Need help with Briggs 8HP problem

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  #1  
Old 02-03-15, 08:02 AM
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Need help with Briggs 8HP problem

Hi,

I own a Toro 828 OXE that's 5 years old, about 15 total running hours.

Engine model is 15D104-0113-E8.

While at IDLE after snowblowing for 30 minutes, it died like if I had shut it off myself. No surging, it was running perfect.

I opened the carb and it was all gummed from being stored full of untreated fuel for 4 winters in a row (ok ok.. now I know). O-Rings were dry, etc etc.. So instead of rebuilding I ordered a new carb. The original was #594014 but the replacement I got is #590907.

Replaced the carb, the spark plug (gapped to specs and verified that it has good spark), checked that compression is good, emptied and cleaned the fuel tank then filled with fresh fuel, verified fuel lines, verified flywheel shear pin (ok).

Now the problem: If I simply try to start the engine with mid-full throttle and any choke position, it won't ever start but will "pop pop" from the carb sometimes, and will kind of back fire at times. If I manually hold the throttle (and the governor) to IDLE position, the engine will start easily and will run smoothly for as long as I let it run this way.

Then if I accelerate (still holding the throttle directly on the carb but slowly turning it to accelerate), it will accelerate to full throttle and then I can release the throttle (or governor) and even throw snow smoothly. The engine will run fine, no surging, governor does it's job. BUT if I switch from IDLE to WOT rapidly, it bogs and dies. If I try to accelerate the engine from the throttle lever not holding the carb's throttle, it also bogs and dies.

Anytime it bogs, if I rapidly push the governor back to idle position, the engine resumes and runs just fine at IDLE and then I can re-open the throttle slowly holding the carb/governor.

I can almost rule out a governor problem as even unattached to the governor, the engine does the same, it bogs if I switch from IDLE to WOT too rapidly.

What does that sound to you ? Do I have the wrong replacement carb ?

Thanks a lot for you help!!!
 

Last edited by blouboy; 02-03-15 at 08:17 AM. Reason: wrong carb #
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  #2  
Old 02-03-15, 08:31 AM
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Sounds more like the idle adjustment screw needs adjusting.
Most often you screw it all the way in and back it out about 1-1/4 turns.
 
  #3  
Old 02-03-15, 08:33 AM
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A possibility is the carb you got may be from an application with an air filter. The jetting would likely be different. If you have a low end mixture screw on the carb and you lean it down it may help the transition from low rpms to high rpms. Richer mixtures tend to bog down since the ratio of gas to air is greater = slower burning fuel/air = bogging transition.
 
  #4  
Old 02-03-15, 11:39 AM
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This carb is supposed to be a direct fit for my engine, it came with the instructions that clearly indicate how to fit the metal mesh that act as an air filter..

Unfortunately, it doesn't have any mixture screw, only an idle screw, and whatever position it is, it does the same, it only idles faster or slower, but as soon as I twist the throttle a bit too fast, the engine bogs..

Is there something else that could lead to this kind of problem ? head gasket leaking air in the intake ? Valve problem ? I guess if it runs fine when I rev it slowly, it's more a carb problem then a mechanical failure ?

Thanks a lot!!
 
  #5  
Old 02-03-15, 04:27 PM
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A lot of that is difficult to say except to look at the recent running of it which seems to be fine with the old carb, then a plug up and stall = changed carb and problem started.

From that you'd have to say it's the carb and not mechanical. Most of the throttle response issues are a transition problem from idle/low rpms to mid/full throttle rpms and that has to do with air flow and how fast the fuel/air is burning in the combustion chamber. That affects air flow through the carb.

With a mixture screw for the idle you would lean it down until you got the throttle response you wanted.

Looking at the extreme of the other end, which is not enough fuel you would see an increase in rpms as the fuel burns too fast, then bogging down as you crossed the not enough fuel threshold, going toward the lean end of things.

To answer your question about the valves, etc. Those types of things affect air flow and will give a poor throttle response like you're seeing. However,from what we know at this point, I would say it's the carburetor.
 
  #6  
Old 02-03-15, 05:08 PM
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What brand carburetor did you get? Or, it's price may be a better indication. Is it an actual Briggs replacement carburetor or a inexpensive clone?
 
  #7  
Old 02-03-15, 05:22 PM
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Hi,

the new carb is a genuine Briggs replacement for this engine. I double checked today and it's the correct part number. Came with the hose that fitted perfectly and with the gaskets for the manifold.

I had to use the snowblower today as we've received a few inches of snow, and it's working perfectly as long as I start it holding the carb to idle position with my finger and rev it up manually and slowly. I found that giving half choke helps though, when the engine is hot and running smooth, I can accelerate using the lever but I have to go really slow.

Is there any kind of tweaking / hacking that can be done with those fixed carburetors ? My old 1977 Tecumseh was a breeze to adjust and I'm under the feeling that I'd have fixed that in no time with the mixture screws..

Thanks,
 
  #8  
Old 02-03-15, 06:04 PM
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I would have to agree that the carburetor seems to be the likely culprit. Since it's new, I'd be tempted to check the valve adjustments and intake gaskets and such just to be sure.
 
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