Kwak ZX7r shy in public - hot starting issue.

[spannermonkey...]

Hi all

I have 2001 kwak zx7r. That has developed a hot start issue.
Bike is standard, really standard, no bolts ons or bells or whistles for extra bling. All carb needles, jets and settings are correct. Normal riding the bike pulls, no issues.

First time I noticed this was after a 25mile ride into the city in the rain/damp. I had sat in traffic for not long and temp crept up fast, faster than usual (thinking I was running lean after a top end rebuild) and had fan cutting in at the correct temp and the bike stalled once or twice from idle. Was stuck in a road works filter queue so no filtering . Once stalled the bike would take a few cranks to start. engine was turning just not running. It did finally start after some, tried choke on and no joy, a little throttle and no joy. just let it sit for a few moments and it would go.

After this I got to my destination and came back out after 20 mins back into the damp and wet and this time it was being really shy. Bike was cranking as I could feel engine rotation, crankcases still hot, could feel pressure waves from the exhaust. It did smell a bit fuel like, no choke or throttle. And just had to let it sit for a while and then as if no one was watching it fired up the normal way, no throttle.

So came home and adjusted the pilot air screws further out 1/4 of a turn out. Bike runs cooler as more fuel and is easier to start obviously. But when hot still has the same problem but not as drastic, now the idle gently hunts, drops to sub 1000 then picks up to 1200 ish again my pilot circuit must be really clean. So my thoughts are it electrical, so going to change the plugs, (when I did valve clearances my plugs were a little sooty before this journey, cleaned and refitted) leads resistance are affected by heat. Check the pick up coil for Ohms and the ign. coils.

The vent in the fuel cap- vents and hisses so that's free.

So going to try the above for starters. If it persists with it shy behaviour.

I will check out the float needle housing O-rings and needles out.
restore the pilots to 2.25 turns out.

Then I will look at the starter motor maybe getting old and not cranking enough. Can they be rebuilt?

Beyond that I have no idea for now. I will report back Tuesday evening with my first plan. But in the mean while if somebody else has an idea or two please share. I might be missing the obvious.

Thanks all.
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Current machines - Aprilia RS250. Kawasaki H1A 500. Past machines - Kawasaki ZX7r P6, Yamaha RD250E (the one that got away), BSA Racing bantam (revs over 10'000 sweet as), Yamaha RXS100, Suzuki GP100, Suzuki GS500K2 - best all year machine ever - come rain, sleet and snow just epic.

[Matt B]

Mileage?

How many miles since the valve clearances were last done?
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stinkwheel: He had an animated .gif of a cat performing fellatio. It's not socially acceptable. It can have real life adverse effects on other people.

[spottedtango]

Hello, it sounds to me like it could be electrical rather than fuelling.

Dampness and heat can cause electrics such as coils, HT leads to do funny things if they've became old and weathered. I would test these first.

I would also stick to one thing at a time, if you're going to adjust the carbs then leave the electrics alone and vice versa. If you make multiple changes and the problem goes away you won't know which change caused the fix.

Just curious, when were the carbs last balanced?

[Nope.]

I had the exact same issue with my ZX7R.

Turns out the fuel line was routed incorrectly from the tank to the pump and the pump the carbs. It was getting too hot and causing vapour lock. I applied extra insulation and re-routed the lines as per the manual and never had the issue again.

[Robby]

You made a reference to a top end rebuild. Has it recently had one?

If a problem crops up, look at what may have changed recently to cause the problem before suspecting anything that has been working perfectly for years.

If there is no obvious cause and nothing has been messed around with, service it before getting into fault finding. As part of the service do the recommended things for a 10 year old bike, such as flushing/changing the coolant and renewing the HT leads.

If it runs a fuel pump with points, it may need a new set of points. Low fuel flow could explain your symptoms.