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Small Engine Slows

My question is about a small engine, Briggs and Stratton 17 hp. It starts just great every time. But, after it warms up, about two minutes, it starts hesitating and quits. If I put the choke on it will go another minute. So, I thought it was starved for fuel. The fuel lines are not clogged and I replaced the filter. I put in new fuel and an additive, Sea Foam, that is supposed to clean things up. No improvement. Any suggestions on what to try next?

Pinch the fuel line to stop the fuel from flowing and remove the carburetor bowl and inspect it for crud in the bottom which will restrict the float from dropping enough to allow the needle to open fully. If any debris is present clean it out and spray cleaner through the main jet. If there is no problem in the bowl hold the fuel line over a can and release the clamp to see if fuel flows unrestricted for 4 to 5 seconds.

One problem I have seen in small engines is that there is a secondary filter/screen just before the needle valve. It will allow the engine to start and run for a while until the screen becomes completely clogged with debris. When the engine stops the debris falls away; the fuel bowl refills; and the engine will start and run for a little while longer. A quick test is to pull the fuel bowl and see if fuel is flowing freely from the needle valve – be fire safe.

My solution is to suck fuel back through the needle valve; clamp the fuel tank line; disconnect the fuel line; drain the tank through the line; reconnect the line; refill the tank; and see how it runs. If the problem still remains, repeat the procedure.

Hope this helps.

Depending on the model B&S, you also may have a diaphram type fuel pump for the carb. They can be bought separate for under $5 or are included in the carb overhaul kit. Usually warming up doesn’t make any difference but once the fuel in the carb is used up it does as well as choke position. If its not the carb, you could have a recessed valve.

Drain the gas tank, and see if this relates. I had that problem once and there was a 1/2 inch high 1/4" diameter strainer in the bottom of the tank that would get clogged with sediment in the tank.

Many thanks everyone for your ideas. First I checked to see if the fuel cap vent was plugged. Not. So, I took off the carburetor bowl off. I wiped it clean using “sea foam” additive. It did not seem dirty but that solved my problem. Perhaps there was water in the bowl. I have now run it several hours and it has great power and no hesitations. Thank you for your suggestion Rod!

I know there has been several replies to this already, but here is my two cents: As a small engine repair guy, this is one of the most common problems that customers come to me with. More often than not, a thorough cleaning of the carb, fuel tank and lines, or if needed, replacement of lines and filter, does the trick. Sometimes the carb cleaning can be done without taking the carb off the engine, but in some cases, the carb must be removed and soaked for a while in order to break up the more stubborn goo in the tiny fuel passages that are machined into the body of the carb. Worst case scenario is that a combination of goo and corrosion/deterioration of metal as a result of moisture/goo mix requires the replacement of the carb. However, replacement carbs for many small engines can be had for under $100, and some for $50 or less. I recently replaced a carb on a snowblower; the cost, including UPS ground delivery, came to $45. This was an aftermarket carb for a Tecumseh Snow King engine, the engine that 80% of all snowblowers use. With a total replacement cost as low as that, it’s hardly worth spending anything more that a short time attempting to clean out a cruddy carb. Time is money, right?
I guess the lesson to glean from the whole gooey carb phenomenom is that when you put away your seasonal outdoor power equipment or other small engine, take the time or pay someone to do a few basic things to increase your chance of an easy, reliable start-up next season. DON’T attempt to run all the gas out of the machine. For one thing, all you are doing is emptying the fuel tank and possibly the fuel line. The carb fuel bowl and fuel passages with not be 100% clear of gas, and that’s where the problem occurs. I know this is the way grandpa did it. Mine did too. And it seemed to work. I believe that two factors are primarily responsible for this metod no longer being effective:
1 - The inferior quality of todays pump gas and,
2 - All the extra crap added to gas that wasn’t in gradpas’ gas.

Rather than trying to get all the gas out, I recommend filling the tank and adding a good quality fuel stabilizer, about double the amount indicated or the label. To mix it in well, fill your tank about half way, then add stabilizer, then top off the tank with gas.
Next, I can not over emphasize the importance of this next point:


I know it cost a little more, but it’s not as if you are filling a 30 gallon tank on a Hummer and getting three miles to a gallon. The price difference filling a one or two gallon gas can with 93 or 94 octane gas as compared to 87 octane will be a couple dollars at most. Very cheap insurance in my opinion. I’ve never had a small engine run worse on high octane than it did on low. Most run better, some run the same. Trust me that doing this is the single best thing you can do for your small engine.
Oh, yes- also VERY IMPORTANT: After you fill your tank with high-octane gas/stabilizer mix, start and run the engine for a few minutes. You need to do this to get the stabilizer treated from the tank, through the lines, and into the carb. Otherwise, all it is doing is stabilizing the gas in the tank, and next season you’ll be in the same pickle!
Thanks for reading!!! Feel free to contact me via email with questions, comments etc.
Mikes Small Engine