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Rear plug fouling.

8K views 13 replies 3 participants last post by  VN400 
#1 ·
Hi guys,

Im from the Philippines and I have a 1997 Kawasaki Vulcan VN400 (400cc Vtwin), and the rear plug keeps fouling, the plug looks black im not sure if its oil or gas but definitely the plug is wet. im actually thinking that its oil that havent burnt out or the plug is not cleaning it self enough, im using CR7E on both cyclinder. also if the piston oil ring is worn out, there should be a white smoke coming from the pipe right? but there is no smoke.

we have cleaned the carb already and adjusted the float valve and Jettings but its quite amusing coz the front plug has a brownish burn (which is right) but the rear is black and looks oily.

what could be the possible cause of this? coz it keeps killing my rear plug. im also using diesel oil because of the viscosity level. since im living on a tropical country i was advice by some harley owners that its better to use diesel oil because its more resistant to heat, is that true?

I also tried to switch the ignition coil it will run fine for quite sometime, but after a few kilometers (60kilometers) the rear plug will start to be fouled again.

i need your advice

PS. ive checked the users manual it only stated the issue with over heating and or cold plug, it doest state anything about oil foul plugs.

heres the photo of my vulcan, havent got a chance to take the picture of the plugs coz im here right now working on cruiseship as photographer, and i left my bike to friend thats fixing it.

Thank you guys in advance for the help and info.



 
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#4 ·
@Sfair - it has 23000 kilometers on the bike.

i owned it for 2 years ( got it second hand),

after the rear fouled plug has been cleaned and dried it works again.

the problem from the rear fouled plugs happened quite often and i keep adjusting the a/f screw to get the right burn on the plugs. the front has a brownish burn and according to the users manual. its the right burn, im just wondering why the rear plug has a different burn, to which its a sigle carb engine.
 
#5 ·
Red rider thanks for the chart, im just curious about the oil fouling plug chart, coz my rear plug doesnt really looked that bad, i can still see the ceramic as white. and it says that it might be the oil ring or too much oil, if its oil burning in the cyclinder shouldnt be showing a white smoke at the rear pipe?

Thanks again!
 
#6 · (Edited)
A few more questions:

1. Any backfiring in exhaust or intake?
2. Any smell of fuel or oil at anytime?
3. Any oil consumption?
4. Are you putting the correct amount of oil in it?
5. Any aftermarket add-ons...pipes, etc?
6. When the plug is clean, does it start/run OK, hot/cold?
7. When the plug is clean, any stumbling or bogging?
8. Did you measure spark plug wire/cap resistance as per manual?
9. Any oil in the air cleaner?
10. Any other driveability issues, no matter how small or unrelated?

Post back.
 
#7 ·
1. Nope no backfiring.
2. theres no fuel fumes just the regular burned gas fumes.
3. oil is fine i looked at the guage window on the side.
4. yup i measured it.
5. yes open pipes, but its been there since i got the bike and it was not fouling the rear plug that time.
6. when its cleaned after it got fouled, its working again, first a little hard starting, but ones fed with gas and a little throtle turn it runs okay.
7. is a littlebit "shakey" maybe because its cold or my idling is too low?.
8 thats the problem i dont have an idea how to measure the spark. we dont have it in the philippines.
9. the oil drain that is connected to the air intake assembly has a little oil in it. you know that little bottle like with a hose.
10. when the engine is hot it doesnt kill the rear plug. it drives okay, but ones its cool enough and the stayed for more than 12 hours. then thats the time im having a problem with the rear plug, specially the second try on the turn on switch because the head lamp is on, it seems there not enough DC to spark the rear, but the front is okay. i tried switching the front coil and rear. it worked for a while but then again it started to foul my rear plug.
 
#9 ·
After reviewing your answer to question 10, could you try this for me:

Pull the fuel line off of the carb and put it in a pop bottle. Check it in a few hours and see if there is any gas in it. Make sure that the fuel line has a straight down run to the bottle and with no kinks.
 
#10 ·
1. I believe the engine has not been opened yet bec there are no marks on the bolt head. and its nearing 24k/kilometers on the odo reading.
2.the sparkplug cables are long enough, and we tried it but didnt worked as well.
3. i have a friend who has a 2003 Vulcan 900. but its EFI so he has no issues with it.
 
#13 ·
Well the first thing to do is a valve check. They probably have never been done and I am sure that it is well past the mileage for a check. Once the valves are done, do a compression check. The engine mechanicals must be up to specification before any more troubleshooting can be done.

Just to re-cap so that I am clear on the problem:

If the bike is running, the plug is fine. Only if it sits for 12 hours or more, you try and start and the rear plug becomes fuel soaked. You dry the plug off, and it starts right up and runs fine until the next shut down. Am I correct?

Post back.
 
#14 ·
Well the first thing to do is a valve check. They probably have never been done and I am sure that it is well past the mileage for a check. Once the valves are done, do a compression check. The engine mechanicals must be up to specification before any more troubleshooting can be done..
Okey sir ill find a qualified mechanic to do this one.

Just to re-cap so that I am clear on the problem:

If the bike is running, the plug is fine. Only if it sits for 12 hours or more, you try and start and the rear plug becomes fuel soaked. You dry the plug off, and it starts right up and runs fine until the next shut down. Am I correct?

Post back.
yes sir this is exactly whats happening.
 
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