[TTT122]

I have a 2007 CRF 450 with a White Brothers titanium / carbon exhaust. It fouls plugs within five minutes or riding on a fast practice track.

It ran really, really good the first few rides, then one day, it went bad. There was nothing gradual, just an immediate shift to fouling plugs.

We have checked and re-checked the jeting, tried a new fuel screw, checked the valves, new plugs, drained the tank and put in new fuel, but nothing has made even a small difference.

In desperation, we took it to our local shop twice with zero luck (except some expensive bills). We talked to a second shop, and they just shrugged their shoulders.

We ran some VP Ultimate 4 this weekend, and the bike was way, way too lean (even after bumping up the jetting). When we got home, we tried supreme pump fuel (from a different station), and immediately fouled another plug.

We thought it might electrical, but the fact that it ran so lean with the U-4 fuel, it does not seem reasonable. However, we are really stuck right now, and can't think of anything beyond starting to throw parts at the bike, but that is going to get expensive!

I have never taken a carb completely apart, but could the choke be stuck on inside the carb, even though we have pushed it in from the outside?

Anybody have any other ideas?

[Asmith]

What are you doing for an air filter?

Oil?

Cleaning regimen?

[crfsonly]

consider a jd jetting kit...and definitely make sure your air filter is "dry" before installing it. oil it and let is stand in a well ventilated area for 24 hours.

ken

[124]

The bike ran fine, then "all of a sudden" started fouling plugs?

Are the plugs actually fouled or are they getting gummed up?

Does the bike run OK?

Are you running the OEM plug when you change it?

Check the simple things. Sparkplug boot OK? Check your exhaust flange nuts. Are they tight? Etc, etc...

[TTT122]

Air filter has not been changed, so I am sure that is not the cause. The plugs have been stock NGK plugs, exactly the same as what came with the bike.

I know the plug boot is has good contact with the plug, although one of the things we're considering is a bad coil. I believe a new boot would come with the coil, but before I start buying parts, I am trying to do this in a "smart" way.

When we do change filters, we currently use PJ-1 spray on oil, and have used this stuff for years with no problem.

Thanks for the responses, I've gotta get this figured out, as I want to go racing...

[JAWS]

Try cleaning your filter and see. That's a cheap alternative as well. Make sure to let it dry for the appropriate amount of time.

When you said it ran lean on the VP fuel, did you check your plug on that or how did you determine the leaness? Did you return your jetting to normal after getting back home and before trying the regular gas? What did your plug look like then?

Joe

[TTT122]

We checked the plug after each ride running the U-4, and it was as white and dry as if it were brand new. Each time, we bumped up the jetting (main, raised the needle, turn out the fuel screw) but never got it to run right.

When we got back home, we drained the U-4, put jetting back to stock, and put in new gas from a different station / company.

Within five minutes, we fouled another brand new plug. The fouled plugs are totally dry, but very, very "sooty" on the upper threads and the ceramic insulator (it is very thick). The spark plug tip is actually clean and dry though.

Thoughts?

[cruisers450]

so its so fouled it doesnt start then?

[124]

Sounds like it's carbon fouled. A picture would be nice that way it can be more accurately diagnosed.

Carbon fouling is most prevelant is our types of engines. Most common causes are too rich of mixture, weak ignition, and/or wrong plug heat range.

My guts are telling me electrical because it happened "all of a sudden". If indeed it ran perfectly fine then one day started $hitting plugs, that to me points to something broke. Weak spark could be caused by failing coil.

A failing coil can be diagnosed by using an ohm meter. I don't have my manual in front of me, but the coil has a specific resistance measured across it. Check it against spec (hopefully someone with a manual handy can quickly answer to what the spec is) If it measures OK, run the bike, get it warmed up and measure it while its heated. Sometimes issues don't show up when at ambient temps.

Have you done a quick spark test by holding against the cylinder? Does the spark look healthy?

Let's get the dirty air filter and spark testing out of the way so we can start eliminating things...

Please advise

[JAWS]

That's most perplexing. Were you using VP U4e or VP U4.1? Either way there isn't that much difference in the octane to make you machine run so drastically lean vs the pump gas. VP U4.1 is 95 octand and VP U4e is 93. A lot of pump premium is 92-93. Granted the additives are much different and octane isn't the whole story.

How is the idle when the plug is fresh? Does the power come on naturally when you give it throttle. Does it settle back down normally when you let off? Any popping, etc? Shooting flames from the exhaust?

Try cleaning the filter first. Have you checked your main and pilot jets to see that they are seated properly? If not, pull the bowl plug and check that.

On the ignition coil, the primary coil resistance is 0.1-0.3 ohms tested when the engine is cold.
Joe

[TTT122]

Thanks for the insight guys, I appreciate your time.

We're going to pull the filter and start over with that today. We're also pulling the carb apart, and checking the choke mechanism.

As for the fuel, I am not sure which version of U-4, but I do know from my '06 CRF 250 that was built by Tom Morgan (at White Brothers), running the U-4 does require richer jetting. The is due to it being oxygenated, not due to any extra octane.

The bike idles fine, and starts right up, with a new plug. However, it almost immediately starts to stutter and fall right off the bottom, and gets worse as I continue to ride. After five minutes or so, the thing won't hardly run under any situation.

It does not seem to backfire when I cut the throttle, like it did with the lean condition running the U-4. Under that scenario, it was popping bad under high speeds and when I cut the throttle.

How do you go about checking the coil? We have a service manual, should it be in there?

[JAWS]

Yes it's in the Service Manual, but not the Owners Manual. I also recommend the Clymers Manual. If you don't have the info I can scan it and send it to you. It's better if you have the manual, though.

Good luck and let us know what you find.

Joe

[124]

It's in the service manual.
With an ohmmeter, measure the resistance across the cap.

[TTT122]

We've never checked a coil before, do you check the resistance from the coil to the spark plug boot?

[JAWS]

You have to disconnect the primary electrical connector and pull the spark plug cap off the plug. Connect your ohmmeter to the primary terminal and the other lead to the coil ground. You should get a reading between the numbers that I gave you above. If it isn't then you have to replace it. If you are in doubt, you can remove the coil and take it to a good Honda dealer and have it tested. I suggest that you call to make sure they can test it before going there.

You should also check the secondary coil resistance while you are at it. Leave the one lead connected to the coils primary terminal and put the other lead into the spark plug cap, making sure that you are touching the metal portion. The reading that you should get there is:9-16k ohms.

Be sure to use the appropriate range on your meter.

Joe