Stock exhaust with Diffuser out CRF250X jetting?

[Kzoo]

06 CRF 250X

If I am running the stock exhaust without diffuser, should I change the jets at all?

 

[Shaw520]

06 CRF 250X

If I am running the stock exhaust without diffuser, should I change the jets at all?

Your question is irrelative,.. what are trying to acheive.

All I can tell ya is that MOST maunfactures jet on the lean side,.. uncorking the exhaust only makes them more lean.

 

[a454elk]

Correct, the jetting is way lean from stock so opening it up makes it worse. You should definately go fatter on the jetting anyway, you'll have to see how it runs but be carefull on running it too lean.

 

[Kzoo]

I have rode a couple of times in the field and on a track. It seems ok. You can tell a difference with the diffuser in and then out. With the diffuser out it is more responsive.

I know how to work on 2 stokes and how to tell if we are lean by spark plug burn and also piston wash, but on this four stoke you cannot see the plug unless you disassemble the bike. You have to take the seat off, tank off just to get to the plug.

Just looking to see what someone else has done, and advice/starting point.

thanks

 

[CarnageZ28]

It sounds like they made it a bitch, but really your gunna have to WOT it, kill switch, then check your plug out ... Unfortunatly, most bikes are jetted lean as already mentioned so ...

 

[Shaw520]

Just looking to see what someone else has done, and advice/starting point.

For minimal cost, a jetting kit will not only assure you that you're not too lean, but can ad power throught the curve.

 

[a454elk]

I agree with Shaw, you should run it fatter anyway, even if you don't do it the right way to check your plug like Carnage said.

 

[XR250rdr]

Plug reads are pretty much worthless with modern fuels.

 

[a454elk]

Not really XR, if they are done right, it'll read just fine, giving you the info to set your jetting.

 

[CarnageZ28]

XR250rdr - Try this then:

Run your bike WOT and kill it, remove plug, and look at the PORCELIN, sometimes its easier to actually remove the threaded part of the plug for a good inspection of it.

Now install a main jet say a few sizes larger, and do the same thing. Compare the two plugs back to back. You'll see.

Only way me and the people I know have ever really worked towards correct jetting.

 

[XR250rdr]

I've done plenty of plug reads, I'm not saying they never worked just that as fuel formulations have changed they don't always work like they used to. Besides I don't seem to have any trouble jetting by ear.

What I mean is on 4 strokes the bike will run good, no pinging or other lean symptoms, but often the plug will read as too lean. Richen up the main and bam the bike starts blubbering and the plug is black. Results might vary depending on what part of the country you live in because fuel formulations vary, but it still makes the test results unreliable.

 

[CarnageZ28]

Oh, I gotcha ...

Well, I'd be a total liar if I said I've never had something similar happen lol so ...

I kinda see where your coming from. You are testing the plugs after a shutdown at Wide-Open-Throttle right? Just making sure. Cause if you close the throttle, it will alter the results, possibly showing a good bit richer than it is. Likewise, there are things that can happen to make it a leaner mixture as well if your not shutting down at WOT. You seem to know what your talking about though ...

 

[Sawed Up]

Would the same principle apply to my 07 CRF150F? If the spark arrester was removed.

 

[Shaw520]

XR250rdr - Try this then:

Run your bike WOT and kill it, remove plug, and look at the PORCELIN, sometimes its easier to actually remove the threaded part of the plug for a good inspection of it.

Now install a main jet say a few sizes larger, and do the same thing. Compare the two plugs back to back. You'll see.

Only way me and the people I know have ever really worked towards correct jetting.

...or you could just get the correct jetting kit for the pipe, (or in your case) pipe modification, and save yourself alot of work. :nod:

 

[XR250rdr]

Oh, I gotcha ...

Well, I'd be a total liar if I said I've never had something similar happen lol so ...

I kinda see where your coming from. You are testing the plugs after a shutdown at Wide-Open-Throttle right? Just making sure. Cause if you close the throttle, it will alter the results, possibly showing a good bit richer than it is. Likewise, there are things that can happen to make it a leaner mixture as well if your not shutting down at WOT. You seem to know what your talking about though ...

Yep.

I should be clear though. If the technique is working for you, great, just be critical of the results if things don't seem to add up.

...or you could just get the correct jetting kit for the pipe, (or in your case) pipe modification, and save yourself alot of work. :nod:

If I were to buy a new off road 4 stroke, a JD Jetting kit would be one of my first purchases.

 

[Kzoo]

I have contacted FMF (sponsor) for a jet kit which is made by Dynojet. After reading the instructions, it will be a better starting point using their kit.

thank you to all

 

[XR250rdr]

Just be warned that Dynojet jet numbers don't correspond to Keihin jet numbers.