TOPIC:

Hi - I recently drained a load of gas out of the oil pan. What could be causing this? The petcock is new and working (which was not the case the first time this happened). Any ideas welcome. Thank you in advance.

The only path fuel can follow from the fuel tank to the oil is through the carbs.

If the carbs were flooding so badly that they allowed a bunch of fuel to contaminate the oil while the engine was running the engine probably would not run for long, or if it did it would run poorly as at least one cylinder would not be firing as fuel flooded through that cylinder.

So, it would seem likely that the flooding of fuel into the oil is happening when the engine is shut off. Assuming you have the stock petcock that shuts off when there is no vacuum from the engine that should not happen even if one or more carbs has a flooding problem. The petcock should stop the flow of fuel when the engine is off unless you have it set to the "prime' position. Also, the carbs should stop the flow of fuel assuming the floats are not sticking or set wrong.

Here's a test I would try - with the engine shut off remove both the vacuum and fuel supply hoses from the petcock and see which (if either) petcock orifice is letting fuel flow. Once you have determined and possibly corrected the petcock issue you should then check to see which carb(s) are not operating properly i.e. shutting off fuel flow once the car bowl is filled. Ed

Every once in a while it’s a good idea to reflect over why shit happens, as it’s usually not just by bad luck.

So why does the bike flood the crank case with fuel?

The most common reason is because water accumulates in the tank causing corrosion (rust) inside the tank, small rust flakes makes its way to the petcock and inhibits the vacuum controlled petcock to close as it should, the rust flakes continues there journey in to the carburetors and makes its way to the float needles and inhibits them to close even if the float is at its top position.
So when you have your Gpz750R1 with Mikuni’s BS34 carburetors (that lacks overflow tubes) parked, fuel will continue to flow from the bikes tank, passing the petcock that doesn’t close, into the carbs where the float needle doesn’t close, causing fuel to escape the only way there is, and that’s down the inlet manifold and if an inlet vales is open the fuel will flow in to the combustion chamber, passing the piston ring and down in to the crankcase.

So what to do about it?

Unfortunately there is no quick fix and I strongly recommend you to do the right thing from the beginning. I have tried to take the easy way out but the problem will come back in no time.

So what do you need to do?
1. Clean the tank and remove the rust.
2. Clean and refurbish the petcock.
3. Clean and refurbish the carbs, replacing all the o-rings while you are at it.
4. Change all fuel lines and ad an external fuel filter.
It might sound like a lot, but trust me it’s worth it, otherwise you will fight an uphill battle and will be become a master of removing your carbs.

So first things first.

Tank cleaning.
Remove the tank, empty it, remove the fuel cap, the tank sender and the petcock.
Wipe the areas around the filler hole, tank sender and the petcock with denatured alcohol and tape them up with good quality racingtape.

Degreasing.
Add ½ liter of degreaser to the tank and a hand full off sharp plaster board screws, seal the tape and shake the tank around for a good 10-15 minutes, the sharp screws will help in mechanically grind of rust flakes in the tank.
Flood and rinse the tank with hot water and remove the screws.
Now tape up the tank again and ad ½ liter of denatured alcohol and shake again.
Drain the alcohol remove and the tape.

Removing rust.
I have tried all kinds of methods, lining, electrolysis, mechanically and acids and there is no better way than using acids to sort the rust problem. You can use a variety of acids from weak like white vinegar (acetic acid) (cheep), Phosphoric acid (expensive) to hydrochloric acid (scary). The stronger the acid the faster the process will be. 30% hydrochloric acid is pretty scary stuff but will clean your tank in 10 minutes and acetic acid will take a day or two. The problem with the weaker acids is that it’s hard get the tape to stick for that long and there will always be a part of the inside of the tank that is not fully submerged ad that part will rust like crazy. Therefor I use 30% hydrochloric acid and take all the needed precautions (use rubber gloves, face shield and a plastic apron).

Rust removal
Tape up the tank again and add ½ liter of 30% hydrochloric acid and slowly and continuously turn the tank around so that the acid gets to all parts of the tank for 5 minutes if there was just a little rust, 10 minutes if it was bad. Stop every now and then ad let out the hydrogen gas that is produced by the process (this is an outdoor activity). After 5-10 minutes drain the acid out on a concrete slab where the acid can be neutralized by the calcium carbonate in the cement.

Rust inhibiter
Now fill the tank up again with ½ liter of tile cleaner that contains Phosphoric acid + ½ liter of water, seal and continuously turn the tank around for another 10 minutes. The Phosphoric acid will now react with the steel of the tank and turn in to iron phosphate which will cover the tank and act as a rust inhibiter, without this your tank will flash rust in seconds.
After 10 minutes drain the tank and flush generously with water and remove the tape.

Rust protection
Now dump 2dl of WD40 in to the tank, approx. half a small spray can and shake about and try to shake out as much water as you can. The use a hair dryer (not a heat gun as they are to hot) and blow in to the filler hole and the fuel sender hole alternately while continuously turning the tank so that water never gets sitting for a good 30 minutes. Heat a long the seams of the tank until you ar completely sure all water is out.
Tank is now done.

Petcock.
Disassemble the petcock and let the aluminum parts run in a ultrasonic cleaner for 30 min with a mild detergent, rinse with water and take a cotton bud with stove top cleaner and polish the plunger seat and check that the seat is not pitted.
Reassemble with a new diaphragm and fuel tap gasket (buy the Kawasaki original, it’s worth it), check that the small spring is in good nick and is not rusted, if it is, buy a new spring.
Unscrew the small brass fitting for the vacuum line on the fuel tap cover 16146-1005, take care for a small gasket fill fall out, make sure it’s clean and refit.
Check that the petcock works as it should, I have a plastic can that I fasten it to, fill up with gas and connect the hoses to, suck on the vacuum hose and fuel shall start flowing, when you let of the vacuum hose the fuel shall stop flowing immediately (2-3 seconds).
Petcock done.

Carburators
Carbs, download Ed Ness’s (Nessism) superb Mikuni BS34 refurbish manual and go over your carbs and change all o-rings, no need in buying the aftermarket kits with all the brass parts as they usually alright, but buy the correct o-rings of good quality.
Check the float heights with the clear tube method on your work bench before putting the carbs back on the bike again.
Carbs done.

Fuel lines
Exchange all fuel and vacuum lines, Suzuki sells 8mm fuel hose of good quality as a spare part it’s the shit. Add a miniature fuel filter (don’t go for a regular paper fuel filter as the will starve your bike of fuel.

Now put it all back together, buy new gaskets for the fuel sender, petcock and tank lid and you will most probably not have any problems.

Or you can try to take the easy way out and just line your tank and you will have a wonderful time periodically clearing your carbs in the future from tank lining that most likely will clog them.

Brgds Anders