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I have a murray rear engine rider with a 10hp tecumseh. the…

Customer Question
I have a murray rear...
I have a murray rear engine rider with a 10hp tecumseh. the mower fires right up and runs. when at idle it surges and spits and backfires out of exhaust if you engage the deck it smooths out and mows fine you will hear a spit out of the exhaust every now and then but not enough to effect how it mows. as soon as you disengage the deck it starts surging and backfiring again out of the exhaust. I rebuilt the carb. and put a new plug and air filter on it and it still does the same. what will cause this?
Submitted: 8 years ago.Category: Small Engine
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Answered in 20 minutes by:
6/25/2010
Technician: Ranwell1, Small Engine Technician replied 8 years ago
Ranwell1
Ranwell1, Small Engine Technician
Category: Small Engine
Satisfied Customers: 10,347
Experience: I Own a Lawn Mower Sales and service business (37years). Have 2-cycle and 4-cycle certification.
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Well if I wanted to be a real snob, I would say that what causes this is that it is a Tecumseh engine. Many Tecumseh engines do this and sometimes there is nothing you can do about it.....but I don't want to be a snob so I won't say that.

 

Actually, That is pretty much true, but ..

 

Another possibility is that the valves need to be ground or adjusted. You may be bypassing compression through the valve system and back into the carburetor and exhaust. Since you didn't tell me what the model and specification number your engine is, I can't tell you for sure how to fix it.

 

If you have an overhead valve engine, you need to check the valve clearance to make sure that the clearance is set at .004" between the valve stems and the rocker arms.

If they are not set correctly you can get running problems.

 

If you have an L-head engine. the most likely thing is that the valves are leaking and may need to be ground. There is much less chance that the valves are out of adjusted, so I wouldn't worry about the adjustments.

 

Another possibility is a partially sheared flywheel key. This will put the ignition out of time.

 

Also if you have an older engine that has points and condenser, they may need to be replaced because they may be burn or dirty.

 

If you have an electronic ignition, you may have an electronic ignition that is not firing exactly at the right time. I don't really think that it is the ignition, though.

 

It still could be the carburetor even if you have cleaned it. These carburetors many times are difficult to get all of the passages cleaned.

 

 

 

 

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Customer reply replied 8 years ago
the model of the engine is a tvxl220. and I agree with the tecumseh being junk. I like briggs much better.
Technician: Ranwell1, Small Engine Technician replied 8 years ago

Ok, This engine is an L-head valve engine. And has an electronic ignition.

 

Your most likely issue is the carburetor that needs to be rebuilt, even if you have done it before.

 

It also may be that this is just the way this engine is going to run. I have worked on hundreds of these engines and they never run smoothly.

 

In any case, the information that I gave you before still is good and you can check these things.

 

Just in case, I will include this fuel and carburetor answer that might help...if not this time, maybe in the future.

 

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.

 

 

One more thing that may help is that we have found that we cannot use regular 87 octane gas in the small engines any more, The 87 octane gas causes a considerable amount of problems. Try using a GOOD BRAND Shell or BP or Sonoco, and use at least 89 octane gas. This might help you engine run a little better.

 

Good luck.

 

 

Ranwell1
Ranwell1, Small Engine Technician
Category: Small Engine
Satisfied Customers: 10,347
Experience: I Own a Lawn Mower Sales and service business (37years). Have 2-cycle and 4-cycle certification.
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Customer reply replied 8 years ago
ok. Thank you for your help. Im going to accept. I put a complete rebuild kit in the card today and all little ports are spotless now. I let it soak in carb cleaner all night and blew out all passage ways even knocked out the two aluminum plates the one on the side and the one above the float and cleaned passages out and replaced the plates. it still ran the same way backfiring and sputting at idle and smoothing out while I mow.Im leaning toward the valves that you mentioned earlier. Any input on the valves would be appreciated. Thanks and have a great day.
Technician: Ranwell1, Small Engine Technician replied 8 years ago

 

 

Here is the Tecumseh L-head service manual.

http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_L-Head_Engines_Service_Information.pdf

 

I think this should help you more than me telling you a few more things.

 

Contact me here again if you need more help and I will be glad to talk with you again.

 

 

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