Well I've searched this for the past 2 hours and although much good information, can't really get a specific answer. I got a K4 600 that's got about 10K now and is starting to bog a bit more in all gears, but especially on take off. I'm 99% sure it's the plugs but am told by a few people to get the iridiums. Most of the searches say I used "this" plug or I used "that" plug and liked it, but my question is why? I'm not taking my bike to a track anytime soon due to money, I stunt alot, and only do occasional bursts maybe a few times a month, but mostly just cruise at 7-8K and shift between 6-10, so I think I'd be fine running just NGK that came from the factory.
Please don't respond with the iridium or NGK or etc. plug worked great. My question for everyone else is when you changed your plugs, why did you go with the specific brand or type that you put in your bike??? Maybe it was friends' reccomendation, power, mileage, long lasting? What was your reasoning for you buying your plug?
You will not notice any performance increase or anything, but I have used CR9 and CR8 NGK Iridiums and they run great: lasted for about 10,000 miles each before I notice the bike starts to bog a bit. I've got CR9EIX in right now and just recently changed them a few hundred miles ago. I only stuck with NGK because it said in the manual it was recommended. I didn't notice a difference between the CR8 or CR9 at all, but they are reliable imo.
I just go to autozone and tell them I need plugs for and my bike they look up which ones it takes and I buy the NGK for probably 2 bucks a piece, never had a problem and since I change them every winter I see no reason to buy expensive plugs.
Ok well thanks for all the info, seems everyone in here runs NGK, some with what the book recommends and some running iridiums.
My view is a regular plug costs about $2-3 a pop and lasts 7500 miles. The iridium a bit more probably and 10K miles, but either way everyone is running NGK so I got my answer, I'll just do the stock version and of it and since no really changes other than a bit longer life, that's an easy decision, thanks everyone.
I use NGK on all of my vehicles because they are dependable. I had Bosch Platinum's in my wife's Camry, and in less than 5k miles the engine started to miss. One of the plugs was firing intermittently. Put NGK's in, still going strong 23k miles later.
Had a Champion spark plug stop firing completely in my XR400 dirt bike, after only 3 or 4 rides. Have had an NGK in it all summer with no issues. Iridiums are nice, but not worth the money IMO, so I just go with the NGK version of the OEM plug.