YS 140 DZ going lean in -ve g maneuvers

[PENNISI Peter]

Thanks for all the tips.
 
I will try these suggestions over the weekend.
 
Peter

________________________________

From: Earl Haury [mailto:ehaury at houston.rr.com] 
Sent: Friday, 14 May 2004 05:04 AM
To: discussion at nsrca.org
Subject: Re: YS 140 DZ going lean in -ve g maneuvers


John
 
It's likely that the DZ isn't any more susceptible to air in the fuel supply
than any other engine, just that the "standard" YS pressure system is very
good at preventing those sort of problems. I've run 3 DZ's in a couple of
different airplanes with a variety of fuel systems. Generally, they all work
well and include a bladder, an open vent / foam clunk, check valved vent /
foam clunk, pipe pressure / regular clunk, combining for around 100 gal. of
fuel or so. I've settled on an open vent / foam clunk system with the vent
routed behind the tank, then forward (1/8" aluminum tubing) to exit.
 
All the various systems work well, however any configuration that doesn't
relieve expansive pressure (say, from sitting in the sun), as well as
bladder systems or a high tank, will flood the engine unless some form of
positive fuel shut-off is incorporated.
 
I've seen a couple of systems where the tank was solidly mounted for use
with an L that would result in a lean stoppage a couple of minutes into the
flight with a DZ. Our old friend - fuel foaming. These systems will
generally run OK on the ground as vibration is damped by holding it. Go back
to basics and isolate the tank from vibration, the foam clunk may reduce
this problem but not fix it.
 
If a high time DZ begins to sag on uplines as the tank nears empty it's
likely that there is wear between the upper pushrod and the pump housing.
It's simply easier to draw air from the high pressure area of the rocker
cover plenum than fuel from the tank a foot or so below the pump. These
engines will also tend to load up during sustained idle as fuel is leaking,
via the same route, into the (now) low pressure area of the rocker plenum.
Replacing the upper intake pushrod and pump housing fixes this. This is not
likely a problem with an engine not having used 50 gal. of fuel.
 
Earl

	----- Original Message ----- 
	From: Lees,John W <mailto:jlees at mwdh2o.com>  
	To: 'discussion at nsrca.org' 
	Sent: Thursday, May 13, 2004 11:33 AM
	Subject: RE: YS 140 DZ going lean in -ve g maneuvers

	 I thought DZ's were crap, had several different tanks, clunk's,
ect. Not until I went to a Bladder tank{no air in media} did the engine run
flawless. Since then it has never even hick-upped. 
	It is of my opinion that the DZ will not tolerate any air in the
fuel delivery system. --john

		-----Original Message-----
		From: PENNISI Peter
[mailto:Peter.Pennisi at publicworks.qld.gov.au]
		Sent: Wednesday, May 12, 2004 5:29 PM
		To: discussion at nsrca.org
		Subject: YS 140 DZ going lean in -ve g manoeuvres
		
		
		Hi all,
		 
		 
		My DZ has only returned from holidays in Japan were it was
repaired by YS from another cam failure.
		 
		 
		The engine is running absolutely superb except when you pull
high negative g manoeuvres like the reverse humpty bump it gets a little
lean for a few seconds put it does come good.
		 
		I have re-plumbed the model put the problem is still there. 
		 
		Running
		 
		APC 16 x 12
		OS F plug
		Tetra 20 oz tank with OS sintered(Spelling) bubble less
pickup.(Yes the expensive one)
		Hatori exhaust (698 pipe)
		Coolpower 30% heli blend
		Model is ZN-LINE Alliance.
		 
		Any suggestions
		 
		 
		Peter
		 
		 

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