Smoking at low RPM

bonyolddoc · 04-12-2009, 01:25 PM

I'm working with an 18hp B&S. Two minutes after I start it, it begins to smoke. I crank up the RPMs and it quits smoking. I can cut the whole yard (1/2 acre) but I do have to add a little oil evry 1/2 hour. I'm trying to get out of pulling the engine apart and replacing the rings so I'm hoping it might be a breather problem. Any hope for me?

MrChooks · 04-12-2009, 02:22 PM

Hi & welcome to TSF

Quick question - is the smoke blue or black.

I ask, as blue smoke is burning oil, BUT black smoke is fuel (over rich)

I ask as it is unusual for an engine that burns oil for it to stop doing so when the engine is rev-ed up and as you say you have replaced the rings - am assuming that you have oil leakage past the rings under control.

One last thing to look at is the PCV - the little breather tube that goes from the crankcase to the inlet manifold - just make sure that the valve is opening and closing properly and that the tube is clear

MrChooks · 04-12-2009, 04:11 PM

bonyolddoc. Sorry I misread your initial post and thought you said you had already re-ringed your engine.

Just as a quick test - pull the plugs from your engine and see what they look like.

If they are grey / brown and dry then all is good.

If they are black but dry - then that would be a symptom of the fuel air mix being too rich and can be fixed by carb adjustment

If they are black and oily - then engine oil is finding its way into the combustion chamber and in the absence of PCV / crankcase breather tube issues - then I would suspect that your engine is heading for a re-ring

bonyolddoc · 04-13-2009, 12:35 AM

Ok, tomorrow I'll fire it up and check the plugs. This smoking started pretty sudenly. My girlfriends idiot nephew was using it to cut some pretty tall and thick grass. I could hear the engine laboring and when I looked out the window I could see that the idiot had the deck lowered all the way, it was in fourth gear and the poor mower was practically hopping to get through the thick grass. Of course I don't dare say anything to offend said idiot so after 20 seconds of listening to the poor mower struggle there is sudden silence. I wander outside and idiot says the mower is overheating because it is smoking.
Fortunately I have another mower, an old restored 318 John Deere, which no one is allowed to touch.
So, after a workout like that, could the rings have gone south?(like I wish the idiot would do?)

MrChooks · 04-13-2009, 01:45 AM

Same old story - you can pick your friends but not their relatives

No - I would be very surprised if a bit of over load would do the rings in - especially over a short period of time.

04-12-2009, 01:25 PM	#1 (permalink)
bonyolddoc Registered User Join Date: Oct 2008 Location: Maryland Posts: 158 OS: XP Pro My System	Smoking at low RPM I'm working with an 18hp B&S. Two minutes after I start it, it begins to smoke. I crank up the RPMs and it quits smoking. I can cut the whole yard (1/2 acre) but I do have to add a little oil evry 1/2 hour. I'm trying to get out of pulling the engine apart and replacing the rings so I'm hoping it might be a breather problem. Any hope for me? __________________ “They who can give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety.” -- Benjamin Franklin

04-12-2009, 02:22 PM	#2 (permalink)
MrChooks Gearhead Join Date: Apr 2008 Location: Sydney, Australia Posts: 613 OS: Windows XP Home SP 3 My System	Re: Smoking at low RPM Hi & welcome to TSF Quick question - is the smoke blue or black. I ask, as blue smoke is burning oil, BUT black smoke is fuel (over rich) I ask as it is unusual for an engine that burns oil for it to stop doing so when the engine is rev-ed up and as you say you have replaced the rings - am assuming that you have oil leakage past the rings under control. One last thing to look at is the PCV - the little breather tube that goes from the crankcase to the inlet manifold - just make sure that the valve is opening and closing properly and that the tube is clear

04-12-2009, 04:11 PM	#3 (permalink)
MrChooks Gearhead Join Date: Apr 2008 Location: Sydney, Australia Posts: 613 OS: Windows XP Home SP 3 My System	Re: Smoking at low RPM bonyolddoc. Sorry I misread your initial post and thought you said you had already re-ringed your engine. Just as a quick test - pull the plugs from your engine and see what they look like. If they are grey / brown and dry then all is good. If they are black but dry - then that would be a symptom of the fuel air mix being too rich and can be fixed by carb adjustment If they are black and oily - then engine oil is finding its way into the combustion chamber and in the absence of PCV / crankcase breather tube issues - then I would suspect that your engine is heading for a re-ring

04-13-2009, 12:35 AM	#4 (permalink)
bonyolddoc Registered User Join Date: Oct 2008 Location: Maryland Posts: 158 OS: XP Pro My System	Re: Smoking at low RPM Ok, tomorrow I'll fire it up and check the plugs. This smoking started pretty sudenly. My girlfriends idiot nephew was using it to cut some pretty tall and thick grass. I could hear the engine laboring and when I looked out the window I could see that the idiot had the deck lowered all the way, it was in fourth gear and the poor mower was practically hopping to get through the thick grass. Of course I don't dare say anything to offend said idiot so after 20 seconds of listening to the poor mower struggle there is sudden silence. I wander outside and idiot says the mower is overheating because it is smoking. Fortunately I have another mower, an old restored 318 John Deere, which no one is allowed to touch. So, after a workout like that, could the rings have gone south?(like I wish the idiot would do?) __________________ “They who can give up essential liberty to purchase a little temporary safety, deserve neither liberty nor safety.” -- Benjamin Franklin

04-13-2009, 01:45 AM	#5 (permalink)
MrChooks Gearhead Join Date: Apr 2008 Location: Sydney, Australia Posts: 613 OS: Windows XP Home SP 3 My System	Re: Smoking at low RPM Same old story - you can pick your friends but not their relatives No - I would be very surprised if a bit of over load would do the rings in - especially over a short period of time.