GPZ900 idle issue

My brother in law has just gotten his gpz going again after quite a few months of cobweb collecting. He's just replaced the inlet boots and had them synched. It's running great through the revs...

But

It idles fine at first, but after a few seconds (5 or 10) starts to chug.

Now since its running fine otherwise, and idles fine at first, we were thinking it won't be a jetting issue, rather a float height problem. Maybe filling the bowls and causing it to run rich and fouling the plugs.

I haven't heard from him yet as he was going to do a plug chop to see if that confirms the plug fouling assumption.

Anyone else have any ideas?

If it was to be the float heights what would the correct height be? Level with the bowl mating surface when the carbs are held horizontal?

If it's actually running rich, also check needles and seats. The needles sometimes don't like being dried out for ages, 'specially if they're a little worn anyway. If fuel was in the bowls and it's dried out, there's also the possiblity there's some crud holding one or two open a touch, which will result in running real rich.

If it's actually running lean until it's revved up, clean out the idle jets with carb cleaner.

if its purely a problem with the idle, then look closely at the pilot screws... and its definately worth checking the float height... sometimes theres a fuel level indicator on the side of the carb, otherwise check the service manual? definately sounds like a carby clean out might be in order... and a full service


have a look here for a guide to getting the pilot screws (and the floats, needles and mains) right: http://66.47.68.116/tech/carbtune,CV,hi ... gines.html

Hi..
I'm currently working on an early 85 GPZ900R with similar issues.

Apart from the HT lead ends being corroded and not screwed in correctly for starters! The #2 carb had a massive air leak at the manifold boot.These things are pigs to get the airbox/carbs in and out and the carb boot locations are critical..A pointer in the head side of the carb boots indicates 12 o clock.Make sure the carbs are correctly seated and tightened then do the airbox.

nb; Carby cleaner sprayed at the carb boots at idle will soon hi light an air leak..(will run smooth)

regards

Mine has the same issues with the manifolds too.
Tell me Ilseofninja, being a person with a modern and old, state of the art beasts. Whats the diferance? Would an old fart like me appriciate a new toy or would it be a waste. I love my old 900 and have avoided test riding a newbie. I would love to here the views of a side by side comparison.

To be honest '65' it relly depends on your prefered riding style I think...
ie If you do more long distance riding then the GPZ with it's lounge chair seat will have your posterior,shoulders and neck thanking you every time over a modern super sport.. If you love attacking corners and want a bike that will accelerate at an insane rate of knots , the 10 is the answer.

The modern bikes feel much more nimble given lighter weight , larger tyres , better frame/ suspension..(GPZ feels mammoth after the 10!!) and if things got nasty I'd much rather be on a newer one as they are far more forgiving if you have to ie change lines etc mid corner!!

The new zx14's look... well I reckon they look gay as christmas but maybe that's just me?? The 12's are a really nice sports cruiser..Probably more of a modern equiv' to the GPZ than a ZX10R supersport..

Engine design does not appear to have changed much between the GPZ9's and the modern bikes more they are somewhat more refined , efi etc...

As most will know it's hard to knock the GPZ donk as it was downright brutal in it's day and a cutting edge sports bike of the era...Even the 750 turbo's in the early 80's could cut 10-11 second quarters (same as a modern ZX10R!!).

I am doing a full rebuild on the GPZ including suspension overhaul , new brakes (completely stuffed!) including rotors,calipers and braided lines , all bearings etc..
The stock airbox is proving to be a pain in the proverbial particularly when trying to sort 22year old carbs !!! So I'm looking at other options ATM that will retain a ram tube , be weather/water proof and easier to service......Hmmmm????? (thinking,thinking...)

Take care over X-mas all

Thanks for that, excactly the sort of stuff I wanted to know.