Push primer 3 x's & pull-engine starts strong for 1 1/2 secs then dies. Ground wire fine, magneto & pick up fine. New spark plug,new air filter,fresh gas. Mower is lawn boy brand with accessary sensor on rear panel-thinking this may be the culprit. Haven't pulled the flywheel yet.
If the engine is running at all then your sensors should be ok. It sounds to me like its starving for fuel? Once the engine runs out of prime then it starves. Does the fuel system have a shut off valve? How about an inline fuel filter? Either could be plugged. I think what you will need to do is remove the carb from the engine and check to see if its clean and if fuel from the tank is flowing easily to it. Once you have the carb off the engine, remove the bowl from the carb by removing the bottom bowl nut. Use a small can or an ash tray to hold the small pieces. Shake the float back and forth to see if there is anything in it. Some floats are plastic and some are tin. If there is any liquid inside the float there is your problem. Otherwise continue on with your diagnosis by using a bread bag wire, minus the outer covering, and a little jet spray to probe and clean the internal jets. Pay particular attention to the center main jet which will have a small perpendicular air bleed hole near the bottom and to the air vent hole that is on the face of the carb where the air cleaner mounts. Any tiny piece of chaff will cause these to plug. For reassembly, the inlet needle slides into the float, and they are held to the casting by a pin. You can push the pin out with a small screwdriver and then grab it with a pair of needle nose pliers to get access to the float. Finally, check the O ring for cracks that goes between the bowl and the casting. This is an easy job, just take your time. Lawnboys are one of the better machines.
I just fixed my mower today after almost giving up on it. It would start, then stop after about 1 or 2 seconds after priming it. So I knew it wasn't getting fuel after starting.
I first tried the standard things such as checking gas cap for venting, I removed the cap and tried, but same problem. I checked the fuel line from tank to carb, but it was OK.
So then I removed the carburator and cleaned all over, sticking a pin in the little jets on the bolt holding the bulb. I pounded it all over with carb cleaner even though everything looked very clean, nothing appeared to be dirty and no visible problems. Then I noticed that the float as I tipped the carb up and down didn't always go down. Then I used WD-40 to blast the hinge / springs around the float.
I reassembled the carb, air intake, and fuel tank back on to the mower and tried it. It worked and saved me a few hundred that I was ready to spend on a new mower.
When primed, fuel is forced into the carburator so it started right up, but since the float was sticking in the UP position, it though there was already fuel in the bulb and this didn't allow more fuel from flowing into the carburator from the tank. The mower is about 8 years old, Tucumseh, but this will let it last me a few more years.
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June 16 2012 I ran into the above 3 second run and stop issue with my 7 year old Toro Recycler. My mechanic neighbor helped me to find the root cause. The jet near the the float had a clog (from dirty gas) in one of the the pinhead-sized intake inlets.
Sounds like the float in the carburetor bowl has a crack in it. Just replaced one on an LV195EA. The part is under 5 bucks and should be easy to get from most mower repair places. The easy fix is start by pinching off the fuel line with a set of vice grips not too tight but tight enough to crimp the hose if of course there is no shut-off valve. Remove the bowl nut on the bottom of the carburetor bowl. There is a gasket on the bowl nut and on on top of the bowl inside so don't damage them. Gas will leak out but will stop (if you pinched the fuel line off) and you will see the plastic float. Eyeball it for any cracks and even if you don't see any obvious ones remove it to check closer. To remove there is a drift pin that holds the float to the carb body on the back side of the carb. Slide the pin out and remove the float carefully, there is a needle valve attached to the float on the rear as well. Don't damage the small wire that holds the needle valve, the valve and wire are on piece and re-usable. Soak the bowl bolt and needle valve in parts cleaner while you go to the parts shop for the float, this will eliminate some other issues the carburetor has. Re-install is easy but the awkward position you will have to get yourself in make it a little harder. Just put the needle valve back on the new float (wire under the metal tabs to hold it solid) and slide the needle valve into the opening then slip in the drift pin. The hard part is over and now put the bowl gasket on the carburetor body first over the ridge. Now place the bowl over the float and re-install the bowl nut with the washer in place. Hopefully it runs fine. Doing this re-build with the carburetor on the engine beats the heck out of removing it and then having to remember which throttle control lever goes to which spot on the carburetor and on the governor. Best of luck all in all it should take about an hour
Inlet needle and seat
I have the same problem, and the issue is the primer bulb. I have a Tecumseh 6.5HP lawnmower engine on a Toro Recycler GTS. I prime the motor, pull to start, then it runs for about 25 to 30 seconds and dies. I noticed a small amount of moisture around the bulb seal on the prime button. Sure enough it was a pinhole crack. This was preventing a sealed chamber. Without a perfect seal the flow of fuel was interupted (as the fuel passes through the bulb to get to the carburator. You can buy a replacement Carburator. It is easy to remove and replace: Tecumseh 640350 or replacement SKU# 50-643(F-207).
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