Neighbor brought a Toro Personal Pace (Briggs 7.0 Quantum) with the blade clutch feature. When it starts with the blade not yet engaged, it surges wildly. But when the bail is pulled thus engaging the blade, it runs great (3200 RPM). Tried several known good & clean (one brand new) carbs & still happens. I even opened the bowl nut jet on one of the carbs with micro drill bits increasing the opening incrementally 3 sizes up from OEM. No success. Am puzzled by this one. Maybe the gov gear inside the engine is the problem. Anyone experienced this?
Toro Briggs Quantum surges at idle but fine when blade engaged
Lets start with the actual model type and code of the briggs engine. so we can see what you are looking at. Some of the Briggs push engines have two governor springs and if they are not set correctly will cause surging. But that surge symptom you are referring to is normally due to a carb issue. But wouldn't be a bad idea to pull the engine cover and inspect the intake tube for cracks or being loose which would introduce air which would cause a lean run condition.
Quantum Model 120000 675 Series. Just one gov spring. Will check the intake tube. But if in fact there is too much air getting in from the tube or elsewhere, why would the engine run great under load (blade engaged) but only surge under no load?
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you can spray down the area around the intake tube, where the carb mounts etc with WD40 in a trigger sprayer, any change in engine speed or if it blows smoke will tell you where the leak is.
Your advice is most welcome. I think you must mean passages clogged to some extent. Perhaps, but I tried 2 other used carbs pulled from working, non-surging engines plus a new carb and the problem persists. The only passages I know of are the two pictured below plus the bowl nut passages which are completely clean. Are there others?
Thanks, will try that in the am. But again, I must ask, if in fact there is too much air getting in from the tube or elsewhere, why would the engine run great under load (blade engaged) but only surge under no load?
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Those two air holes are 1) fuel bowl vent and 2) air bleed for fuel mixture. Neither will cause the carburetor run lean normally.
Sometimes the main jet has to be enlarged ever so slightly due oxidization. And sometimes it is simply too lean to start with. This is why I have a set of micro bits here.
Sometimes the main jet has to be enlarged ever so slightly due oxidization. And sometimes it is simply too lean to start with. This is why I have a set of micro bits here.
Thanks. Maybe you missed it in my original post, "I even opened the bowl nut jet on one of the carbs with micro drill bits increasing the opening incrementally 3 sizes up from OEM." That is, I inserted bits until I found the 1st one that would not go vertically through the OEM bowl nut jet hole. Then I enlarged said hole with that sized bit. Tested; still surging. Drilled out the next size up; still surging. Went up one more; same. Last attempt was with a 0.75 mm bit. Should I go up even more?
