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View Full Version : ZXR250a - High idle problem?


magicmonkey
28th November 2010, 13:01
well then, yet another question for you guys here!

I've got the bike back together after a top end rebuild and a new set of carbs (well, second hand ones new to the bike anyway) and I'm having a bit of trouble balancing the new carbs. firstly, if I sync the carbs up using a mercury manometer I couldn't get the engine to idle below 4k using the idle screw. When the carbs were synced I turned off the engine, reset the pilot screws to 2.5 turns out as per the manual (they were a lot further out than that previously) and started the engine. Now it'll start and run in sync but tends to cut out. If I open the pilot screws to where they seem happiest (between 4 and 9 turns) then I'm back to a high idle problem again. From there I can play with the sync to get the engine speed back down but the sync is way out (3 cylinders matching 1 is waaay off)

I've had a bit of a play around today, checked compression and spark, replaced the coils and checked all that side of things, now I'm beyond the realms of my knowledge unfortunately:facepalm:

Anyone got any ideas what could be causing this as I'm completely stumped, again!
racefactory
28th November 2010, 19:52
air leak maybe mate? secure your vacuum tube hoses and make sure they're on the inlet manifold nipples correctly, alternatively could have pin hole in some old tubing?

Do the revs fall slowly if you blip it?
magicmonkey
28th November 2010, 20:48
air leak maybe mate? secure your vacuum tube hoses and make sure they're on the inlet manifold nipples correctly, alternatively could have pin hole in some old tubing?

Do the revs fall slowly if you blip it?

Ah, I should have mentioned that as well, the revs do fall quite slow,there's some surging as well. Does that mean I'm looking at a vacuum leak then? I could always spray some ether around to test I suppose ...
magicmonkey
29th November 2010, 16:24
air leak maybe mate? secure your vacuum tube hoses and make sure they're on the inlet manifold nipples correctly, alternatively could have pin hole in some old tubing?

Do the revs fall slowly if you blip it?

Yup, that was the problem, nice one :) the leak was around the inlet manifold so I've smeared the outside of it with some gunk to test it and I'll see if I can find a new one from somewhere ...
racefactory
29th November 2010, 22:39
Nice one man, perishing rubber not sealing eh?