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Hi, have an old GPZ900R, old style carbs.
Have done a bit of work and generally all good. But, a full tank of petrol should give me 140-150miles, before turning the fuel tap to reserve. However, it's going to reserve on 110 miles, normal riding.
It's idling beautifully, pulling v smoothly through the range, no lumpiness of grumbling. No signs of smoke, but can sometimes smell slightly petrol-y when stopped and switched off after a run.
The fuel gauge sender is next on my list to fix. The tank has been cleaned and resealed from rust.
Any clues as to what I should look at?
The float chamber valves may have dirt stuck in the carbs causing over fuelling when running and overflow when stopped?
Check the fuel tap itself? It went on my kwaker gt 550 and would slightly leak.
Very nice bike!
Awesome bike. Can't really help sorry.
I think the fuel tap on these was vacuum operated, i.e. should shut when the engine's off. If that's knackered and allowing fuel into a (leaky) carb...
Are you running E10 or E05 fuel?
Thanks all ... I too thought it was over-fueling or leaking, but when it's standing and cold, there's no smell of petrol nor any damp patches or signs of leaks. The smell when stopped after a run is pretty slight, and maybe more in my head coming back to the older carbs/engine!
Running the cheaper standard unleaded ... and must say, the engine's running beautifully, v v clean and steady idle. If I'm getting a good idle etc, does that suggest the carbs are clear of blockages? Previously, the bike had been stood for a good while so I stripped the carbs down and thoroughly cleaned (not ultrasonic) and also gave the tank a really good clean out. V pleased with the smoothness of the engine now!
Will have a nosey at the fuel tap, could be a likely culprit ...
Fabulous bike - a revelation when it first appeared. Would be my contender for greatest bike in history without question!
+1 for leaky float needle valves, especially if you have had the carbs apart. You don't see a puddle because the vacuum fuel tap shuts the petrol off when stopped.
You may see a few drops of petrol from the carb overflow tubes if you leave it idling for a while.
If there's been rust in the tank, some will probably have found its way down to the carbs where the big bits tend to get stuck in the float valve seats, preventing the valve seating properly. If you take the float valves out, you'll probably find some rust flakes behind them if this is the case.
Very nice bike! 🙂
Cool bikes of their time. I used to own one, but I'm not sure it's a 'greatest bike in history' contender - I'd say the original FireBlade, the RC30, maybe the GSXR750 and others are maybe more great though it's all subjective I guess. The RC30 in particular was astonishing, but the first FireBlade was a proper game-changer too.
Anyway, along with all the fuel system/carb stuff, make sure the air filter's in good nick, which is really obvious I know.
The Gpz900 was a massive leap forward in affordable tech and capability, the world’s first 16-valve liquid-cooled four-cylinder motorcycle engine. Fastest production bike in its day and won the tt just after being launched, I think it is pretty much up there for GOAT
I run e5 on All my bikes but especially the carburated ones as ethanol eats the seals.
Go back to about 1974, take the 'GP' bit off your GPZ900, and there's your greatest ever bike. 😊👍
Mine was anyway.
while you’ve got the carbs off, check needles/tubes for wear. Dare say you’d feel it as poor throttle response but if riding it gently you might not.
also, plugs might be due a change.
awesome bike. the GPZ 9 got me into bikes after a lad who worked at Lakeside YMCA gave me a backie around Windermere on his. Riding a ZZR 14 now.
Carbs comments above are a place to look - in addition some other thoughts
Is this issue occuring riding in the winter cool days - these carbs did suffer from icing issues and later models such as ZX1000b1 and 1000RX has carb heaters fitted which was a loop of warm water from the cooling system. This would manifest itself in engine starting to run rougher after a number of miles and needing to use more throttle on accelerations and smelling of fuel when stopping.
Also pull out your plugs and see what mixture is like - if black and sooty check your air filter, air filters on these can look quite clean but still require changing - also check exhaust baffle is running clear - see you have an aftermarket on - this can screw up the mixture and make the bike run rich or lean.
I would also get the carb balance checked out with vacuum gauges - if they are out of sync it will still pull strong but wont be efficient
hope that helps
Looks in better nick than the one I had. However red ones were/are faster. No idea about fuelling problem. Seems a bit strange. I'd try an owners club site to see if they have any ideas.
Thanks all, some good pointers. I agree as well that red is faster, but Mrs A and I toured New Zealand on one of these 25yrs ago, so it's a bit of nostalgia creeping in!
Had the tank off yesterday and possibly the pipe from fuel tap to filter was a bit battered and saggy. So replaced that, and will see if that's a quick, easy fix.
Also, what thoughts on Redex? Getting the carbs out means I'll have badly scraped hands again so interested in a short cut if there is one!