Evidently the PO did have the pump gear replaced as they were all plastic. Hold the pump lever all the way up up see if the line is pumping to the carb and not binding. Maybe some melted plastic from the old gear shaft on the crank shaft worm gear thats causing it to bind. By the way I was thinking of the 250 when I said to block off the cylinder injector. Oil injector on the 300 is on the left side of the carb.You can pull this line,raise the pump arm all the way for a minute or so to see if oil dribbles from the line while at an idle. Wont hurt anything. If it does pump oil,no need to premix unless you want to. If so,then block off the nipple injector on the carb.

 

Fixed!! Bled the lines and then bled the pump and watched the oil flow right up to the carb while i held the pump wide open. Just a clogged oil filter, and dirty lines! She smokes like a 2 stroke now!

 

The pumps on the 250 and 300 (minus the plastic drive gear problem on 94-96 300s) were pretty dependable for the most part. I was still servicing old machines up until I retired that were still using the oil pumps without any problems.The 350 and 400 were a different story mainly because they were mounted at the front and subject to water and mud and corrosion.

 

When I rebuilt my 300 that died from a clogged oil line I actually put the pump in a vice with the arm held in the up position. Took a short piece of 1/4" tubing with a funnel on the inlet filled with fresh injector oil and about a 1' long piece of 1/8 on the outlet. Pulled out the trusty cordless with a wide screw driver bit and ran it until there was fresh oil pumping out and all the old was purged. Satisfied my curiosity as to if it was working or not.


It is cool how instead of a very slow steady stream of oil like you would think from a constant turning of the gear it actually has a "pause...squirt...pause....squirt...." which makes sense considering the very small amount of oil that is being metered.

 

Pulsing action of the pump was what a lot of people were afraid of also. Most thought it should have been a steady stream of oil.Plus don't know how many times I was questioned at the shop about how little oil was used and that the oil tanks barely went down in level. On average most people could get 4 tanks of fuel or more to a tank(2 quarts) of oil on the old 250-300 atvs,but didn't think the oil pump was working or not enough. Some added extra oil that just ended up fouling plugs. And a lot of people blamed the oil pump when pistons were worn out and seized. Almost all the engines I rebuilt,the oil pumps were working fine with the exception of the 94-96 300s that had the plastic drive gear shaft.These were changed back to the metal ones and no problems.

 

OPT, do you remember an issue where over time oil seeps by the pump into the crankcase? My 250 when I first pulled it out of the barn from sitting several years it was full of oil. Now that I have used it a bit I notice if it sits for several days it smokes more so then I think it should at first start. I am guessing the check valve is getting wore. Does that happen?

 

You can remove the oil line from the injector and check it with a low pressure pump and gauge. Should pop off between 2-5 psi. Don't remember any injectors failing,but have seen a couple pumps leaking at the back a little. Possible oil could work it's way down the bushing and gear shaft over a period of time into the crank,but would take a while doing it to have a lot of oil in the crank. What a lot of people do is forget and leave the fuel valve on and over a period of time it can seep fuel into the crank case and will smoke more for awhile,plus as the years go by exhaust pipes and mufflers can become coated with oily residue and as it gets hot, starts melting this crap and smoking more.You might look into pulling the pipe and muffler,soaking in kerosene for a few days or have a radiator shop vat it out for you. There's a stupid clean out plug on the muffler but doesn't help that much.