Motorcycle Repair: 74 MT 125, oil injection system, point gap

Question
Bill:

I recently purchased a 74 MT125 Elsinore, and I am having problems with it that I hope you can help me with.  The first problem is that there is oil blowing out of the exhaust pipe just after I start it.  This seems to go away after a few minutes of running.  The second problem is that the engine does not seem to rev over 4000 rpm.  Are these two problems related?  Any ideas as to how to fix them would be appreciated.  The bike has been sitting for a while, as it has only 5000 miles on it.  Finally, the bike has an oil injection system, but the previous owner was using premix and did not add oil to the tank.  How can I tell if the oil pump is working?  Please let me know if there is any further information you may need.

Thanks for your assistance.

Oscar Malkhoo

Answer
Oscar, probably not my strongest bike of interest or information, however I can make some suggestions:

It is a 2-stroke, so oily exhaust is pretty normal, especially when the choke is on.

The problem with not using the oil injection system is that sometimes the crankbearings are supposed to be lubricated from the injector system, so they may be getting air instead of oil, unless other modifications have been made. You will have to fill the tank and bleed the oil lines and pump before you can determine if it is working or not. I would leave the premix in the tank until you can ascertain that the pump system is working properly, then drain the tank and refill with straight gasoline. You may foul a few spark plugs in the process and transition, however.

You need to determine what sized jets are in the carburetor. Premix has a different viscosity than straight gasoline, so a smart mechanic would increase the jet sizes to compensate for the change in fuel mixture and oil ratios.  My spec book shows 24.0 mm float level, #98 main jet, #200 air jet, #50 slow jet.

Before you start messing with the carburetor, be sure that the ignition timing is set correctly. Point gap is .012-.014" with timing set at 20 degrees before top dead center.
(1.90mm). Stock plug is a B8ES from NGK.

You should remove the exhaust pipe and inspect the piston and ring through the exhaust port and/or remove the cylinder head and check for any problems, like signs of seizures or broken rings, etc.

Get a manual from www.helminc.com  or www.motorcyclebooks.com or www.motorcyclememories.com or Ebay auctions, if you are lucky.

That is all I can tell you about this issue. You could have a fouled plug, incorrect timing, wrong jetting, insufficient compression, plugged up exhaust system, bad air cleaner or many other maladies. Any of those issues can cause the symptoms you mention.

Bill Silver