RG500 Float Valve Diagnostics

The carb fuel level issue is best handled with the bodywork and filters left off the bike until satisfactory float behavior is established. The bike will run perfectly fine without the filters for this process. Be prepared to start and ride the bike. This procedure can't be done on a lift or a dyno. Confirm that your front float bowls are on the correct carbs. Check that the overflow tube (inside the bowl) is located toward the rear of the bowl. The rear bowls only work on their respective carb bodies due to the choke pick up tube. When the front bowls are reversed, the overflow tube is too low in the fuel and will allow gas to escape even when all is well with the float level. While you are at it, fit the bowls with long drain lines secured to the lower frame rail ending behind the driver foot pegs. Make note of which hose goes to what carb. This will help you determine which carb needs attention.
Confirm that the float level is set to 17 mm from the bowl gasket (add 1 mm if the gasket is removed).

Check for fuel filters being present in the rear carb spigots (where the tank lines connect). Check for signs of rust or contamination in the tank or fuel supply. If you find problems here, it is best to address this area first by cleaning and sealing the fuel tank to assure a fuel supply that is uncontaminated.

Turn the gas on. If you see gas coming out of the overflow tubes, turn the petcock off. Pull the choke and start the bike. Let it go through warm up until it starts running out of fuel. Turn the fuel on again and check for fuel overflow. If necessary, repeat this process (controlling the overflow with the petcock) until the bike can be ridden. The floats often hang at the bottom of the float travel when the carbs are drained for service. The purpose of this procedure is to give the floats a chance to settle with the help of engine warmth and vibration and is a normal part of the setup process. Sometimes a gentle tap on an overflowing carb can help free the float. When the bike can be ridden away, continue to alternate between on and off with the petcock until all carb floats have stabilized.

When the RG500 was first introduced, many owners complained about fuel overflow problems. When the bike was bumped or when parked in the sun the carbs would burp fuel. There were many gas petcocks replaced under warranty without much success in eliminating the problem. Suzuki issued a factory service bulletin concerning the gas leakage and stated that this was a natural occurrence caused by the 9 mm I.D. fuel line (the largest ever fitted to a production motorcycle) connecting 22 liters of fuel (again, the large fuel tank capacity mounted so highest above the carbs) stepping down to smaller fuel line to the front carbs. It was the factory's contention that this created a natural siphon effect and the substantial fuel volume in the lines (past the petcock shutoff) will be prone to burping gas out the fuel overflow.

This is also why Suzuki issued an update with replacement belly pans including longer overflow hoses to be routed outside the pan to address this issue. The brand new Mikuni needle seats leaked when properly set by the factory. They still leaked when they got older. Ball valves have been an improvement over the stock parts but do not address the fuel volume and carb location (relative to the gas tank) issues. Those who have fitted TMX carbs (a completely different carb with totally different fuel valve) to the Gamma experience similar fuel problems.

If your ball valves aren't stabilizing the float level enough to keep the plugs clean and running smoothly, something is amiss. However, if you have high expectations of completely fuel tight carb operation, please consider the well documented reputation of the RG500. They have a tendency to burp fuel. I share your desire to optimize the carb behavior of the Gamma and have been hard at work to deliver the best results possible for 23 years and counting.

The Gamma petcock is unique. It has one inlet measuring 9 mm. It has 2 outlets measuring 9 mm each. Such a system will not function properly without a vented plenum (where the inlet and 2 outlets meet). This petcock plenum vent connects the petcock to a fitting on the bottom of the tank, next to the cap area drain. The cap drain hose fitting is the one most centrally located. The petcock fitting is outboard of the cap drain (get these reversed and you will have gas spilling out around the gas cap whenever you brake hard with a full tank). The vent continues up into the tank near the roof.

Its purpose is to allow gas to flow without impedance from the dissimilar flow rates of the inlet and outlet in the petcock. This vent also allows a considerable volume of gas to continue flowing downhill when the petcock is shut off. So, even though you have shut off your petcock, it will still deliver enough gas to soak the area underneath the bike.When possible, it is best to shut the petcock off a block away from coming to a stop to allow excess fuel to evacuate the fuel lines. Supplemental Fuel Petcocks can be installed to absolutely assure no fuel leaks while the bike is parked.

We live in an era that has made motorcycle fuel injection the standard fuel control system. It is easy to forget what were normal behaviors with carburetor equipped machines. With FI systems, all fuel is delivered under pressure directly into the motor with no possibility of overflow. Much like those of us who demand that the Gamma shift and display clutch behavior comparable to the latest GSXR, some consideration must be given as to the differences in design. The Gamma is not a GSXR (that's actually a GOOD thing). However, it IS a phenomenal machine borne of racing and delivered to us for the sheer joy of experiencing all it has to offer as the best road going 2stroke ever sold to the public.

When it does things to remind you that it's a Gamma, cut it a little slack. When you try to rev it to 15k (just like your new R6) and it comes back in one piece, consider the favor returned. With any luck, you two will develop a long lasting relationship without killing each other. We can only hope so.