Engine Fails To Run More Than A Few Seconds

Old 05-07-04, 07:58 AM
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Question Engine Fails To Run More Than A Few Seconds

I'm sure someone has provided an answer to this question before on this forum but there is so much info to scan through that I was hoping for a direct response.

A couple weeks ago, I accidentally ran over a small stump with my push mower and the engine died on the spot. When trying to crank it back up, it would only run for a few seconds and then die out again. I replaced the flywheel key, thinking that would solve the problem but no such luck. First of all, it will only start up with the choke fully on and in no other throttle position. If I try to slide the throttle down to another position while it's running, it dies. And if/when it does fire up in choke mode, it will run for 5-10 seconds and then die out every time.

Is this possibly a timing issue from hitting the stump or is it something else? If it's timing related, I would appreciate any info on how to correct the problem.

It's a Murray mower and a Briggs & Stratton Quantam 3.5 motor.


Edited to note that after reading many other posts on this forum with similar problems, they all tend to be carb related. My only issue with that is this mower ran perfectly fine up until I ran over the stump. Before that incident...never a problem. I don't want to rule out a carb/fuel problem all-together but it just seems odd that if that were the culprit, that it would start immediately following the stump hit unless the jolt screwed something up. I'm clueless at this point and have anal neighbors who are probably not thrilled that my grass is getting higher by the minute.

Last edited by 49erinnc; 05-07-04 at 08:16 AM.
Old 05-07-04, 10:09 AM
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I believe that hitting the stump and your henceforth problem is circumstantial. The fact that it runs only a few seconds indicates fuel delivery/carburetor trouble. Jarring the carburetor shouldn't cause it to lean out. A longshot possibility is that the jarring stirred something up whereas is was then sucked up in the carburetor. You didn't provide engine #'s, but being a Quantum it should be a bowl-type carb. I suggest removing the bowl and inspecting for sediment or other obvious foreign matter. Be sure to shut off the fuel supply so that it doesn't continue to flow once the bowl is off. You may want to try spray carb cleaner once apart. See how it goes and let us know.
Old 05-07-04, 02:04 PM
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I agree with Puey61...

If you do find crud in the carb or even if you don't, use automotive carb cleaner spray called Gumout to remove sediments, trash, and other debries. Also, replace your sparkplug and air filter if you have not done so this year. LEt us know how it goes.
Old 05-07-04, 11:59 PM
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Not sure of which engine you have, but some have a crossover intake tube made of plastic. If you find no problems in the carb, check the intake tube to be sure it hasn't broken from the jar of hitting the object you hit.
Old 05-08-04, 05:41 AM
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Carburetor Repair Tips

Hello; 49erinnc

Some engine running or operating conditions and or problems may appear to be carburetor related. Such may not always be the case. Many possible conditions can cause some problems to appear to be or seem to be carburetor related conditions but not really be so.

Always check for fuel flow out of the fuel tank, when a carb problem is suspected and prior to any suspected fuel related engine problems and always prior to removing any carburetor.

Prior to removing any carburetor, be sure to make note of exactly how the throttle linkage is connected to the carb and the governor linkage, is installed on either end of the linkage. It's important to reinstall all parts exactly as they where originally installed.

Use care handling any springs attached to the carburetors linkage. Be very careful not to overly expand any throttle or governor springs and equally as important not to bend any linkage rods.

Most carburetors have either 1 or 2 fuel adjustment screws. Should there be 2 fuel adjustment screws on either type of carb, one should be marked "H" for the high speed adjustment screw and another marked "L" for the low speed adjustment screw.

Prior to any carburetor disassembly, be sure to make note of exactly how many turns OUTWARDS any fuel adjustment screw is currently set at.

To determine how many turns each fuel adjustment screw is turned outwards, count the number of turns it takes to screw it INWARDS, until the adjustment screw is lightly seated.

The number of turns inwards it takes to lightly seat the screw, will then be the number of turns outwards it takes to set the screw back to it's originally opened position, after the carburetor rebuilding process is completed. Write the number of turns down on paper.

Carefully remove each part of the carburetor and take special note of exactly how each part came off or in the case of part assemblies, exactly how the assembly came apart.

Take special note in which order each part or assembly came off and or came apart. Note which side or which direction each part currently is facing or installed, prior to removal and or disassembly.

It is highly recommend to only disassemble carburetors on a well lighted, clean and completely cleared off work bench. Carburetor parts are usually tiny, often freely fall out of removed parts or assemblies and can become easily lost.

Using scribe marks on metal parts or assemblies (bowl to carb body) of parts will help to replace the parts in the location each part was installed prior to disassembly.

During the carb cleaning process, use canned aerosol automotive carb spray cleaner. Use it to clean the carb body, fuel ports, jets and airway passages.

The plastic extension tube, that comes with the canned cleaner, is an excellent tool to flush out sludge and debris from the jets, ports, fuel channels, airway passages, under welch plugs without removing the plug caps.

This process and procedure above usually works but not always. The intent is to avoid removal of some parts and or carb pieces which are pressed in and or may be more difficult to replace.

Use EXTREME CAUTION with canned aerosol automotive parts cleaner products. Aerosol cleaners are EXTREMELY FLAMMABLE! Wear eye protection. Read the manufacturers product warning label.

An excellent source for original replacement parts, generic service and repair manuals, is your local retail lawn mower and or small engine repair shops. Small engine powered equipment dealers and repair shops are listed in the phone book.

Most retail dealers can help determine what a possible engines problem(s) may be, prior to attempting a carb overhaul. Be sure to take the engines brand name, model and serial numbers with you, if you stop in at the store.

Briggs Web Site Home Page:

Regards & Good Luck. Sharp Advice.
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Old 05-08-04, 09:41 AM
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Good point cheese

Cheese made a good point regarding the intake tube (manifold). This may also be metallic in material. I have seen these break free at the mounting area, as they are merely pressed in. To inspect for possible manifold trouble, usually just grabbing ahold of the carburetor and carefully, forcibly see if it seems loose (as it should not). If it (the carb) does seem loosely mounted, remove such and then grab ahold of the tube to which it was mounted and check for looseness. If so, this will need to be replaced. If this is the case here, post back and we'll walk you through doing such.

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