I am at my wits end dealing with carbon or soot deposit on the firing end of the spark plug in my 1998 Honda 300 Fouttrax, which is restricting the running of the machine. When I engage the throttle the machine bogs down and will backfire.. This issue started after installing a new Carb on the machine last summer. Everything went find on the install. I then adjusted the Carb per specification given in the manual. Everything seem to be working all right until I took a test drive when I found out something went wrong. Thing I know are:



1. I have tested or checked the spark on the tip of the spark plug and It looks pretty good to me. So the spark plug is firing.

2. I have install a new Air filter in the intake box.

3. I have checked the gap on the plug.

4. Spark plugs I am using are all new. I even tried a hotter plug, but got the same results.



What is very strange to me is that the carbon buildup on the plug happens immediately, within five minutes after starting the machine the firing end of the plug is totally black.



I can only assume that the New Carb which is an after market replacement for the original that I used is a piece of crap. Maybe I need to re-install the old OEM Carb and see what happen.



I look forward to getting any suggestions concerning this issue.



Regards,

Bob

 

From what you have described it could be two things...carb is dumping fuel into the cylinder causing a very rich condition causing the fouling or you have a weak spark. Even if plug is new the energy getting to it might be weak. In the boat industry we check spark with a cheap little tool called a spark gap check gage. They are cheap, go between plug and wire. The have an adjustable gap so you can see the power going to the plug while it is running. You should be able to jump a 1/8" gap with a blue spark. If really yellow or wont jump the gap you have weak power to the plug! Never have had any faith in aftermarket carbs, to many bad stories. Normally a good rebuild with a proper kit on oem is far superior! Good luck

 

Dumping fuel into the cylinder or weak spark. I have visually inspected the spark on the tip of plug by grounding the spark plug and the spark was blue and going across the gap. If fuel is is being dumped in the cylinder would there not be a strong odor of gas. What would normally cause dumping of fuel from the carburetor?.

 

Well...dumping enough to foul your plug anyway even though you may not smell it. Wrong float setting, wrong jet size, leaking needle seat, these are just some things that might cause a rich mixture. The after market carbs dont always meet mfgr specs!