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SXP

Pinging/Knocking WR400

11 posts in this topic

My 99 WR400 with about 6000 miles on it has slowly developed a bad case of pinging under acceleration, especially in 5th gear. I always use premium gas (91 octane) and keep the valves in spec. I have tried different brands of gas and it keeps doing it. What could be the possible causes and fixes? Please don't suggest using race gas. Thanks.

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I wonder if the accelerator pump on the carb could be worn causing a lean condition under acceleration.

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Not sure if lean causes pinging but to follow what willy said. Check the air boot very carefully. A leak there will cause a lean condition.

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Sounds lean to me as well. What does the spark plug look like? Would not run like this too long, or you will be buying a new piston soon.

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The bikes run leaner in the winter.

My Dr650 pinged like crazy in the cold before I rejetted.

Carbon build up in the motor can cause this also.

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Are you sure its not chain slap ? i'd be looking there first, chain slap from a loose chain on the yammies can sound very similar to pinging at times...

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The fact that it happens in Fifth gear makes me think that it is chain slap. At least my bike does it more when I'm lugging it in a high gear.

First of all, I would check that your chain tension is within spec. As it stretches, you will hear more and more slap.

Bergermeister

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The fact that it happens in Fifth gear makes me think that it is chain slap. At least my bike does it more when I'm lugging it in a high gear.

First of all, I would check that your chain tension is within spec. As it stretches, you will hear more and more slap.

Bergermeister

A lean bike will also tend to ping more underload in high gear

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Agreed, a lean bike can also be the cause for pinging.

What temperature are you riding in. If it is pinging, it should be more noticeable when the bike is really hot. Let the bike idle for a while and then test it. Try and determine if it is at all temperature dependent.

Before you go rejetting (richening) the mixture, I'd be more inclined to start with the simple stuff... check your chain tension first!

Bergermeister

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Blue Beast and Bergermeister - You guys were dead on. My chain is so unevenly stretched that it should have been junked a long time ago - it's also done a number on the rear sprocket and the inside of the main frame spar. Anyway, I first tightened the chain and found the knocking greatly reduced - about 90% less - the residual knocking was probably because of the uneven lengths of chain. I then changed the chain and sprockets and......SILENCE! It's almost freaky how similar to engine pinging the noise was - so much so that when you guys first suggested checking the chain I pretty much dismissed that as a cause.

THANK YOU GUYS!

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SXP,

I'm really happy to hear you fixed the problem. Your right, the slapping sound does sound a lot like pinging.

While we're on the topic of chains, here's a few things I've learned from my mistakes:

Give that axle nut a really good tightening. Once I tightened mine a little below the specified torque (125 Nm) and the wheel shifted slightly after a few rides - made a nice mess of my sprocket also.

As for chain tension, I have found that setting the tension on the looser end of the tolerance (which from memory is between 48 - 58mm) prevents the chain from stretching as fast. I set mine to about 50mm and the chain just doesn't stretch a bit. As soon as you go higher it seems to put far increased strain on the chain - causing faster stretching.

Anyway mate, thanks for letting us know how you got on!

Happy riding!

Bergermeister

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