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158 cc Briggs & Stratton engine stuttering

#1

S

Smithy

Hi, I just got a pretty beat down lawn mower from a friend, that did not start. I am not an expert and English is not my native language so excuse me for probably using the wrong terms, but I hope you can understand, what I am saying.

I cleaned the Carburator replaced the Carburator gasket, the air filter, the primer (the original one had a big cut) and the spark plug. Now it starts flawlessly with the first pull, but after a few seconds it starts to stutter and seems to run louder, than it should. What could be the issue here? It runs fine right after startup, but after 4-6 seconds it starts stuttering. When I tighten the smaller of the two springs, the stuttering seems to be retarded a bit, but that seems to also increse the rpm in general and after 8 seconds it starts to stutter again non the less.

I would be happy for suggestions, because my friend can not afford a new lawn mower and I told her I would try to fix it.

The engine is a 158cc from the 500 series.


#2

I

ILENGINE

Can you get us the model, type numbers off of the briggs engine so we can see what engine you have out of the several hundred variations in that size range.


#3

B

bertsmobile1

Smithy said:
Hi, I just got a pretty beat down lawn mower from a friend, that did not start. I am not an expert and English is not my native language so excuse me for probably using the wrong terms, but I hope you can understand, what I am saying.

I cleaned the Carburator replaced the Carburator gasket, the air filter, the primer (the original one had a big cut) and the spark plug. Now it starts flawlessly with the first pull, but after a few seconds it starts to stutter and seems to run louder, than it should. What could be the issue here? It runs fine right after startup, but after 4-6 seconds it starts stuttering. When I tighten the smaller of the two springs, the stuttering seems to be retarded a bit, but that seems to also increse the rpm in general and after 8 seconds it starts to stutter again non the less.

I would be happy for suggestions, because my friend can not afford a new lawn mower and I told her I would try to fix it.

The engine is a 158cc from the 500 series.
Click to expand...

Stuttering = going fast then slow then fast then slow then fast then slow ?
If so that is called Hunting or Surging in English and is always caused by not enough petrol getting into the engine.
Usual causes dirt in carb.
Bad pump / pump diaphragm ( on models with carb above fuel tank )
Cracked induction tube ( found under the engine cover connecting the carb to the engine )


#4

I

ILENGINE

Some of the briggs push mower engines have two governor springs, if they are not syncronized can cause up and down throttle also, which is the reason I asked for the model number.


#5

S

Smithy

ILENGINE said:
Some of the briggs push mower engines have two governor springs, if they are not syncronized can cause up and down throttle also, which is the reason I asked for the model number.
Click to expand...
Thanks for the replies.

Yes, there are two governor springs. Sorry I did not know there were that many variations of carburators. I have only seen this one so far on all the B&S engines on Push mowers. I will get you the model number and pictures asap. The whole carburator was covered in sand, when I got it, but I took it completely apart and cleaned it, replaced the gasket, between the fuel tank and the carburator as well.


#6

S

Smithy

Ok. Sorry for the late response. I ordered a replacement carburateur, because the base on the old one is slightly bent, I noticed there was gasoline on the tank, and the gasket is wet all around. I will keep you updated, if this solved my problem.

Anyway, here are the pictures I promised:
IMG_20170613_085919043.jpgIMG_20170613_090243310.jpg


#7

pugaltitude

pugaltitude

I think your problem could be the main jet has fallen out at the bottom of the carb that is under the silver metal filter so a new carb should fix it.


#8

7394

7394

I have a 158 cc B&S on my 11 year old MTD Push mower, While you are waiting on carb parts, behind the carb is a piece of sheet metal covering the engine cylinder fins, now would be perfect time to remove the sheet metal & make sure the fins are totally clean of debris. This is how the engine gets cooled.

Mine needed cleaned, so I had to share this tid bit.


#9

S

Smithy

7394 said:
I have a 158 cc B&S on my 11 year old MTD Push mower, While you are waiting on carb parts, behind the carb is a piece of sheet metal covering the engine cylinder fins, now would be perfect time to remove the sheet metal & make sure the fins are totally clean of debris. This is how the engine gets cooled.

Mine needed cleaned, so I had to share this tid bit.
Click to expand...

I did it already. The fins were totally filled up with sand btw. Maybe thats why the Carb is bent. It must have been running very hot all the time.


#10

7394

7394

:thumbsup: Not sure if sand could bend a carb ? That certainly will help being clean around the fins & etc.

The wet gas on the gas tank on mine was due to many years of bouncing around, carb loosened from gas tank just enough to be wet. All mine needed was a good cleaning & I used Loc-Tite on the screws to try & prevent this from loosening again.


#11

I

ILENGINE

That style carb is prone to warpage under the intake pipe area, and will suck the diaphragm in and allow fuel to be pulled around the edge causing rich running and black smoke sputtering.


#12

7394

7394

I must'a got lucky on mine then. Cause it has been running fine about 2 years now since I had to tighten up the carb/tank screws.


#13

S

Smithy

ILENGINE said:
That style carb is prone to warpage under the intake pipe area, and will suck the diaphragm in and allow fuel to be pulled around the edge causing rich running and black smoke sputtering.
Click to expand...

I think that was the issue. You can see a very slight opening, when you put it against a straight edge. Maybe, because of the hot engine, due to the dirt filled cooling fins, the carburateur got bent, it was the side closest to the engine as well.

Anyway, now with the new carb, it runs flawless again. :smile:

BTW I saw some dirt cheap carburateurs on Ebay, from China, but I opted for an original to be safe and for the faster delivery. Has anybody experience with those after market chinese carbs? Do they work?


#14

7394

7394

FWIW: I have an ebay $9. chinese carb on my Honda Mini-Tiller, runs great. Hopefully it will still run the same next time I have to till the garden.. :laughing:


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