Jacobsen lawn queen advice

I have a late 40's to early 50's Jacobsen lawn queen reel type mower. When I get it running the rpm's won't always stay at a constent level at full throttal. I know that this is a carburator related problem. I just got a spare carburator off a engine that's year or two newer that will fit on my mower. There is not a whole lot of adjustment on the carburator that's on my mower now, and it's been taken off and cleaned. I'am wondering whether I should put the new carburator on it or try and get the carburator that's on it working better? Thanks.

[Andrew Mackey]

The condition you describe (unstable RPM) is called 'hunting', and it has many causes besides the carb. First, is there any play in the throttle and or governor linkages (worn links or worn holes)? Any play or looseness will cause the engine to hunt. Check the throttle shaft where it goes thru the carb body by pushing it in different directions.. There should be no play, and if there is, it will cause an air leak - affecting mixture, and it will cause a change in throttle setting, speeding and slowing the engine as the governor holds a constant setting. By all means, check out the carb main jet. See if it is partially blocked. Also check the float level and condition. Check the fuel supply: is the fuel tank allowing the carb to get enough gas? Look for a kinked fuel line (it may appear OK, but be collapsed inside). Check the fuel filter - is it clear and clean, or is it rusty? Is there any debris in the tank? Is the fuel clear and clean? Check the carb fuel needle and seat, is the needle seating properly? Is the inlet port restricted with debris? And thats just fuel delivery! Next check the carb mounting flange. It should be flat. Many times I have encountered carbs that have been warped (flange ears bent) due to overtightening. Install a new gasket, and check for leaks - take an eye dropper with a couple drops of gas in it and drip the gas on the gasket while the engine is idling. If the engine speeds up, the flange is leaking, sucking air. (WD-40 works too but leaves a mess, dont use carb cleaner-it will remove paint, and will cause internal damage to the engine. Next check the reed plate. Is it tight? Are all the reeds laying flat? (some had 1 reed, others had up to 4 small ones!) If the reeds are not laying flat, mark with an indelable marker and remove 1 at a time and inspect carefully for cracks. If the reed(s) are OK, reinstall reversed, and the reed should lay flat. Check the reed plate for flat also, overtightening will warp it at the mounting flange. Check the block, also, and make sure the bolt or screw holes are not 'pulled'. If they are, carefully file flat, makong sure that no chips get into the engine. Check the engine side plate, and make sure the bolts are tight. (This plate is where the crankshaft is removed from the block during dis-assembly) Check the plate for cracks also. Lastly, check the crankshaft and the seals. First, try to move the crank in the block. There should be minimal movement. If you can lift he crank more than a thousandth or 2 (.001-.002") then the crank bearings are worn This will allow the crank to 'float' while running, and this movement will displace the seals, allowing the engine to suck air thru them, thus leaning out the mixture. (A clue to bad seals or worn bearings is the presence of oil at the seals after running the engine.) If the crank is tight, mix a few drops of dish detergent in a small amount of water (1/4 cup). Remove the flywheel and the spark plug. Open the throttle wide open. Apply a few drops of the soapy solution onto the seals as a friend turns over the engine fairly quickly. You should not see any bubbles at the seals. If you see bubbles, the seals need replacing. Be sure to rinse off the seals and the engine when done, and pat dry - the soap may cause corrosion if it is not washed off! Remember - on a 2 stroke engine, air laeks are not your friends! Good Luck!
Andrew

[Fred_M]

I would add that most governor rods have a spring on the rod that keeps the levers it moves pulled tight to the rod. The spring can break and it allows engine vibration to rattle the butterfly around which wears out the carb where the shaft goes threw it and causes the engine speed to pulse. It the governor linkage is stiff from lack of lubercation then that also causes hunt. Most times though it's just a mixture problem easily adjusted by fiddling with the mixture screw(s). Fred