Raw fuel coming out of exhaust

G'day, I posted this same post on the KZ650 forum but I thought I would post it here as well as I might get some more suggestions, here is what is happening.
G'day, I have been having problems getting my 1979 B3 getting to run properly. So far I have stripped the engine and when I assembled it I had the bores honed and new rings put on pistons. All engine seals and gaskets replaced, also new valve seals. I have replaced the standard ignition with a electronic and it has really good spark on all 4 plugs. Carbs have been stripped and cleaned numerous times. Valve clearances have been adjusted and all are within tolerance. Cams hae been removed and replaced several times to make sure the cam timing is correct.
I have just checked compression and number 1 is at 40, 2 is at 60, 3 is at 100 and 4 is at 115 lbs/sq inch. my previous compression check a couple of weeks ago had them all up over 100.
I can get the bike started and at this stage number 1 exhaust remains quite cold, 2 sort of gets a bit warm and 3 and 4 get hot. Also number 1 pot is spewing raw fuel/petrol/gas out of the exhaust port and into the exhaust pipe where it is dripping onto the floor from the balance pipe.
I would like some suggestions on how raw fuel and lots of it can make it's way from an inlet manifold thru to the exhaust without catching fire, or causing some sort of detonation either from spark plug or from heat transfer from the 2 pots that seem to be working.
At this time I have removed the head to check out the head gasket which seems OK and I have poured some fuel into the combustion chamber to check out the valve seals and the valve mating surfaces. Looking at the tops of the pistons number 3 and 4 are black, number 1 has minor black marks and number 2 is as shiny as the day I assembled the motor after polishing all of the pistons. The motor would have been run for nearly 40 minutes so far.
A mate down the pub has reasoned that the loss of compression in 1 &2 pots would be the fuel washing the oil off the cylinder walls, (at one stage I had over 100 lbs /sq in on all 4 pots). The only thing I havn't done at this stage is measured the float heights as I am waiting on a tool to do this, regards Neil

3cav84a wrote: G'day, I posted this same post on the KZ650 forum but I thought I would post it here as well as I might get some more suggestions, here is what is happening.
G'day, I have been having problems getting my 1979 B3 getting to run properly. So far I have stripped the engine and when I assembled it I had the bores honed and new rings put on pistons. All engine seals and gaskets replaced, also new valve seals. I have replaced the standard ignition with a electronic and it has really good spark on all 4 plugs. Carbs have been stripped and cleaned numerous times. Valve clearances have been adjusted and all are within tolerance. Cams hae been removed and replaced several times to make sure the cam timing is correct.
I have just checked compression and number 1 is at 40, 2 is at 60, 3 is at 100 and 4 is at 115 lbs/sq inch. my previous compression check a couple of weeks ago had them all up over 100.
I can get the bike started and at this stage number 1 exhaust remains quite cold, 2 sort of gets a bit warm and 3 and 4 get hot. Also number 1 pot is spewing raw fuel/petrol/gas out of the exhaust port and into the exhaust pipe where it is dripping onto the floor from the balance pipe.
I would like some suggestions on how raw fuel and lots of it can make it's way from an inlet manifold thru to the exhaust without catching fire, or causing some sort of detonation either from spark plug or from heat transfer from the 2 pots that seem to be working.
At this time I have removed the head to check out the head gasket which seems OK and I have poured some fuel into the combustion chamber to check out the valve seals and the valve mating surfaces. Looking at the tops of the pistons number 3 and 4 are black, number 1 has minor black marks and number 2 is as shiny as the day I assembled the motor after polishing all of the pistons. The motor would have been run for nearly 40 minutes so far.
A mate down the pub has reasoned that the loss of compression in 1 &2 pots would be the fuel washing the oil off the cylinder walls, (at one stage I had over 100 lbs /sq in on all 4 pots). The only thing I havn't done at this stage is measured the float heights as I am waiting on a tool to do this, regards Neil

Hi Neal
Just curious....have you tried using one of the Thermal Temp. Guns to see what the temp is on all 4 pipes? may indicate one or more cyl not firing?
Just a thought, Im sure others will chime in to help also.
As a matter of fact......check with 650ed on this site!! he's pretty darn good!

Raw fuel doesn't burn, it has to be in vapor form. I think you are on the right track with the float levels.

In #1, raw fuel could be rising from the float bowl up into the carb bore and flowing through the intake port into the combustion chamber.

The reason is often a mal-functioning float valve (might be a speck of grit at the needle seat) or other reason such as mal-adjusted float height, leaking float, float erroneously installed upside down, etc.

A functioning overflow circuit is supposed to allow the rising excess raw fuel to escape through the overflow hoses and exit underneath the bike, all before the fuel rises high enough to enter the carb bore.

On carbs that don't have an overflow circuit, or have an obstructed overflow circuit, the non-functioning overflow circuit doesn't allow the rising excess raw fuel to escape through the overflow hoses and exit underneath the bike.

The overflow circuit may be obstructed by crud in the tube, a pinched hose, etc.

Good Fortune!

Raw fuel in the combustion chamber usually makes its way on down past the pistons and rings and into the crankcase where it mixes with and contaminates the oil.

Would sniff-test and examine the crankcase oil to determine whether it's contaminated with fuel (with attendant risk of catastrophic engine damage). And if the crankcase is fuel-contaminated, change the oil and filter (after correcting the carb issue).

Good Fortune!

To determine whether the carb overflow circuit is clear, the float bowl is removed, and carb cleaner spray may be squirted into the open orifice at the top of the tube, whereupon the spray should exit from the outlet nipple located on the underside of the float bowl, and also exit from the hose that's connected to nipple.

Wear eye protection when spraying carb cleaner or any other pressurized product into carb passages, because it always backfires.

Example of overflow tube inside float bowl:



Good Fortune!

If it was mine I would not fiddle with the carbs, etc. I would try to pinpoint the source of problem. You already have found the key symptom - a gross lack of compression in # 1 and #2 cylinders. OK, with that symptom discovered, why not try to find the root cause? I would suggest you perform a leak down test. That will enable you to find out if the compression is leaking out through the valves, head gasket, or past the rings. The bottom line is that if your compression is a mere 40psi on #1 and 60psi on #2 the bike simply can not run right until those compression numbers are increased. Even #3 is low, but what you discover about #1 and #2 may relate to the compression in #3. Ed

As known, a leak down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor man's leak down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air. Or just use a portable compressed air tank.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune!