I have a 120 4 stroke mounted inverted in a Cyclone 3D
Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
runs fine.
Doesn't cut with any other aerobatic manoeuvres

I've checked the plumbing, clunk & tank.  All seems OK

What could be the problem ?

Thanks

Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted 
that runs fine with the model upright (engine inverted) but then when 
you flip 'er over it cuts out. Hum, could it be that it's set up too 
lean but runs fine an upright model/inverted and the inverted engine is 
compensating for a too lean needle setting. I'd set the needle with the 
model inverted so that it's 300 rpm or so less than full bore and see 
what that does. Then it may be a little rich flying upright and then 
just right at the top of that loop. Prolly can't have it perfect in both 
attitudes without a pump.

fred wrote:
> I have a 120 4 stroke mounted inverted in a Cyclone 3D
> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
> runs fine.
> Doesn't cut with any other aerobatic manoeuvres
> 
> I've checked the plumbing, clunk & tank.  All seems OK
> 
> What could be the problem ?
> 
> Thanks 
> 
> 

-- 
Posted via a free Usenet account from http://www.teranews.com

2fast wrote:
> Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted 
> that runs fine with the model upright (engine inverted) but then when 
> you flip 'er over it cuts out. Hum, could it be that it's set up too 
> lean but runs fine an upright model/inverted and the inverted engine is 
> compensating for a too lean needle setting. I'd set the needle with the 
> model inverted so that it's 300 rpm or so less than full bore and see 
> what that does. Then it may be a little rich flying upright and then 
> just right at the top of that loop. Prolly can't have it perfect in both 
> attitudes without a pump.
> 
> fred wrote:
>> I have a 120 4 stroke mounted inverted in a Cyclone 3D
>> Keeps cutting out at the end (top) of an outside loop (bunt) but 
>> otherwise runs fine.
>> Doesn't cut with any other aerobatic manoeuvres
>>
>> I've checked the plumbing, clunk & tank.  All seems OK
>>
>> What could be the problem ?
>>
>> Thanks
>>
> 
are you sure the clunk is far enough away from the tank end?

It will fly OK inverted, its just the outside loop that causes the trouble.
Might get a perry pump for it, and also the fuel lines could be shortened, 
they are needlessly too long.

"2fast"  wrote in message 
news:479a0209$0$15448$88260bb3@free.teranews.com...
> Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted 
> that runs fine with the model upright (engine inverted) but then when you 
> flip 'er over it cuts out. Hum, could it be that it's set up too lean but 
> runs fine an upright model/inverted and the inverted engine is 
> compensating for a too lean needle setting. I'd set the needle with the 
> model inverted so that it's 300 rpm or so less than full bore and see what 
> that does. Then it may be a little rich flying upright and then just right 
> at the top of that loop. Prolly can't have it perfect in both attitudes 
> without a pump.

Yeah, the clunk does not touch the rear of the tank in any orientation.

"Kevin"  wrote in message 
news:8homj.54096$Hc3.45127@newsfe1-gui.ntli.net...
> are you sure the clunk is far enough away from the tank end?

fred wrote:
> Yeah, the clunk does not touch the rear of the tank in any orientation.
> 
> "Kevin"  wrote in message 
> news:8homj.54096$Hc3.45127@newsfe1-gui.ntli.net...
>> are you sure the clunk is far enough away from the tank end? 
> 
> 
even under -G and suction from the motor ,it has to be fuel lines or 
tank I would think

Bottom end mixture set too lean.The engine will always go slightly lean when 
the nose is pitched down in a bunt (outside loop).If you were to keep the 
throttle half open when executing this manouver I bet it keeps running ok.If 
you richen the main mixture any amount to compensate for this you will lose 
too much power in level flight.Richening the bottom end mixture should cure 
the problem but make sure all fuel lines are ok and pressure test the tank.A 
fuel pump is not neccesary unless the tank is a long way from the engine.
"fred"  wrote in message 
news:qJnmj.4539$HV6.4101@newsfe4-win.ntli.net...
>I have a 120 4 stroke mounted inverted in a Cyclone 3D
> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
> runs fine.
> Doesn't cut with any other aerobatic manoeuvres
>
> I've checked the plumbing, clunk & tank.  All seems OK
>
> What could be the problem ?
>
> Thanks
>

Paul wrote:
> Bottom end mixture set too lean.The engine will always go slightly lean when 
> the nose is pitched down in a bunt (outside loop).If you were to keep the 
> throttle half open when executing this manouver I bet it keeps running ok.If 
> you richen the main mixture any amount to compensate for this you will lose 
> too much power in level flight.Richening the bottom end mixture should cure 
> the problem but make sure all fuel lines are ok and pressure test the tank.A 
> fuel pump is not neccesary unless the tank is a long way from the engine.
> "fred"  wrote in message 
> news:qJnmj.4539$HV6.4101@newsfe4-win.ntli.net...
>> I have a 120 4 stroke mounted inverted in a Cyclone 3D
>> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
>> runs fine.
>> Doesn't cut with any other aerobatic manoeuvres
>>
>> I've checked the plumbing, clunk & tank.  All seems OK
>>
>> What could be the problem ?
>>
>> Thanks
>>
> 
> 
bottom end to lean? I would have thought you are going to be at 
somewhere near full throttle at the end of a bunt

>> Bottom end mixture set too lean.The engine will always go slightly 
>> lean when the nose is pitched down in a bunt (outside loop).If you 
>> were to keep the throttle half open when executing this manouver I bet 
>> it keeps running ok.If you richen the main mixture any amount to 
>> compensate for this you will lose too much power in level 
>> flight.Richening the bottom end mixture should cure the problem but 
>> make sure all fuel lines are ok and pressure test the tank.A fuel pump 
>> is not neccesary unless the tank is a long way from the engine.
> 
> bottom end to lean? I would have thought you are going to be at 
> somewhere near full throttle at the end of a bunt

Doesn't it depend which way you do the bunt ?  If you start low then roll to 
inverted and bunt from there then you will finish at low throttle.  If you start 
high and bunt from upright level flight then of course you do end up at full power.

Maybe the OP can tell us which way he does his bunts ?

-- 
Boo

from the top, flying level, push the nose down.........plane is inverted at 
lowest point
engine doesnt want to get up to full power on the climb out, cuts at the 
top.


"Boo"  wrote in message 
news:fndkhc$aua$1$8300dec7@news.demon.co.uk...
>>> Bottom end mixture set too lean.The engine will always go slightly lean 
>>> when the nose is pitched down in a bunt (outside loop).If you were to 
>>> keep the throttle half open when executing this manouver I bet it keeps 
>>> running ok.If you richen the main mixture any amount to compensate for 
>>> this you will lose too much power in level flight.Richening the bottom 
>>> end mixture should cure the problem but make sure all fuel lines are ok 
>>> and pressure test the tank.A fuel pump is not neccesary unless the tank 
>>> is a long way from the engine.
>>
>> bottom end to lean? I would have thought you are going to be at somewhere 
>> near full throttle at the end of a bunt
>
> Doesn't it depend which way you do the bunt ?  If you start low then roll 
> to inverted and bunt from there then you will finish at low throttle.  If 
> you start high and bunt from upright level flight then of course you do 
> end up at full power.
>
> Maybe the OP can tell us which way he does his bunts ?
>
> -- 
> Boo

>>>> Bottom end mixture set too lean.The engine will always go slightly lean 
>>>> when the nose is pitched down in a bunt (outside loop).If you were to 
>>>> keep the throttle half open when executing this manouver I bet it keeps 
>>>> running ok.If you richen the main mixture any amount to compensate for 
>>>> this you will lose too much power in level flight.Richening the bottom 
>>>> end mixture should cure the problem but make sure all fuel lines are ok 
>>>> and pressure test the tank.A fuel pump is not neccesary unless the tank 
>>>> is a long way from the engine.
>>> bottom end to lean? I would have thought you are going to be at somewhere 
>>> near full throttle at the end of a bunt
>> Doesn't it depend which way you do the bunt ?  If you start low then roll 
>> to inverted and bunt from there then you will finish at low throttle.  If 
>> you start high and bunt from upright level flight then of course you do 
>> end up at full power.
>>
>> Maybe the OP can tell us which way he does his bunts ?
 >
 > from the top, flying level, push the nose down.........plane is inverted at
 > lowest point
 > engine doesnt want to get up to full power on the climb out, cuts at the
 > top.
 >

Maybe the fuel tank's too high in the fuselage or there's a lean spot in middle 
of the throttle range ?

-- 
Boo

fred wrote:
> I have a 120 4 stroke mounted inverted 

Is it a Laser or a Weston engine where the carb is directly behind the top of 
the cylinder head ?  If so then you may need to take special action to ensure 
the tank mean level is centered on the carb.  Usually, engines have the carb 
mounted nearer to the crank axis and if a plane has been designed with this in 
mind then the tank position may be wrong.

As an aside, does anyone know why these two engfines have that peculier layout ? 
Quite apart from the tank position issue there is the problem of ensuring enough 
room for the engine to breathe between it and the firewall.

-- 
Boo

Boo wrote:
>>> Bottom end mixture set too lean.The engine will always go slightly 
>>> lean when the nose is pitched down in a bunt (outside loop).If you 
>>> were to keep the throttle half open when executing this manouver I 
>>> bet it keeps running ok.If you richen the main mixture any amount to 
>>> compensate for this you will lose too much power in level 
>>> flight.Richening the bottom end mixture should cure the problem but 
>>> make sure all fuel lines are ok and pressure test the tank.A fuel 
>>> pump is not neccesary unless the tank is a long way from the engine.
>>
>> bottom end to lean? I would have thought you are going to be at 
>> somewhere near full throttle at the end of a bunt
> 
> Doesn't it depend which way you do the bunt ?  If you start low then 
> roll to inverted and bunt from there then you will finish at low 
> throttle.  If you start high and bunt from upright level flight then of 
> course you do end up at full power.
> 
> Maybe the OP can tell us which way he does his bunts ?
> 
I always thought a loop started from inverted was called an inverted 
loop rather than a bunt

Try richening your idle.



fred wrote:
> I have a 120 4 stroke mounted inverted in a Cyclone 3D
> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
> runs fine.
> Doesn't cut with any other aerobatic manoeuvres
> 
> I've checked the plumbing, clunk & tank.  All seems OK
> 
> What could be the problem ?
> 
> Thanks 
> 
>

"Boo"  wrote in message 
news:fndmlu$enu$1$8300dec7@news.demon.co.uk...
> fred wrote:
>> I have a 120 4 stroke mounted inverted
>
> Is it a Laser or a Weston engine where the carb is directly behind the top 
> of the cylinder head ?  If so then you may need to take special action to 
> ensure the tank mean level is centered on the carb.  Usually, engines have 
> the carb mounted nearer to the crank axis and if a plane has been designed 
> with this in mind then the tank position may be wrong.
>
> As an aside, does anyone know why these two engfines have that peculier 
> layout ? Quite apart from the tank position issue there is the problem of 
> ensuring enough room for the engine to breathe between it and the 
> firewall.
>
> -- 
> Boo

@Boo:  Putting the carb directly behind the jug shortens the intake manifold 
and helps prevent carburetor icing.  Used to run into that with one of the 
first Saito 80's.

@ Fred:  Richen up the low end 1/16 of a turn.

In article ,
Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:

| @Boo: Putting the carb directly behind the jug shortens the intake
| manifold and helps prevent carburetor icing.

Is that really a significant concern in model airplane engines --
carburetor icing?



-- 
Doug McLaren, dougmc@frenzied.us
`It takes only one drink to get me drunk. The trouble is, I can't
 remember if it's the thirteenth or the fourteenth.' -George Burns

Thanks for all your comments.

Dug out the instructions and the factory default position for the low end 
idle is:
Unscrew (ccw, richen) low idle until it stops, then screw back in 6 turns.

Mine seem to be screwed in a LOT more than that, which could account for the 
lean setting.

Got the tank back in, the plane is ready to fly with the cowl off for easy 
needle access.

Six_O'Clock_High wrote:
> "Boo"  wrote in message 
> news:fndmlu$enu$1$8300dec7@news.demon.co.uk...
>> fred wrote:
>>> I have a 120 4 stroke mounted inverted
>> Is it a Laser or a Weston engine where the carb is directly behind the top 
>> of the cylinder head ?  If so then you may need to take special action to 
>> ensure the tank mean level is centered on the carb.  Usually, engines have 
>> the carb mounted nearer to the crank axis and if a plane has been designed 
>> with this in mind then the tank position may be wrong.
>>
>> As an aside, does anyone know why these two engfines have that peculier 
>> layout ? Quite apart from the tank position issue there is the problem of 
>> ensuring enough room for the engine to breathe between it and the 
>> firewall.
>>
>> -- 
>> Boo
> 
> @Boo:  Putting the carb directly behind the jug shortens the intake manifold 
>and helps prevent carburetor icing.

It also keeps the elephants away. That gets a *real* problem on outside 
loops.

>Used to run into that with one of the 
> first Saito 80's.

yup. Elephants LURVE them Saitos.

Fred -- 

    It sounds like the tank might be mounted too high in relation to the 
carb CL. In this scenario, you would have to run the engine on the lean side 
to get normal ops; when you go inverted and put some negative G's on it, the 
engine would really go lean causing your sag.

Cheers -- Lyman

"On so-called global warming or climate change, let us not scare ourselves 
with catastrophic forecasts, or use them to defend and promote irrational 
interventions in human lives."

"fred"  wrote in message 
news:qJnmj.4539$HV6.4101@newsfe4-win.ntli.net...
>I have a 120 4 stroke mounted inverted in a Cyclone 3D
> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
> runs fine.
> Doesn't cut with any other aerobatic manoeuvres I've checked the plumbing, 
> clunk & tank.  All seems OK
> What could be the problem ?
> Thanks

"Doug McLaren" <dougmc+usenet-20080125@frenzied.us> wrote in message 
news:1201322678.19963@frenzied.us...
> In article ,
> Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:
>
> | @Boo: Putting the carb directly behind the jug shortens the intake
> | manifold and helps prevent carburetor icing.
>
> Is that really a significant concern in model airplane engines --
> carburetor icing?
>
>
Only if you do touch and goes in cool humid weather and the engine design 
cools the manifold..that was how I discovered it.  It really used to suck to 
make this beautiful approach and touch only to have the full throttle engine 
die just as you rotated during the go around part.  I learned how to make 
excellent emergency landings under varying poor conditions of speed and 
altitude because of that.  Each and every time I would get to the model the 
manifold would be dripping condensation.  That was a clue.

Later models of the Saito 80 had the updraft tube moved slightly closer to 
the jug which keeps it warmer.  I suspect that engine tuning might be a 
factor, but I never did any serious research into that as a solution as 
other easy to implement tricks presented themselves.

Doug McLaren wrote:
> In article ,
> Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:
> 
> | @Boo: Putting the carb directly behind the jug shortens the intake
> | manifold and helps prevent carburetor icing.
> 
> Is that really a significant concern in model airplane engines --
> carburetor icing?
> 
> 
> 


When I used to run a Saito 91 years ago it would get condensation on the 
intake.  I never saw any ice on the outside, and it never seemed to 
affect the performance.

"Robert Reynolds"  wrote in message 
news:13pmk1g581lq076@corp.supernews.com...
>
> When I used to run a Saito 91 years ago

Strewth, how old are you?
-- 
Dave (Sgt. Pepper)       Epsom, England
     My photo galleries at  http://www.pbase.com/davecq
    "I will not tolerate intolerance ... Doh!!"

Dave (Sgt. Pepper) wrote:
> 
> "Robert Reynolds"  wrote in message 
> news:13pmk1g581lq076@corp.supernews.com...
>>
>> When I used to run a Saito 91 years ago
> 
> Strewth, how old are you?
what a difference a "," makes
When I used to run a Saito 91, years ago

still I cant mock Im one of the worst offenders

"Kevin"  wrote in message 
news:MdJmj.67301$h35.37080@newsfe2-gui.ntli.net...
> Dave (Sgt. Pepper) wrote:
>>
>> "Robert Reynolds"  wrote in message 
>> news:13pmk1g581lq076@corp.supernews.com...
>>>
>>> When I used to run a Saito 91 years ago
>>
>> Strewth, how old are you?
> what a difference a "," makes
> When I used to run a Saito 91, years ago
>
> still I cant mock Im one of the worst offenders

:o)   All just a harmless chuckle.
-- 
Dave (Sgt. Pepper)       Epsom, England
     My photo galleries at  http://www.pbase.com/davecq
    "I will not tolerate intolerance ... Doh!!"

Kevin wrote:
> Dave (Sgt. Pepper) wrote:
>>
>> "Robert Reynolds"  wrote in message 
>> news:13pmk1g581lq076@corp.supernews.com...
>>>
>>> When I used to run a Saito 91 years ago
>>
>> Strewth, how old are you?
> what a difference a "," makes
> When I used to run a Saito 91, years ago
> 
> still I cant mock Im one of the worst offenders


That was pretty funny.  I didn't notice the ambiguity until you guys 
pointed it out.

I used to run the Saito 91 on a Big John Biplane, about ten years ago. 
The only reason I mentioned that it was years ago is because I didn't 
think I would be able to answer a bunch of detailed questions.

Dave (Sgt. Pepper) wrote:
> 
> "Kevin"  wrote in message 
> news:MdJmj.67301$h35.37080@newsfe2-gui.ntli.net...
>> Dave (Sgt. Pepper) wrote:
>>>
>>> "Robert Reynolds"  wrote in message 
>>> news:13pmk1g581lq076@corp.supernews.com...
>>>>
>>>> When I used to run a Saito 91 years ago
>>>
>>> Strewth, how old are you?
>> what a difference a "," makes
>> When I used to run a Saito 91, years ago
>>
>> still I cant mock Im one of the worst offenders
> 
> :o)   All just a harmless chuckle.
"What cahhenl are you on? I am on 40"
"Oh, I am on 40, too"
"Oh that's OK then!"

CRASH!

"You said you were on 42...!"

On Jan 25, 11:46�pm, "Doug McLaren" <dougmc
뫇ꝺ20080...@frenzied.us> wrote:
> In article ,
>
> Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:
>
> | @Boo: Putting the carb directly behind the jug shortens the intake
> | manifold and helps prevent carburetor icing.
>
> Is that really a significant concern in model airplane engines --
> carburetor icing?
>
> --
> Doug McLaren, dou...@frenzied.us
> `It takes only one drink to get me drunk. The trouble is, I can't
> �remember if it's the thirteenth or the fourteenth.' -George BurnsCarb icing does not happen often in model engines but you do need to
be aware of it for it will drive you crazy some day. Two strokes do
not seem to have it at all but four strokes do because the carb is
mounted further from the engine on them.

We had a fellow one day with a Saito 80 and he would take off and
after about 2 minutes into the flight his engine would abruptly quit
and would happen every time. By the condensation on the outside of the
carb we expected carb ice. The day before and the day after, the
engine ran fine. You can't see the ice in the carb because by the time
you get to observe it, it will have melted.

Carb ice is formed when the temperature in the venturi goes below 32F
and moisture is condensed by the temperature dropping to the dew point
of the air. This happens most between 40F and 70F because it is
between these two extremes that the pressure drop in the venturi can
cause the temperature to go below freezing and there is enough
moisture to squeeze out of the air.

In small man carrying planes a Lycoming engine is less prone to carb
ice as the carb is mounted on the botton of the oil pan. Continentals
on the other had have the carb mounted on a spider by two studs to the
bottom of the engine. You had better keep the carb heat on it.

IFLYJ3 wrote:
> On Jan 25, 11:46�pm, "Doug McLaren" <dougmc
> +usenet-20080...@frenzied.us> wrote:
>> In article ,
>>
>> Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:
>>
>> | @Boo: Putting the carb directly behind the jug shortens the intake
>> | manifold and helps prevent carburetor icing.
>>
>> Is that really a significant concern in model airplane engines --
>> carburetor icing?
>>
>> --
>> Doug McLaren, dou...@frenzied.us
>> `It takes only one drink to get me drunk. The trouble is, I can't
>> �remember if it's the thirteenth or the fourteenth.' -George Burns
> 
> Carb icing does not happen often in model engines but you do need to
> be aware of it for it will drive you crazy some day. Two strokes do
> not seem to have it at all but four strokes do because the carb is
> mounted further from the engine on them.
> 
> We had a fellow one day with a Saito 80 and he would take off and
> after about 2 minutes into the flight his engine would abruptly quit
> and would happen every time. By the condensation on the outside of the
> carb we expected carb ice. The day before and the day after, the
> engine ran fine. You can't see the ice in the carb because by the time
> you get to observe it, it will have melted.
> 
> Carb ice is formed when the temperature in the venturi goes below 32F
> and moisture is condensed by the temperature dropping to the dew point
> of the air. This happens most between 40F and 70F because it is
> between these two extremes that the pressure drop in the venturi can
> cause the temperature to go below freezing and there is enough
> moisture to squeeze out of the air.
> 
> In small man carrying planes a Lycoming engine is less prone to carb
> ice as the carb is mounted on the botton of the oil pan. Continentals
> on the other had have the carb mounted on a spider by two studs to the
> bottom of the engine. You had better keep the carb heat on it.
As I have not seen this on a model just curious does ice form inside as 
well as outside?

On Fri, 25 Jan 2008 09:28:32 -0700, 2fast  wrote:

>Hum, I'll take a swipe at that - You've got a 4 stroke mounted inverted 
>that runs fine with the model upright (engine inverted) but then when 
>you flip 'er over it cuts out. Hum, could it be that it's set up too 
>lean but runs fine an upright model/inverted and the inverted engine is 
>compensating for a too lean needle setting. I'd set the needle with the 
>model inverted so that it's 300 rpm or so less than full bore and see 
>what that does. Then it may be a little rich flying upright and then 
>just right at the top of that loop. Prolly can't have it perfect in both 
>attitudes without a pump.

http://www.caliburn.nl/topposting

>fred wrote:
>> I have a 120 4 stroke mounted inverted in a Cyclone 3D
>> Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise 
>> runs fine.
>> Doesn't cut with any other aerobatic manoeuvres
>> 
>> I've checked the plumbing, clunk & tank.  All seems OK
>> 
>> What could be the problem ?
>> 
>> Thanks 
>> 
>> 
>
>-- 
>Posted via a free Usenet account from http://www.teranews.com

Barry
=====
Home page
http://members.iinet.net.au/~barry.og

IFLYJ3 wrote:
> On Jan 25, 11:46�pm, "Doug McLaren" <dougmc
> +usenet-20080...@frenzied.us> wrote:
>> In article ,
>>
>> Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:
>>
>> | @Boo: Putting the carb directly behind the jug shortens the intake
>> | manifold and helps prevent carburetor icing.
>>
>> Is that really a significant concern in model airplane engines --
>> carburetor icing?
>>
>> --
>> Doug McLaren, dou...@frenzied.us
>> `It takes only one drink to get me drunk. The trouble is, I can't
>> �remember if it's the thirteenth or the fourteenth.' -George Burns
> 
> Carb icing does not happen often in model engines but you do need to
> be aware of it for it will drive you crazy some day. Two strokes do
> not seem to have it at all but four strokes do because the carb is
> mounted further from the engine on them.
> 
> We had a fellow one day with a Saito 80 and he would take off and
> after about 2 minutes into the flight his engine would abruptly quit
> and would happen every time. By the condensation on the outside of the
> carb we expected carb ice. The day before and the day after, the
> engine ran fine. You can't see the ice in the carb because by the time
> you get to observe it, it will have melted.
> 
> Carb ice is formed when the temperature in the venturi goes below 32F
> and moisture is condensed by the temperature dropping to the dew point
> of the air. This happens most between 40F and 70F because it is
> between these two extremes that the pressure drop in the venturi can
> cause the temperature to go below freezing and there is enough
> moisture to squeeze out of the air.

The fact that you are also vaporising alcohol does not help either.

A spray bar spraying alcohol is a fairly effective refrigerator.

As anyone who has spilt fuel on their hands on a cool day knows.

Kevin wrote:
> IFLYJ3 wrote:
>> On Jan 25, 11:46�pm, "Doug McLaren" <dougmc
>> +usenet-20080...@frenzied.us> wrote:
>>> In article ,
>>>
>>> Six_O'Clock_High <Six_O'Clock_High@Target_Lock.Guns> wrote:
>>>
>>> | @Boo: Putting the carb directly behind the jug shortens the intake
>>> | manifold and helps prevent carburetor icing.
>>>
>>> Is that really a significant concern in model airplane engines --
>>> carburetor icing?
>>>
>>> -- 
>>> Doug McLaren, dou...@frenzied.us
>>> `It takes only one drink to get me drunk. The trouble is, I can't
>>> �remember if it's the thirteenth or the fourteenth.' -George Burns
>>
>> Carb icing does not happen often in model engines but you do need to
>> be aware of it for it will drive you crazy some day. Two strokes do
>> not seem to have it at all but four strokes do because the carb is
>> mounted further from the engine on them.
>>
>> We had a fellow one day with a Saito 80 and he would take off and
>> after about 2 minutes into the flight his engine would abruptly quit
>> and would happen every time. By the condensation on the outside of the
>> carb we expected carb ice. The day before and the day after, the
>> engine ran fine. You can't see the ice in the carb because by the time
>> you get to observe it, it will have melted.
>>
>> Carb ice is formed when the temperature in the venturi goes below 32F
>> and moisture is condensed by the temperature dropping to the dew point
>> of the air. This happens most between 40F and 70F because it is
>> between these two extremes that the pressure drop in the venturi can
>> cause the temperature to go below freezing and there is enough
>> moisture to squeeze out of the air.
>>
>> In small man carrying planes a Lycoming engine is less prone to carb
>> ice as the carb is mounted on the botton of the oil pan. Continentals
>> on the other had have the carb mounted on a spider by two studs to the
>> bottom of the engine. You had better keep the carb heat on it.
> As I have not seen this on a model just curious does ice form inside as 
> well as outside?

Its only inside where it makes a difference.

By restricting air flow, or fuel flow, or both.

Good news.

Went up the flying field today with my buddies.
A few minutes fiddling with the low end needle (was too lean) and a small 
tweak of the main needle, the engine runs well.
The throttle response is a bit non linear, but it can probably be improved 
by improving the throttle arm/push rod geometry and a throttle curve in the 
Tx.

No icing or elephants were noticed in the carb !

YAY!
mk

"fred"  wrote in message 
news:aJ1nj.5546$L73.4237@newsfe1-win.ntli.net...
> Good news.
>
> Went up the flying field today with my buddies.
> A few minutes fiddling with the low end needle (was too lean) and a small 
> tweak of the main needle, the engine runs well.
> The throttle response is a bit non linear, but it can probably be improved 
> by improving the throttle arm/push rod geometry and a throttle curve in 
> the Tx.
>
> No icing or elephants were noticed in the carb !
>
>
>
>