Classic Superbikes for sale
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Taming the big Kat

09/02/2015

Higher throttle openings were fine, but slow running was very poor. The engine only seemed to want to run on three cylinders. We checked the compression, ignition etc. but eventually decided fuelling was the culprit. This 1000cc bike has slide carburettors as opposed to the CV carbs on the more common 1100cc models. The carbs were removed and stripped, cleaned in an ultrasonic tank, reassembled, and refitted (even though we knew the previous owner had recently had this done himself). All to no avail, with No 1 cylinder still refusing to run on idle. All sorts of other checks were made before the carbs were removed and stripped again. This time the blanking plugs were carefully drilled out so that passages within the carb bodies could be verified as clear. New bungs were made and pressed in and the reassembled carbs refitted. No change.  The carbs were removed again and this time, absolutely everything that could be swapped across from No 1 carb to No 4 carb was swapped. This time, after reassembly we all gathered round and…eureka…the problem had moved to No 4. This proved that the carb body was ok. We then moved one piece back at a time: enriching circuit plungers, main jet, emulsion jet, pilot jet, float etc., removing the carbs each time until we swapped back the throttle slide/needle assembly. The fault moved back to No 1. I removed the carbs again and set them face down on the bench and suddenly noticed the needle in No 1 was a slightly different colour! At some point a spurious needle had been fitted, presumably when the original had been lost or damaged. CSB had a needle made using one of the ‘good’ ones as a pattern and after a little fine tuning /fettling, we at last had our idle back as it should be.  We hope the new owner is as pleased with it as we are.