# Surging on Idle and Load



## banders5144

I have a Yardman model number 31ae5klf701 with a Tecumseh lh358sa 159502z engine. I have replaced the carburetor with a new adjustable carburetor https://www.amazon.com/dp/B01D40658I/ref=cm_sw_r_cp_apa_i_-77tCbV52SY3B and brand new gaskets. Also replaced the fuel line but still having noticable surging both under load and idle. Any ideas why?


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## JLawrence08648

Make sure you have no water in your gas tank and gas can then adjust the governor.


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## Dannoman

Bad gas can do that. You might also have a defective gas cap that isn't venting properly. Does it still surge if you run it with the gas cap still on but unscrewed so it isn't airtight? If so, the culprit is the gas cap. Just buy a new one. Or you can drill a small hole into the defective one for now.


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## vinnycom

but did u adjust the high and low speed jets?
donyboy has a vid on that


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## banders5144

I only use TruFuel and I emptied out the gas tank. It surges with the gas cap on or off.


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## banders5144

Any other ideas? Brand new gas tank, trufuel 4 cycle gas, tries both new adjustable and fixed jet carburetor. Still surges pretty bad on idle, on full throttle not so bad.


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## ST1100A

Float could be out of adjustment or slow speed circuit clogged somewhere causing a lean condition. Check your valve clearance while you are at it, a tight valve could do that also.


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## banders5144

Even if it's a brand new carburetor? Straight out of the box?


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## tadawson

Chinese carb? *EVERYTHING* is in doubt, since QA is often so poor. Might also check that gov linkage(s) are not binding, since that can cause it to overshoot and surge as well


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## ST1100A

Yes a brand new carb out of the box can have problems, a float stuck, or needing adjustments, and fuel mixture screws needing adjustments. Some brand new carbs are bad right out of the box, especially one of those super discounted carbs you have to be careful with, the super low price sometimes tells you to stay away from them.


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## banders5144

I have tried 3 different brand new carbs, Governor linkage is good. Still same issue, any other possibility? As for valve clearances, the engine turns over smoothly


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## Grunt

Welcome to SBF banders. Surging is usually caused by a lean condition where more air than fuel is entering the engine. Are you sure you don't have a bad gasket between the carb and manifold or manifold and engine? Spraying carb cleaner around these spots will make the engine surge IF there is an air leak.
Have you replaced the spark plug?


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## banders5144

Brand new gaskets every where. No I will replace spark plug. Did it last season. I did the wd40 trick, no difference


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## tdipaul

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The factory settings on a new carb are only a baseline. They will need to be adjusted depending engine state of tune/condition, engine size, altitude, air temperature, etc

If you've got a fully adjustable carb now with main fuel mixture, idle fuel mixture and idle speed adjustability this is the ritual required to get it running right...


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## banders5144

I have tweaked and adjusted it for over 2 hours and can't find a happy setting for idle, only for full load


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## DuffyJr

banders5144 said:


> I have tweaked and adjusted it for over 2 hours and can't find a happy setting for idle, only for full load


 I'll throw this out there for what it's worth. I have a 1996 MTD with a HSSK 50 Tecumseh and have the same issue as far as getting it set for both idle and full throttle/load so I have it set for full throttle/load since I don't let it idle much. It has the original carb on it and have only rebuilt it once about 15 years ago. 



When it idles it stumbles rather than surges but if I adjust it so it idles smooth it starts stumbling under full throttle/load. I don't think it's a good idea to let these splash lubricated engines idle for very long anyway so I don't do it so it stumbling at idle doesn't bother me. When it's under load it doesn't miss a beat which is more important.


But I get it, I tried for hours to get it running good at both idle and full load but I gave up years ago.


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## tdipaul

tadawson said:


> Chinese carb? *EVERYTHING* is in doubt, since QA is often so poor. Might also check that gov linkage(s) are not binding, since that can cause it to overshoot and surge as well


Indeed 

The original carb on a WH tractor was leaking and a rebuild kit was >$20, so for only $15 tried a new chinese one. It wouldn't run cleanly no matter how it was adjusted. Lots of gurgling going on. Never looked into why, just transferred the bowl gasket to the old carb and threw the new one in the trash. 

New carb first, original carb second:


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## JayzAuto1

Banders, Did you try applying some choke while the surging is going on? Either Hi or Low speed? If the engine smooths outwith the choke applied, it will confirm a lean condition. I agree with the other suggestions here, Valve clearance, Governor adjustments..... But The Carb is the most likely suspect. You are better off with the adjustable version, although those off-shore carbs are always suspect. I use quite a few of them, stocking about 20 for different engine sizes. Some are just bad out of the box. If I cant get it adjusted correctly in 10 minutes, toss it. 1 out of every 10 I get is a defect.....Cost of doing business. Think about this, an OEM Carb is probably $95 -$110, depending on vendor. The amazon carb changed hands at least twice, where the vendors made 40% on each transaction..... AND it was on the slow boat from China.... What was the Original cost to make an Amazon Carb?? 3 carbs for $1??? give or take? How much QC did that carb get?? I'm guessing very little.... My advice....Check basics, try choke trick, order 3 Amazon carbs, use what worx, return the rest. 

GLuck, Jay


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