OT-18 hp B&S Intek mower issue

[user 64972]

Hi:



This is an off topic question about my 18 HP Craftsman lawnmower with a Briggs & Stratton Intek motor. Last year it started a slight miss after I let it sit and run for a few minutes when I was moving something in the yard. Once I got back on and moving, the miss went away. I also changed the plug, fuel filter, air filter, changed the oil/oil filter and cleaned the little hole in the gas cap.



This year it starts an intermittent miss after say 20 - 30 minutes of mowing. I replaced the spark plug, fuel filter, replaced the cracking fuel line, checked the hole in the gas cap and checked the air filter. I also used an air hose to clean off the engine real well...thought it might be a vapor lock type situation. None of this helped and I don't know what to look at next?



I have seen some members state that the do or have worked on lawn mowers for a living and am hoping to get some tips other than "Buy A Deere". Any tips/hints or help will be appreciated.



Thanks, Gary

 

[Todd Z]

I know most of the needle and seats on all mowers tend to dry rot and stick after a while, especially if you use gas stabilizer, OR don't properly winterize...



Can remove the gas line, Run the motor.... once it stalls, Spray some carb cleaner in the fuel line toward the carb and spray some directly in the carb...



IF not, remove the bowl and replace the needle and seat...

IF you never have done that it can be real tricky..



Todd Z

 

[Mark G]

It may also be a sticking intake or exhaust valve. Give it a seafoam treatment and run a little of it in the gas all of the time.

 

[Gavin Allan]

Have you tried adjusting the mixture screw(s) on the carburetor first?



First, make sure the choke is working properly (it fully opens and closes).



Install a clean/serviced air filter.



Then, get the engine running - warm it up to general operating temp.



Make sure the choke is wide open.



Adjust the main jet if you can get it to run at full throttle - preferably under load (turn in to the lean stutter, then out to the rich stutter, then back in about 1/2 way between these extremes).



Then adjust the idle spped.



Then adjust the idle mixture - at no load - (turn in to the lean stutter, then out to the rich stutter, then back in about 1/2 way between these extremes).



Re-adjust idle speed as needed.



You may then go back and repeat/refine the process a second time as the idle adjustment may affect the main a bit.

 

[shawn stonbraker 2]

It sounds like it may be "dumping" on you. It gets a small blockage (that will still alow it to run fine) then the blockage fixes itself and dumps fuel to the engine, causing it to run rough. I would also do what Mark G said. Get some SeaFoam and add a couple of cap fulls to your oil, and add it to the gas. It will clean the carb and Valves and see if that helps first. If not, I'd then check the compression, and rebuild the carb. A rebuild kit for the carb (new seals and needles and seats) will run about $10-$20 and is easy to do, just take your time. Hope this helps.

 

[user 64972]

Thanks to all for the good tips. I did the Seafoam treatment today and most of the miss has disappeared. I will run it in the gas and hopefully it will go completely away after a while. If not, I'll try the other carb tips.



Thanks again,

Gary