Author Topic: 300 sef noise under light throttle - saga continues!  (Read 494 times)

ShercoAdam

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300 sef noise under light throttle - saga continues!
« on: December 21, 2021, 01:25:34 AM »
So the list of issues with the 300 goes on. Honestly, I think I've bought a Friday bike. I've had numerous brands of 2 and 4 strokes over the years but this is by far the worst for a 66 hr well serviced 4 stroke.

Engine seems to be making a 'clacking' noise, most noticeable on light throttle. No noise on overrun or ticker, only when the throttle is slightly open and at certain revs in each gear. Noise can be quite loud, I thought it may have been cam chain noise but when the valves were check last month, the cam chain and tensioner seemed fine. Bike doesn't smoke, pulls hard and doesn't burn any oil. If you find yourself in the wrong gear and snap the throttle open and as a result load the engine up at real low revs the noise is loud for a brief moment until you build the revs!

Possible injector noise?
or ominous bottom end?

Thanks as always guys


JL4049

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Re: 300 sef noise under light throttle - saga continues!
« Reply #1 on: December 21, 2021, 12:23:25 PM »
If it isn't drive chain noise (mine sounds a bit like you describe when the chain/sprockets are about due for replacement) Have you tried higher octane fuel? The symptoms you've described sound a lot like detonation, especially where you mention snapping the throttle open at low revs.

ShercoAdam

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Re: 300 sef noise under light throttle - saga continues!
« Reply #2 on: December 21, 2021, 12:55:18 PM »
Chain and sprockets just done and its always run on super unleaded..... could be piston slap maybe?

ShercoAdam

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Re: 300 sef noise under light throttle - saga continues!
« Reply #3 on: December 22, 2021, 10:52:30 AM »
If it isn't drive chain noise (mine sounds a bit like you describe when the chain/sprockets are about due for replacement) Have you tried higher octane fuel? The symptoms you've described sound a lot like detonation, especially where you mention snapping the throttle open at low revs.

Was thinking about this more today and detonation is often a fair bit quieter than this I think - its loud, like a clacker at a football ground!

TTBadDog

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Re: 300 sef noise under light throttle - saga continues!
« Reply #4 on: December 24, 2021, 02:58:00 AM »
Can you compare it to another of the same model? Could just be the nature of the beast. Ruling that out I would suspect an anomaly in ignition timing. Have you swapped out spark plug and or checked gap? Perhaps throw some octane boost at it just for grins?  BTW many octane boosters do nothing. Only the type containing MMT actually work. The guys on the car forums that heavily SC or Turbo cars like the Lucas or Torco. Lucas should be available at places like Advanced Auto and many chain parts stores.

Whatever it is, assuming it is not just how they are, would be something that could vary from production tolerance or programming errors. Had you had any feedback from others on the board? These are the type of things we need a forum for, tough to crack everything on your own without feedback.
2022 250 SE Factory

ShercoAdam

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Re: 300 sef noise under light throttle - saga continues!
« Reply #5 on: December 24, 2021, 11:36:58 AM »
Thanks for the reply dude (on both messages), responses are slow on here so I appreciate your thoughts.

I had the valve clearances done last week and the guy commented on how clean it was inside / everything within tolerance. Since I cleaned the air filter and fitted another new plug + new tank of super unleaded, it seems to start on the button now.

Gasket replaced also so no leaks now. My recent guy reckons the valve clearances had been checked before as there was some sealant around ht rocker box, no big deal.

The noise however is still there. https://youtu.be/n19G4Ou5hzM Sounds like det on the video but its only on light throttle and especially when lugging the wrong gear. I can't find anything loose, but it genuinely sounds like a rattling heat shield does on a car only more consistent!

Not sure why it would be detonating - its got high octane fuel in it. Ignition timing maybe? How would that be checked?

HMS

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Re: 300 sef noise under light throttle - saga continues!
« Reply #6 on: January 08, 2022, 01:43:16 PM »
Chain slap
Trygve Halverson
603-491-7009
trygve@halverson-motorsports.com

TTBadDog

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Re: 300 sef noise under light throttle - saga continues!
« Reply #7 on: January 09, 2022, 06:28:57 AM »
You can quit chain slap down with proper adjustment. Also, insulate the slider with a pad or "glue" chain slider down top and bottom with a bead of silicone. This will change or reduce the noise so you can see if you are on the right track.
2022 250 SE Factory

Bloodhound

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Re: 300 sef noise under light throttle - saga continues!
« Reply #8 on: January 11, 2022, 02:04:28 PM »
Mystery solved in Thumpertalk. It was chain slap.