xv535 virago - not firing on one cylinder

Hi. My xv535 wouldn't start the other week. It was taking a little
while for the front cylinder to fire the last few times I started it.
Rear cylinder was fine.

I've taken off the carbs and cleaned the jets, checked the float
needle valve is working, and generally it all seems ok. Couldn't get
into the diaphram part because my torx key wouldn't fit the special
screw. I'm not sure I really know what the problem is.

Fuel supply seems ok, and the plug was firing fine. Any ideas
appreciated before I give up and start calling mechanics.

Also intending to check the tappets while the carbs are out.

 

It's more likely to be ignition than fuel ("It's always electrical").

I'd have swapped the plugs and/or coils and HT leads before buggering
about with the carbs, especially if I didn't have the right tools.

Put it all back together properly, and start looking at the ignition
side again. Once you've tested that, and it's pretty simple, then have a
look at the carbs.

Tight valve clearances can make for poor starting, so yes, it's worth
doing that,but if something was starting and running fine and then
suddenly decided not to play ball, it's unlikely to be tappets.

 

If you pull the spark plug lead loose and start the engine with the
plug cap just sitting on the threaded end of the spark plug, and then
hold the cap 1/4 of an inch away from the plug and the engine starts
firing on that cylinder, it means the idle mixture is too lean on that
cylinder.

 

Thanks for the response. The reason I suspect fuel/carb is that I took
the plug out, resting it against the side of the cylinder and it was
firing fine. The breakdown people I called also put a plug tester on
the ht lead and it was fine according to that. There was no smell of
fuel coming from that cylinder with the plug out, after having been
trying to start it - hence the reasoning that it might be something to
do with the carb as fuel was definitely coming up the line leading the
the carbs as evidenced by removing the end of the fuel line and
turning the engine over.

What's really annoying is that to check the float height, I have to
put the carbs back, then fill with fuel, and if incorrect, get them
out again and adjust the float tang - and it isn't easy to get the
bloody things out in the first place!

 

OK, right, that sounds like a decent enough ignition check, so it
probably is a carb issue.

I doubt it's a float height problem, mind. They don't suddenly bend
themselves into a position where they block the flow. A scrap of dirt
blocking the movement, maybe. Or a blocked in-line fuel filter to that
partiicular carb, if fitted.

 

Have checked the operation of the float needle valve on the carb of
the cylinder that wasn't firing and that seems to be fine, nothing
blocking the fuel line feed in (it's a shared feed with just a simple
tube connecting both carbs), it opens and closes ok. Cleaned it with
carb cleaner, checked the jets I could get to (as I don't have the
torx tool to get into the daiphragm side of the carb) and cleaned them
with carb cleaner. The fuel filter is further back towards the tank.

The guy who came from the breakdown company, thought it might be a
fuel shut-off valve. At the front of the carb near the bottom there is
a small device with two electrical wires leading away from it, which
is what he thought this was. I can't find it in either the haynes or
clymer manuals I have (though they are rather old versions), but it
seems some kind of carb heater device was fitted to some models of
this bike. Rather than unscrew it to check I would need to confirm
this first. Can't seem why there would be a shut off device on this
but not on earlier models of the bike. It's also on the 'wrong' side
of the carb, as the fuel feeds in on the opposite side.

 

Could be a carb heater, yes....

Sudden thought.....

It hasn't got one of those dreadful Yamaha electric reserve switches,
has it? They always give trouble. Silly question, but the fuel tank *is*
full, right?

 

Had only done 50 miles since last fill up, as far as I could tell
there was a little fuel in the top tank, and some in the bottom. Fuel
was coming out of the feed pipe to the carbs, also checked it with the
reserve switch on and off. You can hear the fuel pump working - when
it is getting near full it makes an odd noise and tries to
continuously run and it wasn't doing that. Am going to investigate
further today and will post again.

 

Sorry, meant to say when the tank is getting near empty, which it did
once, it makes an odd noise, kind of a ticking sound as it tries to
keep fuel running up to the carbs, and it wasn't doing that. Just the
normal ticking for a few seconds till the carbs float bowls fill -
anyway, will post again after further investigation.

 

Took carbs to mechanic, carb diaphragms fine and inside of carb
according to him "very clean". So, on to checking the other stuff
now...fuel line, filter, pump etc, and adjust tappets as need
everything out anyway to get to tappet cover on rear cylinder. Lucky
it's a sunny day.

 

Yes, checked the jets in jet block, and the spark plugs are relatively
new (2 months or so - iridium). So far have found a dodgy positive
lead from the battery that broke as I was moving it to get to
something, and bit of corrosion around a connection to the fuel pump.
The damage to the positive lead I guess could have made it harder for
the battery and ignition system to get a decent spark going due to
increased resistance. Also checked the tappets, rear ok, front seemed
tight so have adjusted them. Will put it back together thursday and
see if it will run.

 

Battery has been fine, considering I don't ride regularly. I checked
for continuity on the carb heaters which there is, wonder how to check
if they are working? Would they get warm if I connect them to the
battery?

 

Bike Working!!

Not sure exactly what the problem was, partly dodgy positive lead from
battery (half-corroded), some corrosion on terminal on fuel pump, and
slightly tight tappet on inlet on front cylinder. Other than that, it
could even have been that I set the odometer to zero incorrectly when
I last filled up, so that although it read 50 (I usually get 100 miles
per fill), there was less petrol than I thought. Even so, fuel was
getting at least as far as the rear carb initially so it's still a bit
of a puzzle. Done about 60 miles so far since and all seems well.

Thanks for all the advice.