_Β_ΟΠηγη: http://giantscalenews.com/threads/basic-engine-tuning.2806/
_Β_Ο
Basic tuning:
1 - Tune the engine when it is warm, and double check the tune after a flight.
2 - On the DLE there is a little silver screw on the carb that is an "idle set screw". it has a spring on it and it sets how low the low throttle arm will physically go down. Take that screw OUT and deposit it in the trash can. Do not remove the black H and L screws obviously.
3 - Start the engine and run it for a good few minutes with varied throttle and some full throttle run ups to get it nice and warm.
4 - If you have not done so, adjust the servo travel for a consistent idle, does not need to be perfect as long as it is low. 1600 is too high to properly tune that low, it should be much closer to 1200.
5 - Tune low needle first. Now run the engine up to clean it out with a couple full throttle run ups and then go to to low idle. Listen to the engine.........how long does it take to start to "load up" or start to slow down in RPM? If it is rough right away you are likely way to rich. Normal starting point on 100cc engines is 1.5L and 1.5H. I have had to go as low as 1 3/8 on the low needle on the DLE carbs. Adjustments on gas carbs are VERY small, like the width of a screwdriver blade or 1/16th of a turn or less.
A good "safe" tuning on the low needle you should be able to clean it out with some run ups, return to idle and it should have a nice steady low idle for at least 15-20 seconds before it starts to load up. If it does this it is still just a "touch" rich but will not die on you and it will run nice and smooth.
6 - How low should react. Now that you have it running, clean out the engine and let it go to idle. Let it sit for 10 seconds or so and then slam the throttle to full, not slow, nail it!! Listen to what it does. If it dies or almost dies, you are too lean. If it stumbles and works it's way up (may see smoke in exhaust) you are rich. As tuned in number 5 above it should run up quickly with very little or no noticeable stumble.
7 - Now tune the H needle. There are several ways to do this with RPM but the most simple way for a safe needle setting is this. With the engine warm and the low needle tuned run the engine up to full throttle for about 5 seconds. Now chop it in one quick motion to low. Listen to what it does then.
- If it returns to a steady idle, you are very close.
- If the idle goes way low and works it's way up to a steady idle you are too rich.
- If it stays at a high idle and then slows down you are too lean.
- If it dies you are either way too rich or way too lean. With the H at 1.5 you should not be too lean.
8 - When H is set return and double check the L and then double check the H. Then it's time for a flight. Listen to the engine carefully for all of the noted symptoms while you are flying. One engine test I do in-flight is for the H needle. Get the engine nice and hot, maybe a high speed pass or something. Now do a full throttle straight up line. Listen! Engine should be smooth and steady until you can't go higher. If it starts to sag at all, land immediately and richen the H needle just a tad and try it again.
This fade can also be caused from overheating not tuning related so make sure your engine is properly baffled if you now the tuning is correct.
Οδηγος Bασικης Ρυθμισης Βενζινοκινητηρα.
Απάντηση: Οδηγος Bασικης Ρυθμισης Βενζινοκινητηρα.
Like!!!!!!!!!!!!!!!!!
Απάντηση: Οδηγος Bασικης Ρυθμισης Βενζινοκινητηρα.
Παραθεσεων συνεχεια ενας οδηγος διαγνωσης με γνωμωνα την κατασταση του μπουζι._Β_Ο
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Απάντηση: Οδηγος Bασικης Ρυθμισης Βενζινοκινητηρα.
Ενα αναλυτικοτατο αρθρο..., αξιζει τον κοπο να φρεσκαρουμε λιγο 'τα πραματα'... _Β_Ο
Petrol (Gas) Engine Tuning, I used this for years.
Carbs aren't too difficult to tune up if you know what you're doing. First of all, you need to know how the carb works and how the settings interact with each other. About 95% of all the gas airplanes I've seen at the field are somewhat out of tune. How can I tell this? Simple, at some point the engines "four cycle" in flight. Two Cycle engines are not supposed to "four cycle" PERIOD. This is caused by a rich mixture that is forcing the sparkplug to intermittently miss making it sound like a four stroke. This is not good. HOWEVER the good news is; gasoline two stroke engines are very tolerant of rich settings (most of the time) and will run fine. You'll just consume a little more gasoline than necessary, and create a little more oil mess on your plane. You may eventually foul your spark plug as well. So why do so many people leave their engines tuned like this? Simple answer, the engine will start much easier when it's cold AND there's little or no warm up time needed prior to flying. Those are pretty good reasons! But the fact is... the engine is not running like it's supposed to.
(1) The low end needle on a Walbro carb is ALWAYS the one closest to the engine, the high end needle is the closest one to the intake/choke.
(2) There is no fuel adjustment for idle fuel, only air feed set by the idle stop or servo.
(3) Both low end AND high end needles feed the top end fuel supply.
Let's tune up a Walbro!
Set the low end & high end needles to about 1 to 1 1/2 turns each. Choke the carb or prime it, until the carb is wet. Fire up the engine and let it warm up. Let's set the top end first since it's the easier of the two. Go to full throttle. Adjust the top end needle for peak RPM. Leave it wide open for about a minute to see if it changes any. Should the engine go lean, open the low end needle slightly, if this doesn't work... you will have to adjust the needle valve inside the carb.( I will explain this later) If the top end runs OK, then slowly pull the throttle down until the engine begins to "four cycle" hold the throttle there. Adjust the low end needle until the "four cycling" stops. Now lower the throttle more until it "four cycles" again, and adjust the low end again. Keep doing this until you reach full idle. Now, from full idle begin to throttle up until the engine starts to bog or hesitate. Open up the top end needle just enough to eliminate the bog or hesitation.
When this is done right, you will be able to set the throttle in any position and it won't four cycle, plus you will be able to transition from idle to full power without any hesitation at all. -Xipp, Flyingcirkus.com Member
Understanding a Walbro Carb
Ok this is for people who need a little insight into how a carburetor works in this case I will be using a Walbro for example.
Starting from the gas tank, the fuel is pumped from the fuel tank and enters the carb through the inlet. The fuel works its way through the fuel pump through a little diaphragm pump that's controlled by 2 one way valves (little flaps). The fuel then passes through a needle & seat that is controlled by the "float" diaphragm. This "float" diaphragm manages how much fuel is available for the idle, low-speed, and high-speed throttle positions. The "float" diaphragm opens & closes the needle through a small lever attached to the needle. The fuel is then "standing by" waiting in the float area for a vacuum signal at the various jets. The lever setting is very critical since it controls the available fuel to the jets. If the lever is too low, the engine will run lean, if the lever is too high, the engine will run very rich and will likely flood out at idle
The fuel starts its journey through the pump assembly first...
Then the fuel is regulated by the float diaphragm that controls the needle & seat.
All of these parts reside in the float cavity area as well as the fuel ready to be fed through the jets as needed. The amount of fuel available in the cavity is regulated by the lever and its relationship to the float diaphragm. So it's critical that the lever be set properly. Within the cavity, there are distribution holes that are managed by the low end and high end needles. Plus the idle circuit, which is a fixed size.
(Note) All Walbro carbs will run in any position, but they tune "best" as a side draft carb. The down draft position tends to run a little rich at idle, and the updraft tends to run a little lean at idle. No big deal though, it's easily tuned none the less.
This photo depicts one of Walbro's premier carbs, having a large bore and equipped with a high speed check valve and external fuel pump pulse inlet.
Now let's talk about the pulse signal for the fuel pump.
Your ENGINE will determine which pulse inlet type you need! If the engine "carb base" has a hole drilled into the crankcase you will use the STANDARD pulse port and the optional (if you have it) port must be closed off. If there's no hole drilled, you will find a fitting located somewhere on your crankcase. Use a piece of fuel line to connect the crankcase fitting to the fitting on the optional pulse inlet. There's no need to block off the standard port, as it's already blocked off by the engine mounting.
The carb must get a pulse signal from the engine! This signal "pushes and pulls" on the pump diaphragm which feeds the carb fuel.
Now let's check out the "float needle & seat" setting.
This is the single most critical setting on a Walbro carb! Walbro offers a "setting gauge" to properly set the height of the lever for your particular carb. If you don't have one, the setting will be a trial & error adjustment and a real pain in the butt since you have to open up the carb to make the adjustment. For general purposes, the lever will be almost perfectly parallel to the carb base. This will get you close. If the lever is too high, your engine will tend to run a little erratic at idle. If the lever is too low, your idle will be OK but it will tend to run lean on midrange and high end. It may also run the float cavity "dry" at full throttle and die, regardless of your high speed /low speed needle settings.
The needle valve seat is pressed into the carb base, and you should not remove this without having the correct tools and setting gauges. Do not remove it!
Typical PROBLEMS The engine stalls when accelerated: POSSIBLE solution: High end needle way too lean, or low end needle slightly lean
Engine goes rich in flight : Low end needle too rich, float diaphragm needle lever slightly too high
Engine goes lean in flight : High end needle slightly lean AND low end needle is rich, float needle lever may be set too low
Engine runs good, but no idle at all : There's crap in the idle jets, the carb will have to be removed and cleaned. You may also have an air leak at the base of the carb. The throttle butterfly could be damaged or worn out
carb leaks fuel when not running : float needle is bad or has crap stuck in it, or the float lever setting may be too high, or the float diaphragm is bad.
My engine four cycles momentarily when I back off the throttle, then runs normal : This is perfectly normal for carbs NOT equipped with a "check valve" high speed jet. If you do have the check valve, then your float needle setting is slightly too high, or your float needle is leaking a little
the fuel leaks back into the gas tank when it isn't running : Bad fuel pump membrane, or an air leak in the fuel line at the carb
NOTE 1:
A very common problem with cowled in engines is, the air pressure in flight changes the "natural" pressure on the float diaphragm. This causes the engine to run rich in flight. There are several possible fixes available. Most of the time you can simply tune your engine for flight by trial & error. However, the easiest fix is to open up the cowling around the carb area to lower the air pressure. You may also rotate the cover to different positions to see if that works. The "BEST" fix is to solder a piece of brass tubing where the vent is, and route the vent line to a better location. I normally route it into the fuse going through the firewall. It works perfectly every time! Plus, your ground tune doesn't change in flight!
NOTE 2
Carbs equipped with the high speed check valve are greatly superior for flying aerobatics, or flying whereby the throttle will be used extensively. The check valve prevents jet dripping when you back off the throttle. That's all it does...
Straight through (non-check valved) jets always drip a little fuel while the throttle is being backed off, and causes a momentary four stroking of the engine until the jet stabilizes to the new air flow rate. This is completely normal.
Robert lyman, Sep 26, 2015
Καλη συνεχει με τα 'πειραγματα...'_P_P
Χρησταρας
ΥΓ
Παιδιααα, τυπωστετο και εχετετο μαζι σας, μερικες φορες 'κολλας' και χανεις τη σειρα, δεν πιανει χωρο και ειναι τυφλοσουρτης... +(*)
Petrol (Gas) Engine Tuning, I used this for years.
Carbs aren't too difficult to tune up if you know what you're doing. First of all, you need to know how the carb works and how the settings interact with each other. About 95% of all the gas airplanes I've seen at the field are somewhat out of tune. How can I tell this? Simple, at some point the engines "four cycle" in flight. Two Cycle engines are not supposed to "four cycle" PERIOD. This is caused by a rich mixture that is forcing the sparkplug to intermittently miss making it sound like a four stroke. This is not good. HOWEVER the good news is; gasoline two stroke engines are very tolerant of rich settings (most of the time) and will run fine. You'll just consume a little more gasoline than necessary, and create a little more oil mess on your plane. You may eventually foul your spark plug as well. So why do so many people leave their engines tuned like this? Simple answer, the engine will start much easier when it's cold AND there's little or no warm up time needed prior to flying. Those are pretty good reasons! But the fact is... the engine is not running like it's supposed to.
(1) The low end needle on a Walbro carb is ALWAYS the one closest to the engine, the high end needle is the closest one to the intake/choke.
(2) There is no fuel adjustment for idle fuel, only air feed set by the idle stop or servo.
(3) Both low end AND high end needles feed the top end fuel supply.
Let's tune up a Walbro!
Set the low end & high end needles to about 1 to 1 1/2 turns each. Choke the carb or prime it, until the carb is wet. Fire up the engine and let it warm up. Let's set the top end first since it's the easier of the two. Go to full throttle. Adjust the top end needle for peak RPM. Leave it wide open for about a minute to see if it changes any. Should the engine go lean, open the low end needle slightly, if this doesn't work... you will have to adjust the needle valve inside the carb.( I will explain this later) If the top end runs OK, then slowly pull the throttle down until the engine begins to "four cycle" hold the throttle there. Adjust the low end needle until the "four cycling" stops. Now lower the throttle more until it "four cycles" again, and adjust the low end again. Keep doing this until you reach full idle. Now, from full idle begin to throttle up until the engine starts to bog or hesitate. Open up the top end needle just enough to eliminate the bog or hesitation.
When this is done right, you will be able to set the throttle in any position and it won't four cycle, plus you will be able to transition from idle to full power without any hesitation at all. -Xipp, Flyingcirkus.com Member
Understanding a Walbro Carb
Ok this is for people who need a little insight into how a carburetor works in this case I will be using a Walbro for example.
Starting from the gas tank, the fuel is pumped from the fuel tank and enters the carb through the inlet. The fuel works its way through the fuel pump through a little diaphragm pump that's controlled by 2 one way valves (little flaps). The fuel then passes through a needle & seat that is controlled by the "float" diaphragm. This "float" diaphragm manages how much fuel is available for the idle, low-speed, and high-speed throttle positions. The "float" diaphragm opens & closes the needle through a small lever attached to the needle. The fuel is then "standing by" waiting in the float area for a vacuum signal at the various jets. The lever setting is very critical since it controls the available fuel to the jets. If the lever is too low, the engine will run lean, if the lever is too high, the engine will run very rich and will likely flood out at idle
The fuel starts its journey through the pump assembly first...
Then the fuel is regulated by the float diaphragm that controls the needle & seat.
All of these parts reside in the float cavity area as well as the fuel ready to be fed through the jets as needed. The amount of fuel available in the cavity is regulated by the lever and its relationship to the float diaphragm. So it's critical that the lever be set properly. Within the cavity, there are distribution holes that are managed by the low end and high end needles. Plus the idle circuit, which is a fixed size.
(Note) All Walbro carbs will run in any position, but they tune "best" as a side draft carb. The down draft position tends to run a little rich at idle, and the updraft tends to run a little lean at idle. No big deal though, it's easily tuned none the less.
This photo depicts one of Walbro's premier carbs, having a large bore and equipped with a high speed check valve and external fuel pump pulse inlet.
Now let's talk about the pulse signal for the fuel pump.
Your ENGINE will determine which pulse inlet type you need! If the engine "carb base" has a hole drilled into the crankcase you will use the STANDARD pulse port and the optional (if you have it) port must be closed off. If there's no hole drilled, you will find a fitting located somewhere on your crankcase. Use a piece of fuel line to connect the crankcase fitting to the fitting on the optional pulse inlet. There's no need to block off the standard port, as it's already blocked off by the engine mounting.
The carb must get a pulse signal from the engine! This signal "pushes and pulls" on the pump diaphragm which feeds the carb fuel.
Now let's check out the "float needle & seat" setting.
This is the single most critical setting on a Walbro carb! Walbro offers a "setting gauge" to properly set the height of the lever for your particular carb. If you don't have one, the setting will be a trial & error adjustment and a real pain in the butt since you have to open up the carb to make the adjustment. For general purposes, the lever will be almost perfectly parallel to the carb base. This will get you close. If the lever is too high, your engine will tend to run a little erratic at idle. If the lever is too low, your idle will be OK but it will tend to run lean on midrange and high end. It may also run the float cavity "dry" at full throttle and die, regardless of your high speed /low speed needle settings.
The needle valve seat is pressed into the carb base, and you should not remove this without having the correct tools and setting gauges. Do not remove it!
Typical PROBLEMS The engine stalls when accelerated: POSSIBLE solution: High end needle way too lean, or low end needle slightly lean
Engine goes rich in flight : Low end needle too rich, float diaphragm needle lever slightly too high
Engine goes lean in flight : High end needle slightly lean AND low end needle is rich, float needle lever may be set too low
Engine runs good, but no idle at all : There's crap in the idle jets, the carb will have to be removed and cleaned. You may also have an air leak at the base of the carb. The throttle butterfly could be damaged or worn out
carb leaks fuel when not running : float needle is bad or has crap stuck in it, or the float lever setting may be too high, or the float diaphragm is bad.
My engine four cycles momentarily when I back off the throttle, then runs normal : This is perfectly normal for carbs NOT equipped with a "check valve" high speed jet. If you do have the check valve, then your float needle setting is slightly too high, or your float needle is leaking a little
the fuel leaks back into the gas tank when it isn't running : Bad fuel pump membrane, or an air leak in the fuel line at the carb
NOTE 1:
A very common problem with cowled in engines is, the air pressure in flight changes the "natural" pressure on the float diaphragm. This causes the engine to run rich in flight. There are several possible fixes available. Most of the time you can simply tune your engine for flight by trial & error. However, the easiest fix is to open up the cowling around the carb area to lower the air pressure. You may also rotate the cover to different positions to see if that works. The "BEST" fix is to solder a piece of brass tubing where the vent is, and route the vent line to a better location. I normally route it into the fuse going through the firewall. It works perfectly every time! Plus, your ground tune doesn't change in flight!
NOTE 2
Carbs equipped with the high speed check valve are greatly superior for flying aerobatics, or flying whereby the throttle will be used extensively. The check valve prevents jet dripping when you back off the throttle. That's all it does...
Straight through (non-check valved) jets always drip a little fuel while the throttle is being backed off, and causes a momentary four stroking of the engine until the jet stabilizes to the new air flow rate. This is completely normal.
Robert lyman, Sep 26, 2015
Καλη συνεχει με τα 'πειραγματα...'_P_P
Χρησταρας
ΥΓ
Παιδιααα, τυπωστετο και εχετετο μαζι σας, μερικες φορες 'κολλας' και χανεις τη σειρα, δεν πιανει χωρο και ειναι τυφλοσουρτης... +(*)
Απάντηση: Οδηγος Bασικης Ρυθμισης Βενζινοκινητηρα.
The ceremony is about to begin... οπως ελεγε ο Jim.
Αντε και στην πραξη λοιπον.
Υ.Γ. LIKE!
Αντε και στην πραξη λοιπον.
Υ.Γ. LIKE!
-
bladeskiller
- Δημοσιεύσεις: 712
- Εγγραφή: Τρί Απρ 08, 2008 4:12 pm
Απάντηση: Οδηγος Bασικης Ρυθμισης Βενζινοκινητηρα.
Ενα σχόλιο μόνο που αφορά τη ρύθμιση της βελόνας των χαμηλών στροφών. Αν η μηχανή ρυθμιστεί με την παραπάνω μέθοδο και το μίγμα στο ραλαντί δεν είναι κάπως πιο πλούσιο, το πρόβλημα δεν είναι μόνο ότι η μηχανή θα δυσκολεύεται να πάρει μπρος όταν είναι κρύα αλλά υπάρχει και κάτι άλλο ,ειδικά αν η μηχανή έχει σχετικά μεγάλης διαμέτρου καρμπυρατέρ για τον κυβισμό της και το ρελαντί είναι ρυθμισμένο πολύ χαμηλά.
Αν επιταχύνουμε απότομα από το ραλαντί στο φουλ οπότε η πεταλούδα του καρμπυρατέρ ανοίγει απότομα από τη θέση του ραλαντί στο φουλ, τότε και ο αερας μέσα στο καρμπυρατέρ επιταχύνεται καθώς και η ροή της βενζίνης. Ομως, επειδή η βενζίνη είναι βαρύτερη από τον αέρα και κατά συνέπεια έχει μεγαλύτερη αδράνεια, δεν επιταχύνει με τον ίδιο ρυθμό όπως και ο αέρας ,με αποτέλεσμα το μίγμα να γίνεται φτωχότερο μέχρι που η ροή του αέρα να σταθεροποιηθεί. Αν λοιπόν το μίγμα στο ραλαντί είναι ρυθμισμένο "όπως πρέπει", αυτό που λεμε best lean, τότε, σε ένα απότομο άνοιγμα του γκαζιού από το ραλαντί, η μηχανή μπορεί να σβήσει από έλειψη βενζίνης ή να επιταχύνει με διακοπές.
Ενα άλλο πράγμα επίσης ,που συμβαίνει κατά την απότομη επιτάχυνση από το ραλαντί, έχει να κάνει με τον τρόπο που λειτουργεί το καρμπυρατέρ. Για τη λειτουργία στο ραλαντί και στα μικρά ανοίγματα του γκαζιού ,υπάρχουν τρεις τρύπες. Η μία είναι κάτω από την πεταλούδα και είναι για το ραλαντί ενώ οι άλλες δύο βρίσκονται πάνω από την πεταλούδα και αποκαλύπτονται (ας το πούμε έτσι) καθώς η πεταλούδα ανοίγει, για την τροφοδοσία σε χαμηλομεσαία ανοίγματα του γκαζιού και χαμηλές στροφές όπου το κύριο ακροφύσιο ,που βρίσκεται στο βεντούρι, δεν μπορεί να λειτουργήσει σωστά γιατί η υποπίεση στο βεντούρι δεν είναι αρκετή σε τόσο χαμηλή ταχύτητα ροής του αέρα. Στη θέση που η πεταλούδα είναι σχεδόν ή εντελώς ανοιχτή, η υποπίεση στις τρεις τρύπες είναι τέτοια που μόνο μια μικρή ποσότητα βενζίνης, από τη συνολική που χρειάζεται η μηχανή ,παρέχεται από αυτές. Τη μεγαλύτερη ποσότητα στο φουλ τη δίνει το ακροφύσιο στο βεντούρι. Εστω τώρα ότι η μηχανή λειτουργεί σε χαμηλό ραλαντί και ανοίγουμε το γκάζι στο φουλ απότομα. Ειδικά αν η μηχανή έχει βαριά προπέλα ,δεν είναι δυνατό να επιταχύνει ακαριαία. Αν λοιπόν ,στο χρόνο που ανοίγουμε το γκάζι στο φουλ, η μηχανή δεν προλάβει να πιάσει τέτοια ταχύτητα, που το βεντούρι να μπορει να δουλέψει αποτελεσματικά και να τραβήξει ο αερας βενζίνη από εκεί ,τότε το μίγμα θα γίνει υπερβολικά φτωχό και η μηχανή θα σβήσει. Και επειδή η ταχύτητα αυτή είναι τόσο μεγαλύτερη όσο το μέγεθος του καρμπυρατέρ και ,κατά συνέπεια, το μέγεθος του βεντουριού είναι μεγαλύτερο, το πρόβλημα αυτό είναι πιο έντονο σε κινητήρες με μεγάλο σχετικά καρμπυρατέρ σε σχέση με το μέγεθός τους.
Τα παραπάνω για να γίνει κατανοητό το γιατί ,ενώ η ρύθμιση των χαμηλών στροφών μπορεί να είναι σωστή, η μηχανή μπορεί να κάνει άσχημα κόλπα στην επιτάχυνση.
Για να ξεπεραστούν τα παραπάνω προβλήματα, ορισμένα καρμπυρατέρ, διαθέτουν τη λεγόμενη αντλία επιταχύνσεως, η οποία ,σε κάθε απότομο άνοιγμα του γκαζιού, ψεκάζει μια μικρή ποσότητα βενζίνης για να γεφυρώσει το χάσμα. Τα περισσότερα καρμπυρατέρ όμως, που τοποθετούνται σε μοντελιστικούς κινητήρες βενζίνης, δεν έχουν τετοιο μηχανισμό και γιαυτό το λόγο καταφεύγουμε στο "τρυκ" του πλουσιότερου μίγματος στο ραλαντί ώστε το χάσμα να καλυφθεί με τη βενζίνη που περισσεύει κατά τη λειτουργία στο ραλαντί.
Αν επιταχύνουμε απότομα από το ραλαντί στο φουλ οπότε η πεταλούδα του καρμπυρατέρ ανοίγει απότομα από τη θέση του ραλαντί στο φουλ, τότε και ο αερας μέσα στο καρμπυρατέρ επιταχύνεται καθώς και η ροή της βενζίνης. Ομως, επειδή η βενζίνη είναι βαρύτερη από τον αέρα και κατά συνέπεια έχει μεγαλύτερη αδράνεια, δεν επιταχύνει με τον ίδιο ρυθμό όπως και ο αέρας ,με αποτέλεσμα το μίγμα να γίνεται φτωχότερο μέχρι που η ροή του αέρα να σταθεροποιηθεί. Αν λοιπόν το μίγμα στο ραλαντί είναι ρυθμισμένο "όπως πρέπει", αυτό που λεμε best lean, τότε, σε ένα απότομο άνοιγμα του γκαζιού από το ραλαντί, η μηχανή μπορεί να σβήσει από έλειψη βενζίνης ή να επιταχύνει με διακοπές.
Ενα άλλο πράγμα επίσης ,που συμβαίνει κατά την απότομη επιτάχυνση από το ραλαντί, έχει να κάνει με τον τρόπο που λειτουργεί το καρμπυρατέρ. Για τη λειτουργία στο ραλαντί και στα μικρά ανοίγματα του γκαζιού ,υπάρχουν τρεις τρύπες. Η μία είναι κάτω από την πεταλούδα και είναι για το ραλαντί ενώ οι άλλες δύο βρίσκονται πάνω από την πεταλούδα και αποκαλύπτονται (ας το πούμε έτσι) καθώς η πεταλούδα ανοίγει, για την τροφοδοσία σε χαμηλομεσαία ανοίγματα του γκαζιού και χαμηλές στροφές όπου το κύριο ακροφύσιο ,που βρίσκεται στο βεντούρι, δεν μπορεί να λειτουργήσει σωστά γιατί η υποπίεση στο βεντούρι δεν είναι αρκετή σε τόσο χαμηλή ταχύτητα ροής του αέρα. Στη θέση που η πεταλούδα είναι σχεδόν ή εντελώς ανοιχτή, η υποπίεση στις τρεις τρύπες είναι τέτοια που μόνο μια μικρή ποσότητα βενζίνης, από τη συνολική που χρειάζεται η μηχανή ,παρέχεται από αυτές. Τη μεγαλύτερη ποσότητα στο φουλ τη δίνει το ακροφύσιο στο βεντούρι. Εστω τώρα ότι η μηχανή λειτουργεί σε χαμηλό ραλαντί και ανοίγουμε το γκάζι στο φουλ απότομα. Ειδικά αν η μηχανή έχει βαριά προπέλα ,δεν είναι δυνατό να επιταχύνει ακαριαία. Αν λοιπόν ,στο χρόνο που ανοίγουμε το γκάζι στο φουλ, η μηχανή δεν προλάβει να πιάσει τέτοια ταχύτητα, που το βεντούρι να μπορει να δουλέψει αποτελεσματικά και να τραβήξει ο αερας βενζίνη από εκεί ,τότε το μίγμα θα γίνει υπερβολικά φτωχό και η μηχανή θα σβήσει. Και επειδή η ταχύτητα αυτή είναι τόσο μεγαλύτερη όσο το μέγεθος του καρμπυρατέρ και ,κατά συνέπεια, το μέγεθος του βεντουριού είναι μεγαλύτερο, το πρόβλημα αυτό είναι πιο έντονο σε κινητήρες με μεγάλο σχετικά καρμπυρατέρ σε σχέση με το μέγεθός τους.
Τα παραπάνω για να γίνει κατανοητό το γιατί ,ενώ η ρύθμιση των χαμηλών στροφών μπορεί να είναι σωστή, η μηχανή μπορεί να κάνει άσχημα κόλπα στην επιτάχυνση.
Για να ξεπεραστούν τα παραπάνω προβλήματα, ορισμένα καρμπυρατέρ, διαθέτουν τη λεγόμενη αντλία επιταχύνσεως, η οποία ,σε κάθε απότομο άνοιγμα του γκαζιού, ψεκάζει μια μικρή ποσότητα βενζίνης για να γεφυρώσει το χάσμα. Τα περισσότερα καρμπυρατέρ όμως, που τοποθετούνται σε μοντελιστικούς κινητήρες βενζίνης, δεν έχουν τετοιο μηχανισμό και γιαυτό το λόγο καταφεύγουμε στο "τρυκ" του πλουσιότερου μίγματος στο ραλαντί ώστε το χάσμα να καλυφθεί με τη βενζίνη που περισσεύει κατά τη λειτουργία στο ραλαντί.