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Ranwell1, Small Engine Technician
Category: Small Engine
Satisfied Customers: 10304
Experience:  I Own a Lawn Mower Sales and service business (37years). Have 2-cycle and 4-cycle certification.
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I have a Craftsman Platinum 190cc 22 Briggs & Stratton Rear

Resolved Question:

I have a Craftsman Platinum 190cc 22'' Briggs & Stratton Rear Bag Rear Propelled Lawn Mower model 37435. I just tuned it up. It started great. After 5 minutes of mowing it won'ts start. Since filter, oil & gas w/ stabilizer, spark plug are new, I suspect the spark plug was not spaced correctly.

Any ideas or recommendations. Does anyone know the right spacing?
Submitted: 7 years ago.
Category: Small Engine
Expert:  Ranwell1 replied 7 years ago.


The correct spark plug gap is .030"


The most likely problem, though is not the spark plug gap. It most likely is a dirty carburetor and/or bad gasoline.


Gasoline cannot be used if it is over 30 days old..EVEN IF YOU USED FUEL STABILIZER !!!!!


Do not use gas left over from last year! It will cause major problems.


Here is my comprehensive carburetor answer that should give you some more information.


As engines sit or get older, fuel that is left in the carburetor can turn to gum and varnish and cause this and other problems. Also, any gasoline that was left in a gas can for a period of more than 30 days must be discarded because it also has begun to turn to varnish.

Today's gasoline's contain MTBE and alcohol. (Ethanol) They turn to "Junk and garbage" very quickly. Alcohol is partially water (H2O). And they call it "Oxygenated fuels! It is the oxygen that breaks down the organic compounds in the fuel and turns the gas to "Garbage" (Gum and varnish) The fuels we had just a few years ago had no alcohol in it and would store for longer periods of time before going stale... and fuel stabilizers do almost nothing to prevent the fuel from going bad with the changes in today's fuels.

Do not buy gas from the "Discount" Stations. The discount stations get a reduced price on gas because they may be buying fuel that is nearly 30 days old already. You may be getting fuel that's nearly stale right from the pump when buying from a discount station. Purchase your fuel from the well-known stations such as Shell, BP, Sonoco, Phillips 66 etc.

More than 70% of all of our repairs in our lawn mower business are due to this same issue. You most likely have dirt, gum, varnish...etc in your carburetor plugging up the small passageways and jets in the carburetor.

The carburetor must be removed from the engine. Clean all parts with carburetor cleaner and blow out all the small holes and passageways with compressed air. Remove all of the non-metallic parts since the carburetor cleaner will cause them to be disfigured decompose and plug the carburetor as time goes on.

Wash the carburetor cleaner off of the metal parts by washing them in warm, soapy water then rinsing with clean water. Dry them by blowing it off with compressed air. Make sure that all the passageways are blown dry before reassembling.

Reassemble using a NEW carburetor rebuild kit.

DO NOT TRY TO REASSEMBLE WITHOUT USING A COMPLTE CARBURETOR KIT! You will just end up having to do the job again.

ALWAYS clean the fuel tank and replace the fuel line when doing this repair or you may have to do it all over again. The inside of the fuel line disintegrates over time and these small pieces of rubber will plug up the carburetor too. Dirt and water from a dirty fuel tank will also plug up the carburetor. Find the Model, type and serial or code numbers off of the engine and take them to your local dealer to get the carburetor repair kit.

If you do the work yourself, take pictures or at least make a drawing of where all the linkages, gaskets, and component parts go. Correct reassembly is critical.

If the carburetor still doesn't work correctly, you may have to take it to someone who has an "Ultra-sonic" cleaning machine. This machine uses carb cleaner and ultrasonic vibrations to get the very small passageways clean when traditional methods fail.

If you don't feel comfortable with this kind of repair I would suggest sending it to a reputable shop.


Customer: replied 7 years ago.

Thank you. I have no intention of working on the carburetor myself so I'll need to take it in. Before I do, let me first rule out the spark plug. In 4 weeks period I have replaced 2 spark plugs, and I did not gap either. Each time I place the new plug in, it started fairly quickly, but not on later tries. So I have two questions.


1. Would improper gap ruin the plug, thus requiring me to go out and buy another and gap correctly - or- can I cap to .030"


2. Even if not gapped correctly (took straight out of box) is it likely that this really does not matter.


It seems that new plug = good start once.

Expert:  Ranwell1 replied 7 years ago.

The wrong gap will not usually cause a plug to go bad.

The wrong gap can affect how the engine starts and runs.


A clogged air filter can cause the plug to go bad as it causes the engine to run too rich and carbon up the plug.


Usually the problem is either a clogged carburetor or the use of old gas. Make sure that you are using FRESH 89 octane gas. Do not use any gasoline that is over 30 days old!!!! Even if the gas is only 2 or 3 weeks old, it could be bad gas if you purchased it from a discount station.




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