Powermate generator: adjusting 8hp Briggs & Stratton engine

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  #1  
Old 11-21-11, 09:25 AM
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Powermate generator: adjusting 8hp Briggs & Stratton engine

Need some help adjusting the engine (8hp B&S circa 1988) on a Powermate generator I purchased at a swap meet.

I've already cleaned the carb. New float (had gas inside), new valve pin and gasket. Runs but speed all over the place. Also new air filter, new oil, new gas.

There is a needle adjustment on the bottom right at the corner of the carb tube for the angled long main jet (?) and another up near the top on the side.

The throttle is connected to the bottom of the engine by linkage and around this is a very fine long spring. Local Briggs parts guy said the ends of this spring go into same holes as linkage. Was very tight fit but did as he said.

Question is where do I start? So many things will affect speed. Do I remove linkage to set engine speed or??? Please some help to get me going in the right direction.
 
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  #2  
Old 11-21-11, 06:19 PM
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Run the engine at normal speed with the linkages in place, gently tighten the idle fuel mixture screw near the top, then back it out 2 full turns. Then begin to tighten the high speed mixture screw at an angle at the bottom of the carb until the engine begins to surge. Then back the screw out until it runs well, and continue until it begins to stumble, counting the turns as you do. Divide that number in half and screw it back in that many turns. Fine tuning may be required, but this should get you at an acceptable level. If not, you have other problems.
 
  #3  
Old 11-23-11, 12:04 PM
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OK. So I slowly turn in the idle screw at the top all the way in WHILE the engine is running and then back it out 2 full turns or do this before I start the motor up?

Where do I start with the bottom high speed needle set to? How many turns out to start before I turn it back in to get it to surge?

Can you tell me more about the governor system. Exactly how does this work? What inside the motor is causing that lever to move?

Thanks
 

Last edited by outdoormike; 11-23-11 at 12:25 PM.
  #4  
Old 11-23-11, 02:12 PM
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Screwing the needles in and then back out is just to establish a starting point. It can be done before starting the engine. When turning the screws in you want to be gentle and feel when it's all the way in. You don't want to tighten, just feel for the bottom, then back the screw out. The standard two turns should get you something that will allow the engine to start and run. Then from there you slowly turn them in/out to fine tune. It can be slightly frustrating at first since adjusting one screw affects the range for the other so you may have to go back and forth between the two as you zero in on the perfect setting for both.
 
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Old 11-23-11, 07:56 PM
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The governor is a flyweight system inside the engine. Don't tamper with it, it is set at the factory and should never need to be messed with.
 
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Old 11-24-11, 04:24 AM
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Here is a link to the Briggs website describing how their systems work.
 
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Old 11-25-11, 07:45 AM
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Worked on this some more yesterday but still not there yet. I'm not sure the governor is working correctly so I loosened the linkage and have set the throttle to a point above minimum idle speed (see picture). Hoping this will take one variable out of the picture.

www.webtfg.com/b&scarb.jpg

Using a volt meter the throttle at this position gives 120v +- 10 volts so at least I know roughly where the proper speed should be when all is said and done with the adjustments. Problem is it does not run for very long.

www.webtfg.com/meter.jpg

Right now, I'm working to get the motor to keep from sputtering when I quickly flip the throttle up. Is this the correct technique? How much does the idle adjust (top screw) play into this vs the high speed screw at the bottom of the carb?

Question 1: If there is a ring about half way on the high speed needle from past owner(s) over tightening will this affect adjustment that much?

Question 2: As I understand the governor system... the motor will work to increase the speed by opening the throttle more, correct... or is it working in both directions? If working correctly should I see the shaft (at bottom of motor) moving
back and forth as I move throttle?

Thanks!
 
  #8  
Old 11-25-11, 10:05 AM
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The governor sort of works in both directions. The governor pulls one way while a spring pulls in the opposite direction so it can both increase and decrease the throttle as required to keep the engine running at a constant RPM. Most problems with surging or not holding a constant speed are caused by the carburetor and in rare cases the governor linkage is damage somehow or gunked up to the point it can't move freely.

On the carb adjustment screws, when totally removed there should be a long thin cone. The sides of that cone should be straight and smooth. If it's been over tightened you will see a ring pressed into the cone. If it's been cranked down hard enough to leave a mark it is also possible the seat has been damaged.
 
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Old 11-25-11, 12:20 PM
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If I'm not mistaken that seat is the back end of the main jet... the long brass tube.. correct? Or is there another stop before it reaches the jet?
 
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Old 11-25-11, 04:53 PM
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I'm unclear if you have messed with the governor static adjustment or not, so, have you? Do you know what I mean by this absolutely? If not, let us know. If you have not changed the static adjustment then you likely still have a lean carburetor condition. What did you soak the carburetor in during your cleaning? Did you install a new Briggs rebuild kit? What do you mean by valve pin - the inlet needle, or otherwise?
 
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Old 11-29-11, 07:36 AM
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I did loosen the governor "clamp" at the bottom of the engine that attaches to the linkage going up to the throttle. I wanted to be able to get the motor to run without interference from the governor since the speed was all over the place.

Currently it is still loosen. Hopefully I'm not screwed (?) but I still question this is/was even working. Once I get the motor to run I will work on that.

I have just ordered a carb kit for the high speed needle and long tube. The needle had a deep ring from past owner over tightening.

I cleaned the carb with Mr. Clean in ab ultrasonic cleaner and I have for work and then followed up with spray carb cleaner and compressed air for all the holes and ports.
 
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