# Surging B&S Engine



## motomike (Apr 21, 2017)

Hi all, new member from GA. Have a 1999 Murray Select 42" mower with the 17hp Twin II BS engine, auto trans. Having a problem with the engine surging at idle speed and issuing a single backfire when shut down after a hour or 2 use. 

Couple yrs ago disassembled and cleaned the carb(4 screw FP), new gaskets, prolly 3x trying to correct it with no improvement. About a month ago, the engine would not start when warm so figured another ignition had died(got 10 yrs from OE and this one was 8 yrs old). Put a new one on and solved that problem. Found a new factory carb for $160 so replaced it a couple weeks ago. First mowing, it ran great with steady idle. Second time out, back to the surging, maybe a little worse with some popping and sputtering even at cutting speed. 

Engine has new air filter/prefilter, plugs and fuel filter changed in DEC. Using fresh 90 octane ethanol free fuel, Checked intake man bolt torque, good at 90 inch pounds, compression is 100 left side and 110 right. Question: using the white round fuel filter, manual calls for the 5018 which is the red round one but that package calls for 15.5 max hp. Would this be my problem? Any other ideas?


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## jhngardner367 (Apr 5, 2011)

If it's a higher hp engine,yes,it could act somewhat like a choke.
You might also check the static governor setting .


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## FredM (Nov 18, 2015)

might want to check the spark plugs too !!


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## motomike (Apr 21, 2017)

Thanks for the replies! The plugs both are clean, not fouled at all. I just got an ignition tester. Both cylinders show a steady spark, but it its red/orange. From what I understand it should be white/blue in color?


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## jhngardner367 (Apr 5, 2011)

Did you set the armature gap at .012" ?


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## motomike (Apr 21, 2017)

I used a business card to set the air gap, is that ok?


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## Ed_GT5000 (Sep 30, 2003)

I had one of mine run bad and acted like a carb or fuel problem, It turned out to be a coil. your orange spark could be a clue.


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## motomike (Apr 21, 2017)

Got a genuine Briggs armature module, set gap at .010(book calls for .008-.012). Cranks quick, but still surges at idle and shows red/orange spark with ignition tester. 

This engine ran fine the first time after the new carb was put on. What would have changed between when I shut it down and started it the next time? The difference was immediate just like a light switch was thrown.


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## jhngardner367 (Apr 5, 2011)

Several things can cause surging.
Governor (static adjustment) out of adjustment....fuel shut off solenoid sticking/ damaged...moisture in the fuel,...wrong no-load or high rpm setting, high temperature, ....or stale fuel, etc.
With the popping when it shuts down, it could be either the fuel solenoid,or the engine being shut off ,at high rpm .


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## motomike (Apr 21, 2017)

Still having issues with my Murray. New carb, new ignition module, new plugs, new battery. Shows good spark on both cylinders and its definitely getting gas. It will crank when cold but only run a few seconds, then will not restart at all. Turns over good with new battery, compression was 100 and 110 on the cylinders when I checked it when problems started over a month ago. 

I notice the idle control lever does not rest against the idle speed adjusting screw. I can push it to where it contacts it, but it does not stay there. Does this indicate anything? Any other ideas?

Thank you for your help.


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## motomike (Apr 21, 2017)

Update on my Murray.....

Put another new carb on the mower and it runs great. Had an initial problem with gas flooding out of the top right after cranking so swapped the top end from the other carb and that stopped that problem. Did not see a problem with the inlet valve or float so not sure what was going on there. 

So, new carb, new battery, new air filter, new 60 micron paper gas filter, new plugs, new ignition coil and the mower is running great. 

Decided to service the deck and found one of the blades slightly bent at tip so got some new Briggs branded blades from HD. These blades are a bit heavier than what was on it and the ends are solid squared metal instead of the tapered lighter end on the ones coming off. The mower cuts really good with these new blades. Greased the spindles good, put dry lube on all the sliding linkage parts. I had put new spindles and jackshafts on the deck last year. Belts are about 2 yrs old. 

Glad I'm not pushing a mower now that the temps are hitting 90+ here in GA as I'm taking care of 3 yards right now. Thanks everyone for your help.


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## pogobill (Jan 31, 2012)

motomike said:


> Update on my Murray.....
> 
> So, new carb, new battery, new air filter, new 60 micron paper gas filter, new plugs, new ignition coil and the mower is running great.


Glad you got the issue sorted! Thanks for the follow up and up date, I'm sure it will be a great help to other members that may encounter the same sort of isses!


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