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  #1  
Old 10th September 2018, 01:56 PM
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Mr Snapped Banjo String Mr Snapped Banjo String is offline
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Biker.ie Member No. 15069 from Here n there
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Motorbike: 98 fireblade
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Default Decent two stroke mechanic

Have a vintage two stroke dirt bike... 1980 yamaha gt 80... i just cant get the bastard right... time to hand it to someone with a little more knowledge than me...
Any body know of anyone... closer to dublin south the better.. but can travel
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  #2  
Old 10th September 2018, 05:34 PM
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chopper chopper is offline
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Biker.ie Member No. 1841 from meath
53,711 posts since May 2005
My Motorcycle Pics Motorbike: jap brit and euro
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Default Re: Decent two stroke mechanic

Whats it doing on you
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  #3  
Old 10th September 2018, 05:51 PM
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Biker.ie Member No. 15069 from Here n there
3,267 posts since Mar 2009
Motorbike: 98 fireblade
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Default Re: Decent two stroke mechanic

Originally Posted by chopper
Whats it doing on you
Running lean... bogging down.... wont take full acceleration
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  #4  
Old 10th September 2018, 09:51 PM
me2 me2 is offline
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467 posts since Jul 2017
Motorbike: dublin bus
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Default Re: Decent two stroke mechanic

I know nothing about your specific bike.

On two Smokes the combustion oil is variable in delivery in keeping with acceleration, this may be achieved by a splinter on the throttle cable, one side to the carbs and the other to the oil pump. I've heard of peops premixing oil with petrol, not something I've done or recommend as a general rule.

Ya might know that oil starvation in the piston would give the other two symptoms ya mentioned, as in it could be threatening to seize up. Best of much with it.
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  #5  
Old 10th September 2018, 10:24 PM
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Biker.ie Member No. 4444 from dublin
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My Motorcycle Pics Motorbike: KTM 1290 S adventure
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Default Re: Decent two stroke mechanic

Originally Posted by Mr Snapped Banjo String
Have a vintage two stroke dirt bike... 1980 yamaha gt 80... i just cant get the bastard right... time to hand it to someone with a little more knowledge than me...
Any body know of anyone... closer to dublin south the better.. but can travel

Eddie Laycock laylaw racing. knocklyon area. They know classic two strokes. Appointment only .
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  #6  
Old 11th September 2018, 11:07 AM
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REDLINE-0 REDLINE-0 is offline
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Motorbike: SP Blade - Husky 701
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Default Re: Decent two stroke mechanic

Ger Byrne.GB motorcycles.naas-newbridge
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  #7  
Old 11th September 2018, 01:40 PM
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Biker.ie Member No. 1841 from meath
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Default Re: Decent two stroke mechanic

Originally Posted by Mr Snapped Banjo String
Running lean... bogging down.... wont take full acceleration
Have ya tried lift the needle ?
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  #8  
Old 11th September 2018, 01:53 PM
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Mr Snapped Banjo String Mr Snapped Banjo String is offline
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Biker.ie Member No. 15069 from Here n there
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Default Re: Decent two stroke mechanic

Originally Posted by chopper
Have ya tried lift the needle ?
No place on the carb to lift the needle... its preset
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  #9  
Old 11th September 2018, 01:57 PM
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chopper chopper is offline
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Biker.ie Member No. 1841 from meath
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My Motorcycle Pics Motorbike: jap brit and euro
Modifications: mud
Default Re: Decent two stroke mechanic

Originally Posted by Mr Snapped Banjo String
No place on the carb to lift the needle... its preset
Can the needle be removed and a washer put under it? Whats story with bike? Has it been rebuilt or anything ?
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  #10  
Old 11th September 2018, 08:54 PM
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Default Re: Decent two stroke mechanic

Could be intake air leak or crank seals - gives these symptoms too.
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  #11  
Old 11th September 2018, 10:20 PM
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Mr Snapped Banjo String Mr Snapped Banjo String is offline
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Biker.ie Member No. 15069 from Here n there
3,267 posts since Mar 2009
Motorbike: 98 fireblade
Modifications: Nope
Default Re: Decent two stroke mechanic

Originally Posted by Dmac
Could be intake air leak or crank seals - gives these symptoms too.
Air intake is new... the crank seal were replaced i think there may be a very slight difference in one of the seals.... how would you test the crank seals? Leak down test?
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  #12  
Old 11th September 2018, 10:45 PM
DavyH DavyH is offline
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Default Re: Decent two stroke mechanic

You need a 2 stroke specific leak down tester, why was a crank seal with a discrepancy fitted?
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  #13  
Old 11th September 2018, 10:52 PM
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Mr Snapped Banjo String Mr Snapped Banjo String is offline
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Motorbike: 98 fireblade
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Default Re: Decent two stroke mechanic

Originally Posted by DavyH
You need a 2 stroke specific leak down tester, why was a crank seal with a discrepancy fitted?
Was all that was available at the time.... i think it should be replaced with the proper seal... maybe that would be a start...
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  #14  
Old 17th September 2018, 01:10 PM
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Biker.ie Member No. 2533 from "Sunny" South East
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Default Re: Decent two stroke mechanic

You need to plug the exhaust port, then bung the inlet and add some air. it should be fairly easy to see if it's not holding air and go from there.

You could use a old inner tube and a piece of wood to plug the exhaust port -

Put the rubber sheet in first and then a close fitting plug. Something similar for the inlet - and use the tube valve to add air - with a bicycle pump. Don't use a compressor

A squirty bottle of soapy water will show up external leaks, you may be able to hear crank seal leaks from the magneto side or through the oil filler.

The dodgy seal might be ok, worth testing first.
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