1978 KZ400 Fouling Plugs at Idle - HELP!!

So I bought this bike a few months back and it ran great for maybe a couple hours of riding..

First off, the bike is all stock with the exception of UNI pod filters. I found that fuel was pissing out of the pod filters one morning so I drained the bowls and that seemed to work for a couple days, From there I could not get the bike to fire properly on both cylinders, but it seemed to foul on each cylinder randomly. So it wasn't always the left or the right, it jumped back and forth. In the end I decided to take it to a shop and have the carbs looked at, they eventually told me that I should have ultrasonic cleaning performed, so I did, seems reasonable for a 37 year old bike. When in there, I was told that the diaphragms have tears in them and I should have the needle valves replaced. So I had them replaced.

When that was done I was told that the bike seemed to run good when warm but wouldn't idle when cold (plugs kept fouling) and they couldn't figure out why. Eventually I was told that there was too much oil in the crankcase (which I should have checked, but as I bought it from who I thought was a reputable shop owner, didn't think I would have an issue with such trivial details) and that was causing the plugs to foul. So, the oil was changed.

I was then told the bike seems to be running significantly better (I didn't expect perfection with pods on a bike of this age), I picked it up and rode for maybe an hour on Saturday, the only problem I noticed was that the choke had to be left at 50% even when warm and the bike would occasionally idle down and stall when sitting without any throttle attention. I went to ride again on Sunday, topped up with fresh 91 octane fuel and I got maybe a mile from home before I was experiencing dead spots and sputtering when trying to accelerate, I kept riding thinking maybe it was just cold. I rode a total of 8km and by the time I was back to my street the bike was running on just the left cylinder, so I pulled the right plug and it was fouled with gasoline. The same problem I had to start with.

Needless to say, I am a little frustrated that my bike was in the shop for well over a month to come back with the same problem, and quite frankly, I don't have much faith in the shop at this point. So, with that, I am here looking for any advise I can get to get this bike back on the road.

Thanks in advance!

Matt

Sounds like flooding. Fix it by:

1) Remove fuel tank/petcock assembly and clean THOROUGHLY.

2) Install inline filters.

3) Remove float/valves/seats from carbs. Check needle tips and make sure they are mirror smooth so they will seal against brass seats. Polish to get smooth. Polish brass seats. If necessary, replace needles and seats if not usable.

4) Clean carbs, reassemble and set floats using clear tube method.

Flooding will be fixed.

mvttryvn wrote: So I bought this bike a few months back and it ran great for maybe a couple hours of riding..

First off, the bike is all stock with the exception of UNI pod filters. I found that fuel was pissing out of the pod filters one morning so I drained the bowls and that seemed to work for a couple days, From there I could not get the bike to fire properly on both cylinders, but it seemed to foul on each cylinder randomly. So it wasn't always the left or the right, it jumped back and forth. In the end I decided to take it to a shop and have the carbs looked at, they eventually told me that I should have ultrasonic cleaning performed, so I did, seems reasonable for a 37 year old bike. When in there, I was told that the diaphragms have tears in them and I should have the needle valves replaced. So I had them replaced.

When that was done I was told that the bike seemed to run good when warm but wouldn't idle when cold (plugs kept fouling) and they couldn't figure out why. Eventually I was told that there was too much oil in the crankcase (
Matt

Be very careful as this is what happens with carb flooding. You get gas running down into the crankcase and diluting the oil. This is HORRIBLE on the engine and the oil must be changed if this happens.

Pics of plugs.
Steve

Thanks for the insight!

Would those items not have been checked when the carbs were removed and cleaned? I did have new needle valves installed but I was told that all else looked to be in good shape. Maybe I need to go through it myself at this point.

Nothing was done with the petcock and there is not an inline filter in place as of yet, so I will make sure to do that.

I don't have any in my phone right now, I'll take some and post them up after work this evening.

As a reference, they look similar to the middle picture in the attachment, black carbon and wet with fuel when removed.

I need to see your plugs. Might be something fouling the plugs and causing a misfire thus wet plugs.
Steve

Check if the oil smells of gasoline. As someone said it could be the cause of the high level of oil.

No problem, I'll post pics as soon as I can.

TheForumTroll wrote: Check if the oil smells of gasoline. As someone said it could be the cause of the high level of oil.

Thanks! I will check that. The oil was changed lest than 10km ago so I don't know how much contamination I will find.

I like your Avatar. Man in his natural habitat. :woohoo:
Steve

swest wrote: I like your Avatar. Man in his natural habitat. :woohoo:
Steve

Haha you know it.