Vintage Dirt Bike Q & A

yep CR cylinder is bored, honed and im just waiting on the Wiseco small end bearing and i can fit it up. My next problem will be the intake but i may just modify the split OEM one that i have... Carb... well i did see a few CR guys were fitting a Mikuni VM36 round slide carb for around $100, that sounded like a good plan as ive no carb at present, the closest i have on my bench is a PWK28, does anyone think thats a goer? if so im almost ready to roll!

The pipe should fit the 73/74 top end just fine, ive mocked it up and the 73/74 is the same exit and spacing as the MT etc.

Quieter is good round here....

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

You are right, but i will have more power than the MT and yet retain its look. Do you think i will lose top end and perhaps gain some low end?

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

Woosh, I agree. I just think the downpipe is a looks killer. its too frightening to think of what is about to reach up and attack it off road and on road it just looks like a road bike with knobblies which isnt the look i wanted. But... if the pipe i have doesnt work at all with the bike then i will be forced to buy a DG i guess.

Interesting on losing the footpeg, I hadnt even considered that aspect, but of course the pipe sweeps up there.

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

no, i think it is too small.
you can use it on a 250/350cc trials engine or 125cc street bike.
the cr cylinder is designed for high power at topend and it will not work adequate with a small carb and wrong pipe.
i guess a 32 carb is the minimum you need.

if your pipe doesn´t work i think a proform pipe will be better than a DG.
the proform gives your engine a wider usuable powerband than a DG.

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80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

Wish I had ponied up for the Pro-Form pipe instead of the DG. The DG is damn loud & the steel seems thin. I put a nice dent in the bottom of mine already.

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WWW.CADDY500.COM
The High Performance
Big Block Cadillac Forum

Hmm... ProForm sounds good guys.... its tempting.... I'll see how this one runs first i guess...

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

Ray, working back towards the front... my pipe has a 16.75" silencer, then another 4inches of 'bend', then the body of the 'expansion' (term used loosely) is just over 23".

I defo dont have a top clamp, just the lower one... should i weld one on?

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

Jon,

I think it would be a very good idea to use a top mount, especially with a silencer this long. If you don't, you may have a lot of outward pipe motion and possibly leakage around the manifold. I'm also a big believer in redundant pipe mounting, having had to head home early a few times holding a hot pipe on with my leg.

My Bassani came with a simple sheet-metal strap that wrapped around the silencer and bolted to the top shock mount. It applied way too much wrapping force to the silencer for my taste, so I used a long bolt and spacers to mount the pipe for testing. If you're making up a strap from scratch, you can make it the right length to start with and shouldn't need all that.

As you know, it's important for exhaust mounts to allow for pipe expansion, which the strap mount should provide. I was going to weld up a bracket directly from my silencer to the frame, but after reading the warnings in the SuperTrapp instructions NOT to do this I used a large rubber radiator mount from a newer YZ450F I had laying around, in a tab welded to the silencer body. It holds the silencer firmly, but allows for a small amount of motion and damps vibration too.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks Ray, youre thinking along the same lines as I am. Its a light pipe, but its a long 'lever' when it gets knocked at the far end.

My plan wouldnt be to strap it i think or even use a clamp as such, I will weld on a tab to the top and then use the standard MT rubber pipe mount bracket on the shock mount, so similar to what you suggest. Absolutely you shouldnt bolt anything directly to the frame, it should have a rubber damper in there.

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

Jon,

Funny you should mention that mount... I replaced it on my friend's MT a few days ago. Yes, that should work great. I would have done the same on my MR (the MR rear pipe mount is nearly identical to the MT250's) but the new pipe tucked in too far and I had to weld up a new frame bracket using a rubber fuel-tank grommet. Now for a new center mount, and I should be done (for now).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Yeah the MT had some quite good mounts for teh pipe if im honest, probably cos the OEM was a boat anchor thet seriously needed holding!

Interesting on the fitting, Ive so far assumed the fitting will be the same as the MT, as right now i dont have a small end bearing that fits so dont have my top end on, once thats done i can trial fit the pipe..... exciting times!

Do you have any photos of your install Ray? would be keen to see them

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

Jon,

OK, second try ...

Here's the entire exhaust on the bike:

... and here's a composite of the pipe's fit to the frame (left and top) and the various mounts (bottom right):

The mounting is pretty solid even without a center mount; there's no way the pipe can twist or droop unless something breaks. It really can't be tucked in any tighter without hitting something, either.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Ray, superb work as ever my friend! Thanks for that. Once ive got my engine together, i will sort this and do pics for completeness. Cheers!

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MT250 with CR250 top end & Bassani pipe... almost fully restored.

See more of my motorbike builds at my Honda MT250 and Yamaha RD and RZ website, 2Smoked.com

If you like watches, check out my websites: DeskDivers.com & PloProf.com

Ray,

What type of tail-light/plate mount are you using? That looks nice & low. I still have the chrome tower on mine & it has to go.

Thanks
~JM~

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WWW.CADDY500.COM
The High Performance
Big Block Cadillac Forum

JM,

It's an Acerbis Dual Sport taillight:

http://www.amazon.com/Acerbis-Dual-Spor ... B001A6PVLG

I believe it's wired for both tail and brake lights.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric