Carbs flooding. Does this make sense?

I'm getting a KZ650 going for a guy and his son after they bought it out of a shed. It sat dormant for about 25 years. The other guys brought it to me after cleaning the carbs three times with no success. After a GOOD cleaning, the bike ran great. Good low end, good mid range, and good top end. We have a Kerker pipe and new pod filters. All was going well until the son took off and made it 7 miles. He stopped to fill the tank up, went two more miles and the bike started flooding out. Here's what I've theorized after checking things over. (This is the email message I sent to them):

The carbs were still nice and clean inside. We have a major fuel leak where the fuel valve mounts to the tank. I assume that when the tank was filled up that the rubber seal (being 36 years old) finally gave way. I can't really see what the exact cause of the problem is, but my far-fetched theory is that when the seal started leaking it was flowing right into the #1 and #2 air filters, causing them to flood out. When the choke (which is actually an "enrichner" causing MORE fuel to go into the cylinder) was applied cylinders #3 and #4 were able to run. At high RPM #1 and #2 could burn the excess fuel. Sound reasonable?

The bike is getting strong spark, the plugs were fresh (Fuel fouled after this mess) and all four are firing. Anyone have any other thoughts?

If your thinking its the tank remove it and use a remote tank sitting on a bench somewhere see if it still has the same problem with a different tank, Thats what i would try first no money involved there. NO SMOKING!!! Hope this works for ya. John.

I'm not an expert on pods and I'll agree with your line of thinking. Let's just say said Son happened to knee the petcock (ouch) during the fill up. The gas leak would certainly cause a change in the air/gas mixture to cause a stall. Probably if it was actually flooding the spray from the needle which would turn the spray into a stream.

Good analysis!

Was the tank and petcock assembly thoroughly cleaned? Petcock removed and cleaned? Tank cleared of rust and sediment?

After doing that, install good inline filters. As long as there is any crud in the tank, it will flow downhill and cause all kinds of problems. Carb flooding is often caused when a piece of crud gets under the needle valve and it can't close.

OldRider, I tried the remote tank but still have to get fresh plugs. I cleaned them as good as I could but not good enough. It won't even hit when cranked over.

LineArtist, The fuel valve leaks a steady drip right onto the #1 filter/pod. I think filling the tank and extra pressure of about 4 gallons of gas on the seal (if that makes a difference) caused the leak as I had the bike for over a weak with no leaks at all. Lets say it sat leaking for about five minutes right on the filter and then was started to ride away. That filter is now fuel soaked and sucking fuel right down the throat of the #1 carb. Once moving and still leaking, where all is that fuel getting to? Plugs #1 and $2 were SOAKED by the time I got there and he had gone less than 3 miles.

bountyhunter wrote: Was the tank and petcock assembly thoroughly cleaned? Petcock removed and cleaned? Tank cleared of rust and sediment?

After doing that, install good inline filters. As long as there is any crud in the tank, it will flow downhill and cause all kinds of problems. Carb flooding is often caused when a piece of crud gets under the needle valve and it can't close.

I made the mistake of trusting the owner when he said the tank and petcock were spotless. It has a new filter inline that had no signs of sediment that I could detect. I am personally going to rebuild the valve and replace all lines and filter. As I said, the carbs remained spotless after a complete disassemble and scrub. The needles and seats look great and don't even show a wear ring on the needles. I payed real close attention when taking them apart this time to check for debris, as I DON'T want a repeat of sending it away to have it come right back!

Wondering if the air/mix screws need to be adjusted and it was running too rich. Seems pods require more of everything and are outside the FSW specifications. If the tank leak doesn't solve the issue, I would adjust the screws towards the lean side, and make sure they are all equal.

I would tend to agree with you, but it ran so great every time prior to filling the tank. I have a formula for pipes/jets/pods/air screws that I have used on about 10 650's over the last 20 (WOW, I'm getting old) years. I'm actually considering the possibility that the coils are getting hot and breaking down as one factor. I have a set of known good coils that I will try if the symptoms re occur.

SO, I found out the ALL 4 intake rubber manifolds are leaking at the head. Evidently the owner took them off and they didn't seal tight when they were put back on. Why, then did it run great until after it was filled up? My guess is the screws didn't get fully tightened and worked lose. (like the one that was almost all of the way out when I got it back) I sort of blame me for not checking them the first time the carbs were of. Is there a good product to put on them to help them seal to the head, but not glue them on forever?

Buy new ones. Don't even bother trying to glue, goop, or otherwise seal up old ones. That will be a waste of time. Ed

Ed, I agree completely. However it's not my bike. I know patching a bike is a bad omen, however after the owner sees that it's not likely to work he will be willing to pop for new.

If it was me I would simply refuse to do the job poorly. Ed