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Mower starts easily, dies in seconds


justdoit007's Avatar
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10-02-09, 01:37 PM   #1  
Mower starts easily, dies in seconds

This is a Briggs and Stratton 4.5 hp engine on 21 inch rear discharge rotary push mower from Home Depot. It is about 6 years old and never has caused problems before or been worked on. It has always ‘been run out of gas’ before storing a few months during the winter.

After priming with ‘red bulb’, it takes off easily but slowly peters out and dies after about 3-5 seconds. Will not start again unless primed again. Always fails this way. This happens on a relatively warm day. I suspect it is a fuel supply problem and taken off a couple of covers to clean debris out and check for anything broken. Also have looked at the plug which is clean and gaped properly (0.03 in.), checked the oil, and cleaned the air filter.

Rest of engine not easily accessible. Want to avoid complete take down w/o knowing what I’m doing and not having a repair manual.

Anyone seen this type of failure in lawn mower engine? All ideas are welcome.

Thanks much in advance.

Chuck

 
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marbobj's Avatar
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10-02-09, 01:55 PM   #2  
Pretty common.

First loosen the gas cap - see if that helps. It could have a cap venting problem.

If that doesn't change things for the better, pull off the fuel line at the carb and check for fuel flow from the tank let it run out a couple of quarts.

If you still have a problem, the carb will need pulled and cleaned.

 
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10-02-09, 04:09 PM   #3  
You need to install a new diaphram kit, it is Briggs part # 795083 or old # 495770 also Lowe's has a kit #5083 which has the same parts.
Here we go;

Remove air cleaner, there are 2 bolts that hold things together, one on the front of the tank 3/8" and one into the block 1/2", remove these bolts, now "slowly" slide the carb/tank off the intake tube and breather tube, now tilt the tank in to release the throttle linkage and waalaa the carb/tank is removed. Check the intake tube to see if the “O” ring seal and plastic retainer are still on the intake tube, if so remove them and re-install them into the carb. Remove the 5 screws from the carb/tank remove carb(don't loose the spring) now spray all holes, cracks and crevases in both the carb and tank surface with brake parts cleaner, remove the main screen(looks like a thimble), now with a small screwdriver pry out the main jet(carefully) and clean it, check the “O” ring on the main jet for damage, if it is damaged it must be replaced, reinstall the jet, it can be difficult some times to get it to snap back in place(I use the rounded end of a screwdriver handle). Remove and clean the fuel pickup stem(not necessary unless the tank was very dirty). Clean any junk/rust from the tank. Install the diaphram on the tank then the gasket(no goo or sealer) now carefully replace the carb(the spring will try to misalign the diaphram), tighten all screws a little at a time so as not to crimp the diaphram until they are all tight. Install the carb/tank in reverse order and you are done. If I missed something one of the real mechanics will correct me. Have a good one. Geo

 
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10-03-09, 08:31 AM   #4  
Purpose of diaphragm?

I thank both of you for the response. I believe I’ll follow your directions, Geo, to take it apart. They look really good. Obviously you have worked on these little guys.

I suspected it was not a simple lack of gasoline to the carb because there was always a ready supply of fuel for the primer ‘bulb’ pump. If it was the gas cap it should run for a longer time, maybe 10’s of minutes. I suspected it was some fine passage, like a jet, that could be plugged.

The only carb I’ve ever worked on was a 4-barrel Holly on a ’55 V-8 Chevy. It had metering rods, jets, and butterfly valves. Don’t remember a diaphragm. (but could have had it) Is this unique to a small B&S type engine? What is its’ purpose?

Geo, I would really appreciate it if we could explore this a little further.
I obviously don’t have a good feel for the overall hook up, let alone the operation. The throttle cable comes into the back of the engine (push handle side) and the tank/carb is on the right side with the exhaust on the left. I have taken off a couple of covers and the air filter. I still can’t see the linkage that connects the cable to the carb area. How is this done? Does it go thru the engine with a governor included along the way?

Finally, do you know a source online or library check-out that covers the ‘how it works’ for these little engines?

 
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10-03-09, 08:47 AM   #5  
Is really a pretty simple process once you get into it.
There is no need to mess with the throttle linkage other than the link that attaches to the carb(looks like a stealth bomber). Slowly, follow the instructions provided closely, step by step, and you shouldn't have any problems. Have a good one. Geo



Last edited by geogrubb; 10-03-09 at 09:04 AM.
 
justdoit007's Avatar
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10-03-09, 10:01 AM   #6  
Picture is my carb!

Geo, Thanks for your help. I’ll give it a try. Your picture looks like the top of my carb, so I know we are on the same carb(page)!

PS: I didn’t know pictures could be included with posts.

 
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