i have discovered a split in the rubber boot on top of the carb where the accelerator pump shaft goes...
will this cause any problem ?
i notice more of a petrol smell when i put my foot down recently and sometime have a bit of a 'stumble' when i really go for it...

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The split in the boot won't effect carb operation. It will let gas fumes out and dirt in though.

If you are starting to get a stumble on acceleration and the accelerator pump boot is split sounds like time to rebuild the carb. The rebuild kit will have the accelerator pump boot as well as all the other parts needed to refresh the carb.

The rebuild kits don't cost much.

Thanks Gary,
My friend said it was just a dust cover so not so important which agrees with what you say....
Thing is... its only 3 years old brand new carb and done not so many miles....
I expect that its one of the chinese made ones though i bought it from my local motor factors.
I use E20 petrol here... wonder if the ethanol is degrading the rubber prematurely, ?

Ethanol won't degrade genuine Nissan/Hitachi rubber parts.

But will degrade poorer grades of rubber.