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Xairflyer 04-12-2012 04:09 AM

Carb tuning
 
When changing from 25:1 to 40:1 mix would I expect to have to richer my needles or lean them ?

My own view would be to screw in the needles as less oil means more fuel which is a richer mix, but just want to check with you guys who have done it before


w8ye 04-12-2012 04:42 AM

RE: Carb tuning
 
correct

clivemc 04-12-2012 05:44 AM

RE: Carb tuning
 


ORIGINAL: Xairflyer

When changing from 25:1 to 40:1 mix would I expect to have to richer my needles or lean them ?

My own view would be to screw in the needles as less oil means more fuel which is a richer mix, but just want to check with you guys who have done it before


wouldnt say its a richer mix, but i guess more will be passing the needles so the engine is running'richer' -less oil does mean a more viscous fuel. closing the needles will be required to reduce the flow rate with the 'thinner' fuel base. but you are right in saying closing the needles. do i even make sense :)

pe reivers 04-12-2012 05:58 AM

RE: Carb tuning
 
Clive, you may want to change that into less viscous.
This holds true, if oil with the same viscosity is used.

acdii 04-12-2012 07:37 AM

RE: Carb tuning
 
So when you add 8 ounces of oil, do you put in 1 gallon of gas minus 8 ounces? <div>
</div><div>Random thought, why I got it reading this post, don't know. </div>

w8ye 04-12-2012 07:48 AM

RE: Carb tuning
 
I use 8 onces of oil with 128 ozs of gasoline poured on top of it.

av8tor1977 04-12-2012 09:21 AM

RE: Carb tuning
 
You use a 16:1 oil ratio W8YE?

AV8TOR

av8tor1977 04-12-2012 09:24 AM

RE: Carb tuning
 
The OP has a tricky question. Normally one would need to lean the mixture a touch when changing ratios as stated, but that depends on the oil used and if/how much it was burning and contributing to the combustion process.

AV8TOR

Xairflyer 04-12-2012 10:38 AM

RE: Carb tuning
 


ORIGINAL: acdii

So when you add 8 ounces of oil, do you put in 1 gallon of gas minus 8 ounces? <div>
</div><div>Random thought, why I got it reading this post, don't know. </div>
This has always been a debate, 25:1 says one 25 parts gas to one part oil but that is not the same as 4% which you would think it is, because if we say for simplicity sake 10oz oil + 250 ozs gas = 260ozs. There is not 4% oil content only 3.84% in order to have 4% at 260ozs you need 10.4ozs oil :D

I would think when quoted as 25:1 it means just that, 25 parts to 1 part. It is when quoted as a % it gets confusing.

Xairflyer 04-12-2012 10:41 AM

RE: Carb tuning
 
Thanks guys for your replies, will see how it goes on my new mix.

pe reivers 04-12-2012 11:39 AM

RE: Carb tuning
 
The oil mix question is tricky, because it defines the amount of oil in the mixed product.
So 20% oil is 1:5 (100/20) ; 1 part oil and 4 parts fuel
4% is 1:25 (100/4) ; 1 part oil in 24 parts fuel (1+24 = 25)
2.5% is 1:40 (100/2.5) ; 1 part oil in 39 parts fuel.

working with % is easy.
The leaner the oil mix gets, the less important the 1 part oil correction becomes. For 2.5% I just mix 2.5% oil in the 5 liter jar. 0.025x5=125cc oil
Who cares if I am off a little on the rich side? I am sure the engine does not notice.

acdii 04-12-2012 04:02 PM

RE: Carb tuning
 
I would rather have too much oil than not enough, the motor will still run, although not as well as a perfect blend, but a heck of a lot better than not enough oil where galling and scuffing could happen.

unclecrash 04-12-2012 04:05 PM

RE: Carb tuning
 
I sure don't know why tou would want to lean the needles out. If you put 4 ounces to 1 gallon to say make 40 to 1 ratio. Then take away 3 ounces of the oil the motor will run leaner and probably burn up. Because you have leaned the fuel mixture out. If you put more oil it makes a richer mix if you take oil away you are making a leaner mix. Maybe Im stupid but Im not going to take oil away and lean my needles you are destined to burn it down. Hey take all the oil away and tell me what happens. It sure don't take a rocket scientist to figure that one out. But all the pro's in here can tell you to lean it out Im not going to!!!

Xairflyer 04-12-2012 04:09 PM

RE: Carb tuning
 
so 25:1 is one part oil 24 parts fuel not 25 ? interesting.

If you have tuned to 40:1 and decide to add a bit extra oil next time so it is say 37:1 you would now be running it too lean !! so not really a good idea to add a bit extra oil.

unclecrash 04-12-2012 04:12 PM

RE: Carb tuning
 

ORIGINAL: Xairflyer

so 25:1 is one part oil 24 parts fuel not 25 ? interesting.

If you have tuned to 40:1 and decide to add a bit extra oil next time so it is say 37:1 you would now be running it too lean !! so not really a good idea to add a bit extra oil.
You have it backwards !!! The more oil the richer you run. Take the oil out and you run lean and burn your motor up Period!!!!!

mike31 04-12-2012 04:34 PM

RE: Carb tuning
 
Don't think of it as 1 gallon. Instead think of it as a ratio. 20:1 should mean 20 ounces of fuel and 1 ounce of oil. Dosen't matter how many gallons you make. Mix by ratio. Correct me if I am wrong. I am used to abuse.

unclecrash 04-12-2012 04:41 PM

RE: Carb tuning
 
Plain and simple 32 parts gas 1 part oil Now take that and go 50 parts gas to 1 part oil. You are deluting the oil by adding more parts fuel, which will run leaner. You can never go wrong by adding a bit of extra oil, most you might do is foul a plug. But others will tell you too rich is not good either which is true rings will start sticking and carbon deposits are not good either.

Xairflyer 04-12-2012 05:08 PM

RE: Carb tuning
 

ORIGINAL: unclecrash


ORIGINAL: Xairflyer

so 25:1 is one part oil 24 parts fuel not 25 ? interesting.

If you have tuned to 40:1 and decide to add a bit extra oil next time so it is say 37:1 you would now be running it too lean !! so not really a good idea to add a bit extra oil.
You have it backwards !!! The more oil the richer you run. Take the oil out and you run lean and burn your motor up Period!!!!!
What we are talking about here is the air/fuel ratio not the oil/fuel (gas) ratio

In a 2 stroke if you remove the oil the damage is caused mainly by the lack of lubrication, the oil is not really needed or wanted in the combustion cycle.

You mix air and fuel to make combustion, the higher the ratio of fuel to air the richer the mixture, so if you add more oil you are reducing the amount of fuel (gas) so less fuel means higher air content which means a leaner burn.

w8ye 04-12-2012 05:18 PM

RE: Carb tuning
 
I run 8oz oil in 2 gal gas in all my true gas engines with the needle bearing rod and ball bearing cranks

unclecrash 04-12-2012 05:25 PM

RE: Carb tuning
 


ORIGINAL: w8ye

I run 8oz oil in 2 gal gas in all my true gas engines with the needle bearing rod and ball bearing cranks

I think you made a typo I believe 128 fl oz is a gallon.

unclecrash 04-12-2012 05:27 PM

RE: Carb tuning
 


ORIGINAL: Xairflyer


ORIGINAL: unclecrash


ORIGINAL: Xairflyer

so 25:1 is one part oil 24 parts fuel not 25 ? interesting.

If you have tuned to 40:1 and decide to add a bit extra oil next time so it is say 37:1 you would now be running it too lean !! so not really a good idea to add a bit extra oil.
You have it backwards !!! The more oil the richer you run. Take the oil out and you run lean and burn your motor up Period!!!!!
What we are talking about here is the air/fuel ratio not the oil/fuel (gas) ratio

In a 2 stroke if you remove the oil the damage is caused mainly by the lack of lubrication, the oil is not really needed or wanted in the combustion cycle.

You mix air and fuel to make combustion, the higher the ratio of fuel to air the richer the mixture, so if you add more oil you are reducing the amount of fuel (gas) so less fuel means higher air content which means a leaner burn.
So what happens when you run less oil you get more heat which will make it run leaner. Also you loose power with less oil.

unclecrash 04-12-2012 05:42 PM

RE: Carb tuning
 


ORIGINAL: unclecrash



ORIGINAL: Xairflyer


ORIGINAL: unclecrash


ORIGINAL: Xairflyer

so 25:1 is one part oil 24 parts fuel not 25 ? interesting.

If you have tuned to 40:1 and decide to add a bit extra oil next time so it is say 37:1 you would now be running it too lean !! so not really a good idea to add a bit extra oil.
You have it backwards !!! The more oil the richer you run. Take the oil out and you run lean and burn your motor up Period!!!!!
What we are talking about here is the air/fuel ratio not the oil/fuel (gas) ratio

In a 2 stroke if you remove the oil the damage is caused mainly by the lack of lubrication, the oil is not really needed or wanted in the combustion cycle.

You mix air and fuel to make combustion, the higher the ratio of fuel to air the richer the mixture, so if you add more oil you are reducing the amount of fuel (gas) so less fuel means higher air content which means a leaner burn.
So what happens when you run less oil you get more heat which will make it run leaner. Also you loose power with less oil.
My bad I read you post wrong the more oil added will make you run a bit leaner,but I doubt it will be noticable. But don't be stingy on the oil or you will be the one buying lots of parts.

willig10 04-12-2012 10:00 PM

RE: Carb tuning
 
To the Original Poster. It really does not matter. Just start the engine with the new mix and adjust needles accordingly to what the engine needs to run at idle smoothly and then transition to top end with no hesitation. I would on the first flight leave the high speed needle (after adjusting on the ground) a tad on the rich side. Fly a few laps and see how she does. Adjust for best RPM after.

I think you will be fine just be diligent when tuning on the ground first.

However all that said there is nothing wrong with running 32:1

Just my 2 cents.

Regards
Glenn Williams

pe reivers 04-13-2012 02:02 AM

RE: Carb tuning
 


ORIGINAL: Xairflyer

so 25:1 is one part oil 24 parts fuel not 25 ? interesting.

If you have tuned to 40:1 and decide to add a bit extra oil next time so it is say 37:1 you would now be running it too lean !! so not really a good idea to add a bit extra oil.
You guys are too much!
How about tuning those needles like they should?


Xairflyer 04-13-2012 02:30 AM

RE: Carb tuning
 
Pe I dont think many guys even touch the needles again once they have them running ok, but yes you are quite correct everytime you mix new fuel you should be re tuning anyway.


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