Oy, my head hurts trying to read this. <div>
</div><div>Venturi effect!  The low speed ports do not supply any fuel at WOT because the main part of the draw is at the throat of the carb where the venturi is most restrictive.  Once the airflow gets past that point the vacuum drops off dramatically.  Only when the butterfly is closed or near closed does the vacuum point change. Since you have now moved the smallest portion of the venturi to the hole in the butterfly, you now have the strongest vacuum source, so it will now pull off the low end ports. </div><div>
</div><div>If you look at that diagram, notice the big fat blue arrow, thats your main source of vacumm, where the pull is strongest, past that point  you get closer to atmospheric pressure. </div><div>
</div><div>Forced Induction creates a vaccum by blowing air past the venturi to pull the fuel. You can simulate this by blowing air past a straw that is in a glass of water.  You never force air at idle, at that point the Supercharger or Turbos are idle.  At high altitudes where the air is thin you need the boost to give you the equivalent power at sea level.</div>

Thankyou, Thankyou

with the big blue arrow, they key word is MAIN source of vaccum, as well as CLOSER to atmospheric pressure. Any air pressure below atmospheric is going to draw some fuel out. So fuel is still coming out of the port of the low needle, even if its at a reduced amount because of the reduction of vacuum due to the throttle plate being open.

If the low speed needle gives absolutely NO fuel at the top end, then the company that wrote the DLE20 manual are wrong, the guys at Indiana Tiny Gas Engines are wrong and the knowledgeable people at Valley View RC are wrong.

My comment about the aircraft and forced induction have nothing to do with this. It was simply my response to ahicks about the term "vacuum pressure". I understand very well how and why forced induction works and why its used on aircraft. At idle there is not boost (pressure) in the manifold on a turbocharged engine because as you said, the turbo is not turning fast enough to move much air. And at low throttle is isnt getting boost because the throttle plate is blocking air from going in (if you watch a boost gauge on a diesel engine, which does not have any type of throttle plate, it will see a little boost even when cruising at low throttle). Which is the reason why my (centrifugal) supercharged engine doesn't see boost at low throttle. The supercharger rpm is directly related to the engine rpm and is moving more air than the engine (the engine is a pump too), even at idle. Since the throttle plate or "butterfly" is blocking the air put out by the supercharger, a bypass or blow off valve is employed to relieve the excess pressure. And also to keep the supercharger from being over pressured when the throttle is snapped closed from WOT, which would cause a surge and would cause impeller to housing contact and cause all kinds of damage to the supercharger....

But as before, that has nothing to do with the discussion. Im going to keep adjusting my high end needle last to make sure its right, and you two can do what ever you want. Obviously unclecrash isnt going to be swayed from the way he has decided to do it 35 years ago. So Im not gonna argue any more.

If someone like JediJody comes in and says that the low needle has no effect on the top end, then Ill research some more and may reconsider. I think this subject has been discussed on this very thread a couple hundred pages back or so. Maybe I'll scan through it if Ive got time.

Like I said to begin with Im not here to argue. But I believe I read a post somewhere about TiredOldman adjusting like I do but I could be wrong I might have read between the lines. I have done many of weedwhips and chainsaws this way and never ever have had to go back and check a plug for lean condition always have set by ear. And have never burned one down from it, when I change out a plug they have always been coffee and cream..

I find the LS &amp; HS needles a little bit interactive.

When fine tuning for effect during flight, If I make the HS a little richer - I often need to lean the LS a like amount. and vice versa. If I do not adjust both - the midrange will get out of hand if one needle is tuned richer.

I listen to "in flight" high speed acceleration also when adjusting the HS

At 35 years, your experience might be considered still at rookie level in some circles!

I really didn't mean to come across as arguing. My apologies if it were interpreted that way. My comment was meant as a thoughtful exchange of information only! I was just pointing out there is SOME fuel coming from those ports at higher throttle settings. Won't argue it's enough to change a plug reading one way or the other! Somebody else can pick up that torch if they want to....

Yes I believe were all needle fiddlers, especially when it comes to the planes. Especially when the temps and humidity go from one extreme to the other.

I've had some "land and adjust" sessions. They definitely run a little different once you get them up in the air.

hey mach2 thanks for th info bout the feeler gauges! i actly hav som v thos! dad and i farm so got a lil bit of every thing in th shop so managed t find some!!!=)

no problem.

Can the carb be rotated 180*?   I just realized that once installed in my Mustang, I would not be able to reach the adjustment screws.  The links can be attached before mounting the motor if they are on  top, but I really wouldnt want to have holes in the nose just for reaching the screws.

Yes.

More Data on carbs. Capt,n

<table border="0" cellspacing="0" cellpadding="3" width="100%"> <tbody> <tr> <td class="subhead">Message</td> </tr> </tbody></table><hr width="98%" />
<!Message Starts Here><table border="0" cellspacing="0" cellpadding="0" width="98%"> <tbody> <tr> <td align="center"> <table border="0" cellspacing="1" cellpadding="0" width="100%"> <tbody> <tr> <td align="center"> <table border="0" cellspacing="0" cellpadding="2" width="100%"> <tbody> <tr> <td class="info" valign="top" colspan="2" align="left">captinjohn -&gt; Inside the Tillotson Carb DLE30 (7/27/2010 11:59 PM)</td> </tr> <tr> <td valign="top" colspan="2">
<span class="msg">

I did some reading and took apart the Carb on my DLE30cc engine. I wanted to first make sure it was clean &amp; parts in good order. I found there was marks on the 3 sides of the fuel shut off that has a neoprene tip. The 3 sides are metal. I honed them smooth with a fine hone stone. Blew out all passage ways. Checked the inlet screen...it was pretty clean. I decided to do a cut on the throttle butterfly, like I read about doing. I used a small carbide cutter in my dremel and cut the small moon on the edge of plate about 20% bigger to let in more air on Idle...I knew I would have to learn new carb needle settings.

Well after much trouble putting the small spring in place under the pivot arm...I got it all together wetting it as I put it together. It was a" buger" to get the needles right to get running...but when I did it sure runs better ...as with ...it seems to have taken out that rich burble at part throttle. I do not advise anyone to try this....unless you got extra parts you may wreck so you can replace them!!! Some photos below. Note: the moon on edge of throttle plate is bigger now. Spring length unchanger.... .445 on dial indicator. Capt,n</p> </span></td> </tr> <tr> <td class="info" valign="bottom" colspan="2" nowrap="nowrap">
</td> </tr> </tbody> </table> </td> </tr> </tbody> </table> </td> </tr> </tbody></table>
<hr width="98%" />
<table border="0" cellspacing="0" cellpadding="0" width="98%"> <tbody> <tr> <td align="center"> <table border="0" cellspacing="1" cellpadding="0" width="100%"> <tbody> <tr> <td align="center"> <table border="0" cellspacing="0" cellpadding="2" width="100%"> <tbody> <tr> <td class="info" valign="top" colspan="2" align="left">captinjohn -&gt; RE: Inside the Tillotson Carb DLE30 (7/28/2010 12:15 AM)</td> </tr> <tr> <td valign="top" colspan="2">
<span class="msg"><font size="2">Read this before you try this. Please as this thread for now goes on, do not ask to much....read first or if you have done this or know more about this please add to the good data. Asking is best to do after reading or trying it for yourself. It does work. Best Regards Capt,n <hr /> </font>

<u>IMPORTANT:</u> Wherever the idle pickup holes are in your carb throat, make the plate notch in front -or aligned- to them, and make sure you do not grind any more than 2mm. If you grind away too much, the engine will simply have a fast uncontrolled idle that cannot be adjusted with the idle stop screw or the Low speed needle (buy a $0.79 cent spare butterfly plate just in case: Throttle Valve, Walbro # 34-305); For Walbro distributors in your country or state click HERE.</p>

</p>

When you place the throttle flap back, ensure it closes completely before tightening it to its shaft, and don't push too hard while tightening it or you will bend the delicate brass shaft. Add one small drop of LockTite to its central screw. Mount the carb on the engine and make sure the throttle cable permits the complete throttle assembly to open and return &ldquo;all the way&rdquo; against the stop! With this done you will now open the Low speed needle 1 turn (WG8); [WB series: Open the Low speed needle 1 turn and open the High speed needle 1/2 turn to start out] and back out that mashed idle stop screw to where it's supposed to be: about half way out.</p>

</p>

Again, check that the complete throttle assembly works correctly and the throttle flap closes completely and freely. Also test the choke mechanism for free movement. Start your engine and <u>allow it to warm up</u> at low/mid RPM.</p>

</p>

High Speed Neddle Adjustment
If you have a WB series carb, next make a high speed run and adjust your High speed needle at high RPM. The ideal high speed mixture is the richest setting that still permits strong acceleration up to peak RPM. With this in mind, it is always wise to start out slightly over rich and slowly lean the mixture out. If the high speed mixture is too lean, you'll experience weak or "lazy" mid range acceleration. You'll eventually find a narrow adjustment range where peak rpm operation seems unchanged. However, within this range, there should be a noticeable difference in mid to high range acceleration. Finding the setting within this range that gives the best "middle through high range a cceleration" usually requires patience to train your hearing..acceleration" usually requires patience to train your hearing .
</p> <div>Idle Adjustment
Once the engine is operating at normal temperature, you can now adjust the idle stop screw till you achieve a smooth idle.

</p> <u>What did all this achieve?</u>
You now allowed enough airflow for the engine to run properly at idle. You allowed for a smooth controlled idle since the Low speed mixture is finally balanced.

</p> </div> </span></td> </tr> </tbody> </table> </td> </tr> </tbody> </table> </td> </tr> </tbody></table>

Yes. you can only rotate it 180. not 90 or 270 (1/4 or 3/4 turns).

I may not be using the proper terms for the parts im talking about, but the colored outlines on the pic will be sufficient for you to understand what im talkin about. The pic Iattached is from when I totally tore down my engine and carb to clean and inspect it after a crash. So, you dont need to take apart the carb at all like I have pictured.

There are two screws that go all the way through (im going off memory because Im on duty so I hope it's pretty accurate) the carb, through the reed valve and the reed valve "case" or "housing", and into the crank case "back plate" (back plate is shown in the first picture, outlined in red) where the air/fuel mixture enter the engine. The carb and reed valve/housing (shown in the first pic, outlined in green) will be together (lets call that the carb assembly), just leave the screws in it and dont even separate the carb assembly.

Simply remove those screws along with the carb assembly as one unit, from the back plate and flip it upside down. Screw it back in and you're done...

Now I know you wont do this, but Icould see someone removing the 4 screws of the crank case back plate and trying to rotate that, and leave the carb bolted on to it. You could do this and think its fine if the piston is up, but it wont work because the piston skirt will come down and slap it. If you had it off you could look at the side that goes into the crank case and see there is an angle for clearance of the piston skirt. This is shown in the second picture outlined in blue. The angle might also be there to let the air/fuel mixture pass through to the intake port. Either way, dont rotate it. Its there for a reason.

Jeremy

I think I need a Xanax,
BCCHI

Easy way to test this. Close the idle screw all the way. Set up high speed screw to spec. check RPM. Then set up low speed screw for idle. Then check WOT RPM again. If the low speed jet does not add to the WOT then the RPM should not change, either way. I'm not a betting man but if I was I'm saying it is going to change.

ALL the way ?????? R/L

all the way  ?????

RiverLarry, are you getting any air time on the DLE 20cc engine latley? I should have flown today...but we had company over. Seems like the Steelhead fishing should be just about over now. Maybe less boats for you to work on. Itis going to warm up I guess...but with a few days of rain. I sure hope we finally get some good days to fly. Take Care, Capt,n

CaptinJohn P/M sent !!!!! R/L

I will attempt to explain it. The confusion comes from the fact that an automotive vacuum gauge reads zero at rest, when in fact it is under atmospheric pressure, which is of course around 14.7 psi, or 29.92 inches. (Atmospheric pressure, stated in psi, or barometric pressure). The automotive vacuum gauge then indicates anything LESS than atmospheric pressure as a "vacuum". The gauge one finds in an aircraft, and NOT only turbocharged aircraft, is called a "Manifold Pressure Gauge". It is very similar to an automotive vacuum gauge, with one important difference; it shows atmospheric pressure instead of zero when at rest. If you look at one with the engine not running, it will show barometric pressure; somewhere around 29.92 inches, depending on altitude and local weather. When the engine is running, the gauge measures actual pressure in the intake manifold. At wide open throttle, it will show a bit less than atmospheric pressure due to inefficiencies and restrictions in the intake tract, but it will show a high pressure, indicating that the throttle is wide open. Correspondingly, lower throttle settings show lower manifold pressure, and indicate lower throttle/power settings. This, along with rpms, provides a good way to determine how much power the engine is producing, in order to determine performance, fuel consumption, etc. In the case of a turbo or supercharged engine, the manifold pressure gauge can indicate pressures higher than atmospheric, due to the pressure boost provided by the turbo or supercharger.

AV8TOR

Ahh! it makes sense to include atmospheric pressure in the gauge do to that pressure changing with the change in altitude. Where as a car isnt going to get too far away from the 14.7 at sea level.

thanks for that insight.

Pilot here too, with a high performance rating so I know how the gauge is used. In my case it's an absolute requirement to set prop pitch efficiently! Doesn't change what I think about what that gauge is called one bit. I've had the logic of that name defined and beat into my head so many different ways by so many guys I have so much respect for....... and it till make me crazy. I just try not to think about it, and use the info it's feeding me to do what I need to do.

What kind of plane do you fly? When doing my own flying (meaning not with my dad who flies anything from a piston twin to a Lear 31A), I didnt get past a 152, which only had throttle and mixture levers. Im not familiar with any that you have to manually set the prop pitch. The planes I know that have constant speed props adjust the pitch automatically with rpm setting. If I remember correctly, the Cessna 340 has throttle, mixture and rpm levers. If you have an engine die, I believe pulling the rpm lever down past the stop it feathers the prop to reduce the amount of rudder needed to keep it from rolling over. I could be wrong though. I have't gone on a flight with him in quite a while...

I get 8800+ with all my (5) DLE20 on APC17x6 GF nylon props.
I fly near New Delhi with 260M ASL and 25-35*C ambient temps.