Blocked return/spill-back port (trapping the fuel instead of letting it flow back to the tank).
Thermal tank pressure / bad venting (pushing fuel past the pickup tubes continuously).
Mismatched or incorrect diaphragm spring tension (altering pump stroke/travel).
Mixture screw backed out too far (over-delivering through the low-speed circuit).
Choke butterfly staying partially closed (pulling a heavy siphoning vacuum).
The Return Hole Got Blocked: Inside the casting under that side cover, there is a tiny overflow/return port designed to let excess fuel spill back into the tank once the internal well is full (acting just like a float bowl overflow). If a gasket edge gets misaligned slightly, or if pattern-cut aftermarket gaskets cover that tiny return hole, the fuel has nowhere to go. It keeps pumping fresh fuel into the well until it overflows straight out the throat and down the valves.
Thermal Siphoning / Vapor Lock: As the metal tank and carb soak up engine heat for a couple of minutes, the air space inside the sealed tank expands. If the tank cap vent isn't clear, that pressure forces fuel up the pickup tubes continuously, overwhelming the metering wells regardless of the diaphragm's pumping action.
Checking that the return spill-back port is completely clear and unobstructed by the new gasket usually stops them from filling up plumb-full and drowning out.
the small spring tucked under the diaphragm is what controls the tension and travel of the pump paddle/actuator.
If the spring is too long or too stiff, it keeps too much constant pressure pushing the diaphragm inward, which can force the pump to stroke too aggressively or hold a valve open longer than it should. On the flip side, if it's incorrect or mismatched, it upsets the delicate pressure balance against the crankcase pulse, altering the stroke and letting fuel continuously creep or flood into the well instead of metering correctly.
Getting that exact spring tension right—or making sure an aftermarket kit didn't supply a generic spring that's throwing off the pump travel—makes all the difference in stopping that warm flooding.
1. The Mixture Screw (Idle/Low-Speed Adjuster) How it affects flooding: On these carbs, the idle mixture screw meters the fuel drawn up from the idle well. If the screw is backed out too far (too many turns open), it creates a wide-open path for fuel to feed through the low-speed circuit.
Combined with a warm engine or tank pressure, excess fuel rushes through that circuit unchecked, loading up the cylinder and contributing to the flood. (Standard initial setting is usually seated lightly and backed out about 1.5 to 2 turns).
2. The Choke Butterfly Staying On How it affects flooding: If the choke butterfly is even slightly partially closed (or if the linkage/stop is bent so it doesn't open 100% when pushed off), it acts like a permanent choke.
The Result: As the engine runs, a partially closed choke creates a massive vacuum pull right at the throat. That high vacuum acts like a siphon, drawing an enormous amount of raw fuel straight out of the jets, instantly flooding the engine and killing it within a couple of minutes once it's warmed up.
I've always just removed the side cap and stretched the outer spring put it back together and if it revs out too fast on idle put a brass washer behind the cam and set the poppet on C , then I just control the RPM by the throttle control.
But correct Procedure is.
Governor Spring & Calibration Spring Specification: The standard outer governor spring for a G4'LM carburetor is typically the red spring (Part No. CRO3417A), rated at approximately 150g tension. If an incorrect or stretched spring is installed, it changes the vacuum balance against the diaphragm.
Field Workarounds: While stretching the spring or inserting a brass washer behind the cam can force higher revs or adjust idle, doing so bypasses the engineered vacuum governing range, which can lead to unstable governing or over-speeding under load.
Poppet Valve & Restrictor Confirmation Poppet Valve Setting ("A" vs. "C"): Factory specifications for 4-blade disc models indeed require the poppet valve set to "A". This restricts maximum airflow/vacuum response compared to setting "C", intentionally running the engine at a lower, safer maximum RPM to account for the heavier mass and momentum of the 4-blade cutting disc.
Vacuum Hose Restrictor: Yes, the vacuum line or end-cap fitting for 4-blade disc variants features a built-in restrictor (or a restricted nipple hole) to dampen the vacuum pulse. This prevents the governor from reacting too aggressively to rapid pressure fluctuations.
Hi all, I have a 2003 Victa Commando Keystart CKS201K. Someone else in the family has meddled with the carby, so I’ve put a genuine kit through it, new primer cap on, and a genuine new correct fuel jet. The rest of the mower is near-new and all gaskets/seals etc are in good shape with no air leaks.
Can someone please advise me what the correct governor spring for this model is? It runs great but seems to run slower than what I recall in the past. Full actuation of throttle is confirmed and adjustment at both ends is spot on. The existing spring has no colour on it and I suspect has been incorrectly swapped out…. (not by me). I've worked on mowers and small engines for most of my life, but just lack the info for this specific model.
The mower is a 4 blade disc model and has the poppet valve set to “A” - based on a partial service manual I found stating that 4 blade disc models should be set to "A" and operate at a reduced RPM than 2 blade models. It’s an A3C/A4C marked valve from memory. Allegedly, the vacuum hose connected to the end cap on the carby has a restrictor valve in it for 4 blade models. If someone could also confirm that to be true, that would be great.
Hey another question I'm hoping someone can help me with my briggs and stratton 5hp I ended getting a brand new pulse jet carbi iv got it starting again but after a couple of minutes the carbi is full of fuel and floods the engine to a stop, ends up with fuel pouring out the bottom of the throat right at the choke end and even down into the valves,,,,so far iv replaced the pulsejet ,,,gaskets for it and the head electric ignition ratchet clutch and pull start, and a new diaphram I have no idea how this happens any help would be great
Hello good people. A newby to the forum here. I have just got my hands on an old Rover Lawn King 02950/180 and am working my way through it's issues. I have spent a couple of days trolling the net for service manuals for this machine, engine, and transmission. No luck. It has a Briggs and Stratton 28Q777. The transmission is a Hydro Gear with the identifiers 036488 and 6107T4230. I see there is a transmission forum but I thought I would throw that one in here to start with. I dont know if this was a common varation in Australia. My previous experience has been with Greenfields. Thanks in advance.
Hey iv got an old 5hp magnatron B and S engine IV got working again but now it's revs go from full throttle to low,,,,,,all new carb but I knoticed on top of the new pulse jet their is a tiny spring on one of the rods for the revs I'm guessing it is suppose to be hooked to each side but it looks so tiny like fuse wire I can't see it making any difference is their support to be a spring on the top of the pulsejet carbi to stop the serging revs
Cheers for clearing that up for me fellas, on the deck where it reads “model” the numbers are hard to make out but I’m pretty sure it’s 62, would love to see a colour picture, guess there will be one since I’m finished the resto, cheers again
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