Briggs 5hp with no blade

[PTmowerMech]

Most mowers will start and run without a blade. May have and erratic idle. The heavier flywheel or mower blade stores energy to help the engine not bog down when a load is applied.
Back in the day when i built 5hp Briggs go cart racing engines in the stock appearing and outlaw stock classes i would replace the cast iron flywheel with an aluminum one. Start and idle just fine and gave better acceleration out of a corner because engine didn't heve to put as much energy into the flywheel. Better deceleration into a corner because the engine would wind down faster and release the clutch sooner.
I hate those carbs. I have a mower in the shop right now with that carb and it came in for hard starting and surging. I have put 2 new carbs on it. When it starts it still surges a little but is nearly impossible to start. Valves are good and adjusted properly. Good spark, flywheel key good, new fuel. Head gasket good. I am not impressed with these carbs or the engines thay are on.

I'm about to take one apart again. I remember the float not being level. Not much. But enough to be noticeable.
Seems I watch a video about heating up and bending the plastic where the needle rests.

 

[PTmowerMech]

Update: The float level was fine on this one. Guess I was thinking about the other one.
So I drilled out the main jet, one size bigger than the hole, and the surging stopped.

 

[Rivets]

When I said i like to set the level a bit low, I meant when you tip the carb upside down the float is closer to the carb body on the side opposite the float pin. This will raise the amount of fuel in the float bowl, resulting in a richer mixture. On those E-series plastic carbs pictured, the idle jet is in the bottom of the white assembly pressed into the carb body. This carb is designed with such a small jet, to run very lean to meet EPA regulations, which means it will gum up very quickly if fuel is allowed to sit for an extended period of time.

 

[PTmowerMech]

When I said i like to set the level a bit low, I meant when you tip the carb upside down the float is closer to the carb body on the side opposite the float pin. This will raise the amount of fuel in the float bowl, resulting in a richer mixture. On those E-series plastic carbs pictured, the idle jet is in the bottom of the white assembly pressed into the carb body. This carb is designed with such a small jet, to run very lean to meet EPA regulations, which means it will gum up very quickly if fuel is allowed to sit for an extended period of time.

Yes sir. We're on the same page as to those things are located. I had forgotten until working on thsee the last couple of days that the white tube in the middle, that crosses over to the other jet, comes off too. This was important for me because I wanted to make sure there's nothing left in the carb.
Wish there was enough room to get a good filter from the tank to the carb on these.

I have two more that's surging. I'm going to drill one more out tomorrow and see if it fixes that one too. If it does, maybe this will work on the rest of them.

 

[Rivets]

Don’t over size it, will make it too rich. Just clean.

 

[Tinkerer200]

"Most mowers will start and run without a blade."
Not in my experience with vertical shaft engines and even blade slippage may make them very difficult as said above they depend on blade for momentum. EPA requirements have caused Mfgs. to run very lean, slight over sizing of low speed jet will not hurt running and may make much easier to start.
Walt Conner

 

[Rivets]

My experience with these carbs ( I’ve done at least 100) is that even a slight over size can cause smooth running problems. I use a .0145” micro drill (#78). I’ve tried .016” (#77), but don’t get the results I like. Over sizing will make it easier to start, but I’ve found I get rich mixture surging.

 

[Hammermechanicman]

Hey Rivets, throw me a bone here. I have one of the briggs with the plastic carb (auto choke model) that i have put 2 new carbs. Came in for hard starting and surging. New carb, once it starts it runs fine with no surging but you have to use some starting fluid to get it to start. After it runs a few mins it will start right up. Sets till cold no start. Other new carb hard to start and slight surging.
Things i have done, check head gasket, valve sealing, valve lash set, new spark plug. Flywheel key, auto choke. if you have worked on 100 of them you got any ideas why the hard starting?
Thanks

 

[ILENGINE]

It has been my experience that if one of those new OHV Briggs push mower engines come in with a no start the first thing that happens is I dump the fuel and drain the carb. I don't care if it runs in your other lawnmowers, weedeater, blower, etc. I have seen several that will not start with the fuel that was in it. It will pass the smell test, the color test, and the fuel quality test sticks, but will not start with that fuel.

I see either dirt in the carb jets, a half tank of water along with the fresh gas, or a no start due to a fuel quality issue. Only see the issue on the Briggs plastic carb push mower OHV engines. I have good through the all the same things that you have done Hammermechanic but would start the first pull after changing the fuel.

Part of the issue may be related to the very lean run to meet emissions standards that cause fuel quality issues. I don't know.

 

[Hammermechanicman]

The fuel is fresh but i will dump it to morrow and try some i bought last week.
Tks.