I see lots of posts relating to carburetors overflowing and when they overflow, the advice is almost always the same. Let's look at this issue in a bit of detail and try and clear a few things up.
First, overflow can occur when the bike is running or when it is not running.
OVERFLOW WHEN BIKE PARKED:
1. shut off petcock (gravity flow petcock)
2. if you have a vaccum petcock fix the diaphragm or vacuum line.
If gas is not shut off when the bike is parked, the carburetors rely on the float needle and seat to shut the supply of gas. The float needle and its seat were not designed as positive gas valves but only to control and meter (with the float while the bike is running). To make the needle/seat work as well as they can:
1. park on centerstand
2. use inline filter
3. set float levels using service fuel level method
4. make sure that the needle/seat area are clean and free of debris as small debris will cause the seal to be poor.
5. the needle should be replaced if it has any visible wear and the seat cleaned using a q-tip and brasso or other slightly abrasive stuff to give the brass seat a bit of a polish.
6. float may be sticking open; remove bowl to check to see if it hangs in the top of the float bowl and correct reason for it hanging up there, if it does.
BIKE RUNNING OVERFLOW:
The carbs can overflow because of a malfunction in the float system or because there is no combustion. To test, spray water from a pump bottle on the exhaust head pipes. If the water vaporizes on all four head pipes and you have overflow, then it is likely the float system is malfunctioning. The same problems will cause these overflow issues as with the non-running bike.
If the pipes are cold; that is, water runs off when squirted onto the pipes, the problem is NO COMBUSTION. This problem is very common and is often mis-diagnosed as a needle/seat or float issue.
If you are in a NO COMBUSTION category, gas will pour out as it is being drawn through the carburetor for that cylinder, atomized and then dumped out raw into the combustion chamber where it will run down the cylinder walls and foul your oil, run into the airbox and wet your filter and even run out the exhaust pipes. While the raw gas remains a symptom, don't operate the bike till you have changed the oil and dried the air filter.
If you have a NO COMBUSTION Next, pull the spark plugs and clean them to ensure that gas fouling itself isn't the reason there is no current combustion. When you restart the bike with cleaned plugs, if a NO COMBUSTION condition remains (water spray bottle check again), the problem is that there is either no or low compression on that cylinder OR an electrical issue.
NO COMPRESSION?
The no/low compression issue may be a ring issue where an engine rebuild is required but is more likely a lack of valve clearance. Check valve clearances and ensure the proper clearance is maintained THEN check compression to ensure that compression is within spec. A valve that is slightly hanging open from lack of valve clearance will cause that cylinder to lose compression and there will be no combustion. I devoted a whole section on my web site to valve clearance:
www.wgcarbs.com/269767.html
NO COMBUSTION DUE TO NO SPARK:
Most folks know to hold a spark plug up next to the cylinder head and turn the engine over and look for spark but even if there is a spark, it may be inadequate for complete combustion. A service manual can guide you through all normal maintenance and service procedures for checking ignition components except they will not mention underpowered coils as this wasn't an issue when the bikes were new and not anticipated nor were bad connectors/connections.
The most common ignition problems causing a NO COMBUSTION condition are:
1. poor power at the coil
2. coils have much greated resistance than they did originally
3. points/condensors need replaced or the points dwell/gap needs set properly or the condensor has failed
4. plug wires/caps either bad or the plug wires are not seated or installed properly in the coils
5. continuity issues in the ignition wires (wires from points/condensor or pickup coil/ignitor to the coils
6. coils shorting
7. inline ballast resistor resistance much higher than original design value
8. timing way off
9. moisture related short in plug cap
There are probably other ignition related woes that will cause mis-fire or non-fire and hence lack of combustion I am not thinking of.
In any case, a good tune up which inludes valve clearance maintenance and ignition tune up will generally cure lack of combustion issues that cause gas to pour our combustion chambers while a bike is running. That gas pouring out of your carburetors may very well NOT be the result of carburetor tuning problems.
Post edited by: wiredgeorge, at: 2006/07/11 09:50
