Correct Oil ratio via plug reading?

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#1
Can the correct oil to fuel ratio for a given 2 stroke engine be read off the spark plug threads. I have been told you want to see a wet oil film on at least the first three threads of the spark plug ( closest to the combustion chamber ). Is this a valid method for most oils, its seems to have worked for me using Yammalube R. Thanks
 

Rich Rohrich

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#2
Originally posted by SamLS
Can the correct oil to fuel ratio for a given 2 stroke engine be read off the spark plug threads.
No.
 
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#3
I thought the advise sounded kind of strange it came from an Oil rep. How do you determine the correct mix ratio and who gives the more accurate advise the Oil mfg. or the OEM who built the bike. I would think either of those would be on the conservative side. How do you change the ratio based on motor usage. A flat track application where you are WOT most of the time vs Motocross where you are on and off the throttle. Thanks
 

Rich Rohrich

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#4
I tend to follow the advice of the oil blender. I've always felt they have the best understanding of the additive package in their oil and how much of it should be present.

My personal approach in terms of oil & ratio is pretty simple:

- as load and time under load increases oil quantity should increase
- as time at WOT throttle increases oil quantity should increase

So it makes sense for trials bikes that run on short courses, or trail riders that creep along in the single track to run with a lot less oil then an engine that is running a 1/2 mile race with long straights.

I've always believed some basic thought about the application is all that is required to determine an appropriate oil and ratio. All the rest of the nonsense is just something fun to argue about when you are bored. :thumb:
 
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Rich Rohrich

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#6
Originally posted by MikeS


Dang.. You argue, Rich. Never ;)

 
:eek:
 
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#7
I would say that is partially correct because if you are out on the hot desert for example more oil would make you run leaner (less Gas in the mix) therefore hotter. even though the load is higher and WOT most of the time.
 

Jaybird

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#8
You need to be jetted properly for whatever ratio you run, be it in the desert or the backyard.
Adding more oil, no matter where you ride, without changing jetting on all circuits will lead to a leaner condition throughout the range.
 
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#9
I have been told you want to see a wet oil film on at least the first three threads of the spark plug ( closest to the combustion chamber ).
Funny, I was told you use this method to determine if the plug temperature is correct for your application :).
 

MikeS

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#10
Originally posted by Zenith

Funny, I was told you use this method to determine if the plug temperature is correct for your application :).
Heard that too and the oil thing.

There may be a correlation between the wet threads and Jetting/Oil etc.

I think too much wet oil at the plug is a bad thing. Plugs can foul and Oil residue in the combustion chamber is only gonna smoke if the ratio and jetting is way off. The oil should be left in the crankcase as it drops out of the fuel/air mix to lube the crank.

Plug temperature/jetting/oil ratio/fuel type and riding style all work hand in hand. I have had good jetting / race fuel and the proper oil ratio and had to put in a hotter plug to get it to burn nice. I was told that with Good fuel (race) and the proper oil and jetting the plug should be clean with little and no deposits.