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300 Fourtrax - Spark Plug Heat Range?

12270 Views 23 Replies 6 Participants Last post by  rottenscoundrel
Hey guys. I bought a 94' 300 4x4 last April. I just got to see it for the first time a week ago. I moved from Alberta to New Brunswick.

So my bike has a Highlifter 355cc big bore kit, web cam, clutch kit, white brothers stainless steel exhaust, 2" lift, a warn 2x4 kit, 124 main jet ( I believe ).

So I have a few questions, I want to change the spark plug and I'm going to change all the fluids. The original owner ran full synthetic oil with lucas additive. He said when it's cold out you had to let the bike warm up or else the clutch would slip. NO good for me. I'm going to run conventenal oil. BUT my question is... should I change the heat range of the plug considering it has the big bore kit?? He has the stock plug in the bike and says it runs hotter with the kit?!?!

I need to replace the front shocks and the front wheel bearings too. I bought all ball wheel bearings.

Now that I'm in my new house and hopefully get to get out on the bike I'll be on here a lot more.

I know for sure I want the detroit gearless locker and 12" rims so I can install disk brakes. And yes I'll research everything before posting as most stuff is already covered. I couldn't seem to find much on heat range of plugs though.

I'll get some pics of the bike later this week and post em up.

Thanks for any advice.
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I always keep my ATVs stock, so I don't really know enough about the subject of "sparkplug heat range in relation to big bore kits" to be able to give you any helpful information, but here's a couple articles on sparkplugs from the NGK website. You may have already seen these, but in case you haven't, here they are.

NGK Spark Plugs USA

NGK Spark Plugs USA

Unless someone else is experienced enough in this subject as it relates to big bore kits, you may have to just read your plug and use that reading in deciding whether the heat range is correct or not.
But I is it normal for a ss exhaust to get cherry red??
If it's just a dull red where the pipe comes out of the head, I wouldn't worry much about it, I've seen that a lot. If its glowing cherry red past the first bend in the pipe, it could be running lean.
ahh yeah......... it was red past the first bend right back to where it tucks under the fender!!!!!!! He told me it has the largest jet it can take. I 124 I think he said.
That seems too hot to me, but I don't know much about the big bore kits and aftermarket exhausts, I always keep mine stock.
BTW, the stock size main jet for the Fourtrax 300 is s #125.
I would try going up on the main jet and see what happens. I would just change one jet at a time.

I understand the only way to know for sure is to pull it apart and change the jets then go from there.......
Yep, this is true. It's trial and error. You're pretty much just guessing and trying it until you get it right. Sometimes you get it pretty quick and other times, it can be a PITA.
You may have to go to change the pilot jet.
Yeah, sounds like you're real close.
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