Outdoor Power Equipment and Small Engines - B&s 461777

Hi
I resently prchased an old Yard man mower w/ a 20.5 hp b&s engine.
This unit has been inactive for the past few years -after cleaning the carb i got it to run. A spring seems to be missing to close the throttle plate (after several trips to different parts stores I was unable to locate the proper spring) so I fabricated one from a auto store -- it works. The mower will start and idle nicely -- but if the throttle is moved quickly the engine will stall. If the throttle is moved slowly the engine will rev, the same is true if a load is introduced.
My question is -- why? Does the governor need adjustment? If so, how is that done? Any sugestions?

Thanks
Mike

Mike,

This engine is set up to have a governed idle speed of 1300 RPM's. This is achieved with a governed idle spring, What you did by adding a spring is cause this added spring to bump heads with the high speed governor spring. Therefore the governor will not perform as intended and cause lack of power under load.

Remove the spring you added then bend the tag the governed idle spring is hooked to inward just a little to lower idle speed, But remember Briggs states a 1300 RPM idle.

http://i107.photobucket.com/albums/m314/Restrorob/Briggs/L%20Twins/Briggs461777IdleSpring.jpg


Good Luck

Hi
When I remove my spring the throttle butterfly goes to wot and the engine will not start. Do you have a diagram of carb linkage and springs. The diagrams in the parts books are too vague.
Thanks
Mike

Sorry Mike,

I couldn't find a good enough diagram that showed what you wanted, There really isn't that much to this linkage. You have a short link rod from the carb throttle shaft that goes to a pivot arm on the intake manifold.

Then another link rod that goes from this pivot arm down to the end of the governor arm, Then there's the governor spring that goes from the center area of the governor arm to the pivot on the control plate.

The carb throttle shaft is supposed to open to full throttle position when the engine is not running, Soon as the engine fires off the governor pulls the shaft back to the set governed idle speed or what ever rpm the throttle control is set at.

If the engine will not fire off at wide open position as intended you may have other issues.

A) Lack of fuel (carb still plugged up) ?
B) Low compression (not enough engine vacuum to pull fuel for start-up/when load is applied) ?

Hi
Thanks for looking -- I did a compression test and both cylinders were @ 85psi -- no difference when oil was added. As far as the carb still plugged - I don't think so as when it runs (with my spring) it is smooth -- when I did take the carb off -I used carb cleaner through all the passegages that I could find -- I will try it again -- if you have any other suggestion --please send them.

thanks
Mike

If the carb and engine compression/valve operation are in order, it will fire up with the throttle wide open. That is the way it is designed to crank. Even if you put the throttle all the way to slow, it should still be wide open on the engine until it fires up and the governor becomes functional.

Generally if an engine won't start at full throttle, it is because the choke is not closing all the way. It could also be a leak at the intake/carb mounting gaskets, etc..., but that would tend to show up as a problem once it's started as well.

Hi
Sorry a few more questions -- What does the adjustment screw on the throttle do? ( The one on the diagram suggesting to bend the tab to get 1300 rpm). Also which direction do I adjust the clamp on the governor to make the governor engage more quickly? And how much travel does it take to make a difference?

Thanks
Mike

What does the adjustment screw on the throttle do?

If you are referring to the longer one with the spring over it, It is used to adjust wide open throttle RPM's.

which direction do I adjust the clamp on the governor to make the governor engage more quickly?

Adjusting this other than factory specs can cause lack of power/engine over rev and holes in the block.

how much travel does it take to make a difference?

Very little can cause the above, If you haven't done anything with the governor adjustment it's best not too. I don't for-see this being your no start problem.

I agree...the governor adjustment does not cause a no start problem.