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Message started by raydawg on 05/25/13 at 13:18:59

Title: Re: lean running
Post by raydawg on 05/25/13 at 13:18:59

I noticed my bike giving off a few more pops than normal a few days ago....I had put her on reserve as I was pushing the limit until I could get gas, I filled up, put in back to norm. Ran @ 50 plus miles when I happened to just look at the petcock, she was not true. I'm thinking I was just enuff outta plumb to restrict the flow a tad. This is what prompts my question, how is it that running lean is bad for the engine? Not enuff combustion to provide even stroke?

Title: Re: lean running
Post by oldNslow on 05/25/13 at 16:33:43

"running lean" normally refers to an incorrect air/fuel mixture - too much air - not enough fuel - being delivered to the combustion chamber by the carb or fuel injectors. A little bit lean won't hurt anything. Too lean a mixture will cause the engine to run hot and can cause damage over time. A two-stroke run lean is prone to seizing.

A fuel flow restriction between the petcock and carb is not really the same thing. If not enough fuel is getting into the float bowl the engine may run like crap, esp. at high speed, but it isn't likely to suffer any actual damage.

Title: Re: lean running
Post by Oldfeller on 05/25/13 at 17:51:46

Although all will freely admit that some chicken or egg syndrome exists here, but we have collected 4 incidents where a malfunctioning vac petcock led to lean out type stall events while running on fast 4 lane roads and there was some resulting piston ring area "ring stick" type galling damage to the pistons.

We think the ones that unstick themselves just become oil users, and the ones that don't unstick become tear downs.

You can't prove this for much with so few post mortems on such a few bikes, but it is enough to raise the question in folk's minds.

All of the bikes involved had intake filter and exhaust mods -- so that is more fuel for the "if you mod your bike go Raptor" type thinking.

But, yes, your petcock "leaning out" your engine through gas starvation while running at full speed quite possibly can cause damage to your engine -- we just can't totally agree to what degree the lean out did it vs whatever else was going on at the time.

Title: Re: lean running
Post by oldNslow on 05/25/13 at 18:55:59

Quote:

But, yes, your petcock "leaning out" your engine through gas starvation while running at full speed quite possibly can cause damage to your engine -- we just can't totally agree to what degree the lean out did it vs whatever else was going on at the time.

I gotta tilt toward "whatever else was going on at the time". What happened with the petcock was basically just "running out of gas".
In a four stroke with adequate oil pressure serious engine damage just from fuel starvation seems pretty unlikely to me unless the engine is really being flogged beyond reason. If a ring sticks because the engine stalls in such a case the damage comes from a combination of heat and a sudden lack of lubrication as the engine spins to a stop, not from a lean fuel/air mixture.

Probably just semantics; and it won't make much difference to a guy who just trashed his engine, but "running lean" and "fuel starvation" are two different things IMHO. That's what I was trying to convey in my original answer.

Title: Re: lean running
Post by apache snow on 05/25/13 at 20:11:00

Fuel starvation = more air than fuel entering the engine = lean all day long. Just my humble experience. but enough to hurt it probably not. :-?

Title: Re: lean running
Post by Routy on 05/25/13 at 20:19:52

Quote:
This is what prompts my question, how is it that running lean is bad for the engine? Not enuff combustion to provide even stroke?
---------------------------------------------------
Running lean will do damage only if the engine is being worked hard, like needing WOT going up a long mountain grade on a warm/hot day, or pushing it 80+ mph on a warm/hot day.
If/when doing that the piston is getting hotter and hotter, and thefore getting bigger, and pushed to the limits to the point of the piston skirt clearance becoming zero, could seize to the cylinder wall, or worse yet, melt the piston. Un less you were really horsing it hard at hi speed, and warm/hot weather, and you didn't notice any bad running condition, you can bet your life you did not hurt it at all.

Title: Re: lean running
Post by raydawg on 05/25/13 at 20:51:41

I'm sorry gang....I'm just not getting the relationship here. Does more fuel equate to running cooler? I know too much/rich and you get an incomplete combustion don't you? Or is it a matter of proper air/fuel mix equals the proper combustion which equates to your motor getting its maximum horsepower, which means it can respond to the load better without having to raise its RPM which will cause more heat via friction......???? :-?

Title: Re: lean running
Post by Oldfeller on 05/25/13 at 21:20:33

Raydawg, as far as your petcock's lever position having anything to do with your pops, who knows? It could, perhaps .... you mentioned pops when you were running out of gas, but didn't say about when you gassed up to the full tank condition.

You haven't even said what sort of petcock you are running nor which positions you were in between when "I was just enuff outta plumb to restrict the flow a tad".

If you were restricting fuel flow with your petcock lever being out of position (starving your carburetor) then you could be running the bowl level way down low which will give you some pops and it can cause you to run lean at whatever ongoing speed rate you were proceeding at.

And every time you hit a hill, your piston temperature went up higher than normal, the crown/cylinder portion of the piston (the ring area) expanded more than normal and stressed your oil film up there at the rings more than normal.

Running your engine in fuel delivery starvation mode is a feedback situation you see -- your bowl goes low, fuel being sucked up by the jets decreases, your motor starts to slow a bit so what do you do?

Your hand says "more speed" at the twist grip, your butterfly opens bigger, the diaphragm raises the carburetor slide more but the fuel delivered doesn't increase because you are fuel starved down in the bowl and there isn't any more to be delivered. The mix ratio gets whacked, going way way to the lean as more air is delivered by the slide going up but no more fuel is getting sucked up by the jets because the bowl level is so low it isn't there to be sucked up.

Your carb is then continually mis-mixing the fuel ratio for your stated 50 miles and your hand keep making it worse by increasing the twist on the throttle whenever you hit a hill ....

And your piston crown temperature keeps going up and your piston ring area keeps growing bigger and bigger.

Title: Re: lean running
Post by oldNslow on 05/26/13 at 06:22:46

raydog wrote:

Quote:

I'm sorry gang....I'm just not getting the relationship here. Does more fuel equate to running cooler?

According to conventional engine theory , yes it does. The ideal air/fuel mix is somewhere around 14:1.

Extra fuel in the mix won't all burn and has a (slight) cooling effect. The engine may produce more power at the expense of fuel mileage.

Too little fuel in the mix and the engine runs a bit hotter. Economy goes up and power down.

The above refers to the fuel/air mix sent into the combustion chamber by the carb. How much fuel is getting from the tank to the carb - a malfunctioning petcock for example - can effect how the carb is doing it's job, but it's really a seperate issue.

Title: Re: lean running
Post by raydawg on 05/26/13 at 11:55:15

744A4B47554948260 wrote:

raydog wrote:

Quote:

I'm sorry gang....I'm just not getting the relationship here. Does more fuel equate to running cooler?

Thank you.... :D

And just to clarify once again the issue I had. I don't run hard, or long....just ask my wife (sorry ::) ) and I only noticed the popping on decel, it seemed a bit more than norm, but in no way was I running long enuff, or in a manner my bowl was ever in danger of going dry.
Oh, and yes OF, I still have the factory vacsucker on, will till after my warranty expires, then off she comes, and doing a versy too ;D