Briggs 5hp with no blade

[PTmowerMech]

Briggs ohv 5hp, (plastic carb) on a Murray push mower. Just picked it up and trying diagnos it to see if it's worth fixing to sell.
I've cleaned the carb twice and it's still surging. But I'm wondering if the engine running without a blade could cause this. At the moment I don't have a 20" blade to put on it.
Question is what do these run like without a blade.

Btw, both jets in the carb are clean in the cartridge. Needle is seating. Only thing is that one hole that goes from the deepest tube on the cartridge to the ventury seems to be stopped up.

On another note, I'm wondering if drilling out the main jet just a frog hair might be a good idea.


Any advise would be appreciated as always.

 

[Darryl G]

You need to put a blade on it to properly test its running condition.

 

[Romore]

I am surprised it will start without the blade, it probably tried to rip the handle out of your fingers. Drilling out the jet will just make a bad situation worse.

 

[AVB]

It a lot easier to know what you got if you post the model and type numbers of the engine but see if the follow service bulletin applies.

Meet Google Drive – One place for all your files

Google Drive is a free way to keep your files backed up and easy to reach from any phone, tablet, or computer. Start with 15GB of Google storage – free.

drive.google.com

 

[Darryl G]

Just FYI as far as why - the blade supplements the weight of the freewheel - many push mowers have lightweight flywheels that aren't sufficient without the blade. For some mowers with a clutch to engage the blades it won't matter, as they have heavier flywheels. Maybe one of the techs here can elaborate, but that's my understanding and experience.

 

[Rivets]

Cleaning the carb is useless if you did not set the float level properly. A float set a fraction low will cause surging everytime .

 

[PTmowerMech]

It a lot easier to know what you got if you post the model and type numbers of the engine but see if the follow service bulletin applies.

Meet Google Drive – One place for all your files

Google Drive is a free way to keep your files backed up and easy to reach from any phone, tablet, or computer. Start with 15GB of Google storage – free.

drive.google.com

I thought I posted it in a different post, from my phone. But either didn't hit the post button or something. I'm inside now for lunch, will post it when I get back out there.

I took a blade off another one and put it on. And the only real different was that it rev'd higher. Also the surging wasn't constant, as before. 30 second intervals or so. It seemed to clear up for a longer time than it surged. But when it does surge, it's not as bad.

I've got 3 of these this week. Gonna fix them up, and resell when spring hits. And all three of them have this same carburetors 593261 (the ones without the choke). They're spotless clean now. But all of them surge.

From what i understand. surging means it not getting enough fuel. Which is why I was thinking about drilling out that main jet.

 

[PTmowerMech]

Cleaning the carb is useless if you did not set the float level properly. A float set a fraction low will cause surging everytime .

Ah, you may have just solved this for me. I noticed this on the last two. Both are surging. I think this causes the fuel to get too high in the bowl. Am I right about that?

 

[Hammermechanicman]

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.

 

[PTmowerMech]

Engine

09P602-0085-F1