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HelicopterMain Discussion › Head speed increase
01-28-2007 08:10 PM  10 years agoPost 1
mickeyapples

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England

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When i get near the end of my tank of fuel my head speed increases.
I am running in an OS50 SX-H and this started on my 4th tank.

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01-28-2007 08:29 PM  10 years agoPost 2
PaulJC

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Hertfordshire UK

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Starts to run lean, richen it up a touch

Re-entering the atmosphere...

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01-28-2007 09:20 PM  10 years agoPost 3
SkateFreak

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Cambs UK

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Hey,
This is normal, and seems to effect some engines more than others...
The reasons behind this are because the fuel level becomes lower than the carb and the flow to the engine slows a little...
This causes the engine to lean out a tiney bit and the headspeed increases... You might find that the engine will heat up a little more at this point so yeah...
Basically as previously mentioned... Jst richen up a little lol.

If its a drastic change and your having to richen up a fair few clicks then you may want to look into the *uniflow* system
Its been discussed many times on here.

-Jvr

Non-3D heli pilots are planker spys trying to bring down the heli community from the inside - Topher

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01-28-2007 09:24 PM  10 years agoPost 4
heligoole

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yorkshire,uk

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how low is the tank before it speeds up?are you running with an engine governor?
if the tank is too low then you may be taking in air as well as fuel!!a header tank can help here.
If your using a governor is it switched on?

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01-29-2007 08:43 AM  10 years agoPost 5
mickeyapples

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England

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I have no governor and i have a header tank, I am running in the engine and the first 3 tanks where ok but my last 2 tank when nearly empty increased my head speed. I have about 20mm left in tank when this happens.

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01-29-2007 09:14 AM  10 years agoPost 6
TOSH

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UK.Peterborough

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Check for leaks in the clunk tube.

Flybars. Who needs `em.

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01-29-2007 11:19 AM  10 years agoPost 7
mickeyapples

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England

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Just replaced the clunk line, Could it be the rubber gromet on the tank leaking

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01-29-2007 11:46 AM  10 years agoPost 8
Aussy

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Cyprus

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Get a header tank

G3ORG3

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01-29-2007 02:52 PM  10 years agoPost 9
mickeyapples

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England

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i have a header tank

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01-29-2007 03:01 PM  10 years agoPost 10
Raffy

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Chicago, Illinois

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near the end of my tank of fuel

Is that the main tank or the header tank?
Either one, remove both tanks and replace the clunk lines and make them the right size so that it is neither too short nor too long.

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01-29-2007 04:23 PM  10 years agoPost 11
TOSH

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UK.Peterborough

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Could it be the rubber gromet on the tank leaking
l doubt that would cause this problem.

Flybars. Who needs `em.

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01-29-2007 05:08 PM  10 years agoPost 12
mickeyapples

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England

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My header tank is new and i just replaced the clunk line in main tank. it does not touch the back.
It is the main tank when low on fuel about 20mm left when this happens.

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01-29-2007 05:11 PM  10 years agoPost 13
mickeyapples

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England

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I have also replaced all fuel line and a new fuel filter before this happened.
This is a new engine just running in. did 3 tanks ok. last 2 tank head speed increased near end of main tank

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01-29-2007 05:18 PM  10 years agoPost 14
PbThumbs

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Katy, Tx USA

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What’s the temp before this happens? is it on the lean side - right on the edge of being too lean .. Finger to back plate warm or hot?

They all lean a little about where yours is, some more than others. It is usually not so bad it can't be run.

Pump is the best way to solve the problem.

Uni flow has draw backs IMHO ,,I have run it with limited success.

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01-29-2007 05:26 PM  10 years agoPost 15
Colin Mill

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England

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I believe the reason you see this more with some engines than others is that engines with large bore carbs produce a smaller depression (note I'm avoiding the word "suck" ) in the venturi so the change in fuel head has a bigger effect on the fuel flow rate than if the engine were equipped with a smaller bore carb. Because the depression in the venturi is proportional to the square of the flow speed and the flow speed is inversely proportional to the area of the venturi it unfortunately means that the depression falls of as the forth power of the carb diameter. In other words its super sensitive to small increases in carb diameter.

Of course, in most cases, exhaust pressure is also helping the flow but large bore tail-pipes can also make this pressure small.

I'm sure this is the reason for the increase in the number of engines with pumped fuel systems entering the market.

Colin (CSM)

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01-29-2007 07:34 PM  10 years agoPost 16
heligoole

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yorkshire,uk

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fuel filter could be partially blocked if you have one ,sounds as if your leaning out for some reason,shouldnt do this with 20mm of fuel left in main tank,and header full,with No bubbles,does the fuel foam?

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01-29-2007 07:35 PM  10 years agoPost 17
heligoole

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yorkshire,uk

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how long was it between flights did the engine have a chance to cool down?

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01-29-2007 07:39 PM  10 years agoPost 18
Louisiana Helicam

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West Monroe, LA

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I see more and more dance around this issue. Go ahead and do a search on the uniflow system. I do this to all of my helicopters and it works great. I've never had a delivery issue since plumbing my tanks this way. PM me if you have any questions.

www.louisianahelicam.com

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01-29-2007 09:32 PM  10 years agoPost 19
mickeyapples

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England

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I have used a new fuel filter and the engine was cold before each flight, its at the end of the flight this happens after about 10 mins. No bubbles or foaming fuel. and the engine does not burn my finger to the touch as i am runing rich by 1 1/2 turns (thats 3 turns out) as recomended by manual for running in. its strange it started happening on my 4th flight

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01-29-2007 09:40 PM  10 years agoPost 20
mickeyapples

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England

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Great site for info on the uniflow system http://www.fraserker.com

Could this be a problem with my muffler as it is the stock 50 muffler.

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HelicopterMain Discussion › Head speed increase
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