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I have an old Briggs Twin II 18 hp engine. A symptom has gotten worse and that is surging, especially at lower thorttle. Also, sometimes hard starts, where I need to choke it a lot to get it started or run the starter a long time. I have replaced the coil (twice...second time with a Stens and not a cheapie) because it was not starting when hot. I just replaced all the gaskets and springs on the fuel pump, but have the same symptoms. My next suspect is carburetor. I know very little about these, other than jets can be come clogged up. I have created a video that is shared in my google drive to see and hear the symptoms.

Any leads on what to check for next would be appreciated!

Thanks!
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Surging is a lean running condition caused by too much air, or not enough fuel.
The opposed twin carbs are fairly simple to me, to clean.'
I find it easier to remove the intake manifold from the engine, and then remove the 7/16" mounting screws that mount the carb to the manifold.
PART 1 https://outdoorpowerinfo.com/repairs/briggs_opposed_twin_carb.asp
PART 2 https://outdoorpowerinfo.com/repairs/briggs_opposed_twin_carb2.asp
I wouldn't mess with the fuel pump quite yet, scroll down to step #10

Scrubcadet10 said:

Surging is a lean running condition caused by too much air, or not enough fuel.
The opposed twin carbs are fairly simple to me, to clean.'
I find it easier to remove the intake manifold from the engine, and then remove the 7/16" mounting screws that mount the carb to the manifold.
PART 1 https://outdoorpowerinfo.com/repairs/briggs_opposed_twin_carb.asp
PART 2 https://outdoorpowerinfo.com/repairs/briggs_opposed_twin_carb2.asp
I wouldn't mess with the fuel pump quite yet, scroll down to step #10

Click to expand...

Wow! That is a great detailed site with nice pictures! Thank you!

Lot of time people over torque bolts on the carb and intake manifold. Might want to reseal these areas. Also might need to true up the mounting flanges with a piece of plate glass and 220 to 600 grit wet/dry paper.

Most likely your carb is dirty.

wow why make it so hard I never take the carb off these old opposed twins you can clean them right on the engine.

different strokes for different folks.
I like to remove, disassemble completely and lay every thing out orderly. and reassemble.and reisntall.
I have cleaned one or two on the engine with horizontal twins on generators with less than optimal working space.

I sprayed some carb cleaner in it while running. It actually worked and improved things a little before I tear carb apart. I am needing the machine for leaf clean up now, so just getting it working is good enough. Thanks for the input!