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View Full Version : Briggs 18 Twin, ran ok week ago, today surging


Rain Man av
10-18-2008, 12:05 AM
Briggs and Stratton 422707, sitting on a riding mower.

Ran and drove just stinking fine a week ago. Got it in today and when started - surged and hard to find a choke position that didn't have the engine surging - real bad at idle, just a tiny bit a full. When I did finally find a sweet spot, as I drove it, it kept acting like it wanted to die.

I adjusted the screw at the bottom center of the carb. Couldn't really tell that it had any affect whatsoever on the surging. I adusted the small screw on the left side of the carb - the stop/set screw for the governor linkage. If I adjust that two far one way - at slow speed, it idles in real big loops - at full throttle - small surges. If I adjust this screw too far the other way - the engine takes off sounding like it wants to make it to full throttle, and then it slowly comes down in RPMs - but RPMs remain high.

What should I be looking at. I checked the the throttle and choke cables just to make sure neither had slipped in place, they hadn't.

Few months ago I put new fuel line, fuel filter, and cleaned out the tank. Even took the carb off and cleaned it. As I stated, it was running and driving just fine and dandy one week ago.

big_belly4ever
10-18-2008, 12:12 AM
Just my opinion but check fuel filter. I know you say you have changed these but try fuel filter. I think when mine was doing a surging they put a new fuel filter on? I cant remember if they did any other adjustments.

Restrorob
10-18-2008, 12:23 AM
Remove the low speed adjustment screw (center bottom) and give the carb a shot of choke cleaner, Re-install and open 1 1/4 turn then adjust at idle until smooth.

Phil G
10-18-2008, 05:24 PM
Sounds like it's running weak on the main jet. First pull the fuel supply pipe to the carb to make sure it's flowing ok. If it is remove the clean the main jet with carb cleaner or if possible an air line.


Good luck, Phil



parts list here


http://www.briggsandstratton.com/pdf/illustrated_parts_list/100/MS7545.pdf




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AJ Lawnscapes
10-18-2008, 06:19 PM
jUST SOUNDS LIKE BAD FUEL

Rain Man av
10-18-2008, 08:18 PM
Remove the low speed adjustment screw (center bottom) and give the carb a shot of choke cleaner, Re-install and open 1 1/4 turn then adjust at idle until smooth.

Did that, no affect

Rain Man av
10-18-2008, 08:23 PM
Sounds like it's running weak on the main jet. First pull the fuel supply pipe to the carb to make sure it's flowing ok. If it is remove the clean the main jet with carb cleaner or if possible an air line.
=

Took the top of the carb off, sprayed carb cleaner in all ports, drained gas from bowl, sprayed out main jet, sprayed out needle valve orifice, reassembled. Pulled fuel line at carb, gas flow is good. Pulled gas line upstream of fuel filter and let gas flow backwards.

Reassembled, started, ran like it did a week ago. Something must have gotten into the carb. A quick clean and it was running perfectly. Absolutely perfect:drinkup:

Thanks guys.

Rain Man av
10-18-2008, 10:55 PM
jUST SOUNDS LIKE BAD FUEL

Fuel is new. mower was sitting only one week since last run.

derepair
10-19-2008, 11:00 PM
YES IT WAS PROBLY TRASH, IN THE SYSTEM. kUDOS FOR REMOVING CARB. THAT IS NOT A FUN CARB TO REMOVE. I WOULD ALWAYS USE THE BRIGGS AIR FILTER ON THIS ONE . SOME AFTERMARKETS DOSENT ALLOW ENOUGH AIR. ALSO BE AWARE YOU HAVE A FUEL PUMP MOUNTED ON THAT CARB. IF IT HASNT BEEN REBUILT, I WOULD NEXT TIME YOU HAVE A FUEL PROBLEM. DEREPAIR