Vintage Dirt Bike Q & A

Hi- new member here. I have been searching around the internet and come up empty, so I thought I'd try my luck here. I'm building up an MR50 and my project bike is missing the entire throttle. I've tracked down the throttle cable, throttle pipe and a right grip, but the throttle upper/lower and limiter ring (and screw) are basically impossible to find new or used. Well, I did track down some NOS throttle parts, but they are extremely expensive so I'm only considering that a very very last resort. I was told by the good folks at RE-MX that the MR uses a weird diameter handlebar so you can't easily mod a throttle assembly from another bike to work on it. So I'm wondering if anyone has been in the same spot as me and if they've found a solution- maybe a crazy hack of another Honda throttle or a custom-made throttle assembly? Thanks!

If you want to keep your tube and grip, you might be able to find a 7/8" throttle housing that fits them both. Unless you found someone online that had already done this and could point you in the right direction, this will probably be a real challenge. A better way might be to find a complete 7/8" throttle assembly from an XR75 or whatever - possibly the cable too - then adapt those to your bars and carb.

For either of these options, you'll need to build out the 3/4" bar to 7/8", either for just the housing or the complete throttle assembly. The tubing in the link below might work, and if not they have slightly bigger and smaller I.D. tubing with the same 7/8" O.D.:

http://www.onlinemetals.com/merchant.cf ... top_cat=60

There are several ways to fit this tubing, from mega permanent to semi-easily removable later. If you're going to ride the bike, you definitely do NOT want the throttle sliding off (a long time ago a girlfriend of mine broke her wrist when this happened, she was lucky she didn't get run over).

Substituting a throttle assembly can be tricky if you want everything to look and work right. I fit Suzuki right-angle throttle assemblies to both my Hondas, I tried three different cables per bike before I found the right ones (different frames & carbs).

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