Carb question - 2003 Triumph Bonneville

Richard Tool

Richard Tool

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Need some advice please - helping a buddy out with his 2005 Triumph Bonnie.
Twin Keihin CVK carbs . The carbs are joined together with bars and a balance or fuel pipe at the top by the diaphragms. This pipe has a tee in it which feeds an overflow tube . Fuel runs out of the overflow tube when the fuel is turned on
before starting but does not when running. After shutdown fuel again runs out .
Am I looking for unseated float valve and/or sinking float ? I’ve been through the Haynes manual for this bike with no results.
Previous owner had bike gone through by a dealer who had it a long time .
Seems some of the screws for float bowls are seriously buggered. Hoping to not have to remove carbs but screw issue may dictate that I do .
Thanks in advance for any help .
RT
 
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I have a Keihin CVK carb on my KLF300, the overflow occasionally gives out a flood of fuel, tapping the carb or starting the engine stops it, the float must stick but then be released by the tapping or the engine vibration. I replaced all the screws which seems to be made from chocolate with stainless allen bolts.
 
kommando said:
I have a Keihin CVK carb on my KLF300, the overflow occasionally gives out a flood of fuel, tapping the carb or starting the engine stops it, the float must stick but then be released by the tapping or the engine vibration. I replaced all the screws which seems to be made from chocolate with stainless allen bolts.
Click to expand...
Thanks for the input kommando
 
I had to replace the float bowls on my '00 Bonnie for EXACTLY that reason.
 
You’ll definitely need to remove the carbs if you want to be confident you’ve nailed the issue.

Your symptoms are definitely a flooding float chamber. The fact it doesn’t show whilst running may well simply be because the engine is sucking fuel, thus preventing overflow. In this case it will be running rich, may even be petrol washing the bores. So it needs sorting.

Japanese carbs are terribly fussy and can sometimes suffer leaking float needle seats with dirt that Amal’s would just swallow without flinching! Dirt in the tank, degrading fuel lines, rusty tank, can all casue debri, so well worth looking at these and the in line filtration.

As well as dirt, the normal things to check are float needle tip condition, float valve seat condition, float not punctured, float not free / sticking somehow. Also, some Japanese carbs rely on an O ring to seal the float valve seat housing into the carb body (we’re not used to this cos they’re pressed in with Amal’s). If this O ring perishes then fuel will bypass the float needle, flooding the chamber.

As Kommando says, Japanese carb manufacturers seem to have developed a special steel for their screws which is slightly softer than some chocolate. Then they use cross heads instead of Allen heads. Its almost as if they want you to fail… and buy new carbs…! With the carbs off, and on the bench, an impact driver should get them moving, but they’ll need replacing.
 
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Fast Eddie said:
You’ll definitely need to remove the carbs if you want to be confident you’ve nailed the issue.

Your symptoms are definitely a flooding float chamber. The fact it doesn’t show whilst running may well simply be because the engine is sucking fuel, thus preventing overflow. In this case it will be running rich, may even be petrol washing the bores. So it needs sorting.

Japanese carbs are terribly fussy and can sometimes suffer leaking float needle seats with dirt that Amal’s would just swallow without flinching! Dirt in the tank, degrading fuel lines, rusty tank, can all casue debri, so well worth looking at these and the in line filtration.

As well as dirt, the normal things to check are float needle tip condition, float valve seat condition, float not punctured, float not free / sticking somehow. Also, some Japanese carbs rely on an O ring to seal the float valve seat housing into the carb body (we’re not used to this cos they’re pressed in with Amal’s). If this O ring perishes then fuel will bypass the float needle, flooding the chamber.

As Kommando says, Japanese carb manufacturers seem to have developed a special steel for their screws which is slightly softer than some chocolate. Then they use cross heads instead of Allen heads. Its almost as if they want you to fail… and buy new carbs…! With the carbs off, and on the bench, an impact driver should get them moving, but they’ll need replacing.
Click to expand...
Thanks Nigel - I got lucky and draining the float bowls fixed the problem - at least for now .
 
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