Anything and everything GT6.

Apologies for the length of this post but I'm hoping someone can help me with the problem I'm having with my carbs, CD150s on a Mk1.

They had been repeatedly flooding, to the point of fuel coming out the air filters, and occasionally through the gasket between the float chamber and the carb body.

Sticking needle valves seemed to be the most likely culprit (the floats are not holed), so I replaced the needle valves along with the gaskets.

I'm still getting the same problem though, and I think it is the float level. Although I didn't invert the carbs to check the level, what I did was use a straight edge to raise the floats to simulate fuel level until the needle valve was shut , and then measured the distance between the lowest point of the float and the carb body. It was around 19mms which, if this test has the same net effect as the inverted test, is what it should be. Could the lack of inversion be giving me a dud figure? - I can't really see how.

What if the floats were at slighly different levels? If the non-valve side float was slighly lower, could it be raising the assembly in a non-horizontal manner and not allowing the tab to close the valve at the right point? Should I bend the float assembly slighly to ensure that the needle-side float is the lower of the pair?

Presumably the float level is set to determine the fuel level relative to the holes in the bottom of the jet assembly, which are the entry point for fuel into the carb throat. If 19mm float distance gives too high a fuel level for my carbs, how high should the fuel be (visually) relative to these holes in the jet assembly to enable me to experiment with a different level with the straight edge? - should the holes be completely covered? half covered?

Any advice much appreciated.

I sorted out some carbs on a Honda bike once (same priciple) and did what you did - try a short cut rather than take carbs off. The result was petrol flooding out. I took the carbs off and did it properly i.e. carbs upside down so float can seat under its own weight and be measured as per the manual; my manual says 18 mm. Bike was fine after that.

I would also recommend giving the valve seats a thorough cleaning too - if they were stuck then it's likely they arefull of crud and this would prevent them sealing properly.

You may have done this already....

NiG

Don's got me convinced.

What's the best way to remove them whilst making the least disturbances to throttle linkages etc - undo both carbs from manifold, fuel pipes and throttle connector and remove as a oner?

According to my manual all that's needed is to unbolt from manifold and uncouple the clamping bolts on the two connecting shafts. Course the air box and fuel pipe etc all need to come off first. Don't forget that oil will run out from damper.

You might be able to blow down the fuel intake, with float closing valve off and see if its leaking that way but check the float height and the needle valve - you can lap these in, not sure what it is you use though: T cut??

Good luck

Don

Thanks all who offered advice on this, I got it sorted by removing carbs (not as tricky as I had first thought once I'd sussed best way to detach from accelerator rod linkage) and inverting them.

I wonder if I had non-standard needle valves previously? My factory parts manual shows the same ones as arrived from Burlen whereas the ones that were fitted had valves which actually had a needle type point, and the valve body, which was held in the seat by sort of wire clip, had a star shaped cross section rather than cylindrical and could be removed completely from the seat by undclipping the wire.

Section : Carburettors

Carbs flooding

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Carbs flooding

Carbs flooding

Carbs flooding

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Carbs flooding