Zx6r 1999 hot start issue

[BBB]

Hi,
Have a 1999 zx6r g2 carbed and struggling to start it when hot. It starts when cold with a bit of choke and runs and idles cleanly. If I stop to get fuel or for a few minutes it takes a while before it fires, starter spins freely and strongly and I got a backfire on Sunday (standard end can). Bike has done around 35k miles not sure if the valves have be done though.

I'm leaning towards it being an ignition issue, going to replace the plugs but wonder if replacing both coils would be a good idea too.

£70 for a pair of Tour Max coils so not cheap. Going to test the resistance but if it's a heat issue not sure I'll see anything on a cold bike.

Where else should I be investigating?

Thanks

Edit: carved should be carbed

[Skub]

I had a GPZ900R with the same bother,it had run all the valve clearances tight. You'll have to do a process of elimination,as this could be ignition,fuel or mechanical.

[Asian Boss]

As Skub says it could be all sorts. My instinct was electrical I would change the plug caps as well as the plugs and then see about resistance testing the coils and CDI. That's all a bit of a guess.

[Le_Fromage_Grande]

Tight valve clearances would be where I start

[BBB]

I've accepted the inevitable and booked it in to get the clearances checked and adjusted. Need to see if the plug caps can take an NGK set £37 per plug for genuine kawasaki

[Le_Fromage_Grande]

Check the clearances yourself, they're not too bad to do on a ZX6R, once you've got all the white out of the way, adjusting them is a cams out job as the shims are under the buckets, so best leave that to someone who knows what they're doing.

35000 miles sounds about right for the valve clearances to need looking at on a 600 road bike.

The plug caps have the coils in them on later ZX6Rs (possibly early ones as well, I should know, but I can't remember whether the race one I help with has a later ignition fitted or it's original)

[Taipan]

Could be an air leak and it's too lean when hot because of it and that makes them a bastard to start, with it normally spinning over quite a bit before coming into life. Always worth Checking carb rubbers for perishing on an older bike.

[BBB]

No garage so it would involve stripping the cam cover in the garden. Not a job for October, happy to leave this one to the trained professionals.
If its still an issue starting I'll start with the investigation.

Cheers

[wull]

Could be an air leak and it's too lean when hot because of it and that makes them a bastard to start, with it normally spinning over quite a bit before coming into life. Always worth Checking carb rubbers for perishing on an older bike.

I’d expect erratic idling if there was an air leak, OP states perfect idle and running even after using the choke, issue becomes apparent after stopping, switching off and trying to start again if I’m reading it correctly.

[BBB]

@Wull yep that's correct. Starts and runs fine when cold. Switch it off warm and it's a bugger to start. Runs fine once it catches when warm.

[BBB]

Just to add to my mechanical joys this week, it looks like the car may have a blown head gasket. My plans of buying a big workshop/shed may have disappeared in a puff of combusting coolant.

It's always when things look to be getting to some degree of balance.

[Skub]

Just to add to my mechanical joys this week, it looks like the car may have a blown head gasket. My plans of buying a big workshop/shed may have disappeared in a puff of combusting coolant.

It's always when things look to be getting to some degree of balance.

I hear ya. Shit happens while we make plans,but you'll get there eventually.

[BBB]

Dropped the bike off this afternoon, garage are going to check the clips and fit the plugs I've bought too.

Car is going on on Monday to be pressure tested, fingers crossed its a leaky water pump or pipe.

Edit - coils not clips

[BBB]

On a positive note no evidence of head gasket failure on the car and no leaks either, cooling system held pressure at the garage. Had the coolant changed recently so they it might have been an air lock.

[Felix]

Had a GSX750F that would happen with. Turned out to be the coils.

[BBB]

Called the garage, one inlet and one exhaust valve out, the rest were in spec. They're waiting for shims to put it back together. Fingers crossed it solves the issue. If not might look at the coils next.

[Skub]

Called the garage, one inlet and one exhaust valve out, the rest were in spec. They're waiting for shims to put it back together. Fingers crossed it solves the issue. If not might look at the coils next.

If the clearances were just out of spec,I can't see that being the cause of your issues. With mine all the inlet valves were fully tight because they had hammered themselves into the valve seats. A batch of faulty valves apparently.

It's nearly always a process of elimination,check and rule out one thing at a time. It's also good that stuff gets done that needed done.

[wull]

I can’t see it either especially when it’s only two valves that are out but you never know.

[BBB]

Picked the bike up earlier and....
... Two valves adjusted, 4 new spark plugs and fuel hose replaced. The hose that was on there looked to be 3 to 4mm so fairly restricted much wider bore fitted.

Got home left it off for a minute or so and it fired up straight away, same with leaving it of for a few seconds too. 15 minutes needed a whiff of throttle but it fired up.
Fingers crossed the fuel hose was causing the issue.

[BBB]

... And it's back.

Suspect it hadn't got properly warm the last few times. Yesterday and today it wouldn't start unless left for a few minutes. Cranking strongly and fuel smell out the exhaust so coils?

Any ideas on how to test as the bike starts fine when cold. Check for any visible damage and resistance test, sick then in the oven and check again?