Briggs Twin Popping

[38racing]

I assume that you put new plugs in it? Before pulling carb try running it on a 50-50 mixture of seafoam. Might need slight choke applied to run smooth. Has it run on enough fresh fuel to eliminate the possibility of bad gas?

[lefty]

I assume that you put new plugs in it? Before pulling carb try running it on a 50-50 mixture of seafoam. Might need slight choke applied to run smooth. Has it run on enough fresh fuel to eliminate the possibility of bad gas?

New plugs. The owner reported it started last season. He's run several fresh tanks through it from what I understand. He's pretty meticulous with his stuff.

[lefty]

Can I get some advice for carb removal on this? Specifically, the linkages. Facing the front, there is the throttle on the right and the choke on the left. Can't really pivot the carb assembly to remove one because it's tethered on two sides. I could pop the little plastic linkage bushing out of the choke lever on the left but I know there's a right way that someone here knows.

My other option is to completely unbolt the throttle bracket which would give me some movement to release the choke lever. I'm leaning towards that but don't want to reinvent the wheel if I don't have to.

Thanks.

[lefty]

Disregard...she popped right out of the plastic bushing.

[lefty]

I removed the carb and one of the two jets was clogged. I cleaned it and reassembled it. It runs well now.

As many may already know, I need to understand the mechanism. I have little experience with twins. My experience with retarded fuel delivery has presented as surging, no start, etc. My guess is that with a twin, the symptoms would present differently?

My assumption is that because there are two jets, two cylinders, and two pick-up tubes, while one may be deficient, the other is rocking, which may lead to a different behavior? Or maybe it can happen in a single cylinder and I just haven't run into it yet.

Is the popping happening in the cylinder with the lean mixture or the one with the proper mixture?...assuming that this was the problem. Which, at this point, seems to be the case since it's running so well now.

Thanks.

[SUKI]

It take some getting your head around this. V-Twins operate a little different then most thinks. Number 2 leads Number 1 cylinder by 90 degrees so basically number 1 is just a booster when the engine is firing on both cylinders. Basically the engine is coasting for 270 degrees after number 1 fires unlike the old opposed engines that fired every 180 degrees. When one cylinder is down it is hard to tell which it is except when it is loaded. Using an infra red thermometer you find a temperature difference as miss firing cylinder usually runs cooler. Doing a cylinder balance test also works but requires a rpm meter. With experience it gets easier to troubleshoot even then strange problems can still drive you crazy at times.

This when we pool our resources and ask for help. As always when we find a solution we should close out our threads with the solution found as you did. It helps all of us to be better mechanics as personally things do stick in the back of my mind; although, sleeping on problem may be needed. Makes for a restless night sometimes. It isn't like that I been at the shop at 1 AM in the morning.

Twin barrel carburetors do present unique problems too. I even had one that some how had a grain of sand in one of the idle jets several years ago. I had to use magnifier to find it as it was nearly clear but those little cube carburetors on two cycles taught me to look closer as with them the clear welch plug sealant can get struck in the jets and other passages.

I wondering if you ever a single OHV to sneeze (not a full fledged backfire) at idle speeds as I did a couple years ago. It turn out to be a leaky intake manifold square cut O-ring gasket. I took a couple days of thinking and trying things to find it.

So just keep on learning new things. Just make you and all of us better mechanics.

[lefty]

Thank you for the explanation and the advice.

It's amazing how something so tiny can take down a machine like that. I too have had to mount a weapons-grade magnifying glass/light to my workbench...most valuable tool in the shop.