Export thread

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?

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.

seattlepioneer said:

Xperts!

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.

Click to expand...

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...

I would suspect the pickup tube might have a crack or sucking some air. Is it the old metal carb or is it plastic? The plastic ones would warp slightly causing air leaks too.

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.

cpurvis said:

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.

Click to expand...

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???

Tinker Ty said:

I would suspect the pickup tube might have a crack or sucking some air. Is it the old metal carb or is it plastic? The plastic ones would warp slightly causing air leaks too.

Click to expand...

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.

Tinker Ty said:

I would suspect the pickup tube might have a crack or sucking some air. Is it the old metal carb or is it plastic? The plastic ones would warp slightly causing air leaks too.

Click to expand...

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

Try your old diaphragm or rob another one out of one of your kits.

cpurvis said:

Try your old diaphragm or rob another one out of one of your kits.

Click to expand...

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.

cpurvis said:

Try your old diaphragm or rob another one out of one of your kits.

Click to expand...

The type tank/carb you describe generally has an open topped bowl just below the top of the tank. Your diaphragm fuel pumps gas up into this bowl which overflows back into the tank. The bowl stays at a constant level and the carb draws gas from this bowl so no float. When the tank is full, it fills this bowl without diaphragm fuel pump. When you tilt mower back or push back and forth with tank nearly full it will slosh gas into this open bowel or cup. Sounds like this bowl, cup is not being kept full. Hole in pickup tube as said, hole in open top bowl (not likely) problem with diaphragm fuel pump, likely.
Walt Conner

Diaphragm and gasket in correct order?

Sounds like a little bit of water in your carb.
Post your engine's model numbers so we know what you have.

Fish said:

Sounds like a little bit of water in your carb.
Post your engine's model numbers so we know what you have.

Click to expand...

No water.

It appears I have found the problem. It was not the carb. This particular Briggs has the long governor rod. The cover was slightly bent.causing it to bind slightly. I did as I said, recleaned everything, reassembled, and now it is running as it should. I did install another new diaphragm. As to whether that had anything to do with it...I do not know. It was perfectly clean when I took it apart, and perfect when I put it together. All is well in the universe now...Thanks guys! Maybe there was a piece of something somewhere that I knocked loose, unsure, but the governor rod getting stuck was the only thing I saw that needed correction...

<<It appears I have found the problem. It was not the carb. >>

I think there is a tendency to have a theory on a problem, and pursue that repair repeatedly even when it doesn't fix the problem. Part of that is lack of confidence that you have fixed the problem correctly.

But you can fix the carb as many times as you like, and it's not going to help if something else is the actual problem.

I've replaced a part on a furnace I was repairing with a new part, but had exactly the same problem upon replacing the part. I sweated bullets trying to identify the actual cause of the problem.

Ultimately I found that the NEW part had the exact same problem! I had accurately diagnosed the original problem being no good, but I lacked the moral courage to repeat the same diagnosis for the brand new, right out of the box part!

Sometimes, new parts, are not, new parts. Like this, I dropped the spark plug getting it off the counter. Installed it in the engine and it still doesn't run. Then people come here and say they put a new plug in. Just typing out loud here. Glad it is working for you. Replacing carb parts like that builds character.

slomo

<<
Replacing carb parts like that builds character.
>>



Good or bad?

How about posting the engine numbers and the part number for diaphragm and gasket. I’ve got an idea for a solution, but until I know your engine I’m not going to muddy the waters.

Just a quick tip - I'm running a similar post on this forum for a Weedeater 500 push mower that runs only on gas poured through the carb... Not sure it applies to your situation but two things I was given to check...
1. Roughen up the mounting-metal on the front surface area on the top of gas tank where carb mounts and seals the diaphram - apparently there was an air-leakage issue with the design;
2. Check the intake-gas cylinder tube for cracks - where the rubber boot from the carb connects to the engine; if plastic, it may be cracked.

Looks like any place air can enter the the gas supply flow would need to be checked.
greynold99