Briggs Quantum Idle Mixture

[lefty]

Model: 124802-3219-02
Code: 93060756

I just cleaned the carburetor on this and there is an idle mixture screw. Am I controlling air or fuel with that screw? Trying to figure out if tightening leans or enriches.

Thanks

[bluemower]

tightening the screw will lean the idle mixture.
here is the exact wording in the 1991 briggs update seminar.
"Idle passage needle adjustment: Used to meter the precise amount of fuel for engine at idle".

carburetors were also equipped with an Idle air bleed. This allowed a small amount of air to enter the idle fuel passage going to the idle mixture screw. Exact wording from the 1991 update:
"Idle Air Bleed: this opening allows air to atomize the fuel before entering the air stream while the engine is idling. This premixing of the fuel and air increases the efficiency of engine combustion".

[lefty]

Perfect. Thank you.

[lefty]

On this same machine. I've been chasing a surging problem but I think I have it narrowed down to a governor issue, whether it be the actual governor or the spring.

When I go to the carb and hold the throttle steady, the surging goes away. I can change RPM's easily by hand and it runs super smooth. But as soon as I let the governor take control, I get surging. The surging eventually goes away after about 10 seconds. But every time I reduce the throttle and ramp it back up unless I'm holding it steady by hand, it will surge badly for about 10 seconds before leveling out. I performed a static governor adjustment with no difference.

My thought is maybe a weak spring. I'm thinking that if the governor itself was bad, it wouldn't eventually smooth itself out. It would just be bad. But that's a guess.

The spring is expensive so before I go for it, I wanted to see if anyone thought I was on the right track or had any other ideas before I took this path. Thank you.

[lefty]

I have good news. No, I haven't solved the problem but I did find a local supplier that is willing to order parts without charging shipping. So I was able to try the spring for a reasonable price without having to pay 150% of the price for shipping. I"m super happy about that.
I still have my problem though and wanted to just recap to make sure I didn't forget anything.

When this first starts, it surges badly until it's warmed up. About a minute or so. After that, if I go to idle and then back to full throttle, it surges badly for about 10 seconds before leveling out.

During all of this, cold or warm, I can hold the engine steady by bypassing the governor spring with my hand. I think this isolates the problem to a governor issue rather than fuel. At no time, does the engine surge when I hold the butterfly by hand. I can change between RPM's with ease and no surging.

Is it possible for the internal governor to create this condition? The machine is likely not worth opening up for that. The owner would likely not want to pay for it given the age and the fact that he has another machine. I'm just trying to make sure I've done everything. The reason I haven't tried a new carb is that when I hold it by hand, everything is fine. Does anyone think I'm missing a fuel issue here? I went through the carb twice already cleaning it.

Thank you

[38racing]

I had a tecumseh push mower that had a surge that several actions couldn't fix. It actually turned out to be blockage in the fuel filter that had been added inline.

[lefty]

Thanks. I replaced this fuel line initially because I found a crack when I removed it. What's got me hung up on governor is the fact that I can maintain a good running condition by holding the throttle at the carb. Makes me think that the governor is the fail point.

[lefty]

I'm just not sure if an internal governor issue could cause an intermittent problem or if it's one of those things that either works or it doesn't.

[KE4AVB]

A couple things.

Have you set the idle speed to 1750?

A second thing to try is to take a .010" - .015" feeler gauge place it between the carburetor high speed stop while adjust the governor. This will tell if the governor has some slop in the flyweights. I have to do this on some Kohler Courage single cylinder engines that come in surging where there is too much play in the governor assembly.

[lefty]

The idle is set to 1750. I'll try that governor adjustment you described. Thank you.