Briggs Twin Popping

[lefty]

I have this briggs engine on a Husqvarna Tractor

Model 407777
Type: 3195-G5
Code: 130413YG

It starts and runs but experiences a random popping. Sounds like through the carb. RPMs will wander slightly at lower RPMs. Max RPM is about 3100. The machine is maintained and in good condition. My guess was either flywheel key or valve issue. I started with valves because the owner mows a meticulous yard and hasn't hit anything. The blades are a few years old and pristine.

I pulled the covers and found the intake on one side to be about .009 and the exhaust on the other is also .009. Valves appear to fully actuate.
The engine manual says .004-.006 for both. Would this excess clearance cause this? I'm waiting on gaskets for the covers and was wondering if I should be chasing anything else in the meantime. I wanted to try spec settings on the valves before pulling the flywheel.

I remember reading or watching something a while back about having to adjust the throttle cable on a twin because it was leaving the choke partially closed but I can't remember if it was this Briggs. Maybe I'll check that as well.

Thank you

[bluemower]

Not much to go on.
After 8 years of service, I am always suspicious of ethanol fuel. Idle circuits in the carburetor start to plug up and may be causing the idle rpm to vary. Sometimes a gummy residue forms on the intake valve stem and the valve does not seat as tightly or as quickly as it should. Check the sparkplugs for fouling. Both of these could result in the carb popping.

[lefty]

Maybe I'll attack the carb then. I put two new plugs in with similar results.

Thank you

[SUKI]

Appears to have a twin barrel Nikki so it possible to have one or both main jets loose.

[bobodu]

Seems no one ever checks the valves.....I sometimes have to help out the widow next door ( country music playing here..) and she has her mower serviced by one of THE BIG BOYS....valves out of spec
One of the first things I look at. Usually apparent when hard cranking.
I wouldn't bother worrying about anything else until that is resolved.
As Blue said...plugs can be tricky on twins....been lost in them woods a time or two..
Also....hitting something on a TRACTOR is not likely to cause a flywheel key to be damaged....Walk behind direct drive vertical yes.An extreme backfire might cause a problem but a tractor has belts and clutches in between the blade and engine.Someone might have another opinion or additional input but that is my experience.

[KE4AVB]

Lefty,

You don't have to use gaskets on the rocker covers. Here they get Permatex Ultra Black or Ultra Grey application. And it is fairly easy to remove them later provide you know how. Only one draw back and that is that all the oil on mating surfaces must be removed and the covers are installed finger tight only overnight without starting the engine and then torqued to 65 in-lbs. Oil does affect the curing process. Yes takes longer to get things back to operating but it is well worth the extra time. Especially on those Kohler Courage Singles with that V cover. I even use the Permatex surface prep /accelerator spray. One draw back on the surface prep spray with Locktite as it does setup fairly quickly.

At one time I pried these covers off but now I just use a block of wood and a heavy hammer to shear them off.

But Bob is right as many shops don't take the time to check the valves and it is part of any job when it comes to OHV engines. You never know when the last time, if ever, they were adjusted since the engine was new.

And plugs can miss fire and V-twins you might not even notice it until you engage the deck. I just did a Kawasaki V-twin where they were borderline line bad and was causing overheating. The engine was barely able to power the deck upon engagement but did. Engine now running much cooler now with the new plugs.

[lefty]

Thanks guys. I ordered the gaskets mainly because it showed them on the diagram and I got one-day shipping on genuine Briggs. Plus I'm not super comfortable with the gasket maker. I'm getting better but always make a mess. I'll give it a try next time.

The valve adjustment seemed to do the trick. The popping has stopped. The RPM rose a bit too...about 3250 now. I ran her and rode around for about 10 or 15 minutes and didn't have any sign. I hope it's not a coincidence. If it starts at it again, I'll check the flywheel key and move on to the carb. But for now, it feels like we may have gotten it. Thanks again.

Can I assume that this came from the factory with gaskets and someone was in there since?

[lefty]

It's back. So either what I did got undone or I was wrong from the start. I think I'll check the key next, recheck the valves and attack the carb.

Any chance a bad coil would cause this? I have two inline testers now so I could check them simultaneous-like. My second one just came in today. I checked them one at a time the other day but nothing jumped out at me.

[lefty]

I discovered something interesting, or at least to me. I was inspecting the carburetor in order to note how linkages hook up and such when I noticed that when I actuate the throttle, the linkage binds up on the intake manifold, the one on the right if your standing in front of the machine. The plastic manifold interferes with the smooth operation of the throttle. I took a video and tried to upload it through google drive. Hope it worked. Could this be the culprit?

https://drive.google.com/drive/folders/1-UWbCmJcZRCCMJqr2bWcsjpRJpPzxkTY?usp=sharing

[bobodu]

Explain to me how the key could get damaged please.
I would look for a leak on the manifold....
A kink in the linkage will not cause popping...