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Briggs 5hp with no blade

#1

PTmowerMech

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.


#2

D

Darryl G

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


#3

R

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.


#4

AVB

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.

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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


#5

D

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.


#6

R

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 .


#7

PTmowerMech

PTmowerMech

AVB said:
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
Click to expand...

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.
1579900422214.png
From what i understand. surging means it not getting enough fuel. Which is why I was thinking about drilling out that main jet.


#8

PTmowerMech

PTmowerMech

Rivets said:
Cleaning the carb is useless if you did not set the float level properly. A float set a fraction low will cause surging everytime .
Click to expand...

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?


#9

Hammermechanicman

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.


#10

PTmowerMech

PTmowerMech

Engine

09P602-0085-F1


#11

PTmowerMech

PTmowerMech

Hammermechanicman said:
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.
Click to expand...


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.


#12

PTmowerMech

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.


#13

R

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.


#14

PTmowerMech

PTmowerMech

Rivets said:
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.
Click to expand...

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.


#15

R

Rivets

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


#16

T

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


#17

R

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.


#18

Hammermechanicman

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


#19

I

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.


#20

Hammermechanicman

Hammermechanicman

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


#21

R

Rivets

If it’s like the one pictured in post #7, I’ll be glad to help you, but you’ll have to wait till tomorrow as I’ve had a long day. Just so we’re on the same page, shoot me the numbers off the engine and/or the carb part number. I’ll get back to you after I get done with the Sunday Honey Dew list.


#22

Hammermechanicman

Hammermechanicman

It is like the one in post 7 except it has the auto choke. I will get the engine numbers tomorrow. I have a couple riders to pickup for annual maint tomorrow so i will be out in the shop tomorrow afternoon working.


#23

PTmowerMech

PTmowerMech

Hammermechanicman said:
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
Click to expand...

Check to see if the choke is hanging up on the bracket that holds the carb on. You'll probably have to take the top cover off, to ge a good look at the top of the carb. With the choke off, as in when it's running, that choke lever could stick on that metal carb bracket. And when it cools down, it won't return to choked position.

With the engine and the cover off, just move the choke open and closed to see if it's hitting where I'm talking about.


#24

PTmowerMech

PTmowerMech

Rivets said:
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.
Click to expand...

I drilled the 2nd one today and if it's running rich, I can't tell it, or smell it. Gonna run them a little more tomorrow and check the plug. My calipers don't give me enough digits to say what size the bit I used is.
But no surging at all.


#25

Hammermechanicman

Hammermechanicman

PTmowerMech said:
Check to see if the choke is hanging up on the bracket that holds the carb on. You'll probably have to take the top cover off, to ge a good look at the top of the carb. With the choke off, as in when it's running, that choke lever could stick on that metal carb bracket. And when it cools down, it won't return to choked position.

With the engine and the cover off, just move the choke open and closed to see if it's hitting where I'm talking about.
Click to expand...
The auto choke is working as it should. Thanks for the tip.


#26

R

Rivets

When you get the numbers I’ll get back to you.


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