What's on your bench today?

[spudulike]

I have heard a few say that putting more oil in the fuel "Leans" down the mix. Well.....it does as far as the fuel/oil to air mix goes.

 

It also makes the oil content of the fuel/oil to air mix GREATER so it is less likely to seize an engine - that's my take on it and would like to hear if anyone doesn't agree:001_rolleyes:

[GardenKit]

I have heard a few say that putting more oil in the fuel "Leans" down the mix. Well.....it does as far as the fuel/oil to air mix goes.

 

It also makes the oil content of the fuel/oil to air mix GREATER so it is less likely to seize an engine - that's my take on it and would like to hear if anyone doesn't agree:001_rolleyes:

I sort of agree with you Spud.

 

In theory the more oil you add to a mix, the less petrol there is in the finished volume.

 

So this mix combines with the same amount of air, and is, beyond any dispute, a leaner mix.

 

Whether this amount of 'leanness' is sufficient to cause overheating and subsequent siezure is probably unlikley. It is more likely to need a slight carb adjustment to get the low speed idle and pick up correct.

 

I don't believe that any amount of extra oil can prevent a true 'lean sieze' though.

 

Just my thoughts.

[spudulike]

I sort of agree with you Spud.

 

In theory the more oil you add to a mix, the less petrol there is in the finished volume.

 

So this mix combines with the same amount of air, and is, beyond any dispute, a leaner mix.

 

Whether this amount of 'leanness' is sufficient to cause overheating and subsequent siezure is probably unlikley. It is more likely to need a slight carb adjustment to get the low speed idle and pick up correct.

 

I don't believe that any amount of extra oil can prevent a true 'lean sieze' though.

 

Just my thoughts.

 

Don't know Barrie - I think if you ran a 1:50 fuel to oil, that may never seize the engine as it would never start:lol:

 

The point I was making was that if the saw was tuned to the correct max revs and was running say a 40:1 mix Fuel to Oil, you now have the same amount of fuel (oil & petrol) vapour going in to the engine but with a higher oil content and this must surely protect the engine against seizure as it is the oil and not the fuel that lubricates the engine.

 

Sure, the amount of PETROL that is going in to the engine is less so it may not run quite the same power but the oil would protect the saw more.

 

Would you say this is "Lean"........ not sure as the same amount of vapour will be passed by the carb (making allowances for the viscosity of the mix) and you usually say an engine is running lean if the fuel/oil MIX entering the engine is not enough but this won't have changed??

 

It would be interesting to run a saw with 50:1 and 30:1 and register the differences in output, max revs and heat generated - just my ramblings on a slow Thursday:blushing:

 

I run 45:1 mix on all my saws for the record, even the hot ones!

[Eddy_t]

The point of the statement is, whilst the same amount of mixture is going in, the fuel/air ratio is decreased, so the engine revs higher and burns hotter as there is a more complete ignition. The oil prevents a seize for so long, but an extended period of higher rpm would produce a temperature where the oil would reach a flash point before precipitating on the cylinder walls above the piston prior to combustion. This effect would cause a seize.

 

 

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[aspenarb]

Just bolted the two ms880`s back together that had been run on straight petrol.

I think the old pistons are looking a tad second hand:thumbdown: Managed to rescue the bores with a light honing but really could do with a couple of new barrels to get them 100%.

 

Bob

 

[spudulike]

The point of the statement is, whilst the same amount of mixture is going in, the fuel/air ratio is decreased, so the engine revs higher and burns hotter as there is a more complete ignition. The oil prevents a seize for so long, but an extended period of higher rpm would produce a temperature where the oil would reach a flash point before precipitating on the cylinder walls above the piston prior to combustion. This effect would cause a seize.

 

 

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I understand what you are saying but using that theory, if I setup a saw on 50:1 and set max revs at say 13,000 If I were to use 25:1 mix, do you reckon the saw would scream to higher revs or sound like a strangled cat and smoke like hell???

 

IMO, it will be the latter - see what I am getting to, I guess you could prove it but I personally reckon a 40-45:1 mix with the saw set to the correct revs will give the engine more protection than using a 50:1 mix considering our fuel wil proably go the same way as the US with more ethanol content in time!

 

Just my opinion:001_rolleyes:

[Eddy_t]

I understand what you are saying but using that theory, if I setup a saw on 50:1 and set max revs at say 13,000 If I were to use 25:1 mix, do you reckon the saw would scream to higher revs or sound like a strangled cat and smoke like hell???

 

IMO, it will be the latter - see what I am getting to, I guess you could prove it but I personally reckon a 40-45:1 mix with the saw set to the correct revs will give the engine more protection than using a 50:1 mix considering our fuel wil proably go the same way as the US with more ethanol content in time!

 

Just my opinion:001_rolleyes:

 

 

The only way we would know is by sacrificing a saw by tuning it on 50:1 and then dropping 25:1 in it, and then doing the opposite to another. I'm not willing to sacrifice one of mine to prove either theory

 

 

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[GardenKit]

You will just find that the saw runs poorly when the mix is changed. Its not at all unusual to have to retune when the mix is changed.

 

Before I switched to using Aspen in my servicing I always used a 50:1 with Rock oil. It was not unusual to send a machine back to the customer where it would work fine until my petrol ran out and the customer refilled with his own. He would then bring it back and complain, but a quick retune to his mix was all that was required.

 

It could be that his oil ratio was too strong, his oil too poor a quality or even that he was using a different brand of petrol. (tesco is one of the worst culprits)

 

Its just the same now with Aspen, they run fine when they leave but just occasionally need retuning to the customers mix if he swaps back to petrol

 

But I really can't see the purpose in using a 40 or 45:1 mix unless using rubbish oil. It just drops the power and carbons up the exhaust and plug. Dirty,oily engines are always the result of too much oil in the mix.

 

Most main brand oils marked at 50:1 have been formulated and tested to run at up to 80:1 so 50:1 is already ultra safe, no need for further concentration. No amount of extra oil will protect a saw from the temperatures of lean running.

[spudulike]

Got two Aspen conversions coming up, a MS250 and MS210, both have been run on Aspen but are playing up a bit so will change the carb diaphragms and fuel lines, clean the carb and tank then retune - this should sort it!

 

Barries Aspen stickers are going well:thumbup:

[Eddy_t]

The point of a lower ratio is that when the oil precipitates, it creates more of a seal around the piston and ring(s), which increases the overall compression, as the oil seals the cylinder as the port closes, so less mixture can escape, whilst it may not be much in terms of port timing, it CAN make a huge difference in psi, it doesn't always!

 

 

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