Over Fueling only top cylinder

[CarloL]

1997 M900
New Fuel filter
New spark plugs NGK 8eix (iridium)
New choke cable

Took her out for a 80km ride, after roughly 60km she only started working on 1 cylinder, took out the plugs , front is fine , top plug stinks of fuel , cleaned , she's on two cylinders again

80km she used most of the full tank

Any ideas , iridium ? I had NGK dcpr8e

[Luddite]

Did you ensure that the gap was correct. You can't run the iridiums on the standard 0.7ish - they need 0.9 - 1mm to work properly.

I've had them on my Evo for six years with no problems. More info here:

http://www.ukmonster.co.uk/monster/s...72&postcount=4

http://www.ukmonster.co.uk/monster/s...2&postcount=12

[the lodger]

Did you buy your plugs from a reputable supplier? There are a lot of NGK fakes out there.

[CarloL]

Originally Posted by the lodger

Did you buy your plugs from a reputable supplier? There are a lot of NGK fakes out there.

they are an authorised NGK distributor

[the lodger]

Sorry I don't know the answer to this ( Luddite will know ! ) but do M900 have resistor type plug caps as standard ? You really need non-resistor caps to fire an iridium plug efficiently .I'm guessing our old style ignition systems are already being challenged by these plugs.

[Luddite]

Well...this is the workshop manual for the early 900 and you can see they run with 5000 Ohm resistors in the ignition circuit.



Having said that, the standard plugs, (Champion RA6HC), also carry resistors.

I don't think you can get NGK iridium plugs without the resistors.

[CarloL]

Thanks , I will check the gap

Will put in the old plugs to test first, they worked fine

Does each carb on the bike supply a specific cylinder i.e. Carb 1 supplies top cylinder with fuel/air, carb 2 supplied lower cylinder ?

If I do need to chase fueling for the top cylinder be good if I can narrow it down to a specific carb, float bowl height , needles ....will all need to be checked and cleaned next if plug gap is not the issue

[CarloL]

I am better off running a copper plug?

[Luddite]

Originally Posted by CarloL

I am better off running a copper plug?

...or nickel or platinum. I have iridiums in my Evo and they've been fine for 6 years. Their main claimed advantage over standard plugs is a much longer life as the iridium is much more resistant to spark erosion than, say, copper. The thinner electrode and larger spark gap is also supposed to give a bigger spark for better combustion.

But, if you have any doubts, stick to tried and tested copper.

[Mr Gazza]

Surely that's a Copper core not a Copper electrode?

[Luddite]

Correct as always, Mr G. Brain fade I'm afraid

[CarloL]

Iridium's where at 1mm gap , I must of done them a while back and forgot
Coppers are 0.8mm gap

Appears to be working fine on the coppers , my m900 one of the early production bikes , I don't think it like iridium's