Author Topic: 21 SE 300 fouls plugs a LOT!  (Read 750 times)

bondo

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21 SE 300 fouls plugs a LOT!
« on: December 06, 2021, 09:14:05 AM »
I've got a '21 SE 300 Factory (less than 75 hours on the bike) that I use mostly for tight woods.  The bike is awesome!  Makes good power, doesn't stall (unless I really f*** up!) pulls great down low, starts easily every time and runs strong all the way through the rev range. 

However, it fouls plugs about every 4-5 hours (of run time).  Bike has the stock Keihin carb, stock slide, #162 main, #35 pilot,
stock needle with the clip in the second position from the top, air screw about 1 1/2 turn out.  I run ethanol-free pump gas (93) mixed with  Amsoil Dominator @ 60:1.  Air filter is kept clean. BR7ES spark plug.  We ride close to sea level and no higher than about 2000 ft.

The bike runs so clean and so well,  I have a hard time believing it's a jetting issue.   Anyone else had this problem?  How did you resolve it?  Thanks for your help!
« Last Edit: December 06, 2021, 09:44:01 AM by bondo »

alang

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Re: 01 SE 300 fouls plugs a LOT!
« Reply #1 on: December 06, 2021, 09:21:09 AM »
Could be electrical,
But try a n8rh or n8rw
Needle.
2022 Sherco 300 2T Factory
2016 Aprilia Tuono 1100 Factory
2019 Santa Cruz Tallboy Carbon R
Azle, Texas

bondo

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #2 on: December 06, 2021, 01:00:17 PM »
Thank for the recommendation!

possiblytoofast4you

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #3 on: December 06, 2021, 10:30:37 PM »
sounds electrical.

Your jetting is getting quite lean so i think that can be ruled out as the cause.

Take your spark cap off, leave plug in the motor, hold it about 30mm from the head and crank the starter.
Sparks should jump out of the cap to the head, if they dont, it would be safe to assume your problem is electrical.

bondo

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #4 on: December 07, 2021, 11:18:50 AM »
I'll try your idea.  Thank you!

alang

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #5 on: December 08, 2021, 06:25:08 PM »
Stock needle diameter is rich
Which is zero to 1/8 throttle.
2022 Sherco 300 2T Factory
2016 Aprilia Tuono 1100 Factory
2019 Santa Cruz Tallboy Carbon R
Azle, Texas

bondo

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #6 on: December 09, 2021, 12:24:39 PM »
Thanks for the clarification on the needle spec.  Am going to try the spark cap test suggested by  "possiblttoofast . . . ".
If the ignition checks out as good (and even if it  doesn't), will probably try a one step leaner needle.

Also, has anyone ever had issues with the power valve getting clogged with carbon spooge?  I have an older GG 300 and the PV in that bike needs to be cleaned thoroughly about every 100 hours.

bondo

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #7 on: December 13, 2021, 11:36:33 AM »
So here is a follow-up to this thread.  First, I tried the spark test suggested by "possiblytoofast. . . ".  The spark jumps across a gap of approx. 30mm (1 1/4"), so my conclusion is that the ignition system is good.

Didn't have any of the leaner needles recommended by "alang", so as an experiment, I lowered the needle one more notch.
The difference in just that one step leaner clip position was remarkable!  The bike runs so much leaner with just that one small change, I'm considering going up one size on the main jet and leaving the needle where it is.  Will probably order a leaner needle too, just in case.

Gartzza

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #8 on: December 15, 2021, 12:17:38 AM »
If you have possibility, send ECU to dealer for update (or visit dealer with your bike). New program can fix many problems and make bike run better. At least, it never makes bike worse.

Sfade

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #9 on: December 15, 2021, 09:40:41 AM »
I was going to say float level, but that would just be a rich running bike, and it sounds like it runs good so....???  Interested to know what that is.
2021 Sherco 300 SE Factory
2020 Sherco 300 SEF Factory (Supermoto)
2019 KTM 250XC

bondo

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #10 on: December 15, 2021, 11:53:43 AM »
Thanks for the suggestion about getting the dealer to update the ECU.  As you said, it can't hurt. 

As to the float level, I have not checked it, but it doesn't act like a float issue {and I've dealt with a few of those in my lifetime).


bondo

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #11 on: January 10, 2022, 09:57:52 AM »
Here is one more follow-up to the plug fouling issue with my '21 SE 300.  First, the jetting stats I gave in my initial post were incorrect.  I indicated that my bike was running a #162 main, #35 pilot, stock needle in 2nd position from the top, etc . .
In reality, the main jet was a actually #168 (oops!).

I did not have any of the leaner needles suggested, so decided to drop the stock needle to the top clip position.  The bike ran MUCH leaner.  In fact, at 3/4 throttle and up, I could tell a significant decrease in top end pull compared to the previous needle position.  At that setting the tip of the spark plug was white (rather than brown or black) after riding the bike.

I decided to go up one size on the main to a #170, leave the needle clip in the top position and stay with the #35 pilot.

After four rides with the current set-up, I haven't fouled another plug, the bike pulls clean from idle on up and the top end power is good and strong. 

alang

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Re: 21 SE 300 fouls plugs a LOT!
« Reply #12 on: January 10, 2022, 12:59:08 PM »
I'm running 40 pilot, N8RG
Needle in 3rd pos. , 165 main.
2022 300 SE factory.
Stock needle was N8RE.
I could probably go second clip
In warmer weather. 800 ft elev.
2022 Sherco 300 2T Factory
2016 Aprilia Tuono 1100 Factory
2019 Santa Cruz Tallboy Carbon R
Azle, Texas