Spark plug question

Wotcher all ,

Right, I had my curvy dynoed at the weekend. Basically, looking at the readout, everything's fine up until 4 - 5000rpm, where the BHP line starts getting pretty squiggly - basically the bike was vibrating and doing lots of little misfires as it gets up the rev range.

The bloke who did the dyno run was telling me that the most likely culprit for this would possibly be the plugs and plug connections. I had to rejet the carbs again anyway and found a slightly loose connection where the front plug lead goes into the main loom. Took the bike out on Monday and although it was lovely and smooth in the low rpms, when I crank the throttle the bike does start vibrating a lot, more than I remember.

What I'll probably end up doing tomorrow would be to take the plugs out and have a look at them. What I was thinking was that i replace them anyway just to be on the safe side but on the svrider site they recommend the NGK CR9EK plugs as they are a colder plug and they have two electrodes instead of one (more places for the spark to jump from).

Anyone else have any experience with these? I like the idea of the twin electrodes, although I don't rag the bike all the time so I'm not sure if the colder plug would be suitable.

Cheers loads everyone, and sorry about the huge post, I always end up rambling on on these things... I'll try and upload a pic of the dyno run later on

[Spanner Man]

Good afternoon.

For an improved spark try using NGK's Iridium plugs. Part number CR8EIX.


Cheers.

[jambo]

I have put CR9EK's in an SV before, but that was because the wrong plugs had been bought. It ran the same to any extent I could tell.

A "cooler" plug will be more suceptable to fouling on cold starts, and the CR8E plugs seem fine on the bike when on track, so I'm not sure there's much benefit unless you're significntly tuning the engine.

I'd work out what the problem is. There's several hundered bikes on this site running cleanly on CR8E or equivelent, so the plug type's not at fault.

Jambo

[embee]

As advised above, stick to a grade 8, there is no reason for going to a colder plug unless you've made significant mods and advanced the ignition or increased CR.
A grade 9 will be prone to cold fouling, which there are ways of getting round, but for road use it should not be necessary.

The twin earth electrode is for extended service life, the spark will use the gap with least resistance until it erodes away and the other gap is then preferred. There are no other significant benefits.

Iridium electrodes which are much smaller diameter have similar service life properties and also offer improved mixture variation tolerance (lean limit etc, good with carbs especially), better cold starting. lower voltage requirements etc. and would be my recommendation. NGK CR8-EIX

Cheers everyone!

I'll have a look at the iridium plugs, I'll check the ones I have first before anything tho. Fingers crossed these misfires aren't down to anything more complicated, lol!

Cheers again

Whoop forgot to ask...

I was going to put anti-seize compound on the threads of the plugs but would copper grease be ok or would need to be a specific aluminium grease?

Cheers again

copper hrease ive put on myn

[Bibio]

Originally Posted by skyline

Whoop forgot to ask...

I was going to put anti-seize compound on the threads of the plugs but would copper grease be ok or would need to be a specific aluminium grease?

Cheers again

as long as its conductive, personally i don't put anything on the threads of plugs.

Thanks once again everyone, off to hopefully sort it this morning

def dont put anything on the plug threads mate it wouldnt take much to overdo it

i have the irid plugs startup seems smoother but they will be in the bike fo rthe year anyway and its only an extra tenner i think

i will buy them again thats for sure