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Author Topic: 1985 Yamaha MJ50 Towny  (Read 207 times)

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Offline Alain2

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1985 Yamaha MJ50 Towny
« on: October 10, 2017, 07:16:26 AM »
This is my new acquisition. It only needed a new plug, a new battery and a carburetor cleanup. Everything works except of the speedo as the gear in the front wheel is broke, very common problem for Towny and QT50 I believe.

It has 120psi compression so I believe the engine is a bit tired. With the original 70 main jet the bike runs too rich, but it is driveable. I ordered a 60cc big bore kit and then I will re-jet it for more powar!

Can't wait to put a milk crate on that back rack.

With you clothes on, it would be hard to have more fun than driving this thing downtown!

Offline Kraven Morehead

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Re: 1985 Yamaha MJ50 Towny
« Reply #1 on: October 18, 2017, 03:26:39 PM »
Nice noped  :thumbsup:  I have a QT50 which is basically the same engine.  IIRC, the PW50, QT50, Towny and YT60 are all the same with the exception of the YT being 60cc.  If you bought the big bore kit off of Ebay you have the same one I had.  I since upgraded to the Malossi 70cc kit with the matching hi compression head.  I have quite a bit into my build but it rips!! Once the bug bites you will want a MLM "peoples pipe", Mikuni VM18, MLM VM18 intake, HPI CDI ignition and EBC brakes for stop lights.  Have fun!  :cheers:

« Last Edit: October 18, 2017, 03:27:47 PM by Kraven Morehead »
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Offline Alain2

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Re: 1985 Yamaha MJ50 Towny
« Reply #2 on: October 19, 2017, 06:16:17 AM »
I ordered the 60cc kit from partdiscounter (Niche brand), $63 Canadian dollar shipped in 3 days from Ontario, cannot beat that. It took me an hour to install, it would have been faster but I wanted to re-gap the ring ends a bit bigger. They came within specs at 0.008, now I'm not sure why I decided to make them 0.010.

The only other mod I did is a foam filter pod from a gas RC car. The engine is running very good now, but as soon as I reach 30mph the engine 4 stroke and stays there. I believe my jetting is good and the problem being the very restrictive stock exhaust header.

I couldn't find any aftermarket exhaust from the MJ50, would a QT50 MLM pipe be a direct fit on the MJ?

Offline Kraven Morehead

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Re: 1985 Yamaha MJ50 Towny
« Reply #3 on: October 19, 2017, 10:43:03 AM »
I couldn't find any aftermarket exhaust from the MJ50, would a QT50 MLM pipe be a direct fit on the MJ?
It should. The pipe bolts directly to the side case and the cylinder.

this is when I had the 60cc topend on
« Last Edit: October 19, 2017, 10:44:22 AM by Kraven Morehead »
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Online kdsmf

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Re: 1985 Yamaha MJ50 Towny
« Reply #4 on: October 19, 2017, 11:24:31 AM »
Looks a lot like a Chappy.

Offline Alain2

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Re: 1985 Yamaha MJ50 Towny
« Reply #5 on: October 20, 2017, 05:23:47 AM »
Tuned the main jet yesterday, ended up with 77.5. The 80 jet was too rich and I don't have smaller than 77.5. Finally broke the 30mph barrier, but it still 4 stroke in the top rpm.

I don't want to spend too much money on this bike for now, so I will ride it this way for next summer.