I just changed the spark plug on my 300 4x4 about 100 miles ago. I checked it today and it is loaded up with carbon, which is why I changed it in the first place. Should I go to the next hotter plug?

 

NO! Hotter plugs are not the answer! I would say to clean & oil (with foam filter oil) the air filter. Take off carb & clean the jets with compressed air. Take off the fuel tank & dump. Replace with fresh fuel. Check exhaust for leaks at engine. Clean or replace plug. I would think that this will solve your problem.

 

i had the same prob on my 500 so i eventually just went to hte next hotter plug, runs great now.

 

I cleaned the plug last night with a wire brush and got all the carbon off. The wife and kids rode it today for about an hour and the plug is black again. I just ordered a foam filter and oil etc... for it. The filter that is in it is a K&N. I checked for exhaust leaks at the engine-nothing. I am not too comfortable taking the carb off and messing with it. What are the dangers of trying a one step hotter plug if the new air filter doesn't help? Anyone have a part # for the next hotter plug? The NGK plug is DR7EA. Thanks for the help. I am a new ATV owner and don't really know anything other than it is a blast to ride it!!

 

Cleaning jets on carb is as easy as putting in a plug. All you have to do is take bowl off the bottom of the carb add remove the copper colored jets that have a slot for a small screw driver. Blow through them with some compressed air and stick them suckers back in. Be sure that the carb is sealed up good to the intake & you are good to go. There will be a float in the carb. Just try your best not to mess with it. Just let it hang there while you clean jets & put bowl back on without bumping it. Now, about the hotter plug. What this does is make a hotter spark on top of the piston. Notice I said "on top of the piston". This is not good for piston as it eats away at the top of it. This is a temporary fix for a fuel/air problem. This is not the way a PRO would fix it. It will work, just not the best thing for engine.
P.S. Be sure to set your gap on plug.

 

Is the plug actually fouling, or is it still working and just getting very black? If it is still running, it is not fouled. You are running a too rich mixture is all. If it quits running, and the plug is black then the plug is fouled. That is usually caused by oil somehow getting into your combustion chamber. 4 stroke engines very rarely foul plugs unless there is some internal engine problem.

 

It is just getting very black. Still runs. If it is just running rich what should I do? It has been ridden mostly at slower speeds since we got it. It has 1200 miles on it, 200 put on by me. I REALLY appreciate all of the input and advice.

 

Did you put the K&N filter in? If not, chances are whoever did may have rejetted the carb to make up for the added air flow, and jetted too big. If you have any suspicion this may have occured, then when you go to the foam filter it will make you even richer because the foam doesn't flow quite as well as a clean K&N, although they do a better job at filtering fine dust. If the previous owner put the K&N in it, he may have also purchased a jet kit with it, and not followed the instruction correctly and put the wrong jet in too, or have the needle in the wrong clip position.

If the jets had any cloggage they would decrease fuel flow, causing you to be lean, and not black. I would say either the filter is just really dirty, decreasing air flow and causing the black to blacken, or the wrong jetting was installed by the previous owner. You need to know what, if anything he did - Dynojet or OEM Mikuni, they're not the same - can you get a hold of him to ask?

 

It is my understanding that an engine that runs slightly rich, runs cooler (longer life). Minehunter is correct. What your plug is doing is somewhat normal as Arctic-Cat jets their quads a little on the rich side for good measure. I had the same problem as you. I took the bottom off of my carb and removed my main jet to find out what number it was. It was a 150, so I had the dealer order the next size down which was a 148.5 ( I think - Thanks Hightower!). This took care of my carbon problem on the plug and my fuel efficiency went way up. The best that I remember, some of the larger quads have come stock with 145 main jets.. your jet may be anything from a 142 to a 150. I would simply install the next size down and use the factory recomended plug!

If you need more help there are some great posts on this forum on how to get into your carb. It REALLY is easy!

EtherNut

 

ethernet - missprint - I think you mean 148.5

steve154 - the number on the bottom of a dynojet does not mean the same thing as the number on the bottom of mikuni jet - this is why you need to determine what brand jet is in the carb before gettnig the next size down. If it is dynojet, installed by the previous owner with the filter, it has a dynojet needle too, and you do not want to use a mikuni main with the dynojet needle.