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2T mixture. Too much oil? Help?

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stirlinggaz
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PostPosted: 15:57 - 06 Jul 2017    Post subject: 2T mixture. Too much oil? Help? Reply with quote

Hi,
Having a dumb day & have got a few basic things wrong already today.
Anyway, when running a 2 stroke engine & choke (cold start) is switched OFF (which it SHOULD be after starting) the engine is struggling, almost cutting out & definitely not revving as high as it should & will cut out completely if throttle is opened fully.

However, if I put the choke to ON, the engine is idling fine (maybe a little high) & it will rev to the max, right to Wide Open Throttle.

So, do I have my mixture totally screwed up & have TOO MUCH 2t oil in? (its pre mix)

That's what my heads telling me anyway
Am I right?
Or have I REALLY f*cked up & not put enough 2t oil in, & its running incredibly lean, risking seizure.
Help?
I'm watching the tennis till I'm 100% sure Smile

cheers,
GAZ
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Polarbear
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PostPosted: 16:24 - 06 Jul 2017    Post subject: Reply with quote

My immediate thought on your description is it is running lean and not getting enough fuel through. You put the choke on and it runs better.

Presuming it is at operating temperature I would be thinking more of a carb problem. Blocked jet, accelerator pump (depending on carb) etc.

I might be wrong but in all of my 2 strokes (many years ago I must say) I never noticed/knew that altering the oil mix made the running that bad. They worked or seized if you got it wrong.

If you are totally unsure, dump the fuel, put it in a car (they will run on shite) and put new fuel and the correct oil mixture in your bike.
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TbirdX
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PostPosted: 17:28 - 06 Jul 2017    Post subject: Reply with quote

If the engine is cold it may run a bit ropey.

Every 2t I've had needed choke to start, and sometimes to idle for a bit, then the acceleration isn't smooth in first until it's warm.

I don't rag them until I've got a bit of temp in the engine then everything is tickety boo in all gears.
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jaffa90
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PostPosted: 17:32 - 06 Jul 2017    Post subject: Reply with quote

What bike and what premix?
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stevo as b4
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PostPosted: 17:40 - 06 Jul 2017    Post subject: Reply with quote

If you run the low speed fueling a bit lean on a 2stroke you get the symptoms you mentioned, I.e no response to the throttle when it's cold. But it ticks over fine when warm. If you run the pilot jet too rich you get the no tick over symptom where the motor will slow down and run a few revolutions then stop when it's warm.

The pre-mix ratio thing is more myth than true at any sensible pre-mix ratio. They say 30-50:1 doesn't really need up jetting as you don't alter the viscosity of the fuel much at all. Air flow modifications and changing compression ratios need more rejetting than altering pre-mix ratios by moderate amounts apparently.

My bike was upjetted +2 on the MJ on account of going pre-mix fuel and an aftermarket pipe, but on the dyno it went rich well past the ideal as air fuel ratio at high rpm. Its probably costing 1-2bhp too.
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Teflon-Mike
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PostPosted: 17:43 - 06 Jul 2017    Post subject: Reply with quote

Sounds like my strimmer...
1/ What bike or engine? & Is it designed or set-up to run on pre-mix?
If it's deigned to run on an auto-lube system, delivering 2T oil to the crank-case via a pump, then adding oil to the petrol, will make the carburation 'weak'; as you have a carb set up to mix aprox 5% fuel to air by volume; oil isn't fuel, so adding 2% or more il into the petrol, means that the carb will be trying to mix the same volume of pre-mix to the air going through it... but there isn't as much actual fuel in there as it's expecting.
2/ this may be a major over-complication.... like my strimmer, I can never remember which way the bludy choke is 'on'! Are you sure you are turning it on, not off?
3/ What does the plug look like?
Always the start point on any engine, and matter of course to clean and or replace on a 2T before trying to fault find!
4/ How did you mix the fuel & when?
Lawn mower does rather suffer from condensation in the fuel, each spring. The Cota, in years past from crap in the tank, inadvertently added from petrol from rusty gerry can, or funnel full if filth.. could be you have a clogged jet from contamnated fuel, if old or not so careful in the mixing.

IF your pre-mix was too thick; then I'd expect the motor, if it ran, to be very smokey, and not 'clear' when warm; probably be rather 'wooly' on throttle response, and possibly wisper or foul the plug and peter out and refuse to re-start, rather than beg choke.

So does suggest, choke lever dohw moment; crud in fuel, or not set up to run pre-mix at all.
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stirlinggaz
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PostPosted: 06:23 - 07 Jul 2017    Post subject: Reply with quote

Hi all,
& thanks for the replies Smile
Firstly, my apologies, I should have put NBR in the subject/title cos it ain't a bike, its a "brush cutter" (big strimmer) of unknown origin & dubious build quality.
But being attached to a 50 odd cc 2 stroke engine, I thought there would be enough similarities between it & those older 2t bikes from the past, before auto-lube pumps & when the black art/science of pre-mixing was commonplace & understood.
It was more the theory I was interested in, as to why putting the choke to ON made it behave the way it did, by revving high & letting me open the throttle fully, but only when the choke was ON.
I know I have got my mixture wrong, as I was very careless about the way I approached it, whereas, previously I was really quite ocd about it all.

Anyway, i guess i should dump the remainder of whats left in the fuel tank & start again, going back to being quite exact, in how much oil I should add to the fuel as its obviously much more important than I previously thought.

The recommendations are anything between 25 to 1 & 60 to 1 (that seens to me to be quite a big variance) according to the instruction sheet, what's actually printed on the side of the engine & what's suggested on the interweb (I did search a bit before posting on here)
I guess the combination of a new NGK spark plug, fresh fuel, too much cheap mineral oil & a clueless operator has sent it haywire.
I'll mix up some,....say.....33 to 1, to start with...using 330ml of petrol & 10ml of oil in lots of 3, making a total of 990ml of fuel & 30ml of oil.
I have a mixing bottle, marked with various ratios but think I'll go back to my ocd way of using a 50ml syringe for the measuring out the oil & a litre bottle for the fuel.
Everything was OK, till I trusted the supplied mixing bottle.

I"d really like to understand why it behaved like that though & if it was dangerous to continue to use it at full throttle with the choke ON Thinking

I'm now glad all the 2 stroke bikes I have owned, all had oil pumps because my unblemished record of 0 (yes, zero) blown up bikes would have been shattered many times over.

cheers,
GAZ
ps : sorry for going all Teflonian Embarassed
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redeem ouzzer
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PostPosted: 11:02 - 07 Jul 2017    Post subject: Reply with quote

Have to say I am loving premix. Much simpler and the throttle response is far snappier without a train of gears and a pump to turn.
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stevo as b4
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PostPosted: 11:41 - 07 Jul 2017    Post subject: Reply with quote

Yeah it's nice having a light throttle action, less cables to adjust and synchronise and a tad less weight, pipes to bleed and complication.

Downsides are it affects my riding, lots of pulling in the clutch and throttle blipping is a slight distraction. My bike doesn't seem to like ticking over for more than a minute or so when cold, (maybe it starts to oil up the plug), and I've not yet removed the oil tank and sender wiring, so I've constantly got a bright red warning light lit on the dash.

Mixing is easy though if you fill the tank a gallon at a time only, and use an exact size oil container for this amount of fuel.
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Kickstart
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PostPosted: 18:50 - 07 Jul 2017    Post subject: Reply with quote

Hi

Some of the small garden machinery 2 stroke engines seem to be a bit arsey over the oil they use. Neighbours strimmer didn't appreciate some fully synthetic pre mix 2 stroke oil I had handy (although it smelt better). Ran better on the makers own stuff.

All the best

Katy
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stevo as b4
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PostPosted: 18:05 - 08 Jul 2017    Post subject: Reply with quote

That might be true, as I remember Sthil recommending only their own oil in all their machines. I laugh as garden 2t oil is normally as basic as two stroke oil gets.

If you mixed at slightly the wrong ratio, it should be easy to get the motor running well at open and closed throttle with the High and low adjustable carb jets on these engines.

Just remember that if you adjust the H-screw to give the cleanest fastest no load rpm, you need to richen it maybe 1/2 a turn from that point to make it safe under load.
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Kickstart
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PostPosted: 21:33 - 08 Jul 2017    Post subject: Reply with quote

stevo as b4 wrote:
That might be true, as I remember Sthil recommending only their own oil in all their machines. I laugh as garden 2t oil is normally as basic as two stroke oil gets.


Yes it is a Sthil item. I also laughed at the idea of using the cheap stuff in preference to the decent synthetic I have floating around.

Now, not so sure!

All the best

Katy
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bypass2
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PostPosted: 22:01 - 08 Jul 2017    Post subject: Reply with quote

As your strimmer got a prime on the carb were you press it 3times and it sqaurtes petrol into the carb if so is it working ok. my strimmer prime it 3times full choke one pull on the pull cord startes to fire. then half choke pull on the pull cord let it run for about 5 seconds ish turn the choke off then use it.
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lingeringstin...
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PostPosted: 14:21 - 09 Jul 2017    Post subject: Reply with quote

On my two storke motorcycle engines those symptoms were pretty much always to do with perished seals or some air leak like around the base gasket or something. You can't always see where it's happening and it may have been doing it very slightly for ages.

MZ's are like that. The seals start leaking but nobody realizes it and the effects can usually be ironed out by adjusting the carb for a few months. It gradually gets worse and worse until no amount of carb adjustment will compensate and by then it's a real problem.

Most people with two strokes ignore the seals and immediately blame the carb first, so they change that and it makes no difference, so they blame the coil or some other part of the ignition system next and fiddle with all that, which makes no difference, and eventually they give up out of frustration and give it to me for free. Then I fit new seals and it runs fine.


By the way I've found that mixing about 20% diesel into the petrol of any two stroke works great, even in strimmers and lawnmowers. I haven't used two stroke oil in years. I usually have a jug of premix in the garage where I've added one liter of diesel to a gallon of petrol. Works in pretty much all two stroke things. Keeps the engines cleaner too.
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redeem ouzzer
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PostPosted: 16:09 - 10 Jul 2017    Post subject: Reply with quote

Using diesel instead of 2t in premix?

Really?

On a strimmer maybe but fuck doing it on a bike engine.
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Polarbear
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PostPosted: 16:15 - 10 Jul 2017    Post subject: Reply with quote

Phew, I really wish I had known that diesel could have been used instead of 2T oil years ago. To think Yamaha were so stupid to suggest you should put oil in their 2 strokes. It would have saved me a fortune.

They obviously knew fuck all about 2 strokes

I wonder if they had tried diesel in their GP bikes they would have gone faster Thinking

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stevo as b4
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PostPosted: 18:54 - 10 Jul 2017    Post subject: Reply with quote

I suppose the best test for it would be to get say 3 identical motocross bikes, all with a new piston fitted. Then run them up on a dyno to get a baseline figure on a piston with say 1hour on it.
Bike 1, petrol and synthetic pre mix race competition oil.
Bike 2, petrol and 20% diesel.
Bike 3, petrol and caster oil.

Then ride them back to back on track, same riders. And then race them in a few MX events as well as practice play around riding, until they get close to the 15hr service life of the top end.

If any of them blow up or seize first they lose. Otherwise strip them all down at 15hrs and measure everything from piston wear, ring gaps, bore measurements etc, as well as looking at how coked up they are.

Im willing to bet that the complex synthetic esters show less wear than other types of oil, and also diesel. If any of the alternative lubrication bikes suffer seizures then youd have a good case for how synthetic oil is or isn't designed to reduce friction and have more seizure resistance?
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