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andilicious

Closing Throttle Donk?

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Hi guys

My 2014 300 Racing has developed a new noise yesterday!

When I close the throttle I get a pronounced Donk knock noise. Just wondering what this can be caused by?

It was high hours bike when I got it and I'm unsure of the actual maintenance it's had in its former life.....

I'm just trying to single out the cause and parts required so I can fix it all in one go.

Cheers.

Andy

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Ok so I had to pull the top off to have a look........

7667B424-39D6-4530-8A82-35FFD9A57AEC_zps

A95D2EE6-F4DF-4877-824B-B31D3E4532DA_zps

2397BE36-2C18-4F96-919D-D2B8C77B3608_zps

1B89B066-B423-4A2F-88F6-D1790D191128_zps

CF653DD7-76D5-422C-B97C-0B84FD6501F0_zps

There doesn't appear to be much in the line of wear, slight scuffing off of the finish on the piston but nothing major.

I also can't feel any movement in the bearings so I'm at a loss. It didn't sound like pinking noise it was definitely more of a mechanical clunk to it.

Anyone see anything wrong that I'm missing?

Andy

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So difficult to say via the web. Can be something easy as a little air leak, wrong mixture, or worse.

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The pinking is just one donk not several small taps like you may get on a car . It is when you close the throttle .if the was a problem there would be untoward noises under load or tick over or when revs are coming back down and would be constant . It is an annoying sound and worrying when not sure of what it is . It maybe cured by altering timing if posSible or richerning carb up by lifting needle or going bigger on main jet but this could cause it to run rich . It maybe cure able just by using the more expensive fuel like she'll v power

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I've had this with a old 300 raga and my current 300 racing...I've been through numerous things, rejetting the carb, fuel, raising carb plunger, alsorts

 

... the cure? 

 

Decoke the head and piston!  Enjoy riding without "donk" until it carbs up again!

 

Im still not sure why but it seems to affect the 300 more than the other engine sizes...

Edited by waynerobshaw

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It did the noises if I held the throttle slightly open whilst coasting so the engine had no real load if that makes sense.

Well so far I have replaced the small end bearing and cleaned and reassembled everything.

Still does it. Made it even worse I think!

It's going to Sandifords for them to have a look now. I'm at the end of my tether!

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Yes, that what happens when the head coked...My 300 racing is doing it now and will stop as soon as I've decoked it again.

 

Read what I said above...have you decoked the head and piston?

Edited by waynerobshaw

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Yes, that what happens when the head coked...My 300 racing is doing it now and will stop as soon as I've decoked it again.

 

Read what I said above...have you decoked the head and piston?

Looking at the picture there is hardly any carbon on the piston!

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Modern bikes do run hot especially the 300's, The pistons are large compared to the cast cylinder and have thin walls that heat up, The cooling system is only just capable of stopping them boiling over, The GG and Sherco are the worst culprits for running hot and knocking.

 

It seems to be worse with the Keihin carbs as standard setup cause them to run lean at around 1/4 throttle to keep them running clean. The Keihin is a difficult carb to keep running sweet. Even some of the experienced guys on carbs can't get one working right.

 

I used to run a 300 with a high comp head and boyesens with the Dellorto carb and it never knocked once even in summer, being ridden hard.

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My old JT95 (327cc) used to do this big time. I made a 3 mm head gasket out of ali (bit of a bugger machining the O ring grooves) and this drop in compression worked brilliantly. IT also smoothed it out when accelerating off the bottom. Try two base gaskets, or make a 2mm copper one. Then you wont have to keep on cleaning the head and piston.

I also run 98+ octaine which helps.

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