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B&S 15.5 hp surging

#1

D

dkgroce

I have been having trouble with my B&S 15.5 hp motor model 31R7 07 0033 G1. I had fuel solenoid issues got a new one but it still surged so I got a new carb, no better. I am getting 12.34 v to the solenoid. It wouldn't stay running but I kept starting it and it finally stayed running but would stall and almost die then take off again. I have a video of what its doing but it won't let me attach it. This is on a 2016 Troybilt Pony 42" rider


#2

Scrubcadet10

Scrubcadet10

Upload the video to YouTube and paste the link here.


#3

StarTech

StarTech

Sounds like it is either set at too low of an idle speed or the jet is too lean. Also can be intake manifold air leak.


#4

D

dkgroce



#5

D

dkgroce

StarTech said:
Sounds like it is either set at too low of an idle speed or the jet is too lean. Also can be intake manifold air leak.
Click to expand...
I sprayed starter fluid all around the intake and never heard a change.


#6

B

bertsmobile1

This is the problem with trying to diagnose things on the web
That does not sound like surging to me, it is cycling way too quickly.
It really sound like a bad plug or a magneto problem.
Surging happens because the air fuel ratio is too lean to maintain a constant speed
This causes it to slow down so the governor allows the throttle to open up, the sudden gulp of fuel causes the engine to speed up then the governor closes the throttle butterfly to the spot that should allow the engine to run at a constant speed , which it can not because the air: fuel ratio is too lean and the cycle continues .

This is most obvious by looking at the governor arm which will be moving back & forth .
Get an orange in line spark tester and hook it up to the engine.
start the mower then put your finger on the governor to stop it cycling
Slowly increase the speed while watching the tester.
IF the tester does not flash in time with the engine miss you have a wiring / magneto problem
If the tester shows a constant uninterupted glow then change the plug.
On the subject of plugs, what are you using in the engine ?


#7

D

dkgroce

bertsmobile1 said:
This is the problem with trying to diagnose things on the web
That does not sound like surging to me, it is cycling way too quickly.
It really sound like a bad plug or a magneto problem.
Surging happens because the air fuel ratio is too lean to maintain a constant speed
This causes it to slow down so the governor allows the throttle to open up, the sudden gulp of fuel causes the engine to speed up then the governor closes the throttle butterfly to the spot that should allow the engine to run at a constant speed , which it can not because the air: fuel ratio is too lean and the cycle continues .

This is most obvious by looking at the governor arm which will be moving back & forth .
Get an orange in line spark tester and hook it up to the engine.
start the mower then put your finger on the governor to stop it cycling
Slowly increase the speed while watching the tester.
IF the tester does not flash in time with the engine miss you have a wiring / magneto problem
If the tester shows a constant uninterupted glow then change the plug.
On the subject of plugs, what are you using in the engine ?
Click to expand...
I do not know but it is a new plug exactly like what was in from the factory.


#8

B

bertsmobile1

Does not mean it did not foul the instant you started to use it
A photo of the business end of the plug would be helpful
And we still need to know if the governor arm is ossiliating back & forth in time with the engine miss .


#9

D

dkgroce

The spark plug looked good last time I had it out, this weekend. No carbon, still clean. I have pics and a video of it "running". The black valve on top is the choke. It does not move unless I move the lever up top. I cycled the motor to low, which you can see and hear. In the end, I had the choke about half on and it smoothed out, you can hear that too. Sounded like low RPM to me but I manually moved the throttle and it revved up. I did have one little problem. See photo. Is that too rusty for the magneto?


#10

D

dkgroce

Here are the pics that didn't attach.

Attachments







#11

Scrubcadet10

Scrubcadet10

Definitely running lean either cause of a air leak past the carb, or still, dirty carb... Could be a tiny crack in the intake manifold as well.


#12

S

slomo

How is the spark plug wire attached to the terminal on the plug? Looks like a bad plug wire off the magneto. That would explain the quick surge.

Capture.PNG


#13

S

slomo

dkgroce said:
Is that too rusty for the magneto?
Click to expand...
No, rust has nothing to do with magnetism.


#14

B

bertsmobile1

OK now we have seen a better video it is surging
Was not sure before
ANd I will go for a blocked idle circuit
Go to outdoorpowerinfo and follow their instructions for cleaning the carb


#15

S

slomo

Is this some new wireless plug wire on the market?

Capture.PNG


#16

D

dkgroce

slomo said:
How is the spark plug wire attached to the terminal on the plug? Looks like a bad plug wire off the magneto. That would explain the quick surge.

View attachment 57593
Click to expand...
It was stuck and I pulled too hard.


#17

StarTech

StarTech

If it was that stuck I check the terminal for rust. I have seen to rusty on the contact points. Also seen a few ternimals that simply weren't crimped as tight as they could be as I have pull then apart here too and I just crimp on a new terminal.


#18

S

slomo

Any update on this quick surge?

I'm going with a bad plug wire connector crimp. Too fast a surge to be carb or fuel related. Sounds like the plug wire is at the limit to fire.

slomo


#19

R

RRDOUG

I am having the same problem with the same mower,new carb,,,bad surging,,,,


#20

StarTech

StarTech

Well this is definitely one of the causes. Plug wire not attached.
1657740158680.png


#21

S

slomo

RRDOUG said:
I am having the same problem with the same mower,new carb,,,bad surging,,,,
Click to expand...
What have you done to fix it?

New amazon or ebay carb?


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