1 clean plug

i have a 93 200 yamaha txrr i was having surging problems but i narrowed that to where i was getting air in the fuel lines but i thought i was having a slight firing problem. So before going out just for a test run i replaced all the plugs on the engine. The engine ran a little rough and only reached 4200rpms so i pulled the plugs out of the engine to check them all and one plug was completely clean but all the others were a little black from burning. i have just recently went through the whole fuel system from the boat to the engine and on this older yamaha it only has 3 carbs not like the newer ones that have one carb per cylinder it ran great before but now it runs rough and is hard to keep it at low idle. i checked the spark on the engine and that plug it not getting any fire. how would i trouble shoot to see what the problem is?

Re: 1 clean plug

Is the plug just clean or really white? If it's white you could have a water leak on that cylinder causing "steam flashing/scouring" on that cylinder, or you may have a plugged carb jet and a very lean mixture on that cylinder.....Carbs been cleaned? Maybe the lack of spark on that cylinder. Either way, it needs to be fixed before running the motor any further. Good Luck!

Re: 1 clean plug

peak reading volt meter or a DVA adapter with regular meter to read voltage to coil to see if that is in spec
If it is in spec Ohm check coil, plug wire and cap.

If not then test inputs to CDI

Re: 1 clean plug

i tested the spark and it wasnt working it switched coils and it worked bought a new coil and installed it. then i had to deal with the surging problem. i ran the engine of a separate 6 gal tank and i didnt have the surging problem so i hooked back up the the boats fuel system same problem. bypassed the fuel/water separator still same problem checked the hose running to the tank and nothing wrong with it so i have come down to the down tube in the tank or pickup tube that is the only thing left. i have cleaned the carbs replaced all fuel line new fuel pumps new antisiphon valve. the only thing left is the down tube or fuel pickup i noticed it sounded like i was getting air in the tube when i pumed the ball and listened to the tank. could tyhe fuel pickup be my problem and downtube. i have troubleshot everything and that is the only thing left is that a common thing the tank was put in in right before i bought the hull because i fixed the floor after i got it. is their another way of troubleshooting this problem that i missed.

Re: 1 clean plug

http://forums.iboats.com/showthread.php?t=283363

Re: 1 clean plug

I think you are saying there is no access to the fuel pick up in tank? If there is access just pull the p/u out of tank....if not, you could put
a clear piece of vinyl hose in line with a nipple, just in front of engine....and see if you get bubbles....cracked p/u tubes happen, sure.