Briggs Twin II Surging, barely runs at idle.

[cpy911]

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!
cpy

 

[Scrubcadet10]

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

 

[cpy911]

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

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

 

[slomo]

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.

 

[hlw49]

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

 

[Scrubcadet10]

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.

 

[cpy911]

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!