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Is this plug to cold and Rich?


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I have a 2015 YZ250 2-stroke and was wondering if this plug is to cold and rich.  The bike is stock other than a Boyeseen Rad Valve.  Air screw is out 1 and a half turn.

 

Do I just need a next size up plug?  This one here is a BR8EG so would I need a BR9EG?     As far as the jetting goes.....does this plug show from what you can see that it is somewhat ok?

 

The Temperature here was at 58-62 degrees. and the elevation was around 2500-3500. +or- another 1000ft for different riding areas.

 

 

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Looks a bit rich + carbon deposits but within 'normal' for a bike most likely not ridden wide-open on a MX track.

 

I would adjust the jetting to temperature / elevation changes before adding

another tuning variable like the sparkplug's temperature range to the equation.

Edited by mlatour
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Looks a bit rich + carbon deposits but within 'normal' for a bike most likely not ridden wide-open on a MX track.

 

I would adjust the jetting to temperature / elevation changes before adding

another tuning variable like the sparkplug's temperature range to the equation.

 

Thing is.......it has good throttle response from idle to full throttle,even when you whack the throttle wide open.  To me that would say it has the right jets in it.  Now........By the way the plug looks now......would you say it would get a little leaner "say" when the temps warm up some more like @ about 75-85 degrees out.

 

I would like to have it jetted to this temp. the elevation of where I do most of my riding and racing ranges from 1000-2100 ft above sea level.

 

But when I have races down in South Carolina and North Carolina the elevation is just 500ft above.  So I would be good with what I have in now wouldn't I?

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Without changing the jets, the engine will run richer when: 

 

-outside temps are warmer

-elevation is increased

-humidy is high

 

So if you adjust it 'perfect' lets say for 60° / 1000ft, it will be rich when at 85° / 2000ft.

 

All depends how 'in-tune' you like your bike to run,

most people find an average jetting that works 'okay' at most temps and stick with it,

running a bit on the rich side as insurance and accepting carbon build-up & spooge as a trade off.

 

I myself like to tinker around with 'spot-on' jetting and adjust it to the day's ambiant conditions.

Edited by mlatour
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Without changing the jets, the engine will run richer when: 

 

-outside temps are warmer

-elevation is increased

-humidy is high

 

So if you adjust it 'perfect' lets say for 60° / 1000ft, it will be rich when at 85° / 2000ft.

 

All depends how 'in-tune' you like your bike to run,

most people find an average jetting that works 'okay' at most temps and stick with it,

running a bit on the rich side as insurance and accepting carbon build-up & spooge as a trade off.

 

I myself like to tinker around with 'spot-on' jetting and adjust it to the day's ambiant conditions.

 

I just want to basically find a good sweet spot for 70-90 degree weather from 1100-2500 ft elevation.  Now by the way my plug looks would I need to go down a size on the Main jet and on the Pilot?

Will I need to change clip positions on the needle?   I know you really will not be able to answer these ?'s without trial an error and hands on.

 

I just want to know if changing jets are in order for the upcoming warm weather this spring/summer?     or is it just a Air-screw adjustment that is in order? 

 

I adjusted the Air-Screw to where my idle raised to the highest an then went back 1/4 turn and that put it at 1 and 1/2 turn out.

 

Thanks for yur help mlatour!

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It's trial and error, after a while you'll get a feel for a lean or rich running engine.

Buy a lot jets, 3-4 sizes smaller & bigger than what are stock size pilot and main.

Stock needle will do ok until you require the extremities of the available clip positions.

Take a lot of notes, temps vs jet size and what temps range that they work well.

 

There is somewhat of an overlap in actual use but here are some

basic guidelines to what fuel circuits affect what throttle positions:

 

air screw: from idle to 1/8 throttle

pilot jet: idle to just under 1/2 throttle

needle's profile: around 1/4 throttle

needle clip position: 1/4 to a little over 1/2 throttle

main jet: around 1/2 to full throttle

 

The air screw is pretty much there to fine tune the pilot jet circuit,

by turning it you're compensating to obtain a perfect setting that is in between two available pilot jet sizes.

If it's turned in or out more than one turn from it's initial setting, lets say specs are for 1-1/2 turns out,

it means you either have to lean or richen the pilot jet, set the air screw back to the spec setting and test again.

 

Setting the air screw to get highest idle will most likely be too lean. Instead, set it to get best throttle response at low speeds.

Having to turn the air screw in (clockwise) allow less air in the circuit, meaning your pilot jet is too small / engine is running lean.

Having to turn the air screw out (ccw) allows more air in the circuit, meaning your pilot jet is too big / engine is running rich.

 

A leaner than perfect pilot jet circuit runs crisper at low speeds but the engine surges or gets a dull 'ping' when you let off the gas.

Too rich a pilot jet and you loose throttle response and it starts to smoke / spooge at low speeds.

 

 

A too lean needle mixture makes the engine 'bog' on hard acceleration and a too rich one 'cuts out', not getting into the powerband cleanly.

 

A spot-on or tad leaner main jet allows a bit of extra over-rev at the risk of overheating the engine if held wide-open too long.

Too rich is safer but limits over-rev.  Better rich if you ride wide-open on long straigtaways, keeps the piston cool.

 

I test in that order, start off idle and move up gradualy in the rpm range, adjusting pilot then the needle

circuit and finaly the main jet. Both pilot and needle still provide some fuel flow at high rpms, if you fine tune

your main jet first and then lean out either one of the first two fuel circuits, your wide-open mixture will also end up leaner.

Edited by mlatour
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Reading a plug is not the best method when attempting to judge jetting. Entirely too inconsistent. You could throw a new plug in, go to a different gas station and get entirely different results. Learning to jet by feel, and sound is the only real way to get it spot on with the crappy pump fuel avail to us these days. If you are looking for heat signatures, looking at the piston (specifically the underside) is a better method of judging heat.

 

I personally wouldn't touch it if the bike is running well. Stock jetting is "safe" and that is a good thing. If you are looking for performance or want to start modding the bike then I would look to spend some time jetting. As Mlatour stated... jetting is 100% trial and error. But judging by your descriptions, you will be able to tune out any issues that may pop up with only an adjustment of the A/S. 

Edited by BDubb106
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Reading a plug is not the best method when attempting to judge jetting. Entirely too inconsistent. You could throw a new plug in, go to a different gas station and get entirely different results. Learning to jet by feel, and sound is the only real way to get it spot on with the crappy pump fuel avail to us these days. If you are looking for heat signatures, looking at the piston (specifically the underside) is a better method of judging heat.

 

I personally wouldn't touch it if the bike is running well. Stock jetting is "safe" and that is a good thing. If you are looking for performance or want to start modding the bike then I would look to spend some time jetting. As Mlatour stated... jetting is 100% trial and error. But judging by your descriptions, you will be able to tune out any issues that may pop up with only an adjustment of the A/S. 

 

That's what I was thinking. The bike runs great! Has no sputter nor bog revs real quick and has crisp throttle response from off idle to wide open throttle.  When I do come off the pipe and it does bog,I just flick the clutch lever a tad and its back on the pipe. 

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I don't believe you'll get perfection for a 20 degree temp swing. I find 20 degree=mandatory needle adjustment. This does change idle and top end enough to get by.

Any larger temp change I'll tweak brass too. I always running a summer needle ,leaner straight section, and a winter needle.

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Same here, with a 20°F swing in temperature (roughly a 12°C range for us Canadians / metric users)

will require some adjustments if you wan't your engine to run closest to 'perfect' and it's best potential.

 

Going from 50°F weather up to 70°F ambiant temps requires about one step leaner on the pilot, needle clip position and main jet on my bike.

Edited by mlatour
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rich will always give the strongest roll on.

If you are happy with performance ignore the plug. Spooge too.

 

I have had no Spooge so far. Just a tad wet oil on the inside hole of the silencer.  When It warms up this spring/summer to the mid 80's and I can tell a difference in the way the bike is running from by the way it ran when it was in the 50"s I will try a step down on pilot and then the needle and Main if needed.

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I have had no Spooge so far. Just a tad wet oil on the inside hole of the silencer.  When It warms up this spring/summer to the mid 80's and I can tell a difference in the way the bike is running from by the way it ran when it was in the 50"s I will try a step down on pilot and then the needle and Main if needed.

If there is wet oil inside the muffler exit, then spooge will start to happen.

As the other guys already said, I think it's best to experiment. Under some load at various revs, by sound and feel and note according to throttle position. According to your plug, somewhere in the throttle range you are too rich. But who knows where.

Check your squish clearance. Most stock YZ250s are too wide on squish, therefore have rich jetting to make the wrong head setup work best as is possible. It should be 1.2mm. Yours is probably 1.75mm. Under 1.6 is acceptable. Over 1.7 is not acceptable, in my opinion. Under 1.1 is risky if you use the motor when the main and rod bearings are worn out.

Edited by numroe
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Check your squish clearance. Most stock YZ250s are too wide on squish, therefore have rich jetting to make the wrong head setup work best as is possible. It should be 1.2mm. Yours is probably 1.75mm. Under 1.6 is acceptable. Over 1.7 is not acceptable, in my opinion. Under 1.1 is risky if you use the motor when the main and rod bearings are worn out.

 

Excellent information right there!!!

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If there is wet oil inside the muffler exit, then spooge will start to happen.

As the other guys already said, I think it's best to experiment. Under some load at various revs, by sound and feel and note according to throttle position. According to your plug, somewhere in the throttle range you are too rich. But who knows where.

Check your squish clearance. Most stock YZ250s are too wide on squish, therefore have rich jetting to make the wrong head setup work best as is possible. It should be 1.2mm. Yours is probably 1.75mm. Under 1.6 is acceptable. Over 1.7 is not acceptable, in my opinion. Under 1.1 is risky if you use the motor when the main and rod bearings are worn out.

 

 

I will research that!......I'm not to familiar with the method but will search it on here an check it sometime.  Lets say I did check it!......would the next step be:  Take the head (the piece that the plug screws into) to a shop an have them to mill it down?    or is it the JUG that has to milled at the Top?

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