CRF Sparkplug question

[GTRider]

I just my 03 CRF broken in and went riding at the local track this week and I have a few questions. If I warm up the bike (15 min of riding) and then stall or kill the bike it does not like to have the hotstart lever pulled to start the bike (harder to start with hotstart lever pulled). Is this normal? Also when letting off the throttle from high RPMs it sometime backfires. I was thinking that the starting without the hotstart lever pulled w\would indicate a lean condition, but after hearing the backfiring and looking at the plug I don’t know what is causing these conditions. I was hoping someone could shed some light on this for me.

Here are the links to pics of the plug.

Plug pic 1
Plug Pic 2
Plug Pic 3
Plug pic 4

Thanks,
GTRider

 

[Rich Rohrich]

The 02 CRFs came from Honda with the pilot circuit jetted fairly lean. It seems likely that the 03 would follow suit. Deceleration backfiring is fairly common when the low speed circuits are lean. The simplest place to start is to richen the pilot circuit a bit by turning the pilot fuel screw out a bit. One half of a turn out will richen it enough to make a noticeable difference. You can also richen the fuel curve up across the board by running one of the non-oxygenated race fuels that runs to the rich side like VP C12 or Phillips B32.

 

[reynome]

Rich,
I also just got my 03, it seems to be jetted from the factory very well for Denver. I have been running pump fuel 91 octane. Would there be any benefit running B-35 or B-32? I have run B-35 in my 250, will the extra oxygen in B-35 help the crf?

I though it was a little rich on top as it might rev a little higher, also I thought that the throttle responce could be just a tad crisper. The bike has ample power I just want to dial it in and leave it. This is the funnest bike I have ever owned! :yeehaw:

thanks

 

[TRexRacing]

You can be lean and still have the plug indicate rich like you have.The accelerator pump is the culprit here.

 

[GTRider]

If the pump is the culprit, what would be the fix? is it pumping two much gas?

thanks,
GTRider

 

[Shawn Mc]

You can shorten the pump squirt by do whats called a BKmod. Its simply driling and tapping the stop boss for the accelorater pump. You put a screw in the boss that limits the travel of the pump cam, and shorted the pump squirt to about 1/2 a second, instead of the stock 3 full seconds. It made a huge difference on my YZ426.

 

[Shawn Mc]

Here is a link to the site that has pictures of the BKmod. Its easy. Look under tech articles. http://motoman393.forreal.net/

 

[TRexRacing]

Originally posted by GTRider
If the pump is the culprit, what would be the fix? is it pumping two much gas?

thanks,
GTRider

The pump mod mentioned in the last posts will help.I haven't had mine long enough to mess with the tuning yet.You just jet without using the plug for an indicator.Increase your pilot jet size and see if the symptoms described in the first post go away or lessen in intensity.If they get worse,wrong direction.I've got a feeling the CRF has alot of lattitude and jetting isn't as critical as a smoker would be.Just my 2 cents.

 

[Eric82930]

I agree about the black soot around the outside of the plug. It will always be there. I ride above 7000' most of the time so my jetting will be different than most, but I still think the accel pump is to rich. I timed it stock and it is under one second so I didn't mess with it. I haven't heard of any CRF owners doing the BK mod because it seems honda already did it. I also have the leaner pilot jet and fuel screw at 1 out and needle 2 clips lower and still don't use the hot start (unless I'm at 10000' or higher). The hot start usually makes it too lean for my altitiude. (my bike never pops on decel.)

 

[GTRider]

I rode the bike again last night at the track and it did not backfire once from de-acceleration. but it started very time hot with out the hotstart lever, the only time that I used it was after I layed the bike down in a corner (darn k490 in sand), two kicks with ou the lever (didnot start) one more with the lever and she fired right up. the weather conditions were approx. the same as last week.