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Old 04-05-2013, 08:40 PM   #76
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Originally Posted by CharlieT View Post
So unless you can come up with some supporting evidence back-up your peristent claim of the change in viscoaity requiring a change in jet, no offense, but I'm afraid I'd stick with the opinion of my friend over yours.
Most of what I have read (again, many years ago, I need a refresher course) had to do with tuning/jetting for AIR DENSITY. I do not recall ever reading about premix viscosity affecting jetting, but maybe that's because everyone ran bean oil at a 20:1 ratio so it was simply not factored into the equation - I don't know. Thanks, CharlieT, for all your good information. Very educational.
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Old 04-06-2013, 02:08 AM   #77
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Well, since you insist on jetting changes due to change in viscosity, yet either won't or can't provide any supporting documentation, I decided to seek the opinion of a third party.

A friend of mine has a fair amount of tuning experience. Ever hear of a a guy named Trevor Nation and Norton? How about a Ducati rider by the name of Carl Fogerty? He was a race engineer/tuner for both those gents. H-e then moved on to cars and has been the chief engineer for anything from Porsche GT cars to LeMans prototypes.

So I asked him if you increase the premix ratio. Did you change jetting primarily because of the change in the air/fuel ratio or the change in viscosity.

This was his reply: " you are actually burning less fuel and more oil , the viscosity doesn't have much to do with it."

So unless you can come up with some supporting evidence back-up your peristent claim of the change in viscoaity requiring a change in jet, no offense, but I'm afraid I'd stick with the opinion of my friend over yours

I have found the change in fuel viscosity affects mixture strength by personal experience, and do not feel there is any need to provide evidence to support the laws of physics...............
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Old 04-06-2013, 06:55 AM   #78
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Originally Posted by Twin-shocker View Post
I have found the change in fuel viscosity affects mixture strength by personal experience, and do not feel there is any need to provide evidence to support the laws of physics...............

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Old 04-06-2013, 07:03 AM   #79
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Originally Posted by Tim McKittrick View Post


It's probably been mentioned before but it bears repeating: more oil in your mix means there is less fuel per volume of measure and this means your carburation trends lean. Thus a 20:1 mix is going to be leaner than a 50:1 ratio. As to the degree of the leaning effect of viscosity I can't say, but both result in the same tuning considerations needing to be made.
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Old 04-06-2013, 07:40 AM   #80
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I wonder do you know how to alter the laws of physics? If not then maybe admitting you are wrong would be a good idea?
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Old 04-06-2013, 01:08 PM   #81
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Originally Posted by Twin-shocker View Post
I wonder do you know how to alter the laws of physics? If not then maybe admitting you are wrong would be a good idea?

Your self-righteous and over whelming arrogance is hilarious. Tell us again why you are the only one in the universe who believes this, when a factory GP tuner disputes your claim?? When no other reputable 2-cycle tuner or oil manufacturer has elucidated this claim? It is so kind of you to share this tidbit of knowledge based *only* upon your personal experience. Or did you actually flow test the jets to determine this? If so I would have thought such a finding would have been worthy of publication

I'm am indeed very surprised that you are even aware that the word "wrong" exists in the English language. But on the other hand, I'm sure you use it all the time, telling the whole rest of the world they are wrong and you are right

It is not that it does change the flow, but its effect is so minimal that a jet change is unnecessary. Now if you go from an injection unit to a pure castor based premix and its 20degF out, you might be onto something.

Or as in another example. Does humidity affect jetting....most certainly does, however if the humidity changes from 70% to 72% its effect is not going to be sufficient to warrant a jet change. Of course that's just based on my personal experience. :)
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Old 04-06-2013, 01:08 PM   #82
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So do I use Blendzall at 20 to 1 or 24 to 1 in my IT465.
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Old 04-06-2013, 02:08 PM   #83
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Originally Posted by CharlieT View Post
Does humidity affect jetting....most certainly does, however if the humidity changes from 70% to 72% its effect is not going to be sufficient to warrant a jet change. Of course that's just based on my personal experience.
Again, from what I remember from my past (way too many beers ago) jetting was based upon AIR DENSITY - humidity, temperature, barometric pressure at that particular hour, sheesh - but these were professional tuners for RACE bikes on race day. I was just trying to make it around the track without crashing. Now, I only want to go for a ride in the desert (I still have that competitive racer stuff flowing through my blood, can beat my young sons, they think their old man is crazee).
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Old 04-07-2013, 02:30 AM   #84
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Originally Posted by CharlieT View Post
Your self-righteous and over whelming arrogance is hilarious. Tell us again why you are the only one in the universe who believes this, when a factory GP tuner disputes your claim?? When no other reputable 2-cycle tuner or oil manufacturer has elucidated this claim? It is so kind of you to share this tidbit of knowledge based *only* upon your personal experience. Or did you actually flow test the jets to determine this? If so I would have thought such a finding would have been worthy of publication

I'm am indeed very surprised that you are even aware that the word "wrong" exists in the English language. But on the other hand, I'm sure you use it all the time, telling the whole rest of the world they are wrong and you are right

It is not that it does change the flow, but its effect is so minimal that a jet change is unnecessary. Now if you go from an injection unit to a pure castor based premix and its 20degF out, you might be onto something.

Or as in another example. Does humidity affect jetting....most certainly does, however if the humidity changes from 70% to 72% its effect is not going to be sufficient to warrant a jet change. Of course that's just based on my personal experience. :)

Unfortunately unless the laws of physics have changed recently, increasing the viscosity of a liquid will reduce its rate of flow through a carb jet of a given size.

How you feel clarifying that fact in clear and concise terms is arrogant or hilarious, seems to suggest that you may well be just another web warrior with no first hand experience of tuning 2T motors themselves?

I wont bother to go into the area of changes to carburetion required to suit differing atmospheric conditions, as you appear to have problems grasping the basics, and seem to have been blinded by ridiculous advertising blurb, and test data produced 40 years ago!
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Old 04-07-2013, 02:35 AM   #85
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Originally Posted by craydds View Post
Again, from what I remember from my past (way too many beers ago) jetting was based upon AIR DENSITY - humidity, temperature, barometric pressure at that particular hour, sheesh - but these were professional tuners for RACE bikes on race day. I was just trying to make it around the track without crashing. Now, I only want to go for a ride in the desert (I still have that competitive racer stuff flowing through my blood, can beat my young sons, they think their old man is crazee).
Quite so............humidity does have a minor affect on the jetting required on a particular day, but the main determining factor is air pressure. I guess most serious racers running 2T bikes today, will have weather stations, and previous data related to best set up for differing conditions, which will make set up far easier than back in the day.
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Old 04-07-2013, 02:39 AM   #86
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So do I use Blendzall at 20 to 1 or 24 to 1 in my IT465.
Yes if you are running flat out almost continuously, or are using the IT motor for road racing. If not then I would suggest a fully synthetic pre mix only oil at 40:1 for competition use, or the same at 60:1 for recreational riding. If you have been using 20:1 for some while and the bike runs well, you may find a need to reduce jet sizes to work best with reduced amount of oil.
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Old 04-08-2013, 06:50 AM   #87
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I extend an invitation to ride my unresponsive,dull feeling YZ465 fueled on VP U4.4 @ 32:1 to you Twin Shocker. If after that you contend it's unresponsive and dull feeling I'll let you tune that out for me.
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Old 04-08-2013, 10:43 AM   #88
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All this is just metal masturbation. For 90% of the 2 smoke riders out there all this last ounce of tuning that might be obtainable by what you are describing is not practical. If you're running your old smoker to this high of level of tune, good luck.

Me...I'll play it safe, run it a tad heavy on the oil and a tad rich on the jets so I don't sieze. Has worked fine for me since I started riding smokers in 1970. The limiting factor when I was racing was not that extra 1 hp i might get by tweaking mixtures, it was me!
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Old 04-08-2013, 12:32 PM   #89
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I extend an invitation to ride my unresponsive,dull feeling YZ465 fueled on VP U4.4 @ 32:1 to you Twin Shocker. If after that you contend it's unresponsive and dull feeling I'll let you tune that out for me.
If you are a play bike rider, then using more than the required amount of oil wont make much difference, other than the fact your bike wont run as well as it would with the correct amount.
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Old 04-16-2013, 04:04 PM   #90
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Originally Posted by Twin-shocker View Post
Unfortunately unless the laws of physics have changed recently, increasing the viscosity of a liquid will reduce its rate of flow through a carb jet of a given size.
While true, this is negligible when talking about changing premix ratios. As others have pointed out, it is more important to consider that a higher ratio of oil to gas means that there's less gas per volume (much more significant than the slight change in viscosity), so you may need a larger jet. Of course, this will mean that you've also compensated for the slight increase in viscosity.

If you boil down Jenning's article, his recommendation is that you err on the oil-rich side, as too little oil is worse than too much oil. If a good baseline castor oil premix ratio is 20:1, and 15:1 is slightly better, then it stands to reason that if a comparable baseline synthetic premix ratio is 60:1, then a 45:1 ratio certainly won't hurt.

Personally, I use good synthetic 2T oil (Bel-Ray, Motorex, etc.) pre-mixed at about 40:1 in my CR480R riding trails and fire roads up in the mountains. Works for me and I don't really see the need to do anything differently.
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