Back we go again...

Got the GSX back from 'the shop' yesterday evening.

Lovely it was - nice crisp throttle response etc.

Decided in view of this to go 'the scenic way' home.

About 20 miles later, I can feel a slight misfire at lower revs, which
differed from the original problem as it had been misfiring all the
way up the rev range.

Get home, get off, get a strong waft of raw petrol up my nose, and
further investigation reveals fuel absolutely pissing out of carb 2.

*sigh*

At this rate Bonwick will be getting a free *OSM...

 

On a positive note, I reckon I've got the carburetion just about
sorted on the GN. After cleaning out the carb passageways, I had to
reset the mixture setting. Trouble is, the mixture screw, instead of
being in the side of the carb, screws down vertically, just forward of
the slide chamber. So you need to take the tank off to access it. As
carb adjustment has to be done with a hot engine, it's been a matter
of arriving home from work, whipping off seat and tank (I've got that
task down to about 45 seconds now), twiddle the mixture screw, replace
tank and seat, quick run round the block, back home, remove seat and
tank, another twiddle, repeat ad nauseam.

Anyway, got it sorted now. It definitely doesn't like cold weather,
though, and I'm wondering about carb icing. Oddly, there's a guy on an
X-reg Suzuki 400cc dirt bike on my commute, and at the lights
yesterday he was reachng down and fiddling ith the tickover screw.
"Doesn't like this weather," he muttered. "Keeps stalling..."

Anyway, a tenner a week on petrol is now my commuting cost, compared
with a tenner a day last year, so I'm happy.

 

TOG@Toil wrote:

Does it really do 85mpg? Impressed if so.

 

Nope. Checked the first tankful at 72mpg. Checked the last one at
66mpg, but that included much faffing about with carb. Twenty-eight
miles a day, so 140-odd miles a week at about a fiver a gallon.

As opposed to 80 miles a day on a much bigger bike, or in the car.

 

Wots wrong with a few feet of pipe and sit the tank on the seat to twiddle ?.
Or am I being whoooshed ?.

 

You did read the bit about a quick run round the block, didn't you?

 

Excuse me butting in but I used to have a bit of fuel tube pushed into a bit
of bigger tube wiv a cork anna hole specifically for riding round the block
wiv the tank off guvnor. For a Tame Spanner it's a rather good idea.

'Course it only works on Airheads and SOB's, cable tying a K fuel pump to my
leg proved impractical.

 

That'd work. The 400 Four, for some reason, will run for bloody
*miles* with the tank off. Balancing the carbs doesn't require a
separate fuel supply at all. I have, however, blatted a tankless bike
around only to discover when I got back that I'd lost both front tank
rubbers :-/

 

Good good.

The nice man from the AA got to the bottom of what's up with the GSX as
well.

The return feed pipe which runs from near the bottom of the main body of the
carb to the top where fuel then shuts a valve on the top rail once the
pressure has built up, has broken off.

He also said the reason it pulled through and the missing cleared on the
road at higher revs, is because the bike was drawing enough mixture to limit
the flooding, where as tickling along at lower revs was allowing the flow to
overtake demand, and that's why it was pissing out as if someone had turned
on a tap, on idle.

Net result is a completely fucked carb and Suzuki want nigh on £600 for
*one*.

So it's a good job I spotted a set of partially dismantled carbs on eBay
earlier in the week - £30 delivered is what has just been agreed, and the
nice chaps at the bike shop where the bike now sits festering have agreed a
'you've bought the bits, we'll supply the labour FOC as it was quite
possibly our fault as to why said pipe broke', arrangement.

All being well, I may get to ride the fucking thing without any more aggro
for a while once it comes back.

 

Was it pissing fuel before? If not, then they *definitely* broke it. I
imagine it's very easy to do if you (for example) try and replace the
float bowl the wrong way round. You've got to be very delicate-handed
when faffing with carbs.

 

I was assuming he was. Also, there's no pressure as such in a carb-fed
system. The float bowl just fills, the float rises, and shuts off the
fuel supply, exactly like a lavatory ballcock.

 

Indeed, it is usually possible to throw the tank and seat back on
without fixing to get the run around the block, do another twiddle, etc.
Saves a lot of spanner time if you can.

 

Yes, I was doing just that. Still an arse-ache.

 

According the nice AA chappie and the guys at the bike shop, there is
when the carbs are fed by an electric pump rather than simply gravity,
as is the case with the GSX.

Chaps in the bike shop also reckoned that when you've got a leak as
this had, the fuel pump pumps a bit harder because it thinks 'need a
higher rate as no back pressure = system not full yet'.

Maybe, maybe not.

Aye, it's that kind of principal.

 

Similar to that, aye.

 

If it's got a vacuum tap check that.

 

I suspect this is the case, but given they're jolly decent chaps
who've A: never fecked one of mine up before, and B: didn't try to get
out of fixing it, I'm of the opinion that 'shit happens', rather than
'string them up!'.

One of the reasons I put it in to be looked at this time, is because
it's an utter shit to get the carbs in and out of... and the AA guy
reckoned they may have inadvertently done the damage when trying to
prise the carbs off the inlet rubbers.

Tis a good job I love the old girl, else it would be winging its way
onto eBay by now, all the grief I've had with it.

Anyway... main thing is, all being well it should now be reliable for
the summer.

 

Tell you what, though - going for a "quick run around the block"
sitting on a cushion across the frame, with a 2-litre plastic lemonade
bottle (with the bottom cut off) inverted, filled with petrol and
connected to the carb inlet with a short piece of petrol pipe is ...
interesting. Not to mention of dubious legality.

It also really brings home the speed with which a big-engined bike will
suck and snort its way through a litre of fuel - right before your very
eyes, as it were.

 

Fairy nuff.

I really, really, really doubt that. To break something *inside* the
carb, you've got to break *into* the carb. Just levering against it
won't do that.

Also ruminating about whether fuel pump pressurises bike carbs. My
belief is that it doesn't, but ICBW. I also doubt the "pumps a bit
harder" story, but again ICBW. My understanding is that the pup fills
the carbs, and when full, the pump doesn't stop, but simply redirects
the excess fuel back into the tank.

 

The pipe runs up the outside of the carb... ;-)

I'll post a pic up later when I get the pics off my phone.

Am just going by what the AA chap said - he seemed to know his onions,
that's for sure.