Pre-mix ratio for RS250?

[G-Bek]

So i'm borrowing my mates RS250 for a track day and was thinking of pre-mixing the fuel rather than run it through the pump but i dont know what ratio to do it at? Then plan was then to leave the 2 stroke oil tank empty and just run the pre mix but am concerned about the oil pump burning out, or shibby rite?

[Loud]

Unless you're looking to remove the indicators, lights etc. too, I'd have to wonder if it was worth the effort of draining a litre or so of oil, disconnecting the lines and ensuring everything is properly primed upon reassembly?

[rgvlee]

Heh, starter motor

33:1 is the usual consensus. Some racers run leaner. A good quality oil may allow a leaner mix, if in doubt ask the manufacturer.

Plenty of race bikes with the pump still attached to the gearbox with the lines disconnected, doubt you'll do any damage to the oil pump itself.

Of more interest to me would be if you left the pipes connected it'll pump air into the engine via the oil check valves. May or may not be a problem depending on air volume, I haven't run a bike like that. Personally I'd be blocking them off at the check valves, looping 2 lengths of oil pipe between the 4 oil check valves will do it.

Honestly the pumps are reliable, I wouldn't worry about it. Plenty of racers in the UK still run the pump, I'd be using that as my yardstick.

[Loud]

You weren't supposed to see that, I edited it right after I posted it!! The 125 has one, I'm months away from kicking the 250 to drill that fact into my head.

[speed3]

Leave it on the oil pump and add a touch of castor to the tank for insurance and awesome perfume.

[G-Bek]

i wans't concerned as much with the pump failing but more for oiling the piston when rolling off the throttle under brakes, assuming that the oil only pumps with the throttle open as they're linked?

[rgvlee]

The powervalve actuator will keep the pump on full for a bit when you go from WOT to closed.

What do you think happens when you got from WOT to nothing with premix?

[milesiles]

.......

[richarde]

I have heard that you have to mod the cases to get oil supply to the centre main crank bearing if you are running premix. Also, you may have to rejet richer as it will run lean due to oil taking the place of the fuel coming through the carby.

It is more trouble than it is worth anyway, just run the pump like normal and it will be fine. My trackbike still runs an oil pump and I know of several others (trackbikes and race bikes) running a pump too.

[Gangus]

Have fun
riding a 2t round the track is sooooo much fun.
Take fuel. Plenty of high octane fuel, they absolutely drink the stuff.
Bout half a litre a lap.
I'm just about full when I go up there and use atleast 15 litres out of a Jerry.
You will use nearly a litre of oil, so make sure your resi is full.
Don't waste your time with premix. Concentrate on the day and leave the oil pump to do it's job.
Oh, mirrors are the gayest thing on these bikes, get rid of them.

[EEKNOWS]

Aprilia GP 125 and 250's specify 4% (25:1) oil ratio but what would they know? Harder they rev the more oil needed. Remember NOBODY ever killed a two stroke with too much oil. Far cheaper than pistons.
For the RS leave the pump in use.

[Mattis]

As others have mentioned, leave the stock pump setup alone as long as it's never had different oils mixed in it then they rarely get blocked lines. Check it's in adjustment though.

If you're really that concerned about it, run a little bit of oil (maybe @ 5%) in the fuel tank so it will run a little richer. I use to do this after rebuilding a two stroke.

[G-Bek]

so running with the fuel pump seems to be the general idea. ill do that. cheers.

also i just put a fresh top end in it and was wondering about how to prime the 2 stroke oil before starting it. i was just gonna disconnect the plug leads and turn it over for a bit?

[speed3]

Kick it with the kill switch on a couple of times and do as above and put a bit of extra oil in the tank. Castor oil 5% it'll smell so good.

[rgvlee]

I'm guessing you haven't started it since the rebuild?

Start by bleeding the oil pump itself.

Then for the heat cycles put in 4L of 33:1 into the empty fuel tank. On the first heat cycle with the oil lines disconnected start the bike up and once idling crank the oil pump full open by hand. Once you get oil coming out the lines connect them back up. I normally will then continue to keep the oil pump full open for a bit after they are connected to ensure the system is completely bled right through the check valves. The oil flow is quite slow, manually doing it by kicking it over will take forever.

Once you are over the heat cycles and you've check the cylinder and head torques, fill the fuel tank with fuel to dilute the premix and off you go for the piston and rings (and whatever else you have replaced) run in. For pistons and rings only an easy 20k up to around 6k rpm then after that let it have it.

[HK31A]

[QUOTE=rgvlee;2382079]Plenty of race bikes with the pump still attached to the gearbox with the lines disconnected, doubt you'll do any damage to the oil pump itself.

Of more interest to me would be if you left the pipes connected it'll pump air into the engine via the oil check valves. May or may not be a problem depending on air volume, I haven't run a bike like that. Personally I'd be blocking them off at the check valves, looping 2 lengths of oil pipe between the 4 oil check valves will do it.
QUOTE]

WTF
its a positive displacement oil pump not a compressor

i would be pissed if someone ran my oil pump dry around a racetrack and didnt tell me about it

if your are concerned about oil from the pump retard the pump timing dont run it dry

[G-Bek]

Ahh I see. Yeah cheers lads

[speed3]

Castor oil.

I'm going to keep posting it till you do it.

[G-Bek]

Castor oil.

I'm going to keep posting it till you do it.

haha ok. where do i get some?

[G-Bek]

n how much do i use 5%? whats that in a ratio?