R1000 thanks for your input. Very helpful and all the items you mention are being looked at (and rechecked). At this stage the good money is on the ignition control module malfunctioning when more than half throttle is used. The boys have the 2nd hand one and will plug it in next weekend, when I can get the bike to them (their workshop is around 30 mins away and there's the matter of my own work and family to keep me occupied until then!). It that's not it, then it's back tot he drawing board. Carb needles/diaphrams have checked out okay, but still haven't pulled the carbs apart, as throttles are opening fully, and there's no missing and bike idles and responds to throttle as it should under no load. Plug colour is pretty much spot on as well. It may be something in the vacuum system, but we'll see how the ignition thing works out. I've got a wet winter ahead to sort this out in time for summer!!

 

Tried the replacement IC Module yesterday with no success so back to drawing board. The good news is that ignition and valve timing spot on, so likely culprit is fuel. Stripped carbs off yesterday and re-checked diaphragms, main jets etc. This time I cleaned with CRC Carb Clean, using a tube and the aerosol's pressure to spray into jets etc. Everything was clean inside, but it was worth a try. When assembling diaphragms I noticed that thesteel diaphragm coverscould be installed in two ways. One was with the diaphragm and slider/needle full down into the jet (which was the way they were assembled last time I checked. The second method was to hold the slider up with the needle just located into the jet and the rubber diaphragm stading up like a tent. The second way allowed the diaphragm to locate correctly tino the channeling on the car body and the cover to sit correctly. I tried one using the second method, and found that the slider/needle made an entirely different sound when manually lifted and dropped, caompared with the first method. Nothing to lose, so I assembled all the carbs the second way, and re-fitted them to the bike. Took her for a spin this morning and hey presto, we have lift off!!! So, whether it was the CRC Carb Cleaner or the diaphraghm installation, it worked and I can now get on with replacing the chain/sprockets and replacing fork oil knowing that at least I have a full power CBR to play with.

Thanks for all the advice guys.

 

Congratulations. If nothing else you now know everything else on the bike is okay, and your experience has educated a few of us out here. Thanks.