Stagnating/hovering idle

[spannermonkey...]

Hi all.

Just done a top end rebuild on a ZX7r and it runs good after a carb balance. I'm limited to 4000 rpm for the first 100 miles as it's rather tight. But it's the idle circuit at fault I think.

But when you pull the clutch in and let the throttle go. The revs hold at around 3000 or 2000 then slowly drop to idle. Not very crisp.
Feels like the choke is out, but checked that and it has free play in the cable and all the little pistons return back home.

It struggles to maintain idle, sometimes it works when other times it drops straight off.

It can be hesitant from idle when I throttle up, but fine when it's warmed up.

The pilot air screws are set per the book 2.25 turns out, it's completely standard with no bolt on stuff and jets are standard in the carbs, air filter is clean.

New fuel pump, fuel lines and filter.

What are people thoughts - a carb clean? done quite a few of those already, pilot air screw, o ring, washer and spring are correct.

So is it an air leak, any boby else suffered with this kind of thing.
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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.

[spannermonkey...]

Hi all

It was a massive air leak.

I removed the tank, airbox, carbs. I started from the head, I replaced the carb rubber o rings, torqued down. Then mounted the carbs. The rubbers were good and not split.

I fitted new o rings to the carb/air box adapter mount. Then as I fitted this plastic thing I noticed it was bent and had lifted off the no 4 carb face. Massive air leak. So for now I used a soft sealant to close the gap.

Took the bike for a ride and adjusted the idle screw down 2/8's of a turn and sweet, no hanging up.
____________________
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.