upset a few blokes on their hotted up big bikes. Haven't raced it since Coffs but i have been known to disturb the peace at the HBBB on it. Gave it a nice new paint job for the 70's MINI BIKE reunion we had here in Victoria a couple of years ago. I'm not real sure how to post a photo of it on this thread but if you look on my page there is a couple. By the way it's also a methonol burner too.        Regards  Les Barfoot

[35elsinore]

Thanks Les for the reply and memories. Any hints on the bulletproof stuff or are you interested in building another engine. Seems the more I dig the more surprised I get at how many hot XRs are out there. The idea of putting the engine in a 125 frame is for the bigger wheels and ground clearance to hopefully save my knees and kidneys.
Cheers Troy

[smed]

Have a look at these www.xrminiracer.com            There is an XR section on       www.vintagefactory.com    ,If you wanted to use the stock frame an elsinore 125 front end will virtually go straight in using the original front wheel of course you would then need to jack the back up to suit,there is no easy or cheap way to hot up the 4 speed donks but as Les has proven it is possible , I think the 75 motor would be to small for the 125 frame & would go for a hotted up SL100 or 125 motor but i guess that's going away from your original idea        

[EML]

There was a guy that raced one down to Baja one year-that would be a good story to find again. maybe in Dirt Bike or Motocross Action.
I just modded a kids exhaust on an XL185 and it at least sounds the goods now.

[xrBarf]

Yeah Troy the motor runs a kawasaki 550 piston in a SL125 sleeve. Not much room to play with inside an XR barrel so the sleeve fitting must be precise. You will need to do a little head work to fit the piston diameter and not to mention a port job to feed the thirsty mongrel. As previous said a bit of rod work to fit the bigger pin too, a copper head gasket to hold in the compression. Cases must be machined out a tad and re routing of the oil feed. Some just run external lines but mine are interal but modified. A lumpy cam, trick valve springs a nice big carb and manifold that drinks methonol, a CDI ignition mines a 1974 elsinore 125, a barnett clutch and springs and my favourite a grouse reverse cone megaphone so the big bikes hear you coming. If it's all done properly you will have one sweet motor.
 Myself i wouldn't put it into a 125 frame for big wheels. Just lift up your XR with 125 elsinore front forks a DG style swing arm with longer shocks a 17inch front wheel and re upolsted seat a couple of inches higher than stock and you end up with one very roomy XR75 that still looks like an XR 75 with all the leg room you need. I'm 180 tall and 78kgs and its perfect and so much fun to ride. Hope this is of some help.... Regards  Les B

[smed]

What is the capacity of your motor Les? So it's not stroked then?

[xrBarf]

No Smed it's not stroked. Didn't want to start mucking around with spacers etc. Wanted the external of the motor to look stock. To my belief it is around 116cc or there abouts.  Regards Les