GS500 - one cylinder down...

[jonshutt]

Hey folks, on the way to work this morning my gs500 was going really badly. Checking it out before coming home i figured out the left cylinder wasn't firing. (rode the 2km home on just the one cylinder).

Now, i've taken the spark plugs out, and they are really really black and sooty. They've been in for about 1000km at the most - the olds ones I had in before had been in for years - at least 15000km - maybe much more - and are still metallic grey and look fine.

So - with the 'new' plugs - having just the right spark plug in it started fine (as to expect with only one spark plug), with just the left it did nothing at all.

So I put the 'old' ones back in, and with just the right spark plug in it starts ok, with the left plugged in it turns a bit, but not enough to 'catch' and start the engine.

with both old plugs in, it starts ok-ish, but when i try and open the choke a wee bit it just stalls.


Now, to me it sounds like either spark plugs are crap and have burnt out, or the fuel mix has gone wonky. putting the old ones in improved things, but not back to normal levels. I did just drive home 2km (slowly) on one cyclinder - could that have clogged up the dead side side causing it to have probs starting now?

Really I'm just guessing here - any help/ideas/suggestions more than welcome! Cheers

Jon

[jonshutt]

aditional thoughts.

plugs: the plugs are ngk dpr83a-9 - exactly what haynes recommend.

wet. my last ride was really really wet, and i'm wondering if the water has cuased a problem with the firing ignition system...

[Teflon]

clean the air filter

check the HT leads, coils - swap them around

new plugs

Test the battery

Strip the carb.. give them a good blow out with air..check float height and needle

compression check

[Katman]

Is it only the left hand spark plug that is black?

If so, pull the vacuum hose off the fuel tap and see if any fuel drips from it. If it does, the fuel tap diaphragm has a hole in it.

[jonshutt]

Hi katman - actually both spark plugs were totally black...

[Katman]

As mentioned above - have you checked the air filter? Or something blocking the inlet ducts of the airbox?

[jonshutt]

thanks for the info. i'll check the air filter, and the various things above - starting with the easiest things first! could be a while before i get round to it though....
cheers folks!

[geoffm]

Do thes erun a wasted spark (ie both cyls fire at the same time, but only one will be on compression with gas so will actually fire). If so, you probably have a single coil with 2 plug leads - try swapping the leads over which might narrow it down to not being leads or plug caps.