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Cold air feed - too much air!!
davidimurray - 26/4/15 at 06:27 PM

Made a weird discovery with my Duratec today. Took it out last weekend and was fine at idle, fine when accelerating hard but when cruising would go wildy lean and start popping. Assumed it was settings with the new engine so richened up the mid-range and no better. Stripped carbs and cleaned all the jets, threw it back together without airbox and filter - went perfectly - too rich if anything. Re-adjusted the carbs again and all fine again. Refitted the airbox/filter and went out for a spin earlier - going lean again at cruise.

Slightly puzzled, I thought it through and the only connection I could make was the faster you were going, the worse it was regardless of engine revs. As a wild shot, tried disconnecting the cold air feed ducting I’ve put to the front of the car. Took it out for a run and was rich again! Looks like I must have accidentally “turbo’d” it and the air being forced in was making it run lean.

I’ve got the carbs just about perfect on cruise, but still a bit rich on full throttle so need some smaller carb jets( the duratec must be a bit more frugal than the Pinto!)

Anyone ever heard of this with bike carbs?

One thought I did have is that the diaphragm breathers are not connected to the airbox. Should I loop them in say they pick up the pressure inside the airbox rather than the pressure in the engine bay.

dave_424 - 26/4/15 at 06:35 PM

Diaphragm hoses will have to be connected to the airbox to keep all the pressures in the carbs correct. What bike carbs are they? I know that certain bikes like the ZX9 use ram air to try and pressurise the airbox at high speeds. Mine were very picky with running if all the tubes were not connected.

davidimurray - 26/4/15 at 07:06 PM

They are zx6r. Always been fine on the Pinto with an air filter and seem fine without the the cold air feed connected so looks like could be onto something routing the diaphragm breathers into the airbox.

wylliezx9r - 26/4/15 at 07:31 PM

quote:
Originally posted by dave_424
Diaphragm hoses will have to be connected to the airbox to keep all the pressures in the carbs correct. What bike carbs are they? I know that certain bikes like the ZX9 use ram air to try and pressurise the airbox at high speeds. Mine were very picky with running if all the tubes were not connected.


^ What he said. Was the same on my zx9r engine I assume the zx6r carbs are the same.

[Edited on 26/4/15 by wylliezx9r]

BenB - 26/4/15 at 07:36 PM

For a true ram air effect you have to be going faster than most Se7ens will go. But you will get lots of nice dense cold air which will need more fuel to keep a given afr.

davidimurray - 27/4/15 at 08:34 PM

quote:
Originally posted by BenB
For a true ram air effect you have to be going faster than most Se7ens will go. But you will get lots of nice dense cold air which will need more fuel to keep a given afr.


Never expected to get an ram air affect, and that was never my aim. Interestingly it must makes some difference though as at 30mph, light throttle afr is 14.5, at 50mph AFR is 17, anymore and it goes off the scale.