twin earth plugs?

[madandy]

My RF currently has twin earth NGK plugs in it but our local Suzuki mech/shop owner rekons they're wrong and cause the slight flat spot at 4krpm...his NGK book doesn't cover the RF400, though just 600 and 900.Any ideas?

[marty]

i've got some 400cc mates in the UK - i've asked them. they race anything that's 400, so they'll know

[Motu]

If they are not recomended for the bike he's right,if they are what it's suposed to have he's wrong.Give the year and model of your bike,as much info as you've got and I'll delve into all my sparkplug books tomorrow.

[madandy]

Thanx guys!
the bike is 1992 Suzuki RF400(397cc DOHC16, 4 Mikuni carb, import).Has a GSF400 ignitor box and stock everything else. The plugs are NGK dual earth...I forget the number and am too comfortable right now to go remove the tank and a plug to get it but it finishes with a k!they are brand new and I have know idea what the gaps should be...

The engine surges slightly at part throttle around 4-5krpm and will hesitate slightly if given the ask from there but on rolling through this rev band on wot it doesn't happen.mileage is excellent @ 70+mpg and idle is perfectly smooth once warm.

I think the HT leads are stock so maybe I should replace these too?
cheers, Andy

[Motu]

Yep,nothing resembling an RF400 in any of my books - 400cc Jap bikes are often based on something else,usualy sleeved down (my XT400 is just a small bore XT600),so there is an RF600 - it doesn't take a twin electrode plug - K stands for twin earth electrode in NGK speak.CR9E is what the RF600 takes,that means its a 10mm plug,19mm reach,nothing fancy at all,if that sounds right,give it a go.

[madandy]

cr9e sounds right.Thanx, MOTU. 10mm 19mm reach is exactly what these k jobbies are...thanx any idea what the gap should be?
Hmmmm I wonder if the engine could be 'un-sleeved'?hehe

[Motu]

0.07mm gap.

Yeah,if you come across an XT or TT 600 top end let me know.

[madandy]

zero point ZERO seven mm?!!!! gap

wow thats a tiny gap...my 11:1comp. sr20ve car engine's plug gaps are zero point eight mm. should the gaps for my bike's plugs really be almost one tenth of that?

[750Y]

Originally posted by madandy
zero point ZERO seven mm?!!!! gap

wow thats a tiny gap...my 11:1comp. sr20ve car engine's plug gaps are zero point eight mm. should the gaps for my bike's plugs really be almost one tenth of that?

good point, was that a typo? because it'd basically be paper thickness. could be right tho, but just sounds pretty tight. I'd be thinking more around the 0.8mm mark but then I'm not an expert.

[Motu]

Yeah well,I'm an old fart and think in thou for plug gaps - 0.038'' is 0.7mm.Anyway....how did it run on 0.07mm?

[madandy]

I is not that silly, Motu!

Thanks for your help...zero point seven...which is what I guessed you meant is correct and it goes ok...I'll get me some cr9e's soon and she'll be as was made to be