Stage6 PRO Replica Exhaust - Speedfight 2

i agree that it's valid that you can look at a plug on a 2-stroke single cylinder engine and tell that there is something wrong with the engine which needs investigating, but there is no way you tell specifically what is wrong as what you see will always be an accumulation or secondary effect of other problems- there is certainly no way you can tell if the jetting is lean or rich in the way Merlin describes, this can easily be proven indisputably.

in the workshop we would on average dyno and repair easily in excess of 1,000 2-stroke 50'cc autos each year, but in reality none of the mechanics would be looking at the plugs for diagnosis clues, it simply doesn't tell us anything useful from a diagnostics perspective in a professional environment,

there is of course nothing wrong with taking the plug and taking a look but when people post charts saying you can tell specific diagnostic information just from taking a plug out at any time and looking at it this is simply not correct and can be very misleading specifically as people believe they can check their mixture by doing this

 

A fuel mixture is a fuel mixture, no matter if a two stroke or four stroke. The two stroke oil gets burned off, so the colour guide isn't completely invalid; it's a guide, after all.

Simple plug colour covers the whole mixture range at all throttle settings. A plug chop just looks at the effect of the main jet.

Now, who has misunderstood what a plug chop is, or the effect of spark plug insulator colour when applied to fuel mixtures?

If you can find a two stroke plug colour chart, go ahead and post it.

I'll tell you what Andy, you help the guy with his pipe and jetting and we'll critique what you post; how does that sound? Deconstructing our posts in the way you are doing is trolling and isn't helping the original poster.

 

"Simple plug colour covers the whole mixture range at all throttle settings. A plug chop just looks at the effect of the main jet."

absolute nonsense

"If you can find a two stroke plug colour chart, go ahead and post it."

you can't find one because it cannot exist in any useful form for the reasons already explained- think about it, what is the reason that you think you can't find one ? do you think simply no-one has ever thought of doing a plug colour chart for a single cylinder 2-stroke, or might there be another reason?
once more, the chart you posted cannot work with any single cylinder engine for reasons explained in the article I referenced and has no usefulness whatsoever wrt a single cylinder 2-stroke engine

"I'll tell you what Andy, you help the guy with his pipe and jetting and we'll critique what you post; how does that sound? Deconstructing our posts in the way you are doing is trolling and isn't helping the original poster."

and unfortunately this is exactly why people from within the industry do not normally ever post on forums, I have made a statement, calmly backed it up with sound rationale and referenced an article we wrote specifically to document that this is a perpetuated myth which was backed up with practical evidence using a dyno AFR but apparently this is trolling

if you have any critique on the methods we used or critism of my rationale i would of course be delighted to hear and discuss them constructively

 

this pipe will not work at all well if you leave the restrictor in place, I would not consider buying the pipe if you are going to do this, it's designed to run without the restrictor and the restrictor on the S6 pro rep limits the power increase to <10% for homologation reasons (e-marking)- an MOT tester will not know if it is in there or not but *legally* you should remove the e-marking if you remove the restrictor-
upjet by 10% from completely standard

 

@ Andypp

Would you class assessing the fuel mixture using a Colourtune plug as being equally worthless? I'm interested, as I've used a Colourtune plug in the past without issues. Not all of us have a dynamometer or a rolling road and seriously, what would you suggest for us home mechanics? I'm not trolling you, I think it would be great if you could see things from our perspective and advise us accordingly.

Adding 4 to the jet size or adding 10% is only a start, in my opinion - not two bikes are identical and they all have subtle differences. A plug chop just looks at the flat out mixture and doesn't take into account the needle setting and the mid-range, so most people would just set the idle mixture and do a plug chop for the top end. How would you assess the mid-range mixture if you didn't have access to the equipment you have now?

 

Hi Merlin,
by far the most important mixture to get right for a 2-stroke auto 50/70 is full throttle under load. There are other problems with using a colortune on a 2-stroke but the main one is that you cannot put the bike under load, it simply wouldn't be possible to run the bike full throttle under full load, they just aren't designed act as a real spark plug and would melt or worse even if you could see what it was doing. Any mixture measured at full throttle will be completely different if the bike is not at full load, hence if you rev something like a 2-stroke mx bike on the stand it often won't even rev properly until you ride it and it has a load on it.

Unless the scooter is really heavily modified you don't need to worry about anything other than setting the mixture at tickover (easy by ear for a beginner even) and getting the mixture right at full throttle full load. A scooter runs in a limited rev range because of the variator transmission which makes this even easier than on a geared bike where the mixture can change as the revs increase under the same load/ throttle position.
If you get these two settings right you don't need to consider mid-throttle positions at this level of tuning- it's actually very specialist to alter precisely mid-throttle because it immediately has a knock on effect on full throttle or full throttle at different revs and you really don't need to do it unless something has gone really wrong.
If you go back to the 2-stroke mx bike example, they rarely run well at mid throttle positions and often misfire (remember they are also have to cope with a combination of a different large range of rpm *as well as* throttle positions) but as soon you full throttle everything crisps up and runs as it should.
If you a tuning a scooter mildly you will never mess up the mid positions enough to matter so long as you get the main jet mixture correct, if you are tuning more aggressively you won't really care even if it does- a polini evo kit for example is only designed to run at full throttle, even with a just a pipe on most kids ride only accelerate with bursts of full throttle.

I agree that it seems unlikely you can specify specific jet sizes e.g. +10% but if the bike is only mildly tuned this is the safest.
For example all Aerox after '03 have a 62 jet as standard, if you fit any sports pipe to an otherwise completely standard Aerox you need to upjet to a 68. We have dynoed hundreds and hundreds of Aerox's and this is always the case. Occasionally you will get one which needs a 70 jet (usually in the winter) but otherwise they are all identical irrespective of the pipe. If you then fit a sports 70 kit this doesn't really affect the jetting, maybe 2 sizes.
You can really accurately predict jet sizes for most bike setups like this when the exact bike spec is known *except* when the carb has been changed for a non-standard one. If the carb is changed all bets are off due to different manufacturers/ carb types/ copy qualities etc. and although you can have a guess at a jet size for a setup it really is just a starting guess.

 

sorry missed that-
basically exactly what scubabiker stated so concisely in another thread

"put in a big jet and go down until it feels right"

make sure the main jet is too big and do all your testing riding around using full throttle- if it is much too big the bike will start to miss and splutter a little, come down a little at a time until it runs cleanly- at this point it is still rich which is safe, if you keep coming down a little more the power should start to increase a little and the bike should 'crisp up'- if you feel this increase keep going down a little smaller until you don't feel a definite power increase, as soon as you don't feel a definite power increase go back up to the previous size