needle valve sttings for Briggs carb rebuild

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10 Wheeler Rob
Posts: 1523
Joined: Tue Mar 21, 2006 2:44 pm
Location: East Hartford, CT

needle valve sttings for Briggs carb rebuild

Post by 10 Wheeler Rob » Wed Jun 18, 2008 12:18 pm

These are not quite antiquies, but some of you may know the answer.

I rebuilt carbs on 2 Briggs & Straton motors this week.

A 12 hp IC vetical shaft lawn tractor, has 2 neddle valves one up thru the bottom of the float bowl and one on top behind the throtle plate (idle setting I think). Any way what is a good starting point for setting the valves at to adjust from. This carb was leaking fuel through float valve is why I rebuilt.

The other is 4 HP vertical lawn mower with carb on top of tank, it has one neddle valve. Again what is good stating point. This one had a pluged orfice at the tip of the needle valve. I thought it would be a rotted out dipharam, so I repalced it first, but discovered the pluged orfice when I insected and clead it.

I set them near where they were when I took apart, got both running. How do I know what is the best setting.


bob whitmoyer
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Joined: Sun May 11, 2008 8:52 pm
Location: wooster,Ohio

carb setting

Post by bob whitmoyer » Tue Jul 01, 2008 11:01 pm

Hi There
12 hp one... Start up and let the engine warm up.
1. open throttle to better than 1/2 speed
2. turn in bottom (carb bowl) jet until engine starts to lean out
and miss, then back out jet screw until the engine smooths out

Top screw (idle screw) decrease engine speen to idle or near so.
turn screw in until idle becomes rough, then back out until engine
smooths out and is able to idle slowly.

Repeat at least once more if either screw had to be turned more
than one turn.

Small engine... set screw to best idle, rev. engine up, if rough
back out 1/4 turn and recheck idle.

Hope this helps

Bob Whitmoyer

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Joined: Mon Apr 21, 2008 10:34 am
Location: Springfield. MO.

Starting Point

Post by Dave_C » Wed Jul 02, 2008 7:18 am


If you need a "starting point" to get the motor running just lighly turn both needles in until they stop and back both of them out 1 1/2 turns, This will get you up and running! I've rebuilt too many of these to remember but that is where I always started.

I learn something new every day! Problem is I forget two.

10 Wheeler Rob
Posts: 1523
Joined: Tue Mar 21, 2006 2:44 pm
Location: East Hartford, CT


Post by 10 Wheeler Rob » Wed Jul 02, 2008 7:48 am

Thanks, thats what I did. got them running perty good.

The 12 horse with two neddle vlaves, one in the float and one on top, to set is starting on the ritch side, i.e. no choke to cold start & cople puffs of black ritch smoke, but seems to run OK.

The replacment float valve is metal tip, the old one had a rubber tip tha was going bad. So it may be letting a little to much gass in at start. This is one of the engines lets gas inot the oil if the float valve sticks, so you do not see or smell gas dripping if it leaks a little.

The issue of the neddle valve leaking is why I did the rebuild.


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