# Carb problem, surging after ultra sonic, enlarge holes behind Welch?



## JLawrence08648 (Jan 15, 2017)

I have a Tecumseh 8hp on a 15 yr old snowblower that was given to me. The carb has a fixed plug on the bottom holding the fuel bowl on and a low speed adjustment on the side. When I got it, the engine was surging badly that it was unusable. I cleaned it in my new ultrasonic cleaner for 60 minutes using the manufacturers recommended $65/gal Carburetor Shellac and Varnish Buster, the side Welch plug was removed, after cleaning then a dunk in a water bath then immediately every hole was cleaned using a welder's tip cleaner. New Welch plug, sealed with nail polish, let dry for a day, reinstalled and no difference with the surging. 

I The did it again, removed the carb, disassembled, Welch plug removed, in my ultrasonic cleaner a second time using Berryman's Carburetor Cleaner dunk tank as the solution, removed after 30 minutes? 60 minutes? I forget which. cleaned every hole using the tip cleaner, then I cleaned every hole using wire gauge drill bits, then new Welch plug, sealed, next day installed, still surging, No difference.

I was thinking of doing the ultrasonic cleaner again for 30 minutes, then spraying carb cleaner in every hole, then tip cleaner, then wire gauge drill bits. Then should I install it? Or should I enlarge each hole behind the Welch plug using the next size larger wire gauge drill bit? Would enlarging these holes help with the surging?

I don't want to give up and install a Chinese carburetor. I want to learn what is necessary to solve the problem for my future knowledge.


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## paulm12 (May 22, 2015)

what is the part number of the carb? and the engine? I will see if I have worked on one of these. And no, I would not clean again, nor enlarge the jets. Seems like they should be clean by now, something else is going on. 

and I agree with you about wanting to understand the issue, not just get it running. I do the same. 

thanks


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## jsup (Nov 19, 2017)

More ultra sonic cleaning isn't going to help. 15-30 minutes is all you should need. Which cleaner is it? After 30 minutes more isn't better. Could be an intake leak. ALSO, could be the gaskets. I don't know which carb it is, but many carbs have multiple gaskets that come with it, putting the wrong gasket in the wrong place, will do that. 



Make sure all the gaskets are positioned correctly, and in the right place. They have four positions each, and try again. They can be confusing, and I'll admit, kicked my butt once, maybe twice.




Berryman's is very toxic. Rated 3rd to Lucas and Gunk. I use Gunk, I left a really bad bowl I threw in the USC, didn't turn on the USC. The next day, the bowl was almost spotless without even running the USC.


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## tadawson (Jan 3, 2018)

If this is a typical Tecumseh carb, the passages behind the side welch plug are idle, not main, and likely have nothing to do with your problem. Look at the main jet, the main needle (if there is one), and the emulsion tube (if accessible).


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## drmerdp (Feb 9, 2014)

“Fixed plug on the bottom” so non adjustable jet... may just need a richer mixture. You can enlarge the orifice or install just the adjustable jet.

Add a little bit of choke and verify.


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## classiccat (Mar 1, 2014)

is there excessive play in the throttle shaft?


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## jsup (Nov 19, 2017)

Check the governor regulator spring. The one that goes from teh governor to the carb.


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## JLawrence08648 (Jan 15, 2017)

No excessive play in the throttle shaft. Not the carb intake gasket as I sprayed starting fluid there with no change.

I'll loosen and redo the governor spring.

Can I replace the fixed jet with an adjustable jet? Is there enough room for the needle? I'll check my stock and look at my extras.


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## strtch5881 (Oct 6, 2018)

Could be that the last owner disturbed the governor adjustment.


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## micah68kj (Oct 8, 2011)

jsup said:


> Check the governor regulator spring. The one that goes from teh governor to the carb.


This is my guess too, or possibly the linkage was installed in the incorrect hole sometime in the past?


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## jsup (Nov 19, 2017)

micah68kj said:


> This is my guess too, or possibly the linkage was installed in the incorrect hole sometime in the past?



That's why they give you a bunch of holes. I had the same problem, and just moved the spring, took out 95% of it, I stopped there.


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## JayzAuto1 (Jul 25, 2016)

I would start off with governor adjustment first. Then apply the choke to see if it smooths out. If it does, then at least you verified a fuel delivery issue. The holes behind the Welch plug are idle and transition jets. One should be visible with Throttle closed, this is the idle jet. The other 2 are behind the closed Throttle plate, and aid in acceleration lag from low to high speed. If closing the choke smooths the rpm fluctuations, open up the fixed main jet with the mini drill bits. I use the numbers 61-80 for this fine tuning. Or the pin vise and tip cleaning kit from a welding supply store will get you in the ball park. 

GLuck, Jay


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## Lottstodo (Feb 16, 2018)

On some of the Tecs where the throttle slide is there was a screw that could be used for raising RPM or dialing in rpm and I had owners think it was for setting idle. If it was really tweaked out of specs the governor would really bounce as it was trying to override the excessive rpm setting


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## tadawson (Jan 3, 2018)

You might also want to take a close look at the holes . . . Typically, on an older carb, the ones that have been used for years are a bit larger, worn, and rounded at the edges, making it possible to verify that things are in the correct holes if you forgot to take notes . . .


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## vinnycom (Nov 6, 2017)

what happens when u close the choke fully and/or partially?
buy a clone carb, its cheap, buy with adj main jet. good for diagnosing/ testing between the two and elimiating the carb is the problem....thats assuming jets are adjusted correctly


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## tdipaul (Jul 11, 2015)

+2 on the new carb at this point 

for the keeping of the sanity purposes!

.


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## strtch5881 (Oct 6, 2018)

Careful there, I have already had 3 bad repop carbs. Not so good for diagnosing.


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## JLawrence08648 (Jan 15, 2017)

*Update - I replaced the carb, didn't need to touch the governor*



vinnycom said:


> Buy a clone carb, its cheap, buy one with a adjustable main jet. good for diagnosing/ testing between the two and eliminating that the carb is the problem, thats assuming the jets are adjusted correctly





tdipaul said:


> +2 on the new carb at this point
> 
> for the keeping of the sanity purposes!


I ordered and had a new OEM Tecumseh adjustable carburetor, 632334, ready to put on a customer's snowblower that was surging and I couldn't get "cleaned". I actually had 2 snowblowers, 8hp & 9hp, and 2 carburetors with the same problem. Interchanging the carburetors between the snowblowers did not do anything, moving the throttle connecting linkage to another carburetor hole did not change anything. The new Tecumseh carburetor worked fine on both snowblowers eliminating a problem with the governor, so I don't need to check or fool around with that. Now I need to order a Chinese carburetor for the other snowblower, MINE! A free 2005 Ariens John Deere 826D.


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## paulm12 (May 22, 2015)

so you never really figured out what was wrong with the carb? I wish there were some sort of bench test equipment for these, to test out air flow, etc. Probably way to cost prohibitive. Like you, I am always interested in finding the actual fault (if there is time).


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## vinnycom (Nov 6, 2017)

point of having a cheap cloned carb is for diagnostics of hard to fix issues, if both carbs give the same results its the least likely the problem is in the carb, its the cheap $15-20 diy diagnostic procedure, imo, plus u get parts for the oem carb rebuild


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