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Sort of surging and holding back at the same time...

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OneWheelDrive
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Sort of surging and holding back at the same time...

Post by OneWheelDrive on Tue 09 Jun 2015, 9:45 pm

Hello,


  at full throttle, accelerating, at about 8/9000 rpm, my bike feels like it's holding back and surging forward at the same time - a bit like if you had an oval rear sprocket (which I haven't!)...I can hear it in the engine note, too.  I don't know if it's related, but as I came down through the gears to go through the gate at work this morning, the exhaust was popping and banging, too - it's never done that before.


  Has anybody got any ideas what's going on?  I'm using a standard air filter and the carbs are standard - it never used to do this Sad


Any suggestions gratefully received Smile
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wornsprokets
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Re: Sort of surging and holding back at the same time...

Post by wornsprokets on Wed 10 Jun 2015, 12:37 pm

Sounds like dirty carbs say they need a clean, have u changed exhaust for new one?
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eternally_troubled
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Re: Sort of surging and holding back at the same time...

Post by eternally_troubled on Wed 10 Jun 2015, 12:40 pm

Well, from your picture I guess you have the standard exhaust. Mine only started popping (etc) when I had got a rust hole in it, so I would suggest you looked for one of them.

My FUEL replacement can sounds rather better (generally) but also pops on the over-run.

Also worth checking that your fuel tank breather isn't blocked - this can cause a vacuum to be created in the fuel tank which doesn't help the fuel coming out! You can test for this by opening the fuel cap after a fast ride and see if there is any hissing noise as the air sneaks back in (there shouldn't be).

You normally see this problem after a few minutes on the motorway - it can just cut out! If you are unlucky by the time you have coasted to a stop enough air has got back into the tank that it all works again, so you are stumped as to what the problem was.
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OneWheelDrive
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Re: Sort of surging and holding back at the same time...

Post by OneWheelDrive on Wed 10 Jun 2015, 4:57 pm

Thanks for all of that - I'll check the whole hissing tank thing when I get home.

I *do* have a standard exhaust (despite the cheap e-bay badge stuck to it to make it look like I've spent money on a "real" exhaust) and I had to weld up a load of holes in it when I got the bike a few years ago...I'll check none of them have re-holed, as it were...

Thanks Smile
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OneWheelDrive
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Re: Sort of surging and holding back at the same time...

Post by OneWheelDrive on Thu 11 Jun 2015, 7:26 am

Hmmm...re-holing has occured - no hiss from the tank when I opened the cap, though.

I'm going to try a new air filter and see what difference that makes...

Cheers Smile
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OneWheelDrive
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Re: Sort of surging and holding back at the same time...

Post by OneWheelDrive on Thu 11 Jun 2015, 7:34 am

I didn't see the post above about dirty carbs - sorry about that !

It could well be that - it sat with fuel in the tank all winter and I've only really put a couple of tanks through since the weather turned nice enough to dare riding again (I'm not ashamed of being a fair-weather-rider Smile ) so it may be, what the French call, "Merde de carburant".

Handily enough, I have an ultrasonic clear at work - I've never taken carburettors apart before, though - what do I need to do?

Thanks Smile
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eternally_troubled
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Re: Sort of surging and holding back at the same time...

Post by eternally_troubled on Thu 11 Jun 2015, 1:06 pm

@OneWheelDrive wrote:
Handily enough, I have an ultrasonic clear at work - I've never taken carburettors apart before, though - what do I need to do?
Thanks :)

The taking apart bit isn't too hard - you only really need to take a diaphragms out of the top and the float chambers off the bottom (the ultrasonic cleaner will do the rest). This will be easier with the right kind and size of screwdrivers, the Haynes has information.

You also might want to clean some of the inevitable grot off the outside of the carbs before dunking them...

The bit that may be more difficult is removing the carbs from the bike - this involves persuading them to pop out of the gap between the airbox and the engine. Not made easier by the usually ancient rubber bits - can be made eaiser by gentle application of heat.
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OneWheelDrive
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Re: Sort of surging and holding back at the same time...

Post by OneWheelDrive on Thu 11 Jun 2015, 4:39 pm

Thanks for your advice - sounds like a weekend of getting the tank off, looking thoughtfully at the result and stroking of beard...

Thanks Smile
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jchesshyre
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Re: Sort of surging and holding back at the same time...

Post by jchesshyre on Thu 11 Jun 2015, 5:07 pm

Maybe just before you embark on removing and dismantling the carbs you should take it for a long (150-200 miles) run with some Redex or similar in the petrol and lots of high revs. This could be worth trying first.

Also have you tried a new air filter yet?
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Revheadjay
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Re: Sort of surging and holding back at the same time...

Post by Revheadjay on Sat 13 Jun 2015, 10:25 am

Sounds similar to the problems I'm having, my bike is off to be repaired, I will let you know how it turns out.

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