Oil leaking at spark plug? Backfiring?

82 Kz750LTD. Rebuild! This engine leaked like crazy when I got it. shifter seal, oil pressure unit was literally missing, tach cable.

all of this has been rectified. Until this past weekend I was testing out the bike, ran it pretty hard for maybe 30 miles. Felt great! then when I was pulling through the neighborhood going home, it starts backfiring. I get home, tighten all the boots, start it up the next day- same thing.


Now, the petcock over the course of the night, for the first time ever, leaked all of the gas COMPLETELY out. I'm thinking either 1, my o-rings need to be replaced around the plugs and rebuild the petcock...or 2. the gas leaked onto the plug and into the casing? But the plug has oil all over it.


any advice on what to check first...would be terrific! The backfiring is highly disconcerting as is the gas leak. But I just dont want to blwo the engine with a bad plug or something.

I had a bike leak all the gas into the casing and contaminated the oil. I only found it when the clutch quit working. I would guess you have a spark problem, and the valve seals are probably leaking and or the rings need done. Backfiring caused by large amount of gas in the cylinder, so that's either happening with a cylinder not always getting spark, somehow two much gas getting into the cylinder. Come to think of it, if you just rebuilt this engine, and you rode it hard for 30 miles, you skipped the break in?

Define "plug" like spark plug? oily spark plugs (in most cases) mean bad valve stem seals or rings. Sounds like you do need to rebuild your petcock. As for a band-aid to the fuel valve situation, remove the tank, put some gas in it and move it to reserve. Play around with the settings on the valve until it quits pouring out. You could also put in another plastic valve inline to the carbs that you would have to turn off and on manually. Also make sure it wasn't left on prime. 1 of 2 things happened.. The tank leaked gas into the carbs while the bike was shut off, the needles didn't seat in the bowls and they overflowed into the air box. The the fuel traveled from the air box into the crankcase from the crankcase breather hose. Or, the fuel overflowed into one of the cylinders with an open valve and slipped past the rings into the crankcase. Oil contaminated with gasoline can cause backfiring as the rings never completely seal the cylinder and its slipping past into the combustion chamber and pre igniting. I had this issue with my 81' KZ1000LTD. I didnt listen to the guy i got it from when he told me to change the oil. Banged my head against that bike for about a month until i found out that was the issue. I would recommend changing the oil in your bike and fixing the petcock before trying to run it again. Dont want to waste a good oil change and contaminate it with gas again. I would start with simply removing the oil fill cap and seeing if it smells like gas. If so, change the oil. Next i would do a compression test and post what readings you get for each cylinder, then go from there.

Good luck,
KT

Awesome advice, thank you guys.

I'm pretty sure cyl 2 is not firing and that it is the issue. Are the oil seals simple enough to change?


Certainly about to fix the petcock. Are these manual PC solid enough for commuter use?

Well they are kinda made for a lawnmower but i have seen plenty of people use them on mtheir motorcycles. They are plastic. You still keep the original valve on the tank but you put this secondary plastic one in-line to the carbs. i believe it would be OK as a bandaid for the issue.

ldizzle wrote: Awesome advice, thank you guys.

I'm pretty sure cyl 2 is not firing and that it is the issue. Are the oil seals simple enough to change?

The valve seals, no. Unless you have mechanical aptitude and the tools, you should probably have a mechanic redo the head, valves, seals, and adjustments.

Have you figured out why cylinder 2 isn't firing? Make sure the plug end is not loose from the wire. continuity test the wires while moving them around to check for breaks.

Regarding the cutoff..yeah I have these on both my 150cc scoots. Just a simple In-line cut off? No big deal.

I've torn into engines many times before...but never had the head off a motorcycle. Not Really sure if I want to. Is this a huge hassle for one man? Take the head/headers.valves off, pull the plugs, replace the seals/head gasket, reverse?

Certainly have the tools...3 generations of contractors... I have 10+ tool boxes in our garage.

Just making sure you get the timing right and the valves adjusted right is the hardest part. you have to remove the cam, and the timing chain from the cam to remove, then make sure you keep tension on the timing chain during the removal and install of the head so it doesn't come off the the sprocket down below or drop down in. Have to make sure not to drop stuff into the casing.