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Briggs 8 HP Horizontal Carb Adjustment


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10-09-05, 06:29 PM   #1  
joewright
Briggs 8 HP Horizontal Carb Adjustment

I have this 8 hp Briggs horizontal shaft engine on my '60 Wheel Horse mower that I am having a difficult time getting to run right. This model engine has the up draft style carb with 3 adjustment screws.. One throttle adjustment screw, one idle screw at the top (I guess), and one other screw at the base of the bowl of the carb that I don't know what is for. The carb is very clean, and I can get the engine to run on occasion, but it surges. The throttle linkage is very touchy and with the engine off, the throttle cable will move the carb to the closed position to full open in a fraction of an inch. Being that this is a pull start engine, I need to know the function of these screws and a base line of where to start. It's a neat little tractor and I would love for this thing to work right. Let me know if you need further info. It's probably going to take a few write ups to get this thing right.

Thanks,

Joe

 
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10-09-05, 06:39 PM   #2  
one at the bottom is the high speed screw, controls the fuel at full rpm, the other is the idle, should be 1.5 turns out from all the way in snug not wrenched as a baseline, then fine tune when its fully warmed up. should rev up and down with little to no hesitation. also make sure the adjustment screws are not damaged at the tips, if they are, they need to be replaced

 
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10-10-05, 12:23 AM   #3  
Correct, the screw near the top (not the one that moves with the throttle) is the low speed mixture screw. Turn it in until it lightly bottoms, then back it out 1 1/2 to 2 full turns. This is a base setting. Then, with the engine running at full throttle, adjust the high speed mixture screw (the one under the carb). Back it out until the engine sputters and stumbles a bit, then turn it back in until the engine surges and count how many turns it takes to make this difference. Then divide that by 2 and this is how many turns to back it back out. Those are base settings, and you can fine tune from there. Usually, at full throttle, if the engine surges as you described, the high speed screw needs to be backed off a little.


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10-10-05, 06:57 AM   #4  
joewright
What would be a good high speed mixture screw starting point? 1 1/2 to 2 turns from seated also? Thanks~

 
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10-10-05, 09:06 AM   #5  
joewright,

Correct. Both mixture screws are 1 1/2 out from seated as your starting point. You should adjust high speed first with full throttle with the engine warm. Then adjust idle with engine at idle.

God Bless,
Dave237

 
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10-11-05, 02:58 AM   #6  
FYI...the throttle does in fact move very little for correct operation. The butterfly has to move fractions for an increase in rpm. Make sure you have a good governor spring, post back with engine ID numbers and we can provide a part number for such.

 
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10-11-05, 08:14 PM   #7  
joewright
190402 051501 77010310

The numbers were a little hard to read, but from what a buddy of mine told me is that the numbers mean 190cc (or 8 HP), 3 inch long and 1 inch in diameter horizontal shaft, and it was made in January 1977.

I did get the engine running thanks to you guys. The throttle is still very touchy though (i only have to move it a faction of an inch and the carb goes full open). And at full throttle it still surges a bit. I probably still need to spend a little more time adjusting it. I haven't put the engine under any load yet because I haven't bought a drive belt for it.

Thanks again ~Joe

 
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10-11-05, 09:32 PM   #8  
Joe,

Good number crunching! Your parts list is at:

http://shop.briggsandstratton.com/BS...gineType=0515#

Click on the 2nd listing: (MS5848) It is a pdf file.

I suggest you begin with a cleaning. Disasimble the carb. Clean all parts, ports, passages and emullsion tube with carb cleaner and comprressed air. If you need to; use fishing line in all very small holes. Replace all o-rings and rubber washers that may be under the bowel and adustment screws and replace bent or scored mixture screws. Rebuild kit is Briggs# 291763

When this is completed and reasimbiled your engine should be good as new.

God Bless You,
Dave237


Last edited by dave237; 10-11-05 at 10:10 PM.
 
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10-26-05, 05:16 PM   #9  
joewright
Ok.. I finally got around to cleaning the carb. The gaskets and orings were all in really good shape. What measurement does the float bowl need to be set at? I hope I can get this thing running good.

 
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10-26-05, 08:52 PM   #10  
was the float tab, if its a metal float messed with in any sort of way? then it should be ok.

 
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10-27-05, 08:53 AM   #11  
joewright,

The float should set level when the carb is inverted.

God Bless,
Dave237

 
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10-28-05, 12:47 AM   #12  
Correct....turn the carb upside down and adjust the float if necessary, to where the float is parallel to the carburetor bowl mounting surface.


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God bless!

 
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10-28-05, 07:18 PM   #13  
joewright
Ok.. I adjusted the float. Reassembled the carb and put it back on the engine. It still doesn't seem to be running to it's full potential. It lacks power. With no load, it runs fast, but when you load it, it loses rpm. Could the govenor be miss adjusted?? I don't know the history of the engine, so it could have be messed with in the past. It wasn't running when I got it.

Thanks again

 
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10-28-05, 10:09 PM   #14  
joewright,

Yes! It does sound like the governor is not adjusted properly. Look for springs not installed properly or a binding linkage however, it could still be a dirty carb or blow-by the rings if it is a well worn engine.

God Bless,
Dave237

 
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10-29-05, 12:05 AM   #15  
Try backing out the high speed screw (under the carb) a bit and see if it performs better under a load.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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10-29-05, 06:03 AM   #16  
You certainly may still have a carburetor issue whereas you should soak it in a quality bath-type cleaner, but, you also must have good vacuum for the carburetor to function well. In other words, a combustion chamber leak-down test will help to determine if you in fact have a problem. If you do and based on your troubles you may have an intake valve issue. Whether it be the valve itself, the valve seat or possibly carbon build-up on the valve face. Any of which will create a lack of necessary vacuum.

 
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08-27-13, 07:48 PM   #17  
Briggs 7hp on a Cement mixer

Hi guys, was wondering if someone could help me out. I have a 7hp briggs with the updraft carb. This engine is on a towable stone equipment cement mixer. I bought a brand new carb and installed it, however, there is no throttle cable or lever. I set the high speed screw, but there is a knob type adjustment for the govenor. I have never seen this before. I assume this mixer is supposed to run at fixed rpm, but when i tap the throttle linkage with my finger when its running it just takes off and I shut it down so I dont blow the engine. I just need to know how to set this thing up. it seems that knob for the govenor adds tension to the spring, which is goes to the linkage of the throttle plate.

Model off the engine is a 170452-2351-01. any help will be appreciated it.

 
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08-27-13, 08:12 PM   #18  
All the knob does is act like the slide throttle on a lawn mower. It sets the governor which moves the carb throttle plate to keep the speed you set the governor knob for.

If the engine speed isn't being governed to the setting, then the flyweights aren't moving out. From the parts diagram it looks like it has a typical internal gear driven governor. So, I imagine that's where the problem is.

 
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08-28-13, 06:56 PM   #19  
Is there a throttle linkage connected to the shaft?


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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