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Hi Ian,
a very educational posting there; not easy to understand the pump
adjustments in their entirety though; it looks as though there are 4
adjustments:
1. fuel metering screw on back of pump
2. "smoke adjuster" on top of pump under cap
3. diaphragm
4. starwheel
I think I understand that the fuel metering screw is a 'global' adjustment,
so alters the amount of fuel at all revs;
that the 'smoke adjuster' is similar? Although how do they relate? I had
understood that smoke was mainly a sign of unburnt fuel [overfueling];
that the diaphragm/starwheel alter the response curve / sensitivity of the
fuel delivery to higher revs [+ turbo in a turbo engine, I hope the NA pump
is similar in that respect], although how does diaphragm adjustment relate
to starwheel adjustment?
On my NAD, I'm seeing heaps of black smoke at startup, when even mildly
labouring at low revs, when putting on a bit more power at high revs [at
altitude particularly]. The engine doesn't seem as though it's "adjusted for
power" although perhaps a 65hp engine wouldn't! My priority is keeping the
neighbours happy [reducing the smoke] although fuel economy would be nice.
cheers
Mark
"m0bcg" <almacottage@btopenworld.com> wrote in message
news:1123182916.168555.291560@f14g2000cwb.googlegroups.com...
> if you find the power is very high but you have lots of black smoke
> from exhaust at all ranges , undo the fuel metering screw on rear of
> pump and go out 1/4 turn at a time until smoke dissappears .
> youll have to strike balance between power and smoke and so it may take
> a few attempts to get satisfactory .
> this screw is on rear of pum near the injector pipe unions , it has a
> 13mm locknut and a screwthread extending out about 25mm , there is
> screwdriver slot in end of thread , you hold locknut loose with spanner
> and then unscrew or screw the thread in or out as desired .
> IN for more fuel, OUT for less .
> the "smoke adjuster" is on top of pump housing,there is a small [gold]
> blanking cap [15mm dia] on top of casting which has the 4 screws in ,
> pry cap out with screwdriver and youll see 13mm locknut with a 8mm TORX
> grub screw , this screw is screwed in for more fuel and out for less ,
> locknut may be loctited and so might need a bit of effort to undo .
> inside pump, under top casting , ie the housing on top of pump which
> has 4 screws holding it down , is a diaphragm and shaft and a starwheel
> adjuster which alters fuel delivery rates .
> the metal plate holding rubber diaphragm has a dot mark on it and the
> diaphragm can be rotated to change fuel metering rates , this will be
> pointing somewhere between 12 oclock [to rocker cover] and 6 oclock
> [towards wing ] , the leanest position is towards rocker cover and
> richest towards wing .
> just take it that youll position it somewhere from 12 oclock to 6
> oclock , it does not screw in and out but rotates around a 360deg axis
> .
> you can pull the diaphragm assembly out by hand , in one piece with
> rubber and shaft attatched .
> on shaft youll note a tapered and eccentric shape of shaft , this
> rests against a pin down in the pump itself and alters fuel rates
> according to position the taper or eccentric is in .
> the turbo boost pressure is applied upon diaphragm via pipe on side of
> top housing and thus pushes shaft down using the diaphragm , allowing
> pin in pump to come in and allow more fuel thru as revs and boost
> pressure increase etc .
> under diaphragm youll see large spring , this is just placed in there
> and can be removed/reinstalled easily .
> under spring youll see a starwheel adjuster , this has a click stop
> adjustment and if you pry the lock spring using screwdriver you can
> rotate the starwheel .
> to lessen spring pressure effect of starwheel you will screw the
> starwheel in clockwise , but only about 1/2 turn at a time and noting
> smoke from exhaust [under load] after adjustment .
> to lessen spring effect you undo the starwheel .
> this starwheel alters the spring pressure against the diaphragm and
> alters where the turbo boost is allowed to move the diaphragm downwards
> to increase fuel flow .
> basically only minor adjustment of starwheel should need to be made ,
> if any adjustment .
> there is a white nylon spacer on the metering shaft and dont forget to
> make sure it is still fitted when refitting metering shaft/diaphragm
> and spring assembly , as it stops length of travel of metering shaft .
> the main adjustment that makes most difference is the full load
> adjustment on rear of pump , if unscrewed too far youll note lack of
> pull when in top gear at low [25mph ] speed when on flat road .
> hope that is easy enough to understand.
> ive been adjusting my pump for maximum economy , so all my adjustments
> have been in reverse .
> previous owner screwed everything IN , yes it went like stink but i
> only got 23mpg locally and lees on motorway driving .
> cheers , ian .
