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Hi
I have a bought a used LT1500 mower with Briggs and Stratton engine 31C707 3346 G6 engine Code 110510ZD It has a Nikki Carburetor

It starts right up but surges for a minute or so before it warms up. Then it seems to run fine. Maybe a surge when the PTO is first engaged but I have not used it more than a test.

I did the basics to start fresh with the machine, New : spark plug, fuel filter, oil change, air filter. I also changed the gas. I also tried this with the gas cap and air filter off and it did not change the surging.

It had always been garaged and I am assuming in winter was stored with gas in. So I could see how the carb could have blockage and need a break down and clean. I have not done this but seen quite a few videos are posted about this carburetor and it looks easy enough.

1. if it is only running this way at start up , is it the carb or could it just be an adjustment?
2. If just an adjustment, how should I proceed to give a tune up ? the carb?

I have read some say they either did a clean or even replaced the carb and it still surged after. I never saw them post if they found the cause.

I also see allot of kits on amazon and ebay cheap but mixed reviews. It concerns me I do a rebuild and it does not fix if that is not the issues

So i am asking for help as this could just be an adjustment for cold start and I donot need a clean. I don't understand enough about how they work to know what would only cause the surge at cold start.

And when I say cold.... I mean it is NOT cold. It was High 60s and if I turn off for 10 minutes after it smoothed out. It starts to surges again but not as hard and smooths out quicker When it is cold it surges harder at first and as things warm up it surges quieter and quieter and less frequent until it is running smooth.

3. Is there a good aftermarket kit? I don't want to over spend on a $55 briggs kit if many say it does not fix their surging and does concern me that some replaced the carb and it still did not fix.

4. it seemed the owner knew of this and just played with the choke until it cleared out. when I put the joke up the surge stops for a few seconds and then there is too much fuel so it starts to act up and he dropped it back to fast, the surge was start and he would move the choke back up and repeat . I guess he did this so he did not have to listen to the surge.
But this info might give an expert here an idea if it is more of an adjustment than something in the carb.

Thanks in advance for any advice.
So what do I do

At first glance it would appear that the engine is a bit cold-natured. (60° IS cold to an engine!)
This could be due to lean running conditions mandated by the EPA.
They are so concerned about emissions that some B&S/Nikki 2bbl carbs have different sized jets for each cyl!
Moderating the choke til it warms up a bit may be your best option.
It is a bit of a by-feel situation.
I personally would not consider it a big deal.

As for kits, I discussed the $$$ of B&S kits with an actual Briggs engineer.
He said that the high price is due to the expensive materials required to withstand
the ethanol in today's gasoline. We owe another big thank you to the EPA for that............

As for the cheaper kits, I have no experience with them. If you opt for one, I hope you are burning
non-ethanol gas in your mowers.
I have used nothing but since relocating to south Mississippi and I have never experienced another fuel related problem,
carb or otherwise.

Actually to rekit your carb would cost about 6 bux. The noodle gasket and a welch plug. Briggs parts.

Clean real well in a dip or spray all the passages out well, let dry and repeat if you are using a spray. Take the welch plug out before you do that.

You can leave it like it is for a while and run it like it is. When it gets worse then redo the carb ~!~!

Boudreaux In Eunice La. said:

Actually to rekit your carb would cost about 6 bux. The noodle gasket and a welch plug. Briggs parts.

Clean real well in a dip or spray all the passages out well, let dry and repeat if you are using a spray. Take the welch plug out before you do that.

You can leave it like it is for a while and run it like it is. When it gets worse then redo the carb ~!~!

Click to expand...

Well to wait is a thought. It was just that i thought under a little load when I was testing it it might have started to stall but then caught up.

Can you clarify? What is $6? Are you saying get an $6 after market kit and then by the other two pieces mentioned from Briggs?
What about the needle? Shouldn't the needle and seat be changed while I have it all apart?

If I lightly push on the choke, this surging can be reduced or eliminated. Is it then an adjustment or need of clean?

No it's 6 bux or so for the bowl gasket and a welch plug. We call them noddle gaskets down here.

needles are very expensive for that carb. They last a very long time though. You have to take the carb off to do it right because of the way the gasket sets in there.

With the new emissions engines, I have brand new out of the box engines run like crap, meaning surging, backfiring until they warm up in the middle of the summer So what you are experiencing may be normal for that engine.

If you're cleaning the carb., this may help ......

http://outdoorpowerinfo.com/repairs/briggs_intek_single_ohv_nikki_carb.asp

Thanks. The link was helpful . I might have missed some spots.

So I will be using this when it is colder than 60F so don't want an issue. However, I also don't want to waste time and money if this is just the way they all work in this model.

ILENGINE said:

With the new emissions engines, I have brand new out of the box engines run like crap, meaning surging, backfiring until they warm up in the middle of the summer So what you are experiencing may be normal for that engine.

Click to expand...

If it runs fine after a couple minutes or so, I wouldn't overthink it.

A little more testing,

From 4 gear up if I let my foot of the clutch, when it catches there is a power drop or surge for a second and then recovers. This causes a little buck. Does this symptom provide any other information if there is an adjustment that can be performed or if it needs to be cleaned?

Sounds like there may be an issue with the transfer ports. When you go from no load to load there are holes or slots that allow the engine to transfer from the idle circuit of the carb to the main jet. So your carb may benefit from some cleaning. it will look like a series of small holes, or a slot behind the hole for the needle valve in the venturi of the carb

So why hasn't any external adjustments been suggested?
On the cold start, if I push on the choke wire a little to open it more it does not surge. Does a 6 year old carb not need adjustments or is it that a 6 year old carb is probably blocked.?
It just seems like the suggestions jumped to a carb clean and nothing else could be the issue.

Maybe it's just me but i have a B&S 12 hp that does that same thing i just let it warm up and use it:dance1:

mstar said:

So why hasn't any external adjustments been suggested?

Click to expand...

I am not familiar with your carb, but most other current units which I have serviced have no external carb adjustments.....

Valve settings are a typical issue, but you seemed to focus on the carb from the onset.

Fragger said:

Maybe it's just me but i have a B&S 12 hp that does that same thing i just let it warm up and use it:dance1:

Click to expand...

Does yours also do it as you release the clutch, even after warm?

Ronno6 said:

I am not familiar with your carb, but most other current units which I have serviced have no external carb adjustments.....

Valve settings are a typical issue, but you seemed to focus on the carb from the onset.

Click to expand...

Valves are now set to specs. Still surges until warm up.

Now I am back to weighing if it is just normal or if the carburetor should be properly cleaned.


I learned I am a bit too short legged for this machine. Some of my power issues were from slightly lifting off the seat to do of the following. 1. pushing the brake all the way, 2. pushing the PTO all the way down. 3 pushing the any lever to its lowest point.

Honestly they made this machine for people with giraffe legs and monkey arms.
I did not think I was coming off the seat that much but looking how the switch is made and how tight the seat springs are, I am too far on the edge that my full weight is not on the seat so any bounce or left or lean forward can start that anti backfire to kick in and then when I return to the seat caused the engine to come back.

It was more my physical limits than a UNDER LOAD engine issue. So my height coupled with "safety" is to blame for much of what was seeing


So now the only issue seems to be the surging for up to 2 minutes when cold. and if I start after it stis for a few minutes, it will surge a little but takes less time to get back.


This is the part that puzzles me.

If the engine has been running for 20 minutes. Why would it still surge, breifly even after it is warm.
Is the fact it only needs to sit a short period and will still surge even if it had been running for 20 minutes on a 70F day a symptom. If it was a dirty carb why would it surge when cold but also when hot but also run fine after it runs a little with the choke up?

Thanks for any input

mstar said:

Honestly they made this machine for people with giraffe legs and monkey arms.

Thanks for any input

Click to expand...

Careful,now...I resemble those remarks..............
My MTD 46 incher us way too small for me.........
After an hour on it, I almost need a crane to lift me off..........

I hate those Nikki carbs, i just replaced one that was FUBAR, the local dealer suppliers wanted 160$ canadian for a new carb, got the part number and got it on Ebay for 40$, brand new and runs great...you could do that.

mstar said:

Valves are now set to specs. Still surges until warm up.

Now I am back to weighing if it is just normal or if the carburetor should be properly cleaned.


I learned I am a bit too short legged for this machine. Some of my power issues were from slightly lifting off the seat to do of the following. 1. pushing the brake all the way, 2. pushing the PTO all the way down. 3 pushing the any lever to its lowest point.

Honestly they made this machine for people with giraffe legs and monkey arms.
I did not think I was coming off the seat that much but looking how the switch is made and how tight the seat springs are, I am too far on the edge that my full weight is not on the seat so any bounce or left or lean forward can start that anti backfire to kick in and then when I return to the seat caused the engine to come back.

It was more my physical limits than a UNDER LOAD engine issue. So my height coupled with "safety" is to blame for much of what was seeing


So now the only issue seems to be the surging for up to 2 minutes when cold. and if I start after it stis for a few minutes, it will surge a little but takes less time to get back.


This is the part that puzzles me.

If the engine has been running for 20 minutes. Why would it still surge, breifly even after it is warm.
Is the fact it only needs to sit a short period and will still surge even if it had been running for 20 minutes on a 70F day a symptom. If it was a dirty carb why would it surge when cold but also when hot but also run fine after it runs a little with the choke up?

Thanks for any input

Click to expand...

Did you take the welch plug out like I said in a earlier post ??

Did you make sure all the little holes are cleaned out like LIL Engine said ??

If you take the welch plug out and give the holes a good clean with a small wire and a good soaking it will solve your problems. I hope ~!~!

Send a pic of the carb on here ~!~!

I did not take the carb apart yet.
I wanted to see if there was anything else it could be as more than a few with surging said carb was not the issue.

My local repair shop said they normally don't need to take the Welsh plug out when they clean. But maybe that is because the put in a dip basket?

Seafoam in the gas tank , it always seems to help my gasaholic engines . especially in my two stroke engines, walmart has best prices.:laughing:

I had a Honda carb that refused to be cleaned until I dunked it in the ultrasonic tank for a few cycles.

Do I have to remove the welsch plug? He repair place I bought the parts said no.
Do I have to remove the needle adjustment with the plastic cap? If so how do you"pry" it off and not break it? How do you ensure you get it back to the place it was if unscrewing it.

Are either of those two spots what could cause the cold surging?

Update: I did the carb cleaning. The interior was very clean, Everything looked good, My O ring was not deformed , my float needle looked decent but I still replaced it, the O ring and the bowl gasket and the paper gasket.

I am not sure if it fixed anything yet. It started a little rough but then smoothed out. Maybe it was quicker than before but there was a surge if I took it off choke right away and if I pushed it back into choke it could not stay there for long. I had to drop it back down bu then there was a little surge. It seemed not to take as long but I will have to try again.

I did "pry " off the the cap on the fuel mixture screw. Now I know how it is put on. for those who don't know it is a pressure fit over a ribbed end. Just pull it off with pliers with a little wiggle.

OK so what is the recommend procedure to adjust the carburetor. The fuel mixture needle I read you turn to just off, turn to 1.5 turns as a start point.
I had marked the spot before removing It was only 1 1/8 turns.

So I don't know how one knows if it is correct. Do I set when engine is hot? Where should the throttle be when set?

Do I touch the idle screw? What do you look for if you set that first. Again, the idea is to properly tune to stop the cold start surging.
Also should I have set the choke?

Thanks