Engine wont idle down

[KE4AVB]

Briggs 44M777-0149-G1 Twin Barrel Nikki Carburetor. 520 Hrs

Although I think I have finally found the source the problem which I have ordered parts for; I would get others thoughts on this as this the first I have seen this in my shop.

Engine was running at 3600 rpms even when the carburetor throttle plate is closed under no load condition. It will at times throttle down to around 2500 rpms. No intake manifold air leaks.

[HondaG100]

Have not worked on one of these but it has to be getting air from somewhere. Worn throttle rod or compromised idle passage?

[Luffydog]

The carbs are well known to go bad and run one cyc and cause low power. I found that it's best to replace the carb rather try to rebuild with all the plastic parts. There is some o rings in the carb that I had one issue that will cause high rpm and poor running condition. It's under the plastic piece that looks like a four barrel. Some of them leak and suck
Air causing some weird things. Keep us posted and good luck. I haven't had any on this carb yet. Needs to be a better design on this carb I think heat with gas has a lot to do with this carb failure. Good luck

[Mr Mower Man]

I'm not aware of any such problem characteristic of these Nikki carburetors, but I rebuild plenty of them without issue. I guess the first thing I would check in your case is that the throttle plates are actually both tight against the throttle shaft. I can't necessarily say I've seen this happen on that particular carb, but I have on carbs in general. Throttle shaft seal may be bad too, which would be a likely place to suck air.

[bgsengine]

Have not seen it myself yet but have been told of the throttle shaft breaking in two - the far end that is not connected to throttle link hangs open while the governed end goes closed... although I can't for the life of me envision how that would happen unless someone "forced" a jammed throttle and broke it.. end result is it is basically running on one cylinder at 3600 while the other cylinder *would* run at 1800 but it has to be dragged along by the wide open one.

[Walt 2002]

Carb throttle butterfly arm being in closed position does not necessarily mean that the throttle plate is closed. You need to actually see that the butterfly is closed.
Haven't heard of mounting screws coming out of throttle butterfly on this engine but they do on other B&S engines.

Walt Conner

[KE4AVB]

Walt,

I verified that before I posted.

Well it turned the root cause was caused by a monkey (someone that shouldn't have a tool)...Should have known that.

I had to work out all the other carburetor problems to get to the root cause. I too was thinking the worn throttle shaft was the problem.

1. Throttle shaft worn by .oo4 ovaled.
2. Butterflies were worn out from constant use. They looked like they were filed down at the throttle shaft sides.
3. Leaky main jets.
4. Leaky needle valve while in operation.

Oh well for these I just overhauled the carburetor plus install new jets and a throttle shaft kit. Actually all this make it worst.

It turn out someone had mess with the base idle speed adjustment to condensate for surging idling which turn out to be a miss adjusted idle restrictor in the governor control assembly.

1. Set base idle speed at 1300 rpm base; would not idle at 1200 rpm due to age of the age.
2. Set governed idle to 1850 instead 1750; same problem surging was worst at the lower speed due age.
3. Then set the idle restrictor arm per manual.

With these adjustments and repairs it now idles down nicely; although, it dies once or twice when first cranked if idled all the way down.

[KE4AVB]

Sorry about the monkey term just had vent a little after it took so long to fix it which should had not taken so long.

I just been getting one screw-up after another this year. I got a youngster in the area that thinks he knows it all about mowers. He messes more up than he fixes. It takes so much longer to fix things when you got to undo the screw ups first just to get the original problem.