Thread: Brushcutter Fuel

Originally Posted by smidsy

Hey guys,
As per my other thread I upgraded from a D handle to a Bull Handle brushcutter - both Tradetools machines, but the D handle machine is five years old.
The D handle advised 33:1 fuel, I ran it on 25:1 and when I mentioned this to the guy at the shop when buying the bull handle machine he said they actually verbally recommend 25:1.
The bull handle machine states 50:1, I'm wondering if I should richen this up a bit given that it is a chinesium machine, and the metalurgy isn't as good as say a Stihl - I'm thinking 40 or even 35:1?
Also, is there a better oil than the Castrol Garden 2T (I notice Penrite's the same price at Autobarn) and does the oil have a shelf life - I only mix a litre at a time and have a small yard, so my bottle of Castrol is five years old.

What kills small engines is prolonged excess heat rather than not enough lube/oil. Provided they are tuned for it, modern two stroke engines can even run on 100:1 using quality synthetic two stroke lube but the reason this is not recommended is mixing 100:1 required significant oil/petrol mixing accuracy which most folks do not have access to.

Excess heat comes from higher than usual fuel burning temperatures which is dependent directly on the petrol/air ratio. As well as fuel for combustion the amount of (unburnt) petrol that gets flushed thru the motor and out of the exhaust has an important and significant cooling effects. Two strokes are deliberately designed this way. A lean ratio has too much air and not enough petrol so all petrol gets burned and there is none left for cooling. Richening up a combustion engines is done by supplying more petrol relative to air and in the case of two strokes helps cool the motor.

Its counter intuitive but increasing the petrolil ratio on a two stroke reduces the Petrol/air ratio (ie there is now less petrol and more oil) so this LEANS out the fuel rather than enriches it. Provided they are properly tuned most 2 strokes will run OK on anything between 50 and 25:1. BUT if a saw running on 50:1 is already tuned on the lean side and the fuel ratio is reduce to 25:1 the engine will run extra lean and there's a risk of overheating and serious damage.50:1 does a

To richen up a motor the H-jet is adjusted to reduce the max revs by a few hundred rpms which helps protects the engine.
So whatever oil/petrol ratio is use the engined should be retuned for that ratio

Provided there's some oil, adding more oil does very little to protect a two stroke engine. All that happens is the extra oil remains unburned, provides very little cooling and exits the exhaust as extra smoke. This smoke does not contain just oil but all the extra additives like smoke suppressants etc that fog contaminates the local environment including the air around the operator and its not good for the operator. I have used chainsaws with 25:1 a number of times and if there's no breeze I get a headache within half an hour of using them.

I recommend using the petrol/oil ratio the manufacturer provides in the manual. My chainsaws are all run and tuned at 40:1 because thats what the manual says for 2 of them. The manuals for the others say 50:1 but I cant be fagged keeping two different ratio fuels. I use fully synthetic oil as its usually more protective, but they aint cheap.

EXACTLY what he said.

The smoke I don't care about so if it says 25:1 that's what I run. I keep 50:1 for my stihl stuff and 25:1 for some other stuff. At 35:1 probably anything from 25 - 50 will work. I'd just mix up a separate 5l at 35:1 and keep it for that machine.

Expensive oil is probably better but it's a lot dearer, however unlike car oil or premium petrol you ain't using a lot of it so buy what fits your budget and floats your boat. Whatever you do within reason is unlikely to have catastrophic consequences.

The oil ratio has nothing to do with metallurgy. Ok chinese bearings aren't as nice as skf, but you might be surprised the places you find them. If you really care pop it apart knock out the bearings take them to skf and buy replacements but that seems like a lot of fuss...

Speaking of which I need to get out and mow while the sun is shining....

Having run two stroke trials bikes, gardening equipment, construction equipment, chainsaws, outboards for decades, I'm over it - mixing two stroke fuels that is.

With 4 stroke machines there are no issues (well far less imo) with smoke, correct fuel / oil ratios, fouled plugs, rich / lean mixes/running, stale fuel, and they are generally far less cantankerous with starting, maintenance. If there is excess fuel that is unlikely to be used for a while it goes into one of the ULP vehicles.

All our gear is four stroke powered now, or electric (corded / battery), except for one lonely Stihl chainsaw! The Stihl is only kept for small wood recovery projects and cyclone cleanup. We have Honda powered lawn mowers that are 35 yo still running like a charm, with a little servicing & not as often as they should btw. Pity the chassis & wheels aren't as robust as the motors.

There really is not much to justify the use of 2 stroke motors in equipment other than large chainsaws imho.

Originally Posted by Mobyturns

There really is not much to justify the use of 2 stroke motors in equipment other than large chainsaws imho.

In general I agree. The tree lopper I mill timber for has moved everything to battery power except a couple of big brush cutters and their bigger chainsaws.

At home have a battery powered Stihl mower and a hedge trimmer. But my 10+ year old whipper snipper (which I bought before the mower and hedge trimmer) is 2 stroke. Fuel is not that big of a deal as I regularly use big chainsaws I've always got two stroke fuel around - when the whipper snipper dies or I get rid of my saws I will get battery powered ones. Hopefully by then they might be a bit bigger than the currently available stuff.

Good quality two stroke motors that are well maintained can last a long time. My mate has a Stihl 08S chainsaw that he bought as a used saw in 1974. I given it a once over a couple of times (mainly sharpening) and it's still going as strong as new and he regularly gives it a hammering. Most of the issues I see with cheap two stroke chainsaws are the peripherals, hoses, carbies, etc rather than the larger mechanicals.

The OP just bought a machine and asked a question pertaining to that. He posted his decision making process in another thread and it seemed reasonable enough to me.


Yes 4 strokes are nice, but I'm not about to throw out 2 stroke machines which serve me well enough for my home use.


The boss's dad paid for a stihl electric mower for her. It's the self propelled commercial machine. It's nice not to have to get it going and it works well enough (yes I get to DO the mowing), but the finish was like $2 shop rubbish and details in the design are dreadful. It will be interesting to see how it lasts.

Electric mower still have their pluses and minuses.

Our first Stihl battery powered mower lasted for 5 years when I hit a large dog bone hidden deep in the lawn and it stuffed the motor. The motor was a sealed unit so could not get into it without breaking the plastic motor housing apart. The local stihl dealer that I bought the mower from also said they could not perform any repairs. There was a hint of "Oh we know that problem" when he said the "new mowers were much more robust" and he offered me $100 off the price of new mower. Fortunately the new one used the same battery as the old one so I took him up on the offer, The new one is now about 5 years old and still going strong despite hitting a number of dog bones. Its wider and definitely more powerful, meaning it chews the battery quicker but our lawn is tiny so provided the grass is not too long I get thru the mowing with one charge. I suspect I will be up for a new battery in a year or so.

After mower use the battery is removed and placed on charge in the shed. The mower is able to be stored in an enclosed lockable area under the house/ kitchen. This is safer/better than the serious petrol powered motor we had which generated petrol odours and sometimes these would drift up through small gaps in the kitchen floor boards. Even from a number of chainsaws, fuel containers and the whipper snipper stored in the shed, petrol odours are not a problem as the shed air is exhausted on a regular basis.

Originally Posted by BobL

Electric mower still have their pluses and minuses.

I bought an electric Victa in 1978 and it is still mowing our lawn, starts first time every time and I have never run over the cord and all I have replaced is the blades.

Originally Posted by damian

Yes 4 strokes are nice, but I'm not about to throw out 2 stroke machines which serve me well enough for my home use.

Nor would I. However, I would not purchase a new 2 stroke anything now, other than a large chainsaw. Even their superiority in that market niche is being challenged with battery models in some applications, not all though!

I believe the days of being able to use 2 stroke motors in any power equipment are numbered & rapidly closing. Have a look at the pressure being applied to phase out 4 stroke motor vehicles across the globe. Why would 2 stroke powered appliances / tools / equipment be exempt?

as a btw I support the advice of BobL et al about sticking to recommended fuel / oil mix ratios and with using high quality two stroke oil.

In my trials (not trail) bike days in the late 1970's to early 1990's 2 strokes were king. The Honda's 4-strokes were good but not as good and suffered a major fault - they could not supply power like a 2-stroke could and particularly so after a downhill decompression then a rapid burst to go uphill. They simply spluttered and choked.

Now 4 strokes are king, by a country mile, you can't even find a 2-stroke trials bike & electric are making huge inroads.

As per BobL's advice - Well calibrated fuel / oil ratios and correct jetting also made a huge difference to the 2-stroke motors performance. Almost all top trials riders disabled the auto oil systems on the Yamaha's etc - because the system limited performance or more so the predictability of the performance. Oil could be oversupplied!

Originally Posted by Chris Parks

I bought an electric Victa in 1978 and it is still mowing our lawn, starts first time every time and I have never run over the cord and all I have replaced is the blades.

For my Italian mum's 75'th birthday we we bought her a corded Ozito mower and long cord so she could mow her 2 x 10m strip of lawn at the Back of her unit. She really liked doing it herself and did so successfully for quite a few years but then started running over the cord. Repairing the cord gave my brother in law engineer something to do when he and my sister visited because he did not speak Italian. Eventually we started doing it for her up unit she moved in with my sister some 15 years later. The mower was still running but nobody wanted it so it went out for verge side pickup.

The boss bought the electric ozito, the larger corded unit. She isn't very strong but she can mow with it. I've used it a few times and it's great apart from the cord problem. I don't run over it but I spend almost as much time and effort moving it about.


The battery stihl obviously removes that problem and together with the self propelled makes it good to use. Really picks up the grass. I found a youtube video of a bloke who had problems with an electric makita that didn't collect grass well. And please I seriously don't care about the mulching vs catching argument. Everyone does things differently. If a manufacturer supplies a catch option then it should work. If it doesn't it's a fail.

Still love my old B&S rover. It's old and getting hard to start but still mowes my lawn a treat.

They banned 2 smoke outboards years ago. I've several old omc outboards. Legal to use on most waterways but you can't buy them anymore. I note some chinese 2 stroke outboards offered on ebay etc. Not sure they are legal. Outboards, trials bikes etc all have specific issues to address. For one you normally don't carry them on your shoulder...

The battery power Stihl mower we have has a really good catcher and can be used effectively on its zero height setting to pick up leaves etc on the bricks. On one small area of the brick patio that I'm to lazy to weed or use roundup on I just mow the grass in the gaps between the bricks at zero height.

Originally Posted by damian

....

I found a youtube video of a bloke who had problems with an electric makita that didn't collect grass well. And please I seriously don't care about the mulching vs catching argument. Everyone does things differently. If a manufacturer supplies a catch option then it should work. If it doesn't it's a fail.

Still love my old B&S rover. It's old and getting hard to start but still mowes my lawn a treat.

....

Since this discussion has well and truly moved on from simply what fuel mix to use, I'll chime in about the limitations of the Makita battery mower as well. I've contributed elsewhere to another thread about the limited run time I get using 6Ah batteries. Mine turned out to be only just sufficient to do the job I ask of it. Who knew a battery mower would have range anxiety? I miss my old B&S Rover's ability, but I don't miss the fuel mixing and storage.

As to the catcher, I agree it's pretty poor by comparison to a real mower and the mulching plug is pretty much a joke. I've been pondering lately about making my own mulching plug to properly close off the catcher chute to see if that improves effectiveness.

For a brief time I used an Aldi electric plug in mower. The problem with that was the current draw actually melted the 20m extension cord I was plugged in to after only a couple of uses.

BTW. I used to use the old Rover in the old house to mulch my garden prunings as well, small tree limbs and all. Rake them into a pile and go at it with the catcher on until I had just a pile of real mulch left over. The battery mower would pee out it's first battery just looking at a pile like that.

Hey Guys,
Thanks for all the advice.
With the size of my yard I could easily get by with electric gear - but the choice would be mess around with cheap gear or pay about $1000 for a makita mower and line trimmer, and that's way beyond my means as a pensioner.

The reason 2 stroke gear still exists is cost, a 2 stroke engine is much cheaper to produce than a 4 stroke. The trade off is having to mix fuel - but I flew R/C aircraft for many years and for both cost AND convenience I mixed my own three part fuel (menthanol, oil & nitro) so I don't mind mixing fuel, plus mixing it myself I know exactly what's going in the engine.
The other reason I prefer 2 stroke over 4 is that I can strip & re-assemble a 2 stroke engine blind folded, but I've never been able to grasp timing & angles and stuff, so a 4 stroke engine would have to go in for repairs and that's more cost.