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Intermittent Fouling Plugs

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I have been having ongoing issues with my 2006 CR250R.  I had the bikes top/bottom end rebuilt and the carb tuned and jetted for my elevation (3000-4000ft) when I purchased the bike last year.  Since then I have had ongoing issues fouling plugs.  After getting it re-jetted again after the engine rebuild and continued to foul plugs I finally purchased a JD Jet kit and installed the kit myself with the recommended settings.  Now my bike runs better than it ever has with crisp throttle response.  However I am still having intermittent plugs foul.  It has happened on my last two rides now where I rode for 1-2 hours and shut my bike off for about five minutes and when I started it up it fouled within 30 seconds of firing it up.  when I pulled the plug it was fairly wet and black with oil.  Another guy I was riding with suggested I pull my pipe and check to see if oil was running back into the cylinder causing it to foul after sitting.  When I pulled the pipe the pipe was full of carbon caked inside and also there was a fair amount of oil sitting at the base of the pipe where it connect to the exhaust outlet. 

 

Now my question is is this a possible scenario for oil to run back into the cylinder and cause plugs to foul when I fire it back up?  If that is what I causing my intermittent plug fouling would decarbonizing my pipe solve that issue or do I possibly still have a jetting issue.  I'm guessing that I may still be running to rich since there is so much oil going into my pipe? 

 

I mainly trail ride so I quite often have to lug the bike around at low RPM.  I have also considered switching to a BR8EG plug vs the BR9EG because I am trail riding and my not be burning hot enough.

 

Any advice or thoughts as to what might solve my issues would be greatly appreciated. 

 

 

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I would hope the mechanic  would have replaced the crank seal when he rebuilt my bottom end last year.  He replaced the crank I know but I will have to look at the bill tonight and see if he replaced the seal.  The bike does not smoke excessively at all once it is warmed up, but a fair amount when I start it and when its warming up.  I also noticed after I fouled one of the plugs that after I cleaned the plug off and  put it back in and fired it up there was a quick puff of black smoke.  Would that be an indication of crank oil leaking into the cylinder?

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What method are you using to tune the air screw?

What fuel mix ratio do you run? What premix oil?

Whether the pipe is causing the problem or not, clean that carbon and oil out of there. I once bought a used bike that had carbon build up 1/4" thick in the pipe. That kind of build up can throw off the tuned pipes on these 2 strokes, and, in my case, I had chunks that would come loose and stop up the stinger end of the pipe.

Edited by Trailryder42

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I run 40:1 with premium fuel, I used to run Bel Ray H1R but switched to AMSOIL to see if that would solve any fouling issues. 

 

I haven't touched the air screw since It was last had it jetted by the mechanic.  I did adjust the idle screw down however, after I installed the JD jet kit it was idling much faster.  After I clean out my pipe and re-pack my silencer I will try to adjust the air/fuel screw.  From what I have read, to adjust the air screw you are supposed to turn the screw in until the bike start idling poorly (when hot) and then turn the screw back out 1 1/4 turn.  That is supposed to get it close, what the best way to dial it in from there?

 

Also is there any way to test and find out if I have a leaking crank seal?

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You can't change the jetting from what the mechanic had in it to a JD kit and NOT retune the air screw.

Learn how to tune it using the "whack the throttle method". I've found it to be the quickest, easiest and a lot more accurate than an arbitrary setting like you mention.

First, turn the screw all the way in from where its at now, counting the number of turns until you "lightly" feel it bottom out. Now you know where it was set originally. Screw it out 1.5 turns and get the bike started with a new plug. Get it warmed up and ride it around a little to clear it out.

Then set the idle knob so the engine will idle, then quickly whack the throttle open to about 1/2 throttle and close it. You're looking for no hesitation response, no Bwwwaaaaa....., no blubbering. Turn the air screw in 1/4 turn increments between adjustments while trying to clean up the response. You'll figure out pretty quick if you're going the right way with the screw, as response gets better or worse.

After you get crisp response, You want the air screws final setting to be between 1 and about 2.5 turns out. If its less than 1, the pilot jet is lean and needs a size bigger. If over 2.5, the jet is too rich and you can drop a size.

Which Amsoil did you switch to? The H1R has a flash point of 202*, the Amsoil Dominator is 215*, Amsoil Interceptor is 183*, so its the Interceptor you should be running for trail riding.

Edited by Trailryder42

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I switched to the Amsoil interceptor so I will continue to run that.  I cleaned my pipe last night and will play with the air screw tonight and hopefully get it set properly.  Hopefully I will have the bike running with no issues by the end of weekend.  Thanks for all the advice so far.

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I have been trying to adjust my air screw today but I have been having a little trouble.  when i started I found the air screw set at just under 1.5 turns out.

 

I fired the bike up warmed it up and then adjusted the air screw in quarter turn increments.  I wasnt sure if i was supposed to adjust the idle every turn or leave it in one spot so i tried both methods.  I found that adjusting the air screw would speed up and lower the idle as i turned it.  I also was not sure how fast of an idle to set, some of my friends on two strokes have a fast idle and some guys bikes won't idle at all.  For my testing I would set the idle fairly fast which seemed to give the best response. 

 

What I found was that I could get good response between 1 and 2 turns out but it was hard to tell because it wasnt always consistent, it seemed like the idle speed played the biggest factor in the response.  When I tried adjusting the air screw without adjusting the idle speed each turn of the air screw, I found that the bike had the best response around the 2 turn mark but i think that was only because the idle speed was faster.

 

Also what is the deal with smoking? is that a good indication of whether the bike is running to rich or lean?

 

Any tips and advice is greatly appreciated.  Cheers.

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Set the air screw at one turn

Run the bike, get it hot

Adjust the idle as low as it will go

Turn the air screw to raise the idle.

If it goes too high, drop the idle low and repeat

Your goal is to reach the desired idle speed with final turn of the AIR SCREW turns, not the idle screw.

Then check for idle drop speed after a blip, and adjust finer from there.

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Kah Ran Nee describes a different method/procedure than what I posted. He's tuning for highest idle and I'm tuning for best throttle response off idle.

While tuning, I maintain the idle speed I'm going to want to end up with, using the idle speed screw, because I want best throttle response off "that" idle in the end. When tuning the air screw and the idle raises significantly and you are tuning by whack the throttle method, response can be different at a high idle than it would be at your desired final idle that you want to end up with.

I want my final idle speed to be high enough that if I come to a stop on the trail and sit there for a minute, it will idle on its own without trying to die or with me constantly giving input to keep to going. From experience, I know what that speed is and that's what I maintain while tuning.

Now, once you find the sweet spot for best off idle response with no hesitation or bog, you can lean the air screw some more from there if you want, with no more that 1/8 turns, until off idle response starts to suffer.

I also have a Rekluse Core clutch and it will idle, in gear, clutch lever out and not move and have great instant throttle response.

Edited by Trailryder42

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I had my bike out on the weekend and tried playing with the settings a little bit.  I turned the air screw in to about 1.25 turns and fouled a plug after about ten minutes of riding.  after that I turn the screw out to about 1.75 turns and rode for a while but the throttle response did not feel like it was responding very fast.  I then turned the screw to about 1.5 turns (where it was originally) and found that that had the best response of the three options I tried.  I went all day without fouling a plug however I still feel like the response could be a little bit faster from zero to half throttle.  Do you guys have any other tips that I could try to tune the response a little more?  I was comparing my response to my buddies YZ250 and his seemed faster?

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I've found that once I get close, 1/4 turn increment adjustments is too much.

Have you checked your reeds?

Did you ever try the hotter plugs?

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I may have to try smaller adjustment on the airscrew instead of the 1/4 turn.

 

I have not checked the reeds but im pretty sure they should be ok, I have V force 3 reeds and i would guess that they only have about 20-30 hours on them.

 

Last weekend when I was out I fouled a plug when I was warming the bike up.  The way I ussually warm up the bike is start it with the choke on and turn the choke off after its started.  The I ussually let it idle for close to 5 minutes.  After idling for a little bit I will give it revs up to the power band but when I tried to rev it up to the power band this weekend the bike fouled a plug after 5 or so revs.

 

After that fouled plug (BR9EG) I put in a BR8IEX irridium plug.  The bike felt like it was running crisper with the hotter plug with better 1/4 rev throttle response.  I ran that plug all day and did not foul the plug, I will have to get some more hours on to see if this solves my problem.  Am i safe to run a hotter plug or will it wear out my top end faster?  Or does this give any hints as to what my issue is with the BR9 plug?

 

Another factor that may have been the reason for my bike running better is that I was riding at an elevation of 2700' this weekend instead of the 4000' I ussually ride at.

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Don't let your bike idle for five minutes. All it will do is load up and foul a plug. I'm not saying to start your bike and take off right away, but by design your bike shouldn't idle that long. I would also recommend running the pre-mix ratio that Honda specifies as it will further lean your jetting. A hotter plug might help, as well as lower octane fuel. It sounds counter intuitive, I know. What it sounds like to me is, you aren't producing high enough exhaust gas temps/cylinder temps to efficiently burn the fuel. Not sure how lean you're jetted but keep in mind that the lube is in the fuel so don't go to far. Stick with the new plug and try some mid grade or low grade fuel (listen for detonation, adjust accordingly) and see what happens.

Just my 2 cents.

Good luck, and ride on

Edited by avisagio

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