Q: Hi guys, I have a question about my beloved 1984 Kawasaki GPz 900 Ninja. Recently the bike seems to have gone off the boil, which is strange because it’s always ran perfectly, well, for a 30-year old bike that is. It’s covered only 45,000km.
When I start the bike up the whole engine sounds a bit rough, doesn’t idle correctly and splutters a bit when revved hard. I changed the plugs and fitted a new and genuine air filter but it still runs as rough as a bear’s arse, which is very annoying to say the least.
I’ve asked around at my local dealer but they’ve just filled me with horror stories from scrap it and/or sell it, to find a new engine, which isn’t helpful at all.
So I thought I’d ask you first because you seem to have a comprehensive understanding of classic motorcycles?
Tim Booth
A: First thing to do is to check the compression by doing a leak-down test. You’ll need to find someone with that sort of equipment. That will tell you if you have piston damage or problems around the valve area. If there is leakage past the valves check out the valve shims clearance, you might have a ‘tight’ one, which will make the bike feel ‘lumpy’.
Also with a bike of this age the diaphragms at the top of the carbs can become brittle and crack over time, which will certainly cause these symptoms. If they are damaged, torn or cracked replace them ASAP. You’ll find them easily on the Internet, or maybe Kawasaki still has them?
Go through these steps first and let us know how you get on?
