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Newbie Question About 2 Stroke Mix?

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Hi all sorry if this been asked before,but i have riden motocross bikes before but never owned one,i have just bought a yz 500 which i am told is a 492cc or something like that sorry for any ignorance.When ppl say a 35:1 mix what exactly does that mean,or does anybody else think of a better mix for this bike.If someone could say exactly what this would amount to i would be very grateful.Also what 2 stroke oil would any one advise is best to use.Thanks if anyone can help me out and once again sorry for any ignorance,hopefully i will get better as time goes on using this forum.

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i would mix 32:1 just because its simpler than mixing at 35:1 and usually what is called for. you just take the bottle of oil 16oz and mix it with 4 gallons of gas and thats 32:1.

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Also the bike was part being put through to be road legal at one point but it didnt quite get finished hence it has a road/dirt tyre on the back and i want to put a off road knobbly on,what size tyre would i need?? It has got written on the gold rim 1.85x18,any help appreciated.

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I think that bike came with a 2.15x18 - the 1.85 is for 100 series tires, which are for 125's.

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yz 500? as i said up top apparently its a 496 or something its just short of 500cc anyways,need to get that back tyre changed sharpish as went out on it yesterday and on grass/mud the tyre just spins when you put the power down.Quite scary lol.

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I suggest picking up a Ratio Rite, they're cheap as hell and very handy for mixing gas and filling up your crankcase oil. It's always good to know you have the right mixture. :thumbsup:

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So this is one of those oldies or what jw b/c yamaha dont make a 500 2 stroke anymore and ya i run 32:1 with and a mix rite would be a verygood investment. Remember to much is better than not enough so mix it a little over since the bike is older and might get a little past the rings. Thats prolly why the guy said 35:1

:thumbsup::ride:

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Is there anywhere i can check up on the bikes engine number to make sure exactly what cc it is,at least that way if i need any parts anytime i will know exactly what im looking for.Any help appreciated thanks.

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Somewhere on the motor, probably the cylinder, it will say exactly what size displacement it is.

Don't worry about it, though. You don't need to know that for buying parts. All you need to know is the year and model.

For a 500, I would run a 40:1 mix. A pint of oil to 5 gallons. I like Torco GP7, but any name brand synthetic would be fine.

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Im certainly not a 2 stroke expert but are you sure it's not a YZ426F or 450F if so, they are 4 strokes? :thumbsup: I don't think Yamaha made a 500 2 stroke.... Can you post pics?

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Im certainly not a 2 stroke expert but are you sure it's not a YZ426F or 450F if so, they are 4 strokes? :thumbsup: I don't think Yamaha made a 500 2 stroke.... Can you post pics?

Sounds like a YZ490 2- stroke. Those were bears to get jetted and running correctly.

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Yeah i think it's a 490,to be honest it hadnt been ran for 3 years and i have only been out on it 3 times since getting it,starts fine now i have found the right way to do it,runs not bad seems a little bit rough idleing but haven't really gave it a good blast as yet as i need that knobbly tyre to be able to do that.if anything even coming down the gears with no revs on it feels like it just wants to go hopefully it will get better the more i run it.Yes will get a picture of it the next time i get it out.Like i said in early post it was being turned in to a road legal at some point but never got finished a friend of mine bought it with the intentions of finishing it but with 1 thing or another never got round to it,so it sat in his garden under a sheet for 3 years and in that time only ever being started once and all he did was go round his garden on it.So i guess you can't really call that being run,Very pleased with it so far it is a bit of a beast power wise and definately not for the faint hearted.Also could someone tell me what pressure the tyres should run at please as i have no idea thanks.

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Cool bike, love the big old smokers.

You will never get it to idle smooth. It has a massive piston that weighs a lot and it places a good tug on the crank every time it changes directions.

Use the highest octane you can find (I owned an IT465 that I had to run Avgas it or it would ping) and a good synthetic oil.

32:1 might be a little oil heavy (lean) unless you are really heavy on the throttle. Search and read some of the jetting posts, there are tons.

(ie. http://www.thumpertalk.com/forum/showthread.php?t=400188&parentpage=3 )

Tire pressure depends on the terrain. You could run anywhere from 8 – 15 psi.

If you are jumping into rocks then 15psi. If you are riding fast and hard in rocks 15psi. The softer the terrain the softer the tire pressure. The softer the tire pressure the better the tire hooks up. The softer the tire pressure, the more susceptible your rims are to getting dents and tube pinch flats.

My last big bore 2 stroke was a 380 KTM. Sweet sweet bike that seemed to like 40:1 gas/oil mix best. I tried my damdest to wind her out often but it was a-lot of bike to get stopped, or, it got up and going faster than expected effortlessly.

Which brings me to the point. It is a very old and very powerful bike with old technology brakes and suspension. Go over it well, including brakes, steering, swingarm and shock bearings, cleaning, greasing and replace anything iffy.

Look forward to see a picture too…

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Fella, just a little word of advice for you if you don't already know.....

U.S. Gallons and U.K. Gallons are different sizes, so if I were you to keep things simple, convert everything to litres. :thumbsup:

So. If you were to run 32:1 (not a bad mix) you would need to mix approx 31ml into every litre of petrol. So if you're using a 5 litre can like the rest of us, you need to mix 155ml into that. you could go 150ml to keep it simple, that would give you a ratio of just slightly over 32:1.

If you want to run 40:1, then mix 125ml into your 5 litres of petrol.

Hope that helps...... :ride:

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Thanks all for the knowledgeable people and answers,i will get it out today and get a pic posted asap.Thanks to all.

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Done nothing but rain rain rain all weekend so will get the bike out at earliest dry opportunity and take some pictures.

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First thing to do is stop thinking of rich/lean as the amount of oil in your gas.

Rich/lean is the term the carb uses to get a clean burn of gas and air mixture in the cylinder.

More GAS = richer

Less GAS = leaner

More oil you add to your mixture of (gas and oil), means there is less gas.

Less GAS = leaner.

The oil you mix into the gas is mainly there to lube the crank bearings, wrist pin bearings and ring to cylinder contact area.

The amount of oil you add to your gas bepends on the type of riding you do. If you are a low rpm kinda guy then 40:1 might be a good start. If you are always wringing the bikes neck then possibly 32:1 to start. If you are just starting out on a 500cc two stroke then 40:1 would probably carry more than enough oil suspended in the gas to lube everything.

If the previous owner found the bike to run well with a 36:1 mix, why not give that a go before changing the amount of LUBE added to your gas just because you can.

As I said above, I tried hard to be a “on the gas” kinda rider but it was a lot of motor for for me and 40:1 was all the oil it needed.

Use this link to mix ratios.

http://www.csgnetwork.com/marineoilfuelcalc.html

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