MJ50J Yamaha Towny, 1982 model

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MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Mon Jun 03, 2013 6:34 am

Hello to all!,
I'm new on this forum and am looking for some guidance. My dad gave me his 1982 Yamaha Towny several months ago. He purchased this brand new back in 1982. It has always been kept in a garage & is in excellent shape. My son & I made it a winter project to try to get it running again. We succeeded in getting it to run after performing the following maintenance and replacing parts: new air filter, new spark plug, new fuel cock, removing & cleaning the carb, new piston ring set, changing engine oil, draining the old and replacing with new 2 cycle motor oil from the reservoir. Here is our problem, we only get about 30 minutes of riding time out of it before the spark plug gets charred to the point it's black and won't produce or maintain adequate spark to keep the engine running. We've tried different spark plugs with the same results. This Towny requires leaded gas so we ad a lead substitute to the gas can prior the filling the under seat tank. Could the 2 cycle oil injector pump not be functioning properly? What is the correct gas / oil ratio for this model? I want to try premixing the 2 cycle oil in the can to see if that will make a difference. I will, of course, drain the 2 cycle oil reservoir first.

Any thoughts & comments will be greatly appreciated.

Tom
Ft. Thomas, KY
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re: MJ50J Yamaha Towny, 1982 model

Postby John » Mon Jun 03, 2013 9:50 am

Don't add lead substitutes, not needed. Just use reg unleaded 87. Disable the oil pump, block/plug lines and run 50:1 with a good synthetic 2 stroke oil. N obviously. New plug in order. Adjust carb as per the manual.
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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Mon Jun 03, 2013 10:59 am

Okay. I'll do those things. What do you think is causing the plug to char up?.....too rich??....too lean??......the lead substitute?? Is a 50:1 gas / oil ratio sufficient? What is the reason not to use the lead substitute?

Thanks for your prompt reply.
Tom
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re: MJ50J Yamaha Towny, 1982 model

Postby John » Mon Jun 03, 2013 2:01 pm

You just don't need it, my guess that is what is messing the plug up. Also check and see if the choke is coming completely off. Is it an electric bi-starter type or a slide/ butterfly setup.
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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Mon Jun 03, 2013 4:31 pm

I don't know what an electric bi-starter type or a slide/ butterfly setup is. It has a kick start and a manual choke located below the left handlebar grip that is actuated by my left thumb. The choke lever is connected to a cable that runs down to the carb (I guess).
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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Mon Jun 03, 2013 9:55 pm

This evening we drained the gas from the tank (that had the lead additive), removed, cleaned and reinstalled the spark plug, drained the 2 cycle oil reservoir, added 2.5 ounces of 2 cycle oil to one gallon of gas and filled the tank about half way. It started right up on about the 3rd kick and ran like new. I sure hope this keeps the spark plug from getting all fouled up.

Thanks,
Tom
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re: MJ50J Yamaha Towny, 1982 model

Postby John » Tue Jun 04, 2013 5:24 am

Use a good synthetic like Ipone or Elf at 50:1. Ipone is scented. Spark plug electrode will tell you nothing of the burn as the synthetic doesn't leave a tell tale coffee colour like dino oil will when you are dialed in. Plug and or remove any oil injection lines and remove the oil pump and block off or take out its coupling driver. You don't want any air leaks to make the bike run lean and then seize.
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re: MJ50J Yamaha Towny, 1982 model

Postby John » Tue Jun 04, 2013 6:13 am

John

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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Tue Jun 04, 2013 7:00 am

Got it.

Thanks!!
Tom
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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Tue Jun 04, 2013 7:00 pm

Ok....So I removed the oil line between the injector pump and the carb. I put a spare piece of tubing on the 2 cycle hose barb on the carb and doubled it over and wired & taped it up so as to block any entry of air. The 2 cycle oil I'm using is Pro Honda, GN2, 2 Stroke Injector / Premix oil for motorcycles, ATV's & Scooter Applications. I mixed it 50:1 in the gas can and ten added it to the under seat tank. We've been alternating between the factory recommended NGK BP4HS and an Autolite 4123 spark plugs. So this evening we (my son & I) fired up the Towny on the first kick and off he went (I followed on my Honda VTX). About 10 minutes into our ride it stalled and would not start. Fortunately we brought the spare plug and switched it out on the side of the road. It started right up and we turned around and headed for home. I'm very puzzled and starting to get aggravated at this machine. The porcelain part of the plug just below the electrode is the color of a nicely browned marshmallow. The metal parts are a dark sooty gray, but not black. Would a cooler burning spark plug help? I've never replaced the reed valve. Would that help with the movement of air through the engine and with the fuel & air mixture? Is that a difficult fix?

Acceleration & shifting of the 2 speed automatic transmission is crisp & it doesn't hesitate.....until it just decides to stop running.

Frustrated,
Tom
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re: MJ50J Yamaha Towny, 1982 model

Postby John » Tue Jun 04, 2013 7:32 pm

That is a hot plug, wouldn't think it would foul. Is the exhaust clear? Are you
sure there is no air leaks and head tight. Check the bolts at the reed cage are tight. If reeds broken it would just not run at all. Hard to troubleshoot when you are not with the bike. How is the coil and condenser. Sometimes the condenser heats up in older bikes and quits till it cools dow.
Have you read "Freds Guide" in the repair section in the forum header, might help.
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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Tue Jun 04, 2013 9:10 pm

The exhaust is a bit smokey at first then clears up quickly when the engine warms up. We installed new gaskets at both the base and the head of the cylinder when we replaced the ring set on the piston. I don't know where the coil & condenser are. Do they provide a spark via the magneto? I'll check the bolts on the reed cage later this week when I get a chance.

Tom
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re: MJ50J Yamaha Towny, 1982 model

Postby xrongor » Thu Jun 06, 2013 12:12 pm

as you probably already know, the towny is basically a QT50. all mods for that bike will apply, however you do not need to regear the rear end.

i would take the exhaust pipe off and throw it in a campfire to burn everything out of it, then sand it and paint it with high temp bbq paint. Yes i am completely serious :D I do this with both my bikes every year whether they need it or not. Cook it for an hour or two.

When you have it off, check the exhaust port on the cylinder and clean it out as well.

good luck!
randy
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re: MJ50J Yamaha Towny, 1982 model

Postby tomven1967 » Mon Jul 08, 2013 6:31 am

I finally got the CDI & ignition coil replaced. I also tweeked the carb.....been fiddling with that since day one!! It started right up. Ran well for about 30 minutes, then stalled at a stop sign. Was easily able to get it started again. Will keep tweeking the carb. It runs better now than it did.

Tom
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