Rebuild autolube pump or premix

[klebocna101]

Hi guys,

Previous owner of my DT125R 1989, decided to use premix instead of autolube pump so he just disconnected oil warning light, emptied 2T oil tank and filled petrol tank with premix
I have no clue how many miles he had with this setup and since this is my first 2T bike (had many 4T in the past) I have some concerns and maybe you can help:

1. Is 2T oil is also lubricating autolube pump? If so, what parts should I inspect to see if there was some damage done because 2T oil tank was empty for xxx miles?
2. If I continue to use premix, do I need to put bigger jets in the carb because premix thickness is not the same as just petrol.
3. With 30:1 premix, does engine get enough oil on closed throttle?

[Stevie Wonder]

@klebocna101 said in Rebuild autolube pump or premix:

Hi guys,

Previous owner of my DT125R 1989, decided to use premix instead of autolube pump so he just disconnected oil warning light, emptied 2T oil tank and filled petrol tank with premix
I have no clue how many miles he had with this setup and since this is my first 2T bike (had many 4T in the past) I have some concerns and maybe you can help:

1. Is 2T oil is also lubricating autolube pump? If so, what parts should I inspect to see if there was some damage done because 2T oil tank was empty for xxx miles?
2. If I continue to use premix, do I need to put bigger jets in the carb because premix thickness is not the same as just petrol.
3. With 30:1 premix, does engine get enough oil on closed throttle?

1. The internal parts are designed well enough where they should not need replacing in any normal lifetime of the bike. The autolube system does not self lubricate either.
   To reconnect the autolube system you simply have to replace what was removed and then using a Haynes manual adjust the autolube system to the correct setting

2. No. If your bikes set up for a certain ratio then it’s set up for a certain ratio, so in your case if it’s running fine how it is then you haven’t got to worry.

The oil:petrol ratio generally speaking is chosen depending on the application of the bike and the amount the oil being used can protect your engine. Back in the day with old oil two stroke oil 20:1 used to be common place. It is possible to change the ratio (some people do this simply because they have a preference on what ratio they run) however if you decide to do this then you will need to rejet to suit the new oil ratio as adding more oil reduces the ratio of petrol causing a lean mixture, fouled plugs and potential engine damage.

In your case though you should never have to worry about any of all that, just stick to what Yamaha recommends and you’ll be sweet.

3. Yes. You’re engine with premix as with any engine will get enough oil on idle. The only reason you wouldn’t be getting enough oil is if the bike (the same as any other two stroke) wasn’t running and jetted to the manufacturer’s recommended premix ratio.
   However whilst using premix if you close the throttle whilst riding, (engine braking) this will stop your engine being lubricated even though the piston is still moving as your bike relies on fuel to lubricate the engine. (See below)

Hope this helps

[klebocna101]

Oh it helps a lot. Thank you!

[Calum]

@klebocna101 Certainly closed throttle at 8k RPM you won't be getting enough oil. So you will need to remember to blip the throttle on coasting. This should really be done on autolube systems as well.

Two strokes in engine, blipping throttle on downshift, as you go from low RPM to High RPM just injects that little bit of lube forr the revs that it's going to.

Fueling wise, it shouldn't really make much difference. I'm not sure about the above comment about the carb not being designed for premix. The carb is just a fueling mechanism, autolube or not. I am not aware of any carb being context aware as to whether or not it's going to have premix oil in it.

[klebocna101]

Autolube is being run by engine and more rpm, more oil you get. Ofc, throttle adds more oil because autolube piston travels more.

Did you guys experiment how much oil autolube should push to the engine? Watched this video and not sure if it is correct amount for my motorcycle.

Yamaha DT 250 Autolube oil pump explanation, overview, adjustment, and more.

[Stevie Wonder]

@calum
Pretty sure it was a post I read about the design of the TM28SS/Oil delivery system here. Was probably a couple years now and can’t remember the post so maybe my memories off.
Thinking back to what you said there’s really no logic why any carb for that matter wouldn’t still function as intended using premix. Fixed my comment for future readers

Tah for mentioning about during downshifts too, that’s very important.
Those throttle blips will also get you into the habit of covering your clutch lever, something else which is very important because should your bike ever seize and your wheel lock up its you reaction times grabbing that lever that will save your bacon

[SpookDog]

@klebocna101

Hey bud!

Personally I would strip the pump and check for wear (although there are no replacement parts available new, second hand units are £20-30) the 2 stroke oil definitely lubricates the internals of the oil pump. If its been run dry for any amount of time it may be fragged...
I run my bike on premix but have the pump running a closed loop of oil to prevent damage...

There’s no manual for dismantling the pump but it’s pretty straightforward. I’ve done a couple, just don’t break the gasket and take plenty of photos

50/1 is the correct mix. 100ml of oil per 5Litres of petrol or 20ml per Litre

[Calum]

@spookdog The pump on the later engines just come straight off? Leaving the spline intact, but no dramas about that. Although I did remove that as well and just created a blanking plate.