Vintage Dirt Bike Q & A

Greetings from VA! Several months ago I acquired a 1974 MT 250 showing 2300 miles on the odometer. The motorcycle had been stored in a barn and had stopped running when put away some 15 odd years ago. Since my acquisition the following has been performed: gas tank cleaned and POR15 liner applied, carburetor cleaned and rebuilt (stock jetting), NOS petcock installed, new fuel and vent lines, points and condenser replaced, new plug(s), new uni filter, cylinder re-bored and new Wiseco 71.0mm and rings installed (compression=140), new crankcase seals installed, all new engine gaskets, exhaust cleaned, fresh ethanol free gas with Yamalube 2R mixed at 32:1. The majority of these items have been completed by a certified Honda motorcycle technician with many years experience.There have been numerous other non-engine items replaced/repaired as well but they are not relevant to my issue which is the motorcycle continues to run rich with all the symptoms associated with that condition. After conferring with above mentioned mechanic we have concluded the most likely scenario is the apparently compromised starter valve choke assembly, in particular the integral rubber o-ring on the plunger. The starter valve assembly for this Keihin carburetor (Honda part #16046-361-670) is apparently no longer available. I have exhausted my resources including Terry at Western Hills Honda, etc. I'm sorry for the long-winded first post but I thought it important for the members to have a comprehensive overview of what has been done. Any help or guidance will be greatly appreciated as I am about to start parting this motorcycle out.

Here are a couple of threads here about your carb and motor. There's a lot of additional info at this site, but since you can't use the search term 'MT250' you may not be able to find it quickly:

viewtopic.php?f=21&t=4295&hilit=99124

viewtopic.php?f=21&t=3856&hilit=float+height

The MR175 carb is nearly identical except for jetting.

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 for the reply rayivers! Since my initial post I actually found a choke plunger used but appears sound on eBay. It's for a '75 though it appears to be a match. I did replace the jets as part of the rebuild process (Keyster) but did not compare the numbers on the new jets with the old ones. Fortunately I saved the old jets and will compare them in the next day or so. I really feel the problem centers around the carburetor as just about everything else has been eliminated.