75 Yamaha oil injector info needed - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 05-25-2005, 07:49 PM
Kobey
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75 Yamaha oil injector info needed

Hi everyone,

My girlfriend has what I have figured out must be a 1975 Yamaha MX125B. She is a farmer and I grew up in a big city so I never learned anything about oil injected dirt bikes.

Anyway, it has been sitting for years and now the kids are old enough to start running it. It runs fine but the oil deal has me mystified. She was always taught to just put whatever mixed gas was on hand into it, usually about a 50:1 chain saw mix. When I looked in the injector today, no oil even showed up on the dipstick, so I don't know how long it has been since it was used. I was going to fill it with 30 weight just like a lawnmower engine until I looked on the net and found out about oil injection.

So anyway, what I need to know is what is the proper way to do it for this type of bike. Is it better to mix the gas and leave the injector alone, use straight gas and put 2 cycle oil in the injector or maybe even both?

On another dirt bike she has, the guy she bought it from told her to use mixed gas and keep the oil reservoir full. She knows nothing about different types of oils so she has been filling the reservoir with 30 weight since she has had it and it still runs, though she only runs it a couple of times a year. What effects will regular motor oil in an injector have on the engine?

Thanks for any help you can give me. I know this is basic stuff but it's all new to me.

Kobey
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post #2 of (permalink) Old 05-25-2005, 09:15 PM
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Re: 75 Yamaha oil injector info needed

Running any oil other than 2 stroke oil will kill the motor. Your best bet for the oil injection issue is to mix it yourself. It is just safer that way- you know that it is mixed and it doesn't matter if the injector is working or quits. And, there is no need to put oil in the reservoir if you're mixing it. Unplug the injector lines and plug them off (especially on the carb where the line goes). DO NOT USE CHAIN SAW OIL MIX. Chain saw mix is the cheap crap. It is such crap that they won't even use it to tar a road. (If you want to make a chain saw last 5 times longer, use motorcycle 2 stroke mix in the saw). You pay more for the good stuff, but it's cheaper than rebuilding engines and less aggravating. As for mixture, you may want to step it up a bit. You need to go to at least a 40:1 mix, and maybe even 32:1 to be safe. [img]/ubbthreads/images/graemlins/cool.gif[/img]
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post #3 of (permalink) Old 05-31-2005, 09:00 PM
Yamaguy
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Re: 75 Yamaha oil injector info needed

The pump is usually under a small cover on the right front of the engine. The tank is under the seat, or at least is usually filled under the seat. it is not a good idea to keep the pump hooked up if only using premix, as the pump's lube comes from the oil to be injected.
Fill the tank with a good grade of 2-stroke oil designed for motorcycles, i like Si& bel ray, but there are plenty of others. i like the bel-Ray as it leaves little to no carbon from combustion.
Remove the cover on the engine that covers the pump. There is a small phillips screw roughly at the top, on the side outermost towards the viewer. It usually has a small red fiber washer as a gasket. Take out this screw. Eventually, the oil will start to flow out of this hole. You may have to put a small amount of gas in the oil tank to loosen up the varnish enough for the oil to flow. At this point, you will notice a pulley like affair on the front of the pump. this should have a cable attached to it.When you open the throttle, it will open too. If not, do not use as is. Hold this pulley against the pump body the same direction that the cable pushes it when the throttle is opened. This will be towards the back of the bike. Front, back, right left are as viewed by sitting on the bike in a normal fashion and as viewed from normal rider's position. at the rear of the pump, there is a nylon wheel like affair that you can rotate to operate the pump; hold the pulley as stated above and rotate the wheel the direction of the arrow on it down when viewed as you normally would, or more properly, ccw when viewed from the front of the bike.This rotation while holding the pulley back will cycle the pump. If too new to have this wheel, then start the engine, the plunger portion will cycle in and out, and air will start bubbling out of the hole the screw was in. After all of the air is bled out, then you can refit the screw and fiber washer gasket. And turn off the engine if you had to start it.
Next, with the throttle at idle, check that the small pin like affair at the pulley I spoke of earlier. This pin should line up with a small mark on that pulley; if not, adjust cable until it does. (the engine is still off at this point.)
Now it is primed, bled and adjusted. Note that when the plunder cycles at its most outward point, there is about a .008-.010 inch gap between the end plate and the pulley we have been discussing. I just checked the manual, and it is supposed to be as above, with a minimum of .006 inch. This gap is achieved by shims between the washer-like end plate and the plunger shaft. Note that any oil you use must be compatible with oil injection systems. Yamalube and the BelRay I spoke of are. Some pre mix oils are not.
Now you're ready for the final check: see if it actually works. There is a small hose/pipe affair going from the pump up to the rear of the cylinder of the carb on the right side. Undo this at the engine end, start the engine, hold the pulley in as before, and see if the oil starts to ooze fromt the tube. It will come out in a series of gentle squirts in keeping with the motion of the plunger we spoke of earlier. If it is coming out, get rid of the pre mix in the gas tank, make sure the oil pump is still air free by bleeding it again, and check all of your hose connections. Fill the gas tank with fresh premium and top off the oil tank; last, the oil in the gearbox also lubes the clutch, so you need to use motorcycle oil, not car oil. get some at the shop you got the autolube oil at.
I used to work for Yamaha when that bike was new. Some competition types removed the oil pumps, but for farm or woods, or on/off road use, the pump is fine. I put over 50k miles on a CT1 175 and went through two cylinders and a crank due to endless use, but never once had a problem with the pump. Those pumps are as reliable as an anvil. If yours is dead, let me know and I'll mail you another, as I have several lying around here.
Let me know how it works out.
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