YZ Fouling plugs

[Arven]

Hi guys,

I have just gone and got myself a 97 YZ125. Now it was running fine when i bought it, and i was putting around the back yard on it for a little bit afterwards with no problems. Me and a mate decided to go to the beach to give it a good testing, so we got all ready and headed off.

Once at the beach i filled the bike up with some fresh Premixd fuel 32:1 (91 octane fuel) and tried to start it. IT started OK, but then puffed a bunch of smoke, and died. We spent the next 3 hours trying to get the damn thing to go, but it would only ever start after the plug was cleaned and the cilinder left to dry a bit.

After starting, it will rev high, then die. Taking the plug out shows that its wet fouling the plug again.

Now the bike was running FINE on the mixture the previous owner was using. So it must be either A. the oil i used in the premix, B. the low octane fuel. or C. a mixture of the both.

I havn't had time to have another play with it, but i have got some new 2stroke oil, and some 96 octane fuel. (a little better) and a new spark plug. And i will see how it goes.

Do you think i should try mixing it 40:1 to lean it out a bit? Is it normal for the YZ to be so picky about the fuel used? My friends 92 YZ ran fine on the same gas we mixed that day.

Sorry for the novel But i like to give the whole story! Cheers.

Arven.

 

[reelrazor]

a) when you up the ratio of gas to oil(go from 32:1 to 40:1), you actually RICHEN the fuel mixture.

The lower (numerically) the fuel to oil ratio, the more space in the carb jets is used up to pass oil. So, "leaning" it out by using less oil to mix with is wrong, you will be 'leaner' on OIL, but richer of fuel.

b) You didn't say how long you let it sit before restarting it on the fresh fuel. Did you truck the bike there, fill it and then this happened? Was the fuel shut off while transporting?

If the fuel wasn't shut off and you trucked the bike, you likely jiggled the float enough to overfill the bowl, which ran down into the crankcase, which everytime you clean the plug and try to restart, it fires, revs, and then throws enough of the crankcase puddle up the transfer ports to foul the plug.

And/or your float needle/seat is actiuvely leaking and the same happens.

c) 91 octane should be plenty to run that thing unless the head/compression has been modified.

I am betting you need to dry out the crankcase and then ground the plug lead and kick it over without a plug a few times(fuel tap shut off, preferably float bowl drained and wide open throttle). If you have access to an air compressor, use a blowgun in the spark plug hole with the piston at BDC to expedite drying the crankcase.

Run whatever oil ratio the previous owner ran.

I am not kidding about 'a)' up there. I have seen many people think they are treating their engine nice by throwing TOO much oil at it. They get a false reading on the plug being dark, think their jetting is on the safe, side and then they go out and heat seize it because it is running lean(and therefore hot).

All two strokes are liquid cooled, whether they have a radiator or not. The cooling liquid is gasoline(or methanol).

 

[Arven]

Thanks for that helpfull Info! :)

I did 'truck' (rather Trailer) the bike there, and i THINK i turned the fuel off. But i could have flooded it like you mentioned. Cheerss for the info.

I will pull the bowl off the Carb, and give it a bit of a clean out with carb cleaner also.

Yeap, I get what you mean about making the fuel Richer by putting less Oil in it. I was meaning 'Lean the oil' a bit. As it was fouling with oily petrol on the plug.

I usualy run 32:1 oil in my previous bikes. so i think i will stick with that. Better being a little smokey, than having a Detonating engine and a hole in my piston.

Thanks for the help. Hopefully with the fresh gas, and a cleaned Carb the bike will run! Will get back to you tonight and let you know how i get on.

 

[reelrazor]

Thanks for that helpfull Info! :)

I did 'truck' (rather Trailer) the bike there, and i THINK i turned the fuel off. But i could have flooded it like you mentioned. Cheerss for the info.

Yeah, even if the fuel was off, the fuel IN the bowl, and in the line to it is enough to puddle in the crankcase.

Yeap, I get what you mean about making the fuel Richer by putting less Oil in it. I was meaning 'Lean the oil' a bit. As it was fouling with oily petrol on the plug.

The reason it looked oil fouled is that when fuel lays in a puddle in the crank, it doesn't get a chance to be atomized by the carb and so is thrown to the plug as huge(relatively speaking) droplets. These droplets are a decent percentage oil, so you get that oily look. That is not a valid way to judge oil 'richness' or 'leaness'. Wait 'til you have it running on properly atomized fuel before making that call.

I usualy run 32:1 oil in my previous bikes. so i think i will stick with that. Better being a little smokey, than having a Detonating engine and a hole in my piston.

Detonation has NOTHING to do with oil when in a proper mixture ratio. Detonation is an uncontrolled(or improperly timed) explosion of the mixture and is usually due to spark advance, poor fuel, or an air leak.

You are more likely to harm your piston with a fuel lean mix than with an oil 'lean' mix.

You are MORE likely to gum up powervalves, rings and to have lots of carbon deposits with TOO MUCH oil.

I run EVERTHING I own that is two stroke at 50:1. That includes an 80+ hp RZ350 and weed wackers. My old TZ250u was run on 50:1 for three seasons of club racing on one crank. I have NEVER holed a piston in ANY of my bikes. I use yamalube R, castrol R series, or Optimol oil in them all.

Thanks for the help. Hopefully with the fresh gas, and a cleaned Carb the bike will run! Will get back to you tonight and let you know how i get on.

I don't believe it is your carb as much as your crankcase that needs to be cleaned out.

 

[Arven]

Quote:
I don't believe it is your carb as much as your crankcase that needs to be cleaned out.

So leaving the bike with the spark plug out for a day or so wont dry the Crankcasings out? Oil doesnt evaporate tho does it. The petrol will dry up and leave the oil behind. This shouldnt cause too much grief tho should it. Might just run a bit smokey??

Cheers.

 

[reelrazor]

Quote:


So leaving the bike with the spark plug out for a day or so wont dry the Crankcasings out? Oil doesnt evaporate tho does it. The petrol will dry up and leave the oil behind. This shouldnt cause too much grief tho should it. Might just run a bit smokey??

Cheers.

It depends on where the piston is in its' stroke. If it is set to bottom dead center(BDC), then the crankcase is vented. If it is far enough up in its' stroke, the transfer ports are closed and the crankcase is effectively sealed.

You can turn off the fuel, drain the float bowl, remove the plug, short the plug lead, lay the bike on its' left side and kick it over to clear the crankcase. This is semi effective and will likely have you swapping out or re-cleaning the spark plug a couple times before it runs clean.

You can roll the engine to BDC, and use compressed air and an airgun with a bendable tube(a piece of steel brake line with a fitting will fit into the cheap chromey airguns) to blow out the crankcase by applying air to the cylinder. The ideal way to do this is to get the blowgun nozzle right up to one of the transfer ports and use pulses of air. It REALLY works well if you remove the exhaust headpipe, lay the bike on its' side, insert the blowgun into the exhaust port and direct the air into the 'high' side transfer port which will force teh excess fuel/oil out the low side port and back at you through the exhaust.

Alternatively, you can pull the carb off and feed the airgun into the intake port(past one of the reed petals-again at BDC) and blow the fuel into the exhaust.

Or, again at BDC, you can hoist the ass end of the bike to near vertical(rafter, overhead beam, tie down straps) and let the excess fuel/oil drain that way.

With all these methods, be aware that fuel vapor is VERY dangerous, no smoking, no woodstove or pilot light nearby. ALWAYS short the plug lead when rolling over the engine.

And, yes, fuel evaporates, oil doesn't. This is another reason to NOT use too much oil. What doesn't get burned starts to coat the crankcase and port walls and then drains back to the bottom of the crankcase when you shut the engine off. After a while you will have so much of it in there that you get into fouling issues on cold startup.

Old dirtbike and snowmobile two stroke engines often had a drain plug on the crankcase for this very reason. The oils back then necessitated low mix ratios and draining 'cases was a common maintenance dealio.

 

[jmics19067]

"You can roll the engine to BDC, and use compressed air and an airgun with a bendable tube(a piece of steel brake line with a fitting will fit into the cheap chromey airguns) to blow out the crankcase by applying air to the cylinder. The ideal way to do this is to get the blowgun nozzle right up to one of the transfer ports and use pulses of air. It REALLY works well if you remove the exhaust headpipe, "


with my luck I would probably blow out the crank seals doing that.

Pick a motorcycle specific premix oil that is readily available to your location and wallet,pick a premix ratio(32 -1 should be adequate), use consistent,fresh fuel(same brand/octane from the busiest station in town if you don't want to spend the bucks for racing fuel) then adjust the carburator for the conditions that are going to be the easiest for you duplicate every time you ride. When and if you get everything nailed down tight and consistent minor tuning for altitude and weather conditions will be a lot easier if so desired/recquired.
Keep the air filter properly serviced and shut the fuel off any time the bike sets for a length of time especially when transporting and most of your erratic problems will disappear.