Author Topic: Hi performance XR75  (Read 11068 times)

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Offline 35elsinore

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Re: Hi performance XR75
« Reply #15 on: October 18, 2011, 09:51:08 pm »
Thanks again Les your help, its priceless. I guess the cr frame was an idea with the thought to be a bit different aswell. Thanks Smed for the links. I have had a quote off of XRminiracer for a engine $3200 But have to send my engine to the states as they cant supply. Was hoping for a bit cheaper option thats why I posted this topic. The engine I have already prelimenary fit to a frame, it does look a little small next to my 125 but certainly not totally out of place. The rear bottom mount is original with a spacer each side. The front mount I have made out of aluminium and amazingly diameters of engine and frame mounts are the same width. The only hassle I can see maybe the inlet manifold/carby as the cr frame is dual pipe for the side port head. It does seem a shame to see my K1 XR75 sitting there without a heart tho.

Offline EML

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Re: Hi performance XR75
« Reply #16 on: October 19, 2011, 09:24:56 am »
I do like your idae elsinore but check the weight diffs 1st. The Cr frame might work better as you will have room to mess about with weight distribution back and forth as well as up and down for the best balance.
The larger CR wheels will work better if it gets rough as well. And it's not been done before that we know of.

Swiss

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Re: Hi performance XR75
« Reply #17 on: October 20, 2011, 07:04:05 am »
I did this years ago when my boys were growing out of their XR75.  Found an early CR125 frame and a Thor aluminum swingarm to fit it.  Added a Clarke mini tank and MR50 custom seat with some old Curnutt shocks in the back.  They had fun on it running in the desert.  Had to cut and bend the right side frame tube for the carb to run back.  Found out that the early CR frame had some double wall tubes in it!  That surprised me.  I will try to find a pic of it.

Swiss

Offline 35elsinore

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Re: Hi performance XR75
« Reply #18 on: October 20, 2011, 05:48:15 pm »
Thanks Swiss a picture would be great. I guess you rode it aswell, can you remember how you mounted the engine, what position and did it turn like a cr125. Cheers Troy

Swiss

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Re: Hi performance XR75
« Reply #19 on: November 10, 2011, 12:55:08 pm »
Sorry guys, this is the only pic that I have of it other than a distance shot of one of my older boys riding it in the desert.  This was when I was taking it apart to rebuild the stock XR75 frame for my youngest to learn to ride on.  I had just thrown it together with the CR125 frame and the XR75 engine for the older boys to have something to ride.  I had already pulled the pipe off of it.  Mounting was simple since there was lots of room.  Lined up the chain, set the front sprocket at about the same height as the swingarm pivot and cut up some mounts to fit.  Used a sock filter since it was mostly ridden in the desert and we weren't worried about mud etc...  The kids loved playing with it.



This son is now 24 and in the Air Force.  Time flies when you are having fun!

Swiss


IT400C

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Re: Hi performance XR75
« Reply #20 on: November 10, 2011, 01:53:18 pm »
I was reading an article a couple of days ago (Popular Cycling from sometime in 1976) about an XR75, bored and stroked out to 116cc..

I'll dig it out tonight and scan it if you want.

The Dyno charts before and after were quite interesting....  2 to 2 1/2 times the horsepower EVERYWHERE, and the same increase in torque..

Trying to remember what they did.

bored and stroked to 116cc
10.5:1 compression head
new cam
larger head studs to avoid blown head gaskets
bigger carburetor
internal rotor ignition off something else?


Offline 35elsinore

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Re: Hi performance XR75
« Reply #21 on: November 14, 2011, 10:56:31 pm »
Thanks Swiss what a corker. Spose ya wont have to raise the foot pegs for him at 24 then.

Any info IT400C would be appreciated. Was that article on the net or a mag. 2 to 2.5 times more horse power I might have to de-tune it.  :D  What a huge improvement, just what Im looking for. Thanks

Swiss

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Re: Hi performance XR75
« Reply #22 on: November 15, 2011, 08:23:13 am »
I built up one of the XR116 engines and the one in my son's XR75 pictured above was one of them.  Guy contacted me about building the engine up, said that he had found the "Powroll Kit" on EBay and wanted to know if I could put it together for him.  It had everything but the cylinder sleeve and I did some research and found that I could use an old 175cc twin cylinder sleeve for the kit. Worked out real well.  I have the kit info and the article all scanned if someone needs them.

Swiss

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IT400C

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Re: Hi performance XR75
« Reply #23 on: November 15, 2011, 09:12:19 am »
Yeah, it was the Powroll Kit in the article I have.  (from a magazine at home)

Swiss, is your article from the (I think) June 1976 Popular Cycling?

Swiss

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Re: Hi performance XR75
« Reply #24 on: November 15, 2011, 10:33:39 am »
Yes I think it is a '76 issue, I took all of the articles that I thought were of some importance to me (mainly Thumper articles) and pulled them out of the magazines and put them into folders.  Otherwise I would have a room full of old mag issues.  I was getting 7-10 mags per month between bikes and cars for years and had stacks of mags 6' tall along a wall.  Had to trim them down.  Didn't know that years later I could have sold some of them on EBay for more than I paid for them!  HA!HA!

I also have the Powroll build sheets for the engine, and the old Powroll catalog pag where they showed the 116cc dyno run compared to stock.  They showed 10.3hp vs. stock 4.5hp on the Powroll dyno sheet.

Swiss

Offline 35elsinore

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Re: Hi performance XR75
« Reply #25 on: November 15, 2011, 05:03:58 pm »
Swiss would it be possible to email the scans of the mag. Wonder if anyone would have a kit laying around. Cant thank you enough.
Regards Troy

Offline Viper79

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Re: Hi performance XR75
« Reply #26 on: November 15, 2011, 07:12:56 pm »
Troy, I have emailed you three pics of the Powroll article

Rob.
QA50 KO, XR75 K5 Race bike from VMBA days, XR400R1, CRF450R3, RM400T, DR650SE with off road adventure mods, MX360A, YZ400D, YZ465H, IT250H, 1985 Jawa 897 Slider, 2016 Jawa/GM Slider

Offline JohnnyO

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Re: Hi performance XR75
« Reply #27 on: November 15, 2011, 08:00:45 pm »
Why don't you contact Powroll and see if they have the parts you're looking for... they're still in business.

Offline LWC82PE

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Re: Hi performance XR75
« Reply #28 on: November 15, 2011, 08:34:50 pm »
They are in business, still but in big trouble apparantly and really struggling with workload that is affecting their customer service big time. They are currently not operating to their usuall high standards which have dropped considerably. There are several threads on them on some USA sites. Thumper talk is one i think and it is best you read those. I would avoid placing an online order with them and You are unlikely to hear from them. From what i have read, they have a huge amount of back log of work and they are kinda over whelmed by it all and its just 2 guys and the girl in the office trying get through it all. i think the GFC has had a big affect on them by the sounds of it and everyone is hoping they can pull through it as they are te only experts ding this sort of stuff at a high quality with years of experience. I wanted to place an order for a XL250 stroker crank with them but are going to hold off for 6 months a year? till their communication and customer service  picks up because currently a huge amount of emails are going unanswered (worldwide), and you cant even get through to them by phone. The only way i have known people to get incontact with them in recent times is via a secret phone number direct into the workshop, that the public is not supposed to know.

Just one the XR75's, there is a XR75 specialist in USA that has NOS Lockhart Oil coolers for XR75's.
« Last Edit: November 15, 2011, 08:40:52 pm by LWC82PE »
Wanted - 1978 TS185 frame or frame&motor. Frame # TS1852-24007 up to TS1852-39022

Offline 35elsinore

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Re: Hi performance XR75
« Reply #29 on: November 16, 2011, 08:10:54 pm »
Thanks everyone for your time and help. Starting to get a few options now.