I have a Bolens simple rear bag push mower I am repairing for my daughter. I have been working on this style motor since the 70's when I as a kid. Anyway, I have an issue, and it is the second time I have encountered it with this type of Briggs. (Simple Tank mount carb) I went through this thing and installed new diaphragm and gasket, taking great detail on doing it right, and a thorough cleaning of the tank, etc. Also checked the gap on coil, new plug, oil change, etc. Not much else needed on this style motor. It had been searching up and down, as briggs typically does when dirty, and the brake cable was in poor shape so it was replaced as well. So, here is the issue. It starts right up. runs perfect for about 30 seconds, then starts sputtering bad like it is running out of fuel. If I tilt the mower back towards the handle, it runs perfect. What gives? I have double checked, and triple checked the carb assembly, recleaned, and recleaned the tank. I actually washed the inner part of the tank with hot soapy water, and rinsed it, and left it in the sun to dry for a day...as I always have. It is bizarre to me that it will not run smooth unless I tilt it back...oh, and the tank is full. I am human, and as such, I am capable of being stupid and overlooking something, but this has me puzzled. I have considered a faulty coil. and that will be my next step, but wow...any ideas?
This one has me stumped
- Thread starter bbest
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seattlepioneer
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I'm not an Xpert, I'm a Diyer speculating on possible causes for the symptoms you describe.
Since you describe the engine as acting as though it's running out of fuel, I'd take that seriously and suppose that it is running out of fuel. So you have a fuel problem and likely a carburetor problem.
That it runs normally briefly suggests that the carb isn't getting fuel after those first few seconds, which might be a float problem or fuel isn't draining into the carb properly.
Will the engine start again and run normally after this problem has occurred and you have stopped the engine? That might suggest that negative fuel pressure bleeds off once the engine is shut off.
Any engine smoke from the exhaust when this happens? That might suggest too rich fuel rather than too lean.
Since you describe the engine as acting as though it's running out of fuel, I'd take that seriously and suppose that it is running out of fuel. So you have a fuel problem and likely a carburetor problem.
That it runs normally briefly suggests that the carb isn't getting fuel after those first few seconds, which might be a float problem or fuel isn't draining into the carb properly.
Will the engine start again and run normally after this problem has occurred and you have stopped the engine? That might suggest that negative fuel pressure bleeds off once the engine is shut off.
Any engine smoke from the exhaust when this happens? That might suggest too rich fuel rather than too lean.
This is a tank mount style carb...with a diaphragm and gasket. Which is new. Also, there is no smoke, starts right up. The bizarre part, is if I tilt mower back, it stops. It's almost like the thing is starving for fuel...
cpurvis
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Did you fill the tank or just put in a little bit of gas? Did you replace the pickup tube and if so, how close is it to the bottom of the tank?
What I'm wondering is if there isn't enough fuel in the tank and tipping the mower back covers the pickup with gas.
What I'm wondering is if there isn't enough fuel in the tank and tipping the mower back covers the pickup with gas.
It is clear full of fuel. Original pick up tube. This is why I am going nuts. There is no obvious reason why it runs fine tilted back, except maybe it tries to flood with fuel to actually get enough fuel. I am going to remove carb and tank one final time. Clean it all up, and blow it out, again. The part that has me stumped is the fact that it did not sputter like this BEFORE I replaced the diaphragm. It had the typical increase and decrease surging of a dirty carb but it was not cutting out. I am starting to wonder if the new diaphragm is incorrect..which would be odd???
I had considered that, and that will be part of my next inspection. With a full tank the part where it inserts in the carb may be suspect as it is not submerged.. I will look. This is just a basic little mower, belonging to my daughter, but it is small and easy to use. My grandson has cerebral palsy, and he is able to mow with it...so it is important...lol.
With most mowers, I would have bought a new carb by now, and would have been done with it, as it is more cost effective time wise...but I have a dozen or so carb kits for the little bugger, and have rebuilt dozens...never an issue!!! It's the principal...lol
I am installing a new one as we speak. I took it apart, drained the fuel...again, just cleaned the tank with hot soap and water...it's drying in the sun. I cleaned all parts of carb. Looked at pick up tupe, and parts under magnifying glass to assure there are no cracks. All appears good to go. I will reassemble here shortly, and blow things off that I washed before assembly. I have rebuilt these things for years...this one does not like me...lol. If it does not work this time, not sure where to go next, except maybe a misfiring coil?? It has been my experience that they work or they don't, but...occasionally heat will cause them to run poorly, but it isn't even warm before it starts running like crap.