Vintage Dirt Bike Q & A
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Return of the super bike
https://vintagedirtbikeforums.alp-sys.com/viewtopic.php?f=21&t=4676		 Page 1 of 1
Author:  Killer Canary [ Tue Aug 23, 2016 6:50 pm ]
Post subject:  Return of the super bike
I thought that I had my MT running alright but after reading some of Ray's old posts I wanted to make absolutely sure that the muffler wasn't plugged.
I removed the end baffle and inspected the turbine dealy that others have mentioned. I ground a point onto the end of a wire coat hanger and started poking around in the holes that run around the circumference inside the pipe and after awhile got the wire to go completely through two of the holes and into the main muffler body. The other four refused to open, so I used a long tapered punch and a hammer and forced them open.
Now she:
wheelies
spins out
hits redline in all five
sounds like a genuine two stroke.
My new knobby is showing more use from a 15 minute ride than in all of the miles that I've put on so far this summer.
There is much grinning in Vonda, Saskatchewan. :D
Author:  rayivers [ Tue Aug 23, 2016 7:24 pm ]
Post subject:  Re: Return of the super bike
That's excellent! I think the MT250 motor is power-limited by the small carb only if the pipe is clear. Cleaning the pipe out really can wake things up, and it even sounds better too, as you noted.

My MR175 silencer section is very similar to the MT's, and I tried drilling a 1/2" hole through the center cone of the turbine-core section. The bike got a bit louder (not much), but the top end felt noticeably crisper with no hi-rpm burble at all. I don't know if this would work the same way on the MT, but it might be worth a try

I got a chance to work on a '75 MT this afternoon, and was real pleased with the results (although there's plenty left to do). We installed an NGK BP7ES plug (easier starting, a little more low end, and a lot less hi-rpm misfire) and 14/48 sprockets (wow! revs quickly to redline 1st thru 4th, then 5th pulls pretty hard from there (I ran out of room at 6K rpm / 60 mph but was still accelerating, which wasn't the case with the OEM 15/44 sprockets at all). This bike seems to need a 65 pilot jet and 118 main jet right now, but the plan is to check the timing before any carb work.

Ray
Author:  Killer Canary [ Tue Aug 23, 2016 8:09 pm ]
Post subject:  Re: Return of the super bike
It was one of your previous posts about drilling the centre open that got me thinking. I was going to weld an extension on to a quarter inch drill bit and start with that but I got distracted with clearing the holes and now I don't think that I need to go through with it. 8)
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