Vintage Dirt Bike Q & A

A question for those of you who have swapped a CR top end onto their MT250.

What did you do for an air cleaner?

I have one set up that worked OK for the MT cylinder, but it isn't going to work now for the CR top end.

Thanks
~JM~

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Big Block Cadillac Forum

I just put a uni filter on the carb and called it good. It has no airbox to speak of just a carb out in the wind.

I just put a uni filter on the carb and called it good. It has no airbox to speak of just a carb out in the wind.

My worry with just a uni filter is that if you hit any water your engine is going to suck it right in, I am about to fit the CR250 top end on my MT and was hoping i might make the original filter box work with a filter from ReMx, is that a goer or will it be too restricted? Ive not seen any photos of how big the 73/74 CR airbox was originally compared to the MT so its hard to know.

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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

The CR box will not fit the MT frame from what I've been told.

The CR cylinder/head is taller than the MT & places the carb up higher. The carb outlet & the frame are very close to each other, limiting your choices for an air-boot, air-box, etc.

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Big Block Cadillac Forum

Ahh, now i see. Cheers for that. back to the drawing board! LOL

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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

I wonder if the MR250 unit will fit? The 34mm MR250 carb has a 62mm mouth, 43mm spigot, and is 98mm long.

http://cgi.ebay.com/ebaymotors/1976-HON ... 8301157598

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

Looks quite different, but i expect you could make it fit... anything will fit given time and a few deft hammer blows. In think part of the problem for the MT is that the battery sits under the airbox so that leaves a smaller box that sits high in the frame, the lid is on the top as the sides are too small. What I may end up doing is fabricating a box to fit the frame if i go that route, but its a pain as it stands. Perhaps if i ditch the battery... i guess the turn signals will still run when the engine is running, id just need a one of those battery eliminator resistors to stop the charging circuit from buring itself out, hmm... then maybe the MR box might fit... tho isnt the MR based on the 76 CR frame, whereas the MT is the 73/74 CR base? the plot thickens...

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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,

If possible, it might be worth a try keeping the MT airbox and trying to mate it to the bigger carb (Vintage Iron may have a smaller-I.D. accordion-looking 250 air boot like they have for the 125). The early CR250M and MR250 air boots are also worth looking at.

I used an MT250 air filter for two years on my MR175 until I got one of the UNI filters from the eBay guy in New Zealand (dabbernz). The MT filter worked fine, it was certainly plenty big enough for a modified 175 motor. I removed the airbox lid and ground off the top lid ridge, which created an opening around about 70% of the filter's top circumference and let a lot more air into the box and sides of the filter (before that, the top would get dirty way before the rest of the filter).

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

I tried one of the battery eliminator capacitors on my MT & it kept blowing out the taillights. I ended up using a small AGM 6V battery that sits in my original tool tray.

~JM~

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

Ahh yes JM, i remember your thread on that, good call.

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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