I've read through a ton of threads about premix ratios but can't seem to find exactly what I'm looking for.

What premix ratio are you all running? And can anyone tell me what the tall-tail signs are of too lean and too rich mixes. My owners manual says 30:1, everyone seems to run 32:1.

 

I ran 32:1 last time out and there was a lot of blue smoke at operating temps.

 

I was recommended by an acquaintance to run 40:1, and he definitely knows his stuff.

 

2005 yz250

 

EDIT: I was running Yamalube 2R

Edited by Andrew13

Personally I see no reason to run any less than 32:1. Some guys say less oil makes the throttle more "crispy". I think it makes crank bearings more "crispy". To each their own.

You will get a different answer from everybody you talk to.

40-42: 1 is a perfect amount for the Yamaha. I run 3 YZ250's and all at 42:1 with Amsoil Dominator Racing Oil. Never had a issue.

GoYamaha

50/1 synthetic,most are esters,never an issue,original crank,since 05,zillion miles,even recommend by oil companies on the label,,,,my bud ran amsoil 100/1 ,never an issue.

I run 50:1 using Maxima K2....

The engineers that designed your bike know more than us and our buddies.  Run 30 or 32:1 per the manual (the difference between 32 and 30:1 is trivial--like 2/10s of a percent).  The amount of smoke is not really something you should be looking at for jetting (and looking back at your smoke trail has got to be dangerous!).  You want to be paying attention primarily to how the bike runs, spooge presence, engine heat, and plug color.

 

Lean jetting produces sort of a sluggish feel with poor throttle response, surging at steady throttle openings, white plugs, and lots of engine heat.  Rich jetting will produce spooge, poor part throttle engine response (kind of blubbering), and black plugs (or fouling).  If you do a search you will find much more detailed descriptions of lean and rich conditions.   Yamaha is well know for having their jetting very well worked out, so unless you are at a high altitude, or doing something unusual like ice racing or deep sand dune riding, your stock jetting at a 32:1 mix should be really close.  

 

If there is some reason that you want to run a different ratio, then you will have to adjust your jetting for that ratio for best performance.  It will run on 40:1 or 50:1, but comes from the factory jetted for 30:1 and will run best at that ratio.

Edited by rpt50

2014 te 300 I use yamalube at 50:1.

35:1 Yamalube 2R as per my mechanic and the shop manual.

The engineers that designed your bike know more than us and our buddies.  Run 30 or 32:1 per the manual (the difference between 32 and 30:1 is trivial--like 2/10s of a percent).  The amount of smoke is not really something you should be looking at for jetting (and looking back at your smoke trail has got to be dangerous!).  You want to be paying attention primarily to how the bike runs, spooge presence, engine heat, and plug color.

 

Lean jetting produces sort of a sluggish feel with poor throttle response, surging at steady throttle openings, white plugs, and lots of engine heat.  Rich jetting will produce spooge, poor part throttle engine response (kind of blubbering), and black plugs (or fouling).  If you do a search you will find much more detailed descriptions of lean and rich conditions.   Yamaha is well know for having their jetting very well worked out, so unless you are at a high altitude, or doing something unusual like ice racing or deep sand dune riding, your stock jetting at a 32:1 mix should be really close.  

 

If there is some reason that you want to run a different ratio, then you will have to adjust your jetting for that ratio for best performance.  It will run on 40:1 or 50:1, but comes from the factory jetted for 30:1 and will run best at that ratio.

Thank you for the detailed response.

 

From your description it looks like I was running rich. I am going to try 36:1 next time out and see how it feels.

I'm going to go read up on jetting.

I run 40:1 with Spectro SX Platinum...it works great!!

The engineers that designed your bike know more than us and our buddies. Run 30 or 32:1 per the manual (the difference between 32 and 30:1 is trivial--like 2/10s of a percent). The amount of smoke is not really something you should be looking at for jetting (and looking back at your smoke trail has got to be dangerous!). You want to be paying attention primarily to how the bike runs, spooge presence, engine heat, and plug color.

Lean jetting produces sort of a sluggish feel with poor throttle response, surging at steady throttle openings, white plugs, and lots of engine heat. Rich jetting will produce spooge, poor part throttle engine response (kind of blubbering), and black plugs (or fouling). If you do a search you will find much more detailed descriptions of lean and rich conditions. Yamaha is well know for having their jetting very well worked out, so unless you are at a high altitude, or doing something unusual like ice racing or deep sand dune riding, your stock jetting at a 32:1 mix should be really close.

If there is some reason that you want to run a different ratio, then you will have to adjust your jetting for that ratio for best performance. It will run on 40:1 or 50:1, but comes from the factory jetted for 30:1 and will run best at that ratio.

You really belive that the engineers know best?

I ran Golden Spectro 4.5 gal to 12 .oz for 20 years and now running Maxima K2 same ratio for the last couple. No problems what so ever.

premix ratio has nothing todo with blue smoke. Jetting is rich. 32:1 is a great univeral ratio. I ran 25:1 in my mod rm250 never any smoke nice brown plug.

 

Problem 1, jetting, its jetted to rich for how and where you ride if its blue smoke all the time and a black wet ugly spark plug.

 

Problem 2, the stock yz250 has horrible squish, the yz250s stock head is garbage, You need to take a squish measurement and have the head machined and setup for pump fuel (or race if thats what you want to use)

 

rb-designs.com is who everyone uses. His work is the best ive ever seen. Setting up the head for proper squish will give you more power and zero detonation on 91 octane. and jetting becomes cleaner and alot easier to dial in.

You really belive that the engineers know best?

 

I would wager that the engineers knew best how to "spec" the bike so that Yamaha would see as few as possible warranty claims while giving racers enough room to easily modify the engine to perform to their liking.  I imagine that the conversation was something like this, "Build a race bike that as devlivered will give the user long service life, but still give the tuner enough to work with enable them to reach a near factory race spec."

Also keep in mind that the yz250 is a motocross bike. The recommended ratio in the manual is for a race bike on moto tracks which means high rpm and wide open throttle. The bikes are jetted for this, the same as the recommended oil mix ratios and service intervals (in my 95 manual everything is by number of races not hours).

The oil mix ratio is meant for motocross racing, so if you aren't doing that, it will not be the ideal ratio for you. If you ride trails and just put around, you will want to run a little less oil. 40:1 is a good start, but I think 50:1with a high quality synthetic would be fine also. Then adjust your jetting to match the new ratio

What does the instructions say on the bottle?

i run 32:1 with 91 octane and amsoil interceptor.  Does anyone know the difference between interceptor and dominator?

Also keep in mind that the yz250 is a motocross bike. The recommended ratio in the manual is for a race bike on moto tracks which means high rpm and wide open throttle. The bikes are jetted for this, the same as the recommended oil mix ratios and service intervals (in my 95 manual everything is by number of races not hours).

The oil mix ratio is meant for motocross racing, so if you aren't doing that, it will not be the ideal ratio for you. If you ride trails and just put around, you will want to run a little less oil. 40:1 is a good start, but I think 50:1with a high quality synthetic would be fine also. Then adjust your jetting to match the new ratio

I agree completely, and the key is your last sentence.  There is no doubt that putting around on trails is less demanding than racing applications.  The point remains however that the bike comes from the factory jetted to run best on what the owners manual states.  If you want to run 40 or 50:1, re-jetting will be required for optimal performance.  It will surely run on different ratios, but it will not run optimally.  I normally jet my bikes to run best at 32:1.  Being somewhat forgetful as I get older, there have been times where I had to borrow gas from someone else.  I have found that 40:1 works OK, but 50:1 causes a very noticeable decrease in performance and throttle response.

2 strokes ad oil.

 

more oil means

 

  • cooler running
  • slower piston wear
  • slower ring wear
  • slower cylinder wear
  • longer bearing life
  • longer crank life
  • better ring seal
  • more power
  • more consistent power

 

the manual recommend 30:1 I recommend 32:1 and factory race teams would run ratios in the ball park of 20:1. when they had 2 strokes in the mix. (mix, pun intended)

 

 

But yes, go ahead and run 50:1, someone on the internet said 50:1 is fine so it must be true. and you get to save a few $ in oil. win friken win

 

 

If i wasnt wide open on MX tracks, i would go as far as 40:1.

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