CRF250X Spark Plug: Jetting Changes?

[MNThumper250]

I'm tearing down my '06 CRF250X for winter prep. I checked the spark plug (see pics).

I've rode with this plug for most of the summer. I'm thinking it's a bit rich, so for the other 250X owners out there, what jetting are you running/what do you think I should run? The only mods I've done is install the JD Jet Kit (165 main, 42 pilot, Red needle 4th clip, and thick o-ring), FMF Q4, and 4" x 4" hole in air box (with No Toil Super Flo Kit). The bike seems to run alright, but should I drop a few on the main jet?

[mlatour]

Reading spark plugs on pump gasoline isn't accurate as the formulation and additives can alter the colour no matter the jetting.

(this is where the consistency of race fuel removes that variable and simplifies tuning in race engines)

 

Pilot jet and needle settings are best experimented by 'feel', like low speed transition from idle/pilot circuit into mid-throttle position (needle),

only the main jet (3/4 to full throttle) can be judged by plug coloration, not at the tip but deeper inside at the base of the insulator

by the plug chop method of running wide-open, shutting the engine off and reading the colour, see link: http://www.braigasen.com/howtoread.htm

 

Before you make any jetting changes, make sure your float is set at the specified height and inlet needle and seat are sealing properly.

Higher than spec. fuel level in the bowl will richen all metering circuits.

Edited November 19, 2017 by mlatour

[MNThumper250]

23 minutes ago, mlatour said:

Reading spark plugs on pump gasoline isn't accurate as the formulation and additives can alter the colour no matter the jetting.

(this is where the consistency of race fuel removes that variable and simplifies tuning in race engines)

 

Pilot jet and needle settings are best experimented by 'feel', like low speed transition from idle/pilot circuit into mid-throttle position (needle),

only the main jet (3/4 to full throttle) can be judged by plug coloration, not at the tip but deeper inside at the base of the insulator

by the plug chop method of running wide-open, shutting the engine off and reading the colour, see link: http://www.braigasen.com/howtoread.htm

 

Before you make any jetting changes, make sure your float is set at the specified height and inlet needle and seat are sealing properly.

Higher than spec. fuel level in the bowl will richen all metering circuits.

Sounds good. I read about the plug chop method a while ago, just never tried it. I'm tearing into the carb anyway, so I'll check the float and needle while I'm in there.

I also noticed my choke either doesn't work, or doesn't need to be used. I can start the bike cold (after giving it a squirt or two of fuel) without the choke. If I pull the choke (when idling) my bike dies. I've seen a lot of videos of other 250X's continue at a high idle when their chokes are pulled, so shouldn't mine do the same? Maybe another sign that my bike's a little rich?

[mlatour]

Yes if the engine (cold) starts easily and idles without the choke (actually an enrichment circuit) 

that would be a sign it may be running rich on the pilot jet or fuel screw settings,

perhaps even the choke plunger / circuit that continues to feed fuel even when pushed in.

 

Your #42 pilot jet size is typical to most 250X's, what are your fuel screw settings?  (aftermarket screw?)

 

 

Edited November 19, 2017 by mlatour

[MNThumper250]

I think it's about 1 3/4 turn (which is what the jet kit recommended), maybe closer to 2 turns. I still have to get it dialed in though. The bike ran decent, so I just left it alone.

I remember a while back, when I first started to mess around with the fuel mixture screw, I couldn't get the bike to die, even when I turned the screw in. This made me think that my pilot was too big, so I tried a #40, but I had similar results.

Once I check the carb checked out, I'll test and see if this still happens. I can't remember if I fixed this or not...

[mlatour]

With what you've described (turning it in fully and engine still runs)

check the fuel screw to make sure the washer & o-ring etc. are in proper order.

 

Sometimes the o-ring from an old screw can be forgotten in the carb. body when installing a new screw assy.

[mlatour]

A few other thoughts,

an aftermarket fuel screw of lesser quality may have the wrong shape or taper.

Also, over-tightening can damage the tip, richening the fuel metering.

Edited November 19, 2017 by mlatour

[MNThumper250]

Last time I was in the carb I made sure there was no extra o-ring in there. I had a Tusk fuel screw in there for a while, but swapped it out for a stock one due to the fear that it was incorrect. I might get a different fuel screw though, since the stock screw is difficult to turn. I'll probably go with the JD screw (brass).

[Leardriver]

You're so close that I wouldn't worry. The JD kit is a tad rich, because it has to be to take human error out of the equation. A 160 main is probably perfect, but that's only for WOT anyway.