Hi,
Chasing some help guys.
Have a 13HP Vertical Shaft Briggs and Stratton off a ride on mower.

I have just pulled it apart and overhauled the engine. New piston, rings etc. Cleaned everything out, inlcuding the carby. However when I started it, about 1yr later. The idle is ridiculously high, as if it is almost full throttle. I immediatey thought I made a mistake with the governor but held this at minimum RPM and still. Full throttle.

I got the Carby apart and checked everything according to the Briggs Repair Manual for my model (Not very much detail I might add). Couldnt find anything odd.
Adjusting the idle mixture screw makes no difference. Which troubles me.

The only way to make it idle at all is to set the choke closed slightly, making it cough and splutter and blow black smoke. To much fuel I think. Now is this the way it should be, or during normal engine operation, should the choke butterly (the drilled butterfly) be fully open. I assumed it should be fully open.

I dont know what to do. Any suggestions. Im not sure if buying a new carb or an overhaul kit will fix the drama. As Ive honestly checked the Carb and nothing appears to worn (Except the throttle shaft bushing...maybe leaking air???)

Any help would be appreciated, as I do not have huge expirence in these little engine carbs.

Engine Model: 28M700
Carb Type: Walbro LMT 77

Many thanks
James.R

Check the operation of the throttle plate in your carburetor. Make sure it's attached to the throttle shaft and is opening and closing. There is no way for the carburetor to deliver enough air and fuel to the engine if the throttle plate is closed for the engine to run at full speed. Even if the throttle shaft is worn this will not allow the engine to run up to full speed. I have seen the throttle shafts break in half, and I have seen the throttle plate come out resulting in WOT operation.

Not sure how. But again I pulled the carb to pieces. Checked everything I could understand, again. Then put it back together. This time I left the governor linkage off. And controlled the throttle with my fingers. No prolem. Engine starts fine. Idles and was able to adjust idle mixture and RPM with my new digital tacho.

All linkages and springs back on. This time it went straight to 3000rpm. I then shut it down and moved the position of the governor leaver on its shaft. Re started the engine. ALL good. Took a little bit of fiddling around to find what I think was the correct spot. Now runs great. No load max RPM is now set correct. ALL works great. Im really happy!

I think the problem was me...The throttle must not have been fully closed when I thought it was. The governor was obviosuly set wrong and holding it open.

Thanks to everyone that had a look.

Cheers!