2 x 90HP two stroke ********g oil consumption?

[CharlieH]

Hello, I have 2 x 90HP two strokes (2006). Over the past year I've noticed that one engine is using far more oil than the other. I've inspected both oil tanks and hoses and there doesn't appear to be any leaks. Its kept in my garage and no oil on the floor. The question is, how do I know which engine is using the correct amount?

[robert graham]

If you have a problem with the Autolube on one motor and the oiling system defaults to wide open then the spark plugs on that motor may show heavy oiling/carbon…maybe check them.

[CharlieH]

Thanks Robert, I've just removed both sets of plugs and as far as I can tell they look pretty much the same. They were replaced about 35 hours ago and look as you would expect, slightly dark around the top edge and dry electrodes, slight oiling on upper threads?

[99yam40]

inspect the oil pump linkage to make sure they are still attached to throttle linkage.


also service manual will have a procedure to measure usage and adjust the linkage

[boscoe99]

inspect the oil pump linkage to make sure they are still attached to throttle linkage.


also service manual will have a procedure to measure usage and adjust the linkage

Excellent advice.

[boscoe99]

Hello, I have 2 x 90HP two strokes (2006). Over the past year I've noticed that one engine is using far more oil than the other. I've inspected both oil tanks and hoses and there doesn't appear to be any leaks. Its kept in my garage and no oil on the floor. The question is, how do I know which engine is using the correct amount?

Usually;

The motor using the lesser amount of oil is wrong.

The motor with the higher temperature is wrong.

The motor with the lower oil pressure (four stroke) is wrong.

The motor with the lower water pressure is wrong.

The motor with a funny sound is wrong.

I know this to be true because I read it all of the time at the other website.

[CharlieH]

Thanks for your input. I have checked the oil pump linkages on both engines and they appear to be identical. Both start pretty much where they should and open right up on full throttle to the same position and as in the service manual - page 3-12. Page 3-10 gives the oil discharge rate which I will try next after making some premix. Its just puzzling as what is the cause and what to do if the rate is incorrect?

[CharlieH]

OK rather than try and measure oil output direct I thought I would measure oil consumption vs petrol used. After 4 hours running at my cruising speed of 20 knots at 3600rpm I discovered one engine running at about 65:1 and the other at about 43:1. I've been informed locally that they should run at 100:1 at idle and 50:1 at full revs. Assuming this is correct then the 65:1 engine would be about right and the 43:1 is using too much oil. I backed off the throttle to oil pump link by two turns and got it from 43:1 to about 57:1 doing another two hours at 3600rpm. Does this all sound to be correct? I appreciate your feedback as I live in a fairly remote village in the SW tip of Cornwall, England with the nearest service centre over 100 miles away.

[boscoe99]

Most Yam Precision Blend Systems vary the ratio from 200/1 at idle to 50/1 at WOT.

[CharlieH]

After several fine adjustments on the oil pump linkages and sea trials I think I have both engines running at about 80:1 at 3600rpm which is my cruising speed of 20Knts. If the oil ratio is linear from 200:1 at 700rpm to 50:1 at 5600rpm then is this too much oil at these revs? I think it should be more like 100:1 but will air on the side of too much oil rather than too little. The previous 43:1 engine appears to idle much better now and gives off a lot less smoke.

[boscoe99]

I don't know for sure but would doubt that the oil flow increase is linear with an RPM increase.

[Keithbaja]

With looking it up for the can adj. I would with out question set them up as manual dictates. Most have a slot or scibed line at idle setting. DO NOT run above 50 to 1 in the mid RPM & higher RPMs. A tried and trued mix. Its FAR better to run richer than leaner (oil) I always set to the richer side of the adjustment.

[Keithbaja]

Without looking it up. cam... ARRG !! Spell checker is broken.

[CharlieH]

The maintenance manual only gives a range of values. It says to put the throttle at max revs while the engine is switched off. Then to set the oil pump lever in the max position and then to back off 1mm. Obviously there is a certain amount of play in the linkages so 1mm could easily be 2mm or 3mm depending on how tight you start the set up. However, it rotates about 90 degrees between fully open and idle which gives quite a bit of scope. The oil consumption tolerance is pretty large at 3.1cc +/- 0.7cc per cylinder per 3 minutes at 1500rpm which is about 20%. So if I measured 80:1 the acceptable ration could be say 65-95:1.

It would be really good to know if any two stroke users out there have measured oil consumption and come up with figures or know anywhere where I can find out please? Running with too much oil I have found frequently stalls the engine when idling and frequently clogs up the plugs, but as you say it is probably better then running with too little oil.

Thanks very much for your input.

[CharlieH]

I don't know for sure but would doubt that the oil flow increase is linear with an RPM increase.

Why? What would you expect it to be? Options would be a lower oil ratio for longer at lower revs, or higher ratio quickly and tailing off increase mid revs onwards?