Craftsman Slight Backfire

O

OldDiyer

Well-Known Member
Craftsman Tractor:
Model Number 917.272452
Serial Number 042902A005400
Briggs & Stratton
21.5 HP I/C Platinum Intek
Family: YBSXS.7242VF 274844
Model: 445777
Type: 0154 E1
Code 010418Y G

I am not a parts changer; I'd sooner go after the direct problem and only fix the problem. So, heres my problem, this winter I did notice a slight miss or backfire well doing snow but didn't think much of it yesterday had to cut grass and did my front yard and towards the end I got a miss fire or slight backfire so went to the rear yard and turned it off. I let it sit for a while and then started it again and at higher rpm it miss or backfire was still there. Now I'm thinking lean mix or ignition issue so to not go nuts I put in new spark plugs, check and replace fuel filter and disconnected the fuel line after pump and seems to be pumping fuel. Also checked and the fuel solenoid it clicking with key on and off. Heres another thing that may help with helping me I did get the grass cut by just barely putting choke on and I mean just a little bit. Still seems to have plenty of power but without the choke the miss or backfire is there. I take very good care of this machine and clean under all the shields, change oil by seasons and full tune every two years including adjusting the valves. I just don't want to state throwing parts at it without getting to the fix. Now I am thinking but just wondering could it be I just got bad fuel and it is just now showing up? Because of how it is acting up could or should I try a cleaner in the gas first like Seafoam to see if it's just a small hiccup in the carb. I did rebuild this carb a few years ago when it had a stalling and rich problem and was a bad needle and seat. So, any help or guidance will be appreciated. Thanks in advance
 
I do not believe in replacing parts until they are proven bad, basic troubleshooting, servicing and inspection will usually resolve many problems.

From your description this favors a moisture/ condensation problem in the fuel tank. A simple thing to try is add a little 80% isopropyl rubbing alcohol to the fuel tank to break up the moisture droplets. A 1/4 to 1/2 cup full would be plenty. Run it under load for 30 minutes driving and operating to mix in the rubbing alcohol. Just running at idle will not solve the problem.

Note: Rubbing alcohol is not the same as the Ethanol alcohol that is added to most modern gasoline. Ethanol is plant based and isopropyl is petrol based.

The next possibility is that the carburetor fuel bowl needs to be removed and cleaned. Often times, fuel cans collect moisture and dust from the air very slowly and this stuff finds its way into the carburetor bowl.

Hope this helps you.
 
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Auto Doc Thanks for the reply I can give this a try for sure but not today seeing as I live in se Wisconsin you know what we have been getting for weather. I did get the grass cut yesterday because it got up to 72 and sunny. We are supposed to get some better days this week, and I will try the Rubbing alcohol and be back with the results Thanks again
 
Hello O.,

A product called HEET also works really well. The red bottle is for gasoline, and the yellow bottle is for diesel. They have methanol in them that breaks down water.
 
I would start like suggested by several others, with fresh fuel, add a fuel drier and see if that helps. Can also be a little sticking on a valve, or engine in need of a valve adjustment. Can be a bad plug, chewed plug wire, etc., but I would start with the fuel. Check for critter nest too if you can.
 
Appears to be a dual throat Nikki carb when looking at the engine parts IPL.
I've seen those carbs do just as you indicate. Little bit of choke making it better is a hint of the carb.
If the fuel tank additive in the suggestions does not get a fix, I can quite often while the carb is still on the engine remove the 3 screw top plate and use low pressure air (20 psi) into the orffice slits re-install the top plate and get a good run. Most generally the old gasket can be re-used but if not you can easily make one. Use eye protection when using the air. Gas will spray up out of the carb bowl.
Whatever you do hang onto your OEM carb. Do not give it a toss if you get another carb. The OEM is the best carb for repairing.
The replacement clone carbs are a roll of the dice.
 
Sorry For the delay in posting an update on my problem didn't need to really use the tractor till yesterday. So, I put in the Heet as suggested by Auto Doc drove the tractor around a bit had a slight issue but did seem better. So yesterday was a grass cutting day and got all the grass done and seems things are doing fine. I also picked up some SeaFoam and put a bit of that in it also. At this point I think the problem is fixed but will see if it lasts. Again, Thank all you people that gave me the directions and helping me with my problem.
 
OldDiyer said:
Sorry For the delay in posting an update on my problem didn't need to really use the tractor till yesterday. So, I put in the Heet as suggested by Auto Doc drove the tractor around a bit had a slight issue but did seem better. So yesterday was a grass cutting day and got all the grass done and seems things are doing fine. I also picked up some SeaFoam and put a bit of that in it also. At this point I think the problem is fixed but will see if it lasts. Again, Thank all you people that gave me the directions and helping me with my problem.
Click to expand...
So to me, this was a water in the fuel issue. If so, NOW you need to figure out HOW you got water in your gas.

Do you have an open spout gas can or the new style EPA o-ring sealed spouts? Which one?

1777028185594.png
 
I don't have any plastic gas cans mine are all metal, large 4gal for unmixed gas and two 1gal cans for mixed fuels they all have gaskets on the caps and are always on the containers I was wondering the same thing. Could be got a bit from the gas station but who knows, I can't remember but maybe I got gas in the can when they were getting a gas delivery and mixed up the underground tank sediment. Cap On tractor also has a good gasket as well. I also keep the tank full on the tractor as I have run out of gas and don't like hauling the can around the yard to fill the tank. You do bring up a good point so I will check the can before using anymore of the fuel in it I hate to through out fuel but will if needed.
 
Check in the bottom looking for water and trash. Anything that doesn't belong in there. Tip your can UP and fill a glass jar. See what comes out.

You should be able to siphon out the gas and the water will stay in the bottom of your can.
 
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