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The throttle plate sits about 3/16" away from the idle screw, so turning the screw isn't affecting my RPMs at all. I've loosened the throttle cable clamp and looked to see if it was binding, but there's plenty of slack there to move the plate (but not too much). When you move the dash lever from low to high and back, the whole mechanism moves. But the plate never quite makes it all the way. If you hold the plate against the screw, it moves up to the screw just fine, but the minute you let go it drops back to that point I mentioned. Something wrong with the link, maybe? Any other advice?

Thought a photo might help. Looking again, it seems like a bit-tighter Governor Link Spring* would fix it right up and move that plate to sit against the screw. This picture was taken before we loosened the cable clamp. Just releasing the clamp cut reduced the gap to about half of what you see. Could the wire be stretched out and need replacing? Or can you just re-bend the end of it to make it a bit shorter?

*I'm assuming that this is the real fine piece of wire that forms itself into a spring next to the choke link. In fact, the choke link next to it actually goes through the spring at the bottom of the picture. If I've got the wrong part, please let me know. I've got the Briggs Part List, but the drawing is a bit wonky.



B&S Vanguard V-Twin 23hp
Model 386777
Type 0111-E1
Code 0705241
Part 2690752
Purchased February 2009
Snapper YT2350 YT400 Series 50" Lawn Tractor (aka Riding Mower)

It appears that engine has a governors idle which is controlled by a spring and not the idle adjustment screw. the only purpose of the idle adjustment screw is to prevent the throttle from slamming shut when going from full speed to full idle really quickly. There should be two governor springs one controls the idle speed and the other is the high speed spring, and then are synced together to control the high speed setting.

So unless the engine is running the springs will hold the throttle slightly open and should go to full idle when the engine is running. Now you need to hold the throttle lever all the way to the idle speed on the carb, and turn the idle adjustment screw until it touches the throttle stop and then about another 1/4 turn to reset to factory setting.

When you idle down an air cooled mower engine, you drastically kill essential cooling of the block and head/s. Oil pressure or oil splash gets the same treatment. Neither are a good idea for engine longevity.

Run it at 3600rpm all the time as Briggs recommends.

Thanks for the replies. Our family mower has been down for the last six weeks, and two acres of Ohio grass is pressuring me to get this fixed. I only know what I know, and that's pitifully little. So, thanks for your advice and patience. It only has 550 hours, so I really think it's worth fixing.

I've been working on quite a few issues with this engine. I've got the Briggs Repair Manual, Operator's Manual and Parts Manual. They're very specific about the 380700 series, and that's where I got the instructions for setting the carb. Briggs is insistent that the adjustments are done on Low at 1200. We do always run the mower on High at 3600 (when it used to run, anyway), but Briggs says to do this work at 1200. Are they wrong? I went back over the manuals and couldn't find anything about always running it at 3600. I'll give them another search tomorrow for that instruction. I don't want to do this wrong.

I'm confused about the factory settings. This TK carb has (1) idle speed screw and (2) idle mix screws. In addition to setting them while at 1200 idle, Briggs says that factory settings for this unit are CW until hits slight resistance and then CCW 1-1/2 turns for idle speed screw and CCW 3/4 turn for both idle mix screws. The manuals say to hold the throttle plate against the idle screw while making the adjustments. (Hard to do when they put the air duct over the top of everything, but we're trying.)

That's when someone told me that the throttle plate should always be touching the bottom of the idle screw when the dash lever is on Low. I even tried lowering the idle screw until it touched the plate (thinking I had it too open), but it doesn't touch the plate even when completely closed, so that's a no-go.

So, I'm more confused now. Does the throttle plate in that photo look like it's in the right place, then, nowhere near the bottom of the screw? Unfortunately, since they don't touch, turning the idle screw does nothing at all. The engine just keeps surging and eventually shuts itself off. And it just sits in the 1300s, at that, because I can't get it down to the 1200 it needs. I'm sure it wants gas. Replaced the fuel filter, removed carb and cleaned thoroughly, replaced air-cleaner-to-carb gasket, new air filter + plugs + oil filter, checked hoses, replaced valve-cover gaskets (lash was spot on as it stood), replaced dipstick tube and seals, etc. All B&S parts, as called for in the Parts Manual for this particular model, from reputable parts stores.

Before I can go any further, guess I'm stuck until I find out where that throttle plate is supposed to sit. I'm game to set the carb screws, but so far turning any of the three of them has no effect on the engine at all. (FWIW -- starts like a dream.)

So, should the throttle plate be touching the idle screw while it's idling (Low)?

No. This engine uses governor idle speed of the 1750. The carburetor is tuned at 1200 rpm while holding the throttle plate against the stop screw.

You need a copy of the Vanguard V-twin service manual and follow the carburetor tuning instructions. If not tuned properly the engine will surge.

Thanks. I have all three manuals (service, operator and parts), and that's what I was going by. Then two people told me that I'm supposed to be making the adjustments at 3600. Another person told me that the throttle plate should be touching the screw by itself when the dash lever is set on Low (idle). I've reset the three screws (one idle, two mix) to what the manual says, but the engine just sits there surging. If I manually hold the throttle plate against the screw, the engine dies. So, I'll try opening the screw a bit at a time until it stops stalling?

I really appreciate your answer. It's hard to get advice these days.