Briggs & Strat wont idle stable, rough/low idle

Scrubcadet10 said:
Did you ever check the plastic intake manifold for cracks?
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Yes I checked the intake manifold and the tube that runs to the other side, no noticeable cracks and gaskets are all in good shape include the gaskets I just changed.
bertsmobile1 said:
If this is a single speed mower and it runs fine if you stretch the spring, then bend the anchor point to stretch the spring.
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No, the engine still surges if I place the spring tension higher. I'm not having a low idle issue per se, I'm having a idle stability issue. The low idle seems to be a secondary side effect.
 
Now I am confused.
Didn't we establish that you have a fixed speed engine with no throttle cable that has the rabbit & turtle on it .
If so it has no idle
It is supposed to run at high idle all the time.
 
Since the engine model and type number has never been posted that I can tell take the following with a grain of salt.

IF this engine has a float type carburetor using fuel bowl retaining bolt type main jet it may need enlarge one or more jet sizes. We are talking of less than a few hundredths of millimeter but before attempting this make all wax like residue is removed as have seen this to be the cause of the lean burn governor hunting.

An example of this resizing is going a #29 drill bit to a #28 can a lot of the time make a correction. The size used depends on the current size and up sizing is done step at a time and test as to not over richen the main jet size. Anyway this can over done and a new main jet would be required.
 
Since it is surging the govenor is working. That carb has no idle circuit. If the engine runs slow enough to not be on the high speed circuit it bounce on the govenor. You need to adjust the govenor spring anchor point so that the engine runs about 3400 RPM. Unless you change to a different carb it will not idle smoothly. I have seen where people have shoved the mower under stuff and hit the carb linkage and bend it and get the problem you have. That mower is made to just run full speed all the time.
 
AVB said:
Since the engine model and type number has never been posted that I can tell take the following with a grain of salt.

IF this engine has a float type carburetor using fuel bowl retaining bolt type main jet it may need enlarge one or more jet sizes. We are talking of less than a few hundredths of millimeter but before attempting this make all wax like residue is removed as have seen this to be the cause of the lean burn governor hunting.

An example of this resizing is going a #29 drill bit to a #28 can a lot of the time make a correction. The size used depends on the current size and up sizing is done step at a time and test as to not over richen the main jet size. Anyway this can over done and a new main jet would be required.
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it's a 12 series Quantum.
 
Sorry Scrubcadet, I have yet to learn the various series code names. I prefer to go by the actual model and type codes for looking up an engine's IPL.

This is especially true for me as I working across multiple brands, multiple OEM engines, and multiple equipment types. Basically if it is a machine I can work on it. Currently I got two Stihl trimmers, 1 Stihl backpack blower, 2 Husqvarna chainsaws, a walk behind mower, Yamaha ATV, and a Farmall Super M in the shop currently. Just sent out a Honda ATV, Polaris ATV, JD LT133 rider, and few other chainsaws. Then I got Hustler Super Z due in late next week for hydro work.

The biggest pain in the backside currently is the Yamaha since is has 50 psi compression where it should have a minimum of 150 psi. I got to pull the engine so I can disassemble the engine.
 
Im just wondering if there is an issue with the float and or needle. Might not be letting enough fuel into the bowl.
I had that problem once with the same mower, replaced the needle,seat and float and fixed it.
 
I ended up buying a cheap used mower for $25 I the neighborhood. This should get me through a couple seasons, but I still want to fix my mower. My dad bought this for me when I bought my first house, and I want to keep it going.
 
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