KATANAMANGLER Posted November 6, 2016 Share Posted November 6, 2016 Right chaps, I need the power of the OSS brain. The story goes that I bought a very low milage RF900 (7000 miles) but the carbs had been sat with bad fuel in them for 10 years and they needed a complete rebuild. the jets were all badly corroded. I replaced the worst ones and every o ring and seal was replaced and the carbs were ultrasonically cleaned. Thee bike now starts and runs reasonably well. There was no wear on the emulsion tubes and needles. Carb rubber o rings were replaced too and there are no air leaks.Mixture screws set to spec. The problem I have not reseolved is that number 1 and number 3 cylinders foul the plugs. The plugs are very sooty the bike smells very rich at tick over too. At iddle it lopes a little like a cylinder is missing and cutting back in. All four cylinders give the same psi reading on a compression test of 150 psi. The the valve clearances are all within in spec. I have swapped out the coils,leads and caps for spares from a gsxr but the problem persists. I have also fitted an ignition advanced ( 4 degrees) and run it with the standard ignition trigger but it makes no difference. I haven't tried another cdi yet. So that's the story what suggestions do you have? Quote Link to comment
Gammaboy Posted November 6, 2016 Share Posted November 6, 2016 Has some dickhead snapped the end of the idle screws off in the carbs? Quote Link to comment
KATANAMANGLER Posted November 6, 2016 Author Share Posted November 6, 2016 No they're perfect. I have another RF900 owner that's going to pop the carbs on his bike and see if it does the same. i know this is an unusual diagnostic approach but It's better than diagnosing with my wallet. Quote Link to comment
Dezza Posted November 7, 2016 Share Posted November 7, 2016 Sounds like a really sensible diagnostic approach to me. If his bike starts acting up when your carbs are on it then you know something is still up with your carbs. In my experience ultrasonic cleaning of carbs is not the cure-all panacea it is often made out to be by some. You still may have a blockage somewhere. I split my carbs to their absolute basics and soaked each of the metal bits in a mixture of cellulose thinners and acetone for 2 days, then ultrasonically cleaned them. They have to go into a container with a lid on or the solution evaporates quickly. It will kill anything plastic or rubber so you have to be careful not to accidentally place anything non-metal in. I was amazed at all the shit that came out. Also, if your carbs are painted, they won't be after soaking. Quote Link to comment
jacktar01 Posted November 7, 2016 Share Posted November 7, 2016 Another issue with ultrasonic cleaning is some people do not use the correct carb ultrasonic cleaning solution, the difference is massive when it comes to the cleaned product Quote Link to comment
Jaydee Posted November 7, 2016 Share Posted November 7, 2016 36 minutes ago, jacktar01 said: Another issue with ultrasonic cleaning is some people do not use the correct carb ultrasonic cleaning solution, the difference is massive when it comes to the cleaned product Sometimes it's the tank itself. Not high enough wattage or not enough transducers. The KHz matters too. Usually most tanks are 40KHz which produce smaller bubbles for cleaning action. 25KHZ produces bigger bubbles just not as many but is used in industrial heavy duty cleaning. 1 Quote Link to comment
KATANAMANGLER Posted March 6, 2017 Author Share Posted March 6, 2017 Well, I like to think I know my way around carbs and I was sure I had stripped cleaned and rebuilt these RF carbs correctly. To test that I sent them to someone who had a couple of RFs and could test run them on a known good runner. The verdict was that they were perfect. That told me that my problem was not the carbs. Closer inspection of the plugs after running it for a week revealed heavy oil deposits. Compression tests and leak down test conluded the the top end wasn't sealing completley. So the engine came out and went down to @YoshiJohnny for a top end inspection and refresh. The rings were good, the bores were good ( a little glazed) but the valve stem oil seals were as hard as a whores heart and had been passing a fair amount of oil into the combustion chamber. A clean up and new seals by uncle John and the engine was ready to be refitted.I chucked a 4 degree advancer in it for good measure. Test runs this week confirm that the bike is now running as it should. 10 years on its side stand doing nothing had taken its toll on this bike despite the mere 7500 miles it had done. If it hadn't been rescued by OSS it might have been a goner. Its a little modern for my usual tastes but having hooned it around this weekend I can say its a thoroughly capable and enjoyable machine. A long road for a short cut but all is well that ends well. 3 Quote Link to comment
Guest YoshiJohnny Posted March 6, 2017 Share Posted March 6, 2017 They were and still are a really underrated bike... so glad it's running OK and hopefully now it will stop making you frown lol... They are allowed on the CBT trackdays and Nolan hustles his round proper quick Quote Link to comment
KATANAMANGLER Posted March 7, 2017 Author Share Posted March 7, 2017 I now have a choice of the Kat, the RF or the slabby ( if I get it finished) when I think of which one is expendable the RF scores best Quote Link to comment
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