Stihl BG75 Blower surging at WOT


Old 08-09-06, 04:45 PM
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Stihl BG75 Blower surging at WOT

Ok, oh great wizards of small combustion engines, I have a problem that really has me confused. It will not run at full throttle. This is a Sthil FG75 Blower with a Zama C1Q carb, the carb does not have a H and L adjustment screws, only the single Main Fuel Adjustment screw. It uses and RB-66 rebuild kit. When I received the blower it had old fuel, I put in new fuel, I would start but not stay running, it would spit, sputter and eventuall die. Since then, I carb disassembled and cleaned with spray carb cleaner and brake parts cleaner in all available holes cracks and crevases(the Zama website says not to soak in dip cleaner), I also didn't use a high pressure hose to blow through the holes only the carb cleaner which was Berryman B-12 Chentool. A carb rebuild kit was installed(RB-66), attention was paid to gasket,diaphragm sequence etc. and all that stuff. Fuel lines were flushed, filter/fuel pickup checked and clean. It started but would not go to full throttle. I ran 1/4 tank of fuel with heavy concentration of Chevron Chemtron Fuel System Cleaner at idle, removed muffler, burned all the oily gunk from the muffler, the piston, rings and cylinder walls were spotless. Now it will start first pull and idle but will bog and surge as I give it throttle. I actually got it to full throttle while playing with the throttle and choke at the same time, then when at full throttle I removed the choke and it remained a full throttle until I released the throttle(5 min) then it was back to the bogging. I did not remove the welch plug. That's as detail as I can get, sorry for being so long winded. Have a nice day. Geo
Old 08-09-06, 04:53 PM
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Still sounds like a carb problem.What you do. take it apart remove all rubber from the carb and soak in a BATH type cleaner. No break fuild.let it sit following the instructions on the cleaner.try another kit.You might have runied it with brake cleaner.There not made to use on rubber.Don't use carb cleaner on any of the rubber parts. Its like an acid to them.If you don't want to do that all over again try this trick with the engine running spray some WD-40 or like oil at the gaskets between the 2 halfs of the engine. If it bogs down or speeds up the gasket needs to be replaced.Are you using the right mixture
Old 08-09-06, 10:57 PM
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Is the lever on the inlet needle set properly? It does still sound like a carb problem. I don't generally like to use bath type cleaners on small 2-stroke carbs either. If I do use it, I don't like to let the carb soak for more than 20 minutes. I do suggest using compressed air to blow it out well.

This doesn't sound like a crankcase leak to me.

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