Briggs & Stratton Backfire

[thekidd76]

I have a Yamaha G2 that has an 8HP B&S motor in it. As it stands it runs pretty well, my only concern is that when letting completely off the gas after running wide open it backfires horribly. Other than gently letting off the gas and reducing the speed slowly I haven't been able to get rid of the backfire. And unfortunately that isn't always an option.

Has anyone had this problem, or have any suggestions on trying to resolve it?

[smokindawg]

What type exhaust/muffler do you have on it? What type air cleaner do you have on it?

Does it backfire every time you decelerate quickly?

Sounds like you may be running lean. I'd pull the spark plug out and take a look at it to see if it's showing signs of running lean.

[thekidd76]

Thanks..ill start there.

As for the muffler, it's just a small "coke can" style/size muffler. It's a cart I picked up recently as part of a package deal, I'll try to take some pics of the muffler and air cleaner tomorrow.

[smokindawg]

When you start changing parts on an engine that allow it to breath better, such as a more open breather and exhaust then you get more air into the carb/engine. When you do this it leans out the amount of fuel that you get. This has too be followed up by bigger jets in the carb. Otherwise the engines performance suffers.

The lean condition can cause all types of problems depending on how severe the lean problem is. These problems can be from something as small as backfiring to catastrophic engine failure. When they run lean they run hotter.

If you keep that cart you may want too eventually replace the small engine anyway. A G2 has so much potential. Install a bigger engine and they make one nice cart for just about anything. And, you won't slow so much on hills.

[sho305]

Try the following:
Richen the idle mixture, you may need to remove a plug to get at it or modify the carb or buy a screw to go in it or enlarge the idle jet.
Make sure you don't have any exhaust leaks.
Make sure you don't have any intake leaks.
Experiment with either turning the idle all the way off (wont matter if you have pedal start) or setting it slower/faster.
Personally I find that with no leaks verified I make the idle very slow, you must adjust the idle mix to get it to idle slower, then make the mixture slightly richer than it needs on a warmed up engine. And I don't have problems with backfires plus it starts with no choke. But every engine is different, every muffler different. Some say setting the idle speed to off works better.

[thekidd76]

Pulled the plug wire, and the plug was cracked. Plug itself though doesn't look like it's running lean. I'll pick up a new plug and play with the idle adjustment, and then look at a bigger jet.

As for the potential of the G2, any guidance here would be appreciated. I'm brand new to carts, so what kind of options do I have here with the engine or across the board in general?

[sho305]

Cheapest option for more power than stock is put a clone in it, check threads on that here and in clones section. Or you can go to a twin. Its easier to fix the stock engine but if you already have a swap, though depends on what clutch setup you have for that.

[thekidd76]

I'm assuming it has been swapped at some point yes. Whoever decided to put a bed on this thing obviously wasn't planning on doing any engine work, as I'm not going to be able to even get to the carb or air cleaner until I remove it.

[thekidd76]

There is only an idle screw on this carb, no air/fuel mixture screw.

[sho305]

Many newer ones don't, you either have to jet it or some have the screw covered up with a plug. I don't know about that one you would have to look it up.

You would need a 1 3/16 belt clutch for the engine the standard GC size (except for some club car), that is some smaller clutch. But looks like the stock yamaha primary that is good.

So you could drop a clone right in there with a clutch and be good (align the belt of course), make the exhaust, maybe an airbox, hook up the throttle and stuff. I used a car airbox and put pvc to the front of the cart because its really dusty at times in some places I ride. A few minutes and the engine is covered in brown dirt.

When I put my clone in the dealer wanted $600 for a full rebuild short block out the door with my core, I install it. Though the stock engine comes out in 20 min if you take your time.