Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Have an 8 year old Murray Lawnmower from HD with a 5HP Easy Start B & S Quantum engine. 

Tried the typical press prime three times, pull and nothing, press prime a few more times and nothing.  Used to start right up.

Runs only after studdering three or four times with some sprays of an old ether can into the spark plug hole.  Will start again instantly if warm.

Replaced the air filter, spark plug and cleaned out the fuel bowl (was pretty clean) and the carb nut orifices (with spray cleaner and compressed air) along with an oil change.  Using fresh mid grade fuel.  Cleaned up typical dirt and stuff around the carb area.

Could this be a problem with the priming, and if so, what should I do?  What else could it be?

Runs pretty good once it's in use.

is the plug properly gapped? & does it have good blue spark? if the spark is yellow its firing on the weak side. Coil and/or condensor could be weak,  If the ignition system is ok, then check for air leaks into the fuel system, causing it to run lean. its possible too when you cleaned the carb you loosend some crud that didnt get removed when you bleo it out with compressed air & have a partial blockage so its not recieving enough fuel. if it has the type of carb with a bowl & float the float could be partially sticking closed.

as you said it runs "ragged" at low speed & surges at all speeds though im guessing air leak somewhere. try spraying around all potential leak areas with wd40 or a similar spray lube, if you find a leak you will notise a substantial difference in the way it runs. also check the carb mounting bolts, occasionally ive seen these loosen on small engines & this will cause the symptoms you discribe

Thanks, spottedpony.  Will check with some spray for leaks. 

The plug is perfectly gapped and the spark looks good.  Clarification: I didn't clean the carb further than using some spray, wiping the bowl clean and clearing anything that might have been in the orifice of the bowl nut.  

Overlooked adding that I cleaned a bit of surface rust off the magneto and the coil with a brass brush.  Gap is exactly where it was; didn't measure thickness but it's a very small clearance. 

Also tried running it awhile with the gas cap a bit loose just in case it was creating a vacumn.

Hoping to find a leak.

It sounds like you may have a obstruction somewhere not allowing fuel to get to the carb or the carb is the one not allowing. The first thing I would do though is loosen the gas cap and try to start it. If you still can not start it, then take the carb apart and you should get gas trickling out of it. If not, your fuel line or connection to the tank is obstructed. Please let us know what you find.

No signs of leakage after spraying.  I unbolted the air cleaner housing to snoop around and discovered the gasket was slightly mushed over the small prime hole, otherwise things looked fine.

Good fuel flow.  Baffled.  Any help appreciated.

Since its a older Quantom engine, you should not have carb adjustment, but it sounds like a issue with your carb. You can start it with gas in the sparkplug hole but then it stops. That is a symtom of the carb. Somwhere along the line you carb is not giving you fuel. You should have a bowl type carb on that engine, take it apart and remove the float. Shake the float near your ear, if you here a liquid swooshing sound, than, thats the culprit. The float must be perfectly sealed and air tight and it must move up and down freely in the carb. If there is liquid inside the float, than the float needs to be replaced. Make sure that the needle valve seat it clean aswell. Make sure the tiny holes in the bowl nut are blown with compressed air. Let us know how it goes.

I still have not forgotten about you, how are things going? Did any of which I said help you in any way?

theres a possibility the head gasket is leaking a bit or if you havnt replaced the plug, then try that......i cant count the times ive seen a plug show good blue fire when you pull it and ground against the block, yet not run for beans. sometimes a plug gets weak enough the fire blows out under compression. if that fails check compression both dry and wet. (check it then squirt a teaspoon of oil in the cylinder and test again) you'll have to get compression specs from a briggs source, but it it shows low, and then substantially higher after the wet test, rings are worn. if it remains low, usually its a burned valve.

Follow up:

After priming several  times and trying to start it, there is gas on the spark plug electrode.  Significant?

   One thing I have found in the past is to make sure you have a very tight seal between the filter housing and the carb if you have a primer type carb. It will act just as you have described. If you have a hole in your float or a bad float valve, most of the time it will cause the carb to leak fuel. A bad float valve will not stop the fuel from over filling the float bowl and a hole in float will do the same. The float will sink in the float bowl, which in turn will not allow the float needle valve to do its job, which is to shut off the fuel from the gas tank. This all works on the same principle of a toilet bowl tank. The only thing that stops a toilet from overflowing if you have bad parts is an overflow pipe.

Fixed the starting problem, it seems, by using a tad of gasket sealant between the air filter housing and what it bolts onto. 

Actually, it's started easier than it has in years....  that was easy.