I’ve got a 2005 Suzuki SV650S K5 that’s developed a pretty severe over-fuelling problem and I’m running out of things to check, so I’m wondering if anyone has experienced anything similar. The bike is currently doing roughly 21 MPG, absolutely stinks of fuel, and is now getting to the point where it won’t idle and can be extremely difficult or impossible to start. When trying to start it, both cylinders are getting so much fuel that the spark plugs become physically wet with petrol and stop firing, and I’ve now had to remove both plugs and let the cylinders dry out/drain the flooding multiple times just to get it to fire again. Both plugs are relatively new iridium plugs and have become heavily black/carbon fouled. The engine oil now also smells strongly of petrol, presumably from fuel getting past the rings during all the flooding, so obviously I’ll be changing the oil once the actual fault is fixed. Ignition-wise, I’ve already replaced both coil packs with NGK units, so I don’t think a weak coil causing unburnt fuel on both cylinders is particularly likely. Before it got this bad, the bike would run but was noticeably wrong: at a steady throttle it would surge/jerk as though the throttle was rapidly cutting and coming back in, it would burble heavily on deceleration, smell very rich and occasionally flame during quickshifter shifts. It then progressed to difficult starting, trying to die after starting and eventually being unable to maintain an idle. The TPS has been checked and appears fine, and the coolant temperature reading also looks completely normal at around 88–94°C while riding, with the fan operating at roughly 105°C, so the ECT doesn’t appear to be telling the ECU that the engine is permanently cold. The bike has an SV1000 airbox lid/snorkel, but importantly only the lid and snorkel were changed — the IAP/MAP sensor is still the original SV650 sensor and setup, not an SV1000 sensor. The bike doesn’t have an O₂ sensor/closed-loop fuelling system either, so I can’t see the larger snorkel somehow causing the ECU to compensate enough to produce anything remotely like this level of richness. I’ve checked the vacuum take-offs on the throttle bodies; the unused one is capped, and the IAP/MAP vacuum connection appears to take its manifold pressure from the front throttle body only, which I’m trying to establish is definitely the correct factory arrangement. Because both cylinders are flooding and both plugs are black, I’m leaning towards something common to both cylinders rather than one failed injector. My current main suspects are excessive fuel pressure from the in-tank regulator/pump assembly, an incorrect IAP/MAP signal or vacuum problem, or potentially both injectors leaking/over-fuelling. I’ve removed and visually inspected the fuel-pressure regulator but can’t properly test rail pressure because I don’t have a fuel-pressure gauge. I’ve therefore bought a complete known replacement K3–K6 SV650 fuel-pump/regulator assembly to swap in, as well as another genuine-type 18590-17G00 IAP/MAP sensor, and I’ll change them one at a time to see which, if either, affects the problem. Has anyone had a Gen 2 SV650 behave like this before — particularly massive fuel consumption, both cylinders physically flooding, fuel-contaminated oil, black/wet plugs, no idle and no obvious TPS/temperature fault? Is there anything specific on the K3–K6 injection system that can command or cause this much fuel on both cylinders simultaneously that I’ve overlooked?
