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richard.goode(at)russiana
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 Posted: Mon Oct 11, 2010 8:26 am Post subject: AK-14P carburettor |
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AK-14P carburettor
I have to repeat that I am NOT an expert in these carburettors –but I have been involved with them for almost twenty-five years. Some points:
<![if !supportLists]>Ø <![endif]>Although not an expert I have seen experts tuning the carburettors and the differences can be dramatic. This is why it is disappointing that so many people continue to fly with the carburettors as they bought the aircraft, making no effort to improve them. There is such a world of difference between a really well set-up M14P and a poor one!
<![if !supportLists]>Ø <![endif]>Reading the different inputs on this topic, it does seem to me that many owners either do not have the detailed engine manual OR have not bothered to read it.
<![if !supportLists]>Ø <![endif]>There is an extremely detailed technical description of the carburettor; how it works; and how to tune it.
<![if !supportLists]>Ø <![endif]>BUT this is not for the inexperienced. The adjustments are VERY interdependent; the amount of individual adjustment can be incredibly small.
<![if !supportLists]>Ø <![endif]>The compensating jet (as I said before) what the Russians call the “suction jet” is NOT the main fuel jet.
<![if !supportLists]>Ø <![endif]>However the compensating jet affects fuel consumption (and very importantly CHT) at all power settings – i.e. from low-cruise to full throttle.
<![if !supportLists]>Ø <![endif]>As people have pointed out, CHTs can vary hugely depending on which cylinder. This is particularly important in aircraft doing high powered and zero air speed manoeuvres, like torque-rolls. In this case the cylinder that is to the left of the engine sump (as you look at the engine from the front) has most of the air-flow from the prop blanked, so will run very hot.
<![if !supportLists]>Ø <![endif]>In any case a JPI instrument showing ALL CHT’s is clearly a good idea.
<![if !supportLists]>Ø <![endif]>One of the best exponents of this carburettor was the late and much-missed Alex McLean in Spain.
Richard Goode Aerobatics
Rhodds Farm
Lyonshall
Herefordshire
HR5 3LW
United Kingdom
Tel: +44 (0) 1544 340120
Fax: +44 (0) 1544 340129
www.russianaeros.com
[quote][b]
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mark.bitterlich(at)navy.m
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| Posted: Mon Oct 11, 2010 10:13 am Post subject: AK-14P carburettor |
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Richard, you said:
Ø The compensating jet (as I said before) what the Russians call the “suction jet” is NOT the main fuel jet. However the compensating jet affects fuel consumption (and very importantly CHT) at all power settings – i.e. from low-cruise to full throttle
Please understand that I am not trying to debate the fine points of what a certain part is called. The Russians call this a suction jet. Others call it a “compensation jet” which (I think) actually comes from what it is doing inside the carb in order to cause the actual change in fuel delivery.
I called it a “Main Jet” simply because in most NORMAL carbs (meaning the kind that are bowl and float types) the MAIN JET impacts the delivery of fuel across the whole RPM range of the engine once it gets above idle, which is exactly what the “suction jet” causes to happen. While it is indeed NOT THE MAIN JET as you say, to those that work on engines other than this one, you can think of this adjustment impacting the engines performance exactly as the MAIN JET normally would in a normal carb. The suction jet is not, however, actually flowing the fuel which is why … yes… you are correct … it is not the MAIN JET and I stand corrected… technically.
More and to the point, I would really appreciate it if someone ran through a step by step explanation of how this thing works. It is one thing to read a Task Card translated from Russian and then try to apply it, when the cost of making a mistake is possibly a ruined engine, or at least one that requires a re-build. Which is why no one really wants to mess with these things without knowledge and experience. This is a perfect Catch-22 since in order to gain knowledge and experience you have to actually DO IT.
Yep, I have read everything I can get on this unit and understand that a lot of the flow and reactions are controlled by diaphragms and air bleeds. Some of these bleeds are the ones we are looking at now. The manual for this puppy dog does indeed talk about how to adjust it, but it sure as blazes does not go into a good explanation of how it actually works. I like to understand theory before attempting practical application. Comes from doing the job I do professionally.
Below is Task Card 205. It tells you exactly how to adjust the suction jet.
Task Card 205
1. Check operation at all ratings on the initial adjustment starting form the take off rating Ref 072.00.00 Task Card 202
Note: If engine operates poorly at separate ratings, adjust the carburetor.
2. Adjust fuel consumption at take off and nominal ratings using the following procedure:
(1) Unlock and undo suction jet plug (2) Ref. Fig 202)
(2) Select and replace the suction jet.
Note: It is allowed to install jet diameter 1.3 to 2.0 mm. Increasing the jet diameter leans out the mixture, decreasing it, enriches the mixture. The jet diameter change of 0.05 mm changes specific fuel consumption at take off rating for 2 to 5 g/hp-h.
(3) Install and lock suction jet plug (2).
3. Adjust the engine in cruise rating II using the following procedure: (1) Unlock metering needle adjustment screw (4) Ref: Fig. 201)
(2) Turn adjustment screw (4) to the required, aide to obtain the desired fuel consumption
Notes:
1. Adjust the carburetor on the shutdown engine. Rotating the shaft clockwise enriches the mixture and vice-versa.
2. Turn the metering needle screw up to the limit stops in either direction from the initial setting.
3. The adjustment range to stop is eight clicks. One click of the metering needle adjustment shaft changes fuel consumption from 4 to 8 /hp-h
4. Start the engine and check engine operation at cruise rating I and nominal rating II (Ref 072.00.00 Task Card 202) since the change in metering needle position affects fuel consumption. 5. Perform additional adjustments with the metering needle screw in case of deviations at cruise I rating and nominal rating II.
Caution: Never turn the metering needle adjustment screw beyond the stops. Otherwise previously adjusted fuel consumption for take off, nominal ratings I and II would be abruptly changed and carburetor initial setting could not be adjusted.
End Task Card 205 Quote Unquote Good luck.
From: Richard Goode
Sent: Mon 10/11/2010 12:23 PM
To: yak-list(at)matronics.com
Subject: AK-14P carburettor
AK-14P carburettor
I have to repeat that I am NOT an expert in these carburettors –but I have been involved with them for almost twenty-five years. Some points:
Ø Although not an expert I have seen experts tuning the carburettors and the differences can be dramatic. This is why it is disappointing that so many people continue to fly with the carburettors as they bought the aircraft, making no effort to improve them. There is such a world of difference between a really well set-up M14P and a poor one!
Ø Reading the different inputs on this topic, it does seem to me that many owners either do not have the detailed engine manual OR have not bothered to read it.
Ø There is an extremely detailed technical description of the carburettor; how it works; and how to tune it.
Ø BUT this is not for the inexperienced. The adjustments are VERY interdependent; the amount of individual adjustment can be incredibly small.
Ø The compensating jet (as I said before) what the Russians call the “suction jet” is NOT the main fuel jet.
Ø However the compensating jet affects fuel consumption (and very importantly CHT) at all power settings – i.e. from low-cruise to full throttle.
Ø As people have pointed out, CHTs can vary hugely depending on which cylinder. This is particularly important in aircraft doing high powered and zero air speed manoeuvres, like torque-rolls. In this case the cylinder that is to the left of the engine sump (as you look at the engine from the front) has most of the air-flow from the prop blanked, so will run very hot.
Ø In any case a JPI instrument showing ALL CHT’s is clearly a good idea.
Ø One of the best exponents of this carburettor was the late and much-missed Alex McLean in Spain.
Richard Goode Aerobatics
Rhodds Farm
Lyonshall
Herefordshire
HR5 3LW
United Kingdom
Tel: +44 (0) 1544 340120
Fax: +44 (0) 1544 340129
www.russianaeros.com
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