Briggs 3hp Carb (397939) running rough..help..

[hatteras451]

Could anyone help me with a carb problem...I have a Briggs 3hp on a Mclane edger. Carb part no. 397939. It has not ran smooth since I purchased it used. I have taken it apart and soaked in carb cleaner, blown out with compressor, put a new kit on (twice) and adjusted mixture screw. First, it is hard to get started. Most of the time I need starter fluid to get going. After warmed up, it cranks fine but runs very rough. It surges and sounds like it wants to cut off. Runs like there may be trash in it but I have cleaned it twice along with the soaking. Or either the mix id off which I have played with for quite a while. Is there anything else I can look at when I take it back off? Thanks

 

[Rivets]

Please post the engine model numbers, which may help us.

 

[Carscw]

Could anyone help me with a carb problem...I have a Briggs 3hp on a Mclane edger. Carb part no. 397939. It has not ran smooth since I purchased it used. I have taken it apart and soaked in carb cleaner, blown out with compressor, put a new kit on (twice) and adjusted mixture screw. First, it is hard to get started. Most of the time I need starter fluid to get going. After warmed up, it cranks fine but runs very rough. It surges and sounds like it wants to cut off. Runs like there may be trash in it but I have cleaned it twice along with the soaking. Or either the mix id off which I have played with for quite a while. Is there anything else I can look at when I take it back off? Thanks

When you rebuilt the carb did you change out the welch plug?

Take it easy with the starting fluid it can do piston damage.

(( cowboy up and get over it ))

 

[hatteras451]

When you rebuilt the carb did you change out the welch plug?

Take it easy with the starting fluid it can do piston damage.

(( cowboy up and get over it ))

it has been awhile but i finally started playing with this carb again...no i have not changed out the welch plug...today i found out something new about the issue...i dont know if it has anything to do with the problem but twice i noticed just before running out of gas..about 3-5 minutes before cutting off, it ran just as smooth as you could ask for...after putting some gas in, it starts back with the rough running...i have gotten the surge out and do not need to use starter fluid any longer but it just sounds terrible...but just before running completely out of gas, it runs fine...could this be a welch plug issue?..i have inserted a picture of the carb for reference...thanks...

 

[Rivets]

All you need is an adjustment which you can do yourself. Start up the unit with the air cleaner on and run it at full throttle. While it is running slowly turn the fuel adjusting screw on the side of the carb in until it runs smooth. Continue to turn the screw in until it starts to bog down and then turn the screw out 1/8 turn. Stop, should solve your problem.

 

[silver1]

it has been awhile but i finally started playing with this carb again...no i have not changed out the welch plug...today i found out something new about the issue...i dont know if it has anything to do with the problem but twice i noticed just before running out of gas..about 3-5 minutes before cutting off, it ran just as smooth as you could ask for...after putting some gas in, it starts back with the rough running...i have gotten the surge out and do not need to use starter fluid any longer but it just sounds terrible...but just before running completely out of gas, it runs fine...could this be a welch plug issue?..i have inserted a picture of the carb for reference...thanks...View attachment 20281

Well the picture shows a governor spring that is not in good shape. It should be attached to the loop in the throttle linkage.
Did you replace the diaphragm on the other side of the carb.? They can get damaged by Ethanol in the gas. If your gas tank has
any crude in it that can make fuel pickup problems.

 

[hatteras451]

Well the picture shows a governor spring that is not in good shape. It should be attached to the loop in the throttle linkage.
Did you replace the diaphragm on the other side of the carb.? They can get damaged by Ethanol in the gas. If your gas tank has
any crude in it that can make fuel pickup problems.

I have replaced the governor spring. That photo was actually taken while waiting on the spring to arrive. I did replace the diaphragm on the first round of service. I actually have taken it back out again since to clean again thinking I may have missed something. I replaced the throttle cable yesterday along with all gaskets again. I am doing things 2 and 3 times because I am out of ideas. Carscw suggested replacing the welch plug which I have ordered and waiting on it to arrive. After I replace that, I will definately be out of ideas. Thanks for your suggestions.

 

[hatteras451]

All you need is an adjustment which you can do yourself. Start up the unit with the air cleaner on and run it at full throttle. While it is running slowly turn the fuel adjusting screw on the side of the carb in until it runs smooth. Continue to turn the screw in until it starts to bog down and then turn the screw out 1/8 turn. Stop, should solve your problem.

I have been adjusting the mixture screw with no luck getting it to that smooth point. I just went out and put the air cleaner back on as you suggested and played with it again but with no luck. I have cleaned the screw and jet multiple times but I have not replaced them. I did pull a screw and jet from another carb just the same and installed but with the same results. Frustrated....Thanks for your suggestion!

 

[silver1]

I have been adjusting the mixture screw with no luck getting it to that smooth point. I just went out and put the air cleaner back on as you suggested and played with it again but with no luck. I have cleaned the screw and jet multiple times but I have not replaced them. I did pull a screw and jet from another carb just the same and installed but with the same results. Frustrated....Thanks for your suggestion!

I had a 2 Hp that the head was FULL of carbon and it ran poorly until I cleaned it out. It had the same carb.

 

[Rivets]

You have an adjustable Pulsa-Jet carb. Take a look at section 3 of this manual, which may give you some help. Page 17, figure 31. shows the pump assembly and the rest of the section may give you some clues. This carb is very simple, I can't understand why we can't figure it out.