Craftsman riding mower w/ B&S 17.5hp - white smoke and gas from exhaust

Hey guys, first time posting though I have been lurking a lot. I appreciate any advice in advance!

I just bought a used Craftsman mower with a Briggs and Stratton 17.5hp 31C707 - 0230E1. When I checked it out they informed me it had been sitting for about a year - I could tell the gas was old and the oil was black and right at the ADD mark. I started it up very briefly just to make sure it would fire up - it did, and I killed it after about 3 seconds. So I did not notice the issues outlined when I first looked at it.

Upon getting it home, I changed the oil dumped the old gas replaced the short fuel line put new gas in it and fired it up. The old oil while very dirty did not have even a slight gas smell. When I first tried cranking it it didn't start immediately but rather spit a lot of gas out of the exhaust. I tried it again and it started and immediately started smoking white smoke. I turned it off, let the smoke clear and tried it again letting it run until the first signs of smoke. I did this probably a half dozen times, with each time getting less smoke and more time until the smoke started.

I checked the oil again and it was slightly over the full mark (not even 1/8" over) so I drained a small amount of oil and got it right to the full mark. Still smoking (though better).

When I changed the oil I did raise the left hand side up about 5 inches (so the carb was up in the air, and the oil drain was at the bottom). I thought thats what you are supposed to do, am I mistaken?

At this point from my lurking it sounds like the next step is checking the needle in the carb. But I wanted to get this started to see if I maybe messed up by slightly tilting the mower, and also if smelling is an adequate test for gas in the oil. It seems like everything I've been reading is saying if the needle is sticking and/or theres gas out of the exhaust then there should be gas in the oil - I dont seem to have gas in the oil. I should also note that the gas out of the exhaust seemed to only happen the first time trying to start it.

One last thing, theres a small notch on the throttle about midway, I am guessing that is the choke? There doesn't seem to be a traditional pull choke. When I try to move the throttle higher or lower from that notch the engine dies. Not sure if thats an additional symptom or a separate problem.

 

I checked everything out last night after the mower had been sitting about 30 hours from the initial oil change, and there is definitely gas in the oil now. I'm guessing a piece of a debris found its way into the carb between the time I initially got the mower and changing the oil etc.

I took the plug out and turned it over, no gas sprayed out of the cylinder.

I took the carb apart, cleaned it and ordered a rebuild kit, including needle and main jet. Ordered a new fuel filter and a gas shut off valve.

Is there anything else I should do from here other than rebuild and put the carb back together, change the oil and fire it back up?

 

Does it have a nikki or walbro carb?

 

Sorry meant to mention and forgot, it's a nikki

 

On the nikki, there is a white plastic piece that holds the float, needle, and main jet. At the top of it is a formed o-ring gasket and then a smaller o-ring around the fuel inlet. That small o-ring around the fuel inlet is a common place for fuel leaks that cause the problem you described. Replace it.

 

Its in the rebuild kit I ordered - I will update with results in a few days when I put it back together. Thanks!

 

Also, add a manual fuel shut off valve and most likely your problem will go away.

Briggs & Stratton Inline Fuel Shut Off Valve-698183 - The Home Depot

I suspect that the inlet valve is not seating properly. Since the smoke seemed to slow down with each consecutive start I am suspecting that your carb probably seats enough when running but with the extra storage time and the bumpity bump of getting it home, the gas runs into the carb and overflows into the intake manifold.

My mower did the same thing and all I did was install a $7 manual fuel shut off valve that I turn to the closed position when I am done mowing and I have never had gas flooding issue in the 7 years that I did this.

Those mowers should have a shut off valve installed at the factory, but better late then never. It won't hurt anything if it is not your problem.

 

It won't hurt to have a shutoff valve but I wouldn't recommend using it to avoid fixing the problem. It's not a sure thing that you will always remember to use it or that it will always work and gas leaking out into your garage or shed is a potentially dangerous situation.

 

Yep I ordered a shut off valve as well as the full rebuild kit. It will be here today and I should be able to get it fixed tonight after work. Unfortunately won't be able to actually mow anything till the weather cools down due to severe fire conditions.

 

So that seemed to do the trick with the smoking. It ran without issue in that regard, probably for a good 10 15 minutes until I turned it off. However, it would die when I throttled it up (and the automatic choke closed) - it would run good for a few seconds then start popping and puffs of black smoke coming out and eventually die. If I bring it down (open up choke) it starts running good again. Not sure where to go from that. I noticed the gas line is cracked and is leaking, so I will replace that, could that be the issue?

The deck also doesn't engage, I suspect that's a mechanical issue so I'll take the body off this weekend and start poking around in there.

 

Wait, I'm confused. Choke is supposed to close the airway. On my motor full throttle closes the airway and lower the throttle it opens it up. There's also a notch in the middle of the throttle. So am I supposed to go full throttle if I need thr choke and then bring it down to thr midway notch while running it? I've never dealt with an auto choked carb before, seems really odd.

 

Above the notch is choke. You put it all the way up to choke the engine for starting, then bring it down until it clicks into the notch, which is where full throttle is and where you would be for mowing. Anything lower than that is just for driving around or hauling stuff without the blades on.

The blade deck probably won't engage because of stuck brake arms and/or tensioner arm. The arm with the cable or linkage connected to it is supposed to move to tighten the belt and the brake arms move away from the blade pulleys when the tensioner arm engages. There are little rollers on the undersides of the inside ends of these brake arms and they need to be able to spin freely. Oil them and work them free if they do not.

 

Im a bit embarrassed I didn't think more about what the choke was doing sooner, but it all makes sense now. When I engaged the blades it was very hard to move the lever and I looked under the mower when engaged and thr belt was loose, so I suspect it is the tensioner. I will check tomorrow or Saturday and I'll post an update.

Thank you for the help thus far, I appreciate it.

 

Was waiting to update until I was able mow, and finally got to it this morning. Works and runs good. While idling it "pops" a little bit, but not enough to cause concern, but under load it's great.

Edit: the blades issue was in fact the tensioner, cleaning it out, breaking it loose and greasing it up did the trick.

Thank you again for the help!

 

Glad you got it fixed, thanks for the update!