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Tuning a 8 HP Briggs

#1

J

jakesmurray

I have a 1985 8 HP Briggs and Stratton that I need to tune. It runs, but it never really finds a set RPM level. It also puffs a little bit of white smoke while it is running. Also, while I am drifing around on the mower, it bogs down and does not idle up like it should. I have attached pictures of the adjustment screws. There is one on the top, one on the bowl, and a little adjustment screw on the throttle butterfly. I also noticed that the fuel line from the tank to the carb is lopping down. Will a good fuel supply get to the carb if it is like this? I have taken a picture of that as well. I jut need to know the procedure for adjusting the screws to get it to run properly. Thanks

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#2

OzRanga

OzRanga

The main jet is the one on the bottom of the bowl, set at about 1 1/2 turns to start off...
The one on the top of the carby is the idle mixture...this is normally set about 2 turns out
Idle speed is on the throttle shaft.

Adjust the main jet at full rpm winding in or out about 1 turn either way until you find a central point

Adjust the idle in a similar fashion when engine is idling...slightly richer is better

What alot of people dont understand is even when the engine is running at full RPM with no load, most of the fuel mixture is going through the idle circuit.... Its not until the engine is under load that the main jet works to its maximum efficiency...

Hope that helps :)


#3

J

jakesmurray

OzRanga said:
The main jet is the one on the bottom of the bowl, set at about 1 1/2 turns to start off...
The one on the top of the carby is the idle mixture...this is normally set about 2 turns out
Idle speed is on the throttle shaft.

Adjust the main jet at full rpm winding in or out about 1 turn either way until you find a central point

Adjust the idle in a similar fashion when engine is idling...slightly richer is better

What alot of people dont understand is even when the engine is running at full RPM with no load, most of the fuel mixture is going through the idle circuit.... Its not until the engine is under load that the main jet works to its maximum efficiency...

Hope that helps :)
Click to expand...

Ok, thanks for the help. I'll try and tune it today.


#4

J

jakesmurray

Alright I went out today and with a few tweaks, it's running perfectly now. Thanks for the help!


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