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jonny68

Joined:

Mar 09

Posts: 768

jonny68 says:

Help please - CBR125 problem

Don't know if anyone can help with a sick CBR.

Started the little 125 up today after being parked up for a month. Bit of choke and hit the starter, the bike started ok but then began to die as though the fuel had been shut off. I pushed the choke in completely but the engine died.

I hit the started again and turned the engine over but it was lifeless and as the engine was cranked I noticed fuel in a steady slow stream comming from the vent pipe under the bike. Fuel only came from the vent pipe when the engine was cranked.

Anyone have any ideas what may be a miss.

Cheers

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  • Posted 3 years ago (13 May 2012 18:49)

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MakemRider

Joined:

Jul 11

Posts: 244

MakemRider says:

Vent Pipe?

Is this from the carb? If so most likely problem is the fuel in the card evaporated & the float dropped to the bottom. Due to standing a while it may have 'stuck' leaving the jet open. When you tried to satrt fuel would have been pumped in & the bike started but as fuel wasn't shut off it flooded the engine, stalling it. Excess fuel would then drain out of the overflow.

Two things to try,

1: tap the float chamber on top & side, it may release float.

2: Best option is to strip carb & clean the float & neddle valve & reassemble.

If 2: not done it could happen again.

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jonny68

Joined:

Mar 09

Posts: 768

jonny68 says:

MakemRider

Thanks for the reply.

I suspected the float may have stuck, I gave the float chamber a few hard knocks with the butt of a screwdriver but had no luck. Is it normal for the fuel to evapourate from the float chamber after three weeks as this has never been a problem before or is there also an underlying problem with the seals ?

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MakemRider

Joined:

Jul 11

Posts: 244

MakemRider says:

AFAIK

there are no seals that would allow fuel to leak out. There's not much fuel in the chamber and it could happen. I have had similar with cars (in the days when all cars had carbs).

It could have happened laods of times before but you would not notice if the float hadn't stuck before.

After you 'wellied' it did the fuel still leak?

If not have you dried the plug, remove, dry with cloth, warm on cooker ring or blow torch (warm not melt :biggrin:), refit & start ASAP.

If it did leak clean float pin & neddle jet. Dry plug as above & try to start.

PS a metallic knock is butter than the dull knock that a screwdriver handle delivers. Don't use a 7lb mel hammer though.:laugh:

[This Reply has been modified by the Author]

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jaffa90

Joined:

Mar 09

Posts: 8892

jaffa90 says:

overflow

If the bike started ok after a few weeks and then the petrol started to flow down the overflow pipe this means the  needle valve is not shutting the petrol off.

The carb and fuel pipe/tap diaphragm  will have to be cleaned and checked (fuel shut off) also the petrol tank will have to be checked for crap.

If possible fit an inline fuel filter between tank and carb.

[This Reply has been modified by the Author]

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jonny68

Joined:

Mar 09

Posts: 768

jonny68 says:

Sick CBR

I took the plug out and dried it off thoroughly. I managed to flatten the battery so its been on charge all night.

I will have another look at it tonight after work but like you say I think I will need to take the carb off, if The floats will not free from external persuadence. It sound like the carb could do with an overhaul anyway even if just for piece of mind .

So to summerise its either the float has stuck or the needle valve has jammed. Either way the internals are cruddy and it will need cleaning up.

Thanks again for your help

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MakemRider

Joined:

Jul 11

Posts: 244

MakemRider says:

One more thing to check

It's posible (but unlikely) that the float has a hole in it and is full of fuel so won't float. If it's not see through then give it a shake & listen for fuel inside. Submerge in wam water & watch for bubbles to rise that would show if there is a hole.

As I say posible but unlikely but if you have the carb stripped an eatra few mins to check isn't time wasted in my book.

 

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babyrocket

Joined:

Aug 11

Posts: 3732

babyrocket says:

like has been mentioned

give the carb body a sharp rapwith a screw driver handle, and open the little brass screw on the side of the body with the fuel switched on let it run for a few seconds then shut the screw up tight, job done. and yes its the needle valve sticking this unleaded petrol is notorious for evoporating and leaving rather large flaky deposits in the float bowl.

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jonny68

Joined:

Mar 09

Posts: 768

jonny68 says:

sick CBR

Mnaged to get the bike started after tapping the carb. but the bike will not idle properly now it revs at about 5000rpm, putting pressure on the throttle return on the carb reduces the revs but then on blipping the throttle its back at 5000rpm idle. I think the carb will have to come off ! 

[This Reply has been modified by the Author]

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