# Snow blower engine surging after carb replacement



## Frostikins (Dec 17, 2020)

I could not get my OEM Tecumseh carb to work right so I replaced it with an after market carb made in China. The new carb has adjustable main and idle jets. The engine starts and runs well except it surges quite a bit. Would this possibly be due to maladjustment of the jets?

I've seen on YouTube where a guy unmounted the throttle control and slightly bent the spring to give it a bit more tension to dampen the surging and that cured his problem. Before doing that he diagnosed the problem by holding the governor arm still and that stopped the surging. Mine seems to keep surging even while holding the governor mechanism still.

One other point is that the new carb looks and fits exactly the same as the OEM one EXCEPT the Welch plug that covers the hole in the top of the carb, right above the float, is not present in the new one but is in the OEM. The new one starts and runs ok except for the surging.


----------



## orangputeh (Nov 24, 2016)

Frostikins said:


> I could not get my OEM Tecumseh carb to work right so I replaced it with an after market carb made in China. The new carb has adjustable main and idle jets. The engine starts and runs well except it surges quite a bit. Would this possibly be due to maladjustment of the jets?
> 
> I've seen on YouTube where a guy unmounted the throttle control and slightly bent the spring to give it a bit more tension to dampen the surging and that cured his problem. Before doing that he diagnosed the problem by holding the governor arm still and that stopped the surging. Mine seems to keep surging even while holding the governor mechanism still.
> 
> One other point is that the new carb looks and fits exactly the same as the OEM one EXCEPT the Welch plug that covers the hole in the top of the carb, right above the float, is not present in the new one but is in the OEM. The new one starts and runs ok except for the surging.


by surging do you mean up or down or just high rpms?

up and down means it's hunting for fuel. possibly fuel delivery problem or a clog somewhere

high rpms may mean needs an adjustment or a linkage/spring reinstalled incorrectly

I dont know these Tec carbs but most carbs have the same basic components..


----------



## JLawrence08648 (Jan 15, 2017)

The Welch plug inside does nothing, absolutely nothing as there is a large opening next to it. The Chinese carburetors fit a cheap need. They usually work but not always. Order another, it's good to have backup parts on hand and it's only $15. The surging comes from the holes behind the side Welch plug. You could remove that,clean the holes with a welding tip cleaner then you have to buy a new Welch plug and seal it.


----------



## ST1100A (Feb 7, 2015)

Most likely you have a clog in the slow jet. That will cause the surging when it is not under a load because it is taking fuel from the slow jet while running without a load because the throttle plate is barely open even though it may be running at full speed.
Once it is under a load, the throttle plate opens further and then it will take its fuel from the main jet, then the surging will stop.


----------



## db130 (Feb 16, 2013)

You'll have to adjust the jets a bit after installing a new carburetor. It sounds like you'd need to let more fuel in with the high speed jet.


----------



## RIT333 (Feb 6, 2014)

You can verify that it's running lean by given my it some choke. If it smooth things out, then you know for sure that you have to adjust the carb to make it give more fuel.


----------



## paulm12 (May 22, 2015)

I agree with ST1100A that surging at low and med speed is usually the idle jet, either plugged or mis-adjusted.

tx


----------



## ST1100A (Feb 7, 2015)

He can adjust the idle mixture screw but it wont help if the little jet is clogged, which is most likely the problem.
Too many people try and adjust the main way out and all they do is cause a problem when it is under a load from being too rich. They would never guess almost all your surging problem is caused by a clogged slow jet when running it UN-LOADED.
The reason being, I mentioned earlier, even when it is running full speed unloaded, the throttle plate is barely open, so it is only taking fuel from the slow jet.
It dies out, when it slows down the governor spring opens the throttle plate up and then it recovers by taking fuel from the main circuit, then after it speeds up, the governor closes the throttle plate enough because it is over-speeding and doesn't need as much fuel, when it closes down, then it has to take fuel from the idle circuit, which it has none, and the surging begins again and the whole process repeats itself over and over again, causing the surging effect.
And that is a very common problem.


----------



## Frostikins (Dec 17, 2020)

Thanks for all the replies. It surges up and down in rpm when in full throttle or in lower throttle. You can see the arm to the governor and the linkages oscillate back and forth. 

It's a brand new, albeit Chinese carb, so it "shouldn't" have dirt in the jets.

Choking it does not seem to correct the surging.


----------



## Frostikins (Dec 17, 2020)

db130 said:


> You'll have to adjust the jets a bit after installing a new carburetor. It sounds like you'd need to let more fuel in with the high speed jet.


Is the high speed jet the one in the bowl nut at the bottom of the bowl?


----------



## mdubby (Nov 16, 2019)

This is a good video Ive watched before related to surging and cleaning out the idle pilot jet. Seems pretty easy.


----------



## db130 (Feb 16, 2013)

Frostikins said:


> Is the high speed jet the one in the bowl nut at the bottom of the bowl?


Yes, here's a good video that shows both high speed and idle adjustment a typical Tecumseh carb by forum member @Sblg43:


----------



## 140278 (Aug 27, 2020)

mdubby said:


> This is a good video Ive watched before related to surging and cleaning out the idle pilot jet. Seems pretty easy.


that's a honda clone carb different than on a tech


----------



## orangputeh (Nov 24, 2016)

Frostikins said:


> Thanks for all the replies. It surges up and down in rpm when in full throttle or in lower throttle. You can see the arm to the governor and the linkages oscillate back and forth.
> 
> It's a brand new, albeit Chinese carb, so it "shouldn't" have dirt in the jets.
> 
> Choking it does not seem to correct the surging.


I have had surging problems with chinese carbs right out of the box. it was the idle jet in my case. i removed it an put the old idle jet in and then no more problem.

however, you have surging at both idle and fast throttle so not sure. have had that with Honda carbs and it was a clogged emulsion tube. That is why I would rather deal with an OEM carb. Chinese carbs are so hit or miss.

I don't like those odds . getting too old to waste precious time.


----------



## Frostikins (Dec 17, 2020)

orangputeh said:


> I have had surging problems with chinese carbs right out of the box. it was the idle jet in my case. i removed it an put the old idle jet in and then no more problem.
> 
> however, you have surging at both idle and fast throttle so not sure. have had that with Honda carbs and it was a clogged emulsion tube. That is why I would rather deal with an OEM carb. Chinese carbs are so hit or miss.
> 
> I don't like those odds . getting too old to waste precious time.


Yeah, I might try to replace the needle seat on the old oem carb and see if that works. I can't swap idle jets I don't think. The old carb was non-adjustable and the new one is adjustable.


----------



## JLawrence08648 (Jan 15, 2017)

Now as I think about, I had the same problem with a Chinese carburetor, put the original jet in and it ran good.


----------



## ou2mame (Dec 23, 2019)

I would take the needles out and blow some carb cleaner through it... could be machining pieces leftover. They're infected with covid and making carburetors for 35 cents an hour... Chinese slave labor on its best day isn't known for its quality, nevermind during a pandemic. So I would clean it out and reassemble, reset needles to stock position which I think is 1.5 turns out from closed and adjust as necessary.


----------



## ST1100A (Feb 7, 2015)

Those cheap Chinese carbs may have been sitting on the shelf for years collecting dust, plus during manufacture they are not in a very clean space.
Many times the tiny jet hole in the plastic slow jets are never machined out properly, if at all. The same goes with the metal jet parts in them.
On that type carburetor the slow jet is usually external mounted under the idle speed screw that you have to remove, then a black plastic holder, then remove the jet, and hope it has the tiny "O" ring on it.
If it is that type, you don't have to remove the carburetor or the fuel bowl, just the idle speed screw, then you can remove the jet. Some have a metal little screw that has to be removed, and under that is the slow jet passage. There are different style carbs made for a lot of them by those Chinese companies. Some are exact copies, some are different looking.
I'm just giving an example of how different carbs are put together, I would have to see what you have to get a better idea how its built and where the parts are on it.
The main jet is located at the bottom of the bowl and screws in. Some bowl retaining nut type jets have both the main and slow jets drilled into them, some use an adjustable main jet mixture screw located on the bottom of the bowl retaining nut.
Some are part of the nut that holds the bowl on, some are separate and screw in at the same spot the bowl bolt is if it uses a nut in the center, some use 2 screws on the outside edges.


----------



## JLawrence08648 (Jan 15, 2017)

Last 2 replies are correct, possibly poor machining. Try blasting some fuel cleaner up the main fuel tube. Otherwise remove the carburetor, remove the side Welch plug, use a welding tip cleaner in the holes behind the Welch plug, squirt carb cleaner through the holes, install a new Welch plug and seal.


----------



## Julien Morrissette (Oct 7, 2017)

make sure to you put the linkages in the correct holes


----------



## 3vanman (Nov 21, 2017)

Julien Morrissette said:


> make sure to you put the linkages in the correct holes


Yes, I'll confess to that error, but high or lower speed, not surging was my problem.
As far as surging, usually related to one of the jets in the carb.


----------



## Julien Morrissette (Oct 7, 2017)

3vanman said:


> Yes, I'll confess to that error, but high or lower speed, not surging was my problem.
> As far as surging, usually related to one of the jets in the carb.


sometimes issues are so simple that we don't see them  so better make sure


----------



## Frostikins (Dec 17, 2020)

Julien Morrissette said:


> make sure to you put the linkages in the correct holes


I scratched a mark on the link plate and took a photo, lol.


----------

