DLE 20cc unable to idle low enough
 

DLE 20cc unable to idle low enough or stay running at idle. Help needed desperately. I think I have worded everything done below including back story of engine. I am not sure what might be going on here

Original setup:
1. Separate batteries for ignition and radio
2. Opti-kil switch
3. Tank with fill line, vent line and fuel line
a. Fill line had clunk installed
b. Vent line curved brass tube to top of tank
c. Fuel line had filter installed
4. NGK CM-6
5. Stock ring without reed/carb mods

Crash details:
1. Total radio black out
2. Throttle stuck at about ¼
3. Plane struck ground at angle destroying the fuselage
4. Engine had pulled off firewall
5. Prop was intact
6. No visible dirt in carb
7. One small chunk of cylinder fin was broken off
8. Hall sensor wires on ignition side stripped off

Engine Prep for new plane:
1. Cleaned engine surface all around
2. Repaired stripped wires with new servo connectors
3. Rebuilt carb to be sure no dirt made its way into it
4. Replaced spark plug
5. Reset needles to stock settings

New plane setup:
1. Profile plane
2. Throttle arm in same position as the choke arm
3. Throttle setup with 90% endpoints on both ends
4. Radio/power setup
a. Futaba R7008SB Receiver
b. 2 A123 batteries connected to 2 receiver ports
c. Ibec running from receiver to ignition with 5.3v

First run up:
1. Needles set to stock settings 1 ½ turns out
2. Engine starts up and runs fine from mid-range to high
3. High set to about 8200 rpm
4. Low will not go below 4800 rpm
5. Low needle richened to 4 ½ turns out in 1/8 runs without change
6. reset needles again to stock engine will either drop to 3200 rpm and die or drop then run back up to 4800 rpm
7. needles chased for over 2 hours and looked at by the local gas engine expert
8. Suggested to rebuild carb checking for anything abnormal and checking the inlet needle valve assembly.


Carb rebuild:
1. carb disassembled
2. no visible damage with gaskets, reed, needles/seats, jets or needle valve assembly
3. all gaskets, reed, needles/seats, jets or needle valve assembly replaced with parts from K20-WAT kit
4. while carb removed – reeds inspected – found to be not sealing on either side pulling away from the reed block at tip
5. removed reeds and flipped over
6. reeds now sealing all around

Engine startup:
1. Spark Plug replaced again to rule out
2. Needles set to stock settings 1 ½ turns out
3. Engine starts up and runs fine from mid-range to high
4. High set to about 8200 rpm
5. Low will go down to about 3600 rpm then runs back up to about 4500 rpm
6. Engine runs back up to 4500 rpm then dies out as though it is not getting gas
7. Only way to get the engine to run back up is to re-choke engine every time

Man, that's a good one! My first move would be to pull the carb and look at 3 things.

First would be throttle plate alignment. Has the screw loosened, or is something else going on that won't allow the carb to close completely?

Second, I'd pull the idle adjust screw and squirt some carb cleaner in there while watching the tiny fuel ports by the throttle plate. You should see at least some carb cleaner coming through. I'd also check the idle screw itself, looking for a damaged tip.

From there, I'd look for something that might be causing low fuel pressure on the idle. Is it possible the vacuum port is partially blocked by the carb gasket? A gob of gasket sealer blocking the port somewhere?

Nice job on your documentation....

Best of luck -Al

I had that same problem, it was a dirty fuel filter screen in the carb. It just as easy to replace as to try and clean the old one. You can get the at any small engine repair shop its the same as the one used in Walbro carbs. I put a filter in my gas can and one in the supply line.

I have had engines that had set like yours did for a period of time and not a long period either, Only to find they wouldn't go past a certain RPM and ran out of gas or needed to be partially choked to stay running. Mine turned out to be a small amount of varnish or dried up oil in a couple of places, one was the fuel inlet itself, the other was under the needle and i am thinking also under the pump was giving some grief as well. This engine had sat for less than a few months and did this ,while I have had had others set for several years and not have any issues what so ever. Same oil Same gas type, but maybe not bought at the same station. Oh Oh Oh also the screen was partially plugged up.
Good luck and let us know what you find, in my case a rebuild on the carb was not necessary just a good cleaning and guys this stuff was almost clear to the eye so it was hard to spot.

air leak or timing

why 1/4 throttle when ..black out""?? "fail safe" should have put throttle to idle !!?? If,, you did, bind with idle setting

Had a very similar problem on a VVRC 20 cc.(very similar to a DLE) The needles kept requiring attention and I noted oil on the crankcase. It turned out the four bolts holding the head to the case were loose ever so slightly causing an air leak, Tightened them, problem solved.
As you hit hard enough to break a fin this may be possible, It may also be possible the ignition is damaged? Eliminate the Opti-kill to see if that is part of the problem they sometimes act up? Had an RcExel mod. that worked for seven mins. on each flight and started missing and would quit, changed it and problem solved.
Good luck!

Not how Futaba failsafe settings are set. With Futaba, F/S settings are set in the failsafe menu for each model setup. The only exception is when one is using a conversion module in an older non 2.4Ghz transmitter, then throttle F/S is set when linking the receiver ala Spektrum.
Pete

I say probable air leak as well. Damaged front bearing and/or seal? Leak at cylinder base or crankcase halves? Leak at carb mounting block/reed valve assy.?

AV8TOR

Close the high speed needle, try to run the engine. IF it still runs high there is probably an air leak. IF it won't run at all it is the low speed circuit, clean it.
Do you have another carb you could try?

Good advice. However, if it is a fairly large air leak, it might not run with the high speed needle closed even if the low speed carb circuit is functioning properly. When I rebuild a carb, I ALWAYS squirt WD-40 through every single circuit to verify that it is open and flowing.

AV8TOR

Seeing is believing, I like to spray through those circuits while observing for flow myself.

Just as a FYI, don't use carb cleaner spray if you happen to be working on a Zama carb. It will instantly ruin any check valves in the carb. Been there, done that, unfortunately.

AV8TOR

Thanks for all the replies guys,
I have ordered a new rebuild kit and will be tearing the carb down this morning to check things out, You all have given me a lot of places to look at
I will also be replacing the guts of the fuel tank to rule that all out
I will keep you all posted, hopefully in a few hours we will know results

Jerry

Yes, please keep us posted. It helps everyone when the answers to puzzling problems are revealed.

As mentioned, excellent work on posting all the info and history of your setup and problems.

AV8TOR

I find a vacuum/pressure checker handy for working on two strokes. You can buy a hand vacuum pump pretty cheap from harbor freight. Then you make a plate to seal off the exhaust and the intake right where the carb mounts. Use rubber gaskets to seal the plates, and in one of them put a valve such as used on auto tires. With all in place, pressurize the engine to no more than 5 psi. It should hold the pressure, and you can chase down any leaks with soapy water. Then, remove the valve core from the valve, hook up a hose, and pump it down to a vacuum. It should hold the vacuum. If it passes these tests, you know the engine is well sealed and your problem lies elsewhere.

(Jim, add to "sticky??)

AV8TOR

Carb
1. Engine removed
2. Carb removed
3. Reed valve assembly removed
4. All circuits cleaned out with carb cleaner
5. Throttle plate and choke plate intact and screws tight
6. Screen removed
7. Carb inspected for cracks, varnish and pitting – none found
8. Needles removed, cleaned and checked – no issues
9. Carb allowed to dry why other bits checked

Engine
1. All bolts checked for torque
2. Inspected for any visible damage – none found
3. Barings appear to be good
4. Good compressions found
5. Hall sensor appears to be fully intact – unable to check timing but bracket seems to be in standard middle area

Fuel tank
1. Disassembled
2. New fuel lines, clunks and stopper installed with barbs on brass tubes
3. Leak tested – no leaks found

Carb
1. New screen put in for inlet
2. All gaskets carefully reinstalled
3. Reed valve assembly checked and reinstalled
4. Reinstalled carb
5. Reinstalled engine and fuel lines
6. Needles set to default 1 ½ out on both

Engine start up
1. Setup currently on ibec with a123 batteries from buddyrc fully charged
2. Chocked engine
3. Started right up at ½ throttle and died when brought just one click below ½
4. Needles richened out 1/8 turn increments till engine settled around 4200rpm and dies – low needle now at 4 turns out
5. Muffle removed to rule out any back pressure issues – no change
6. I got the engine to settle down to around 3700 rpm but then promptly died
7. Restart requires choking every time still
8. Tested with carb cleaner around all gasket areas at around 5000rpm – no change until cleaner got to throttle throat

I am wondering if maybe the issue is the timing or the ignition, either this or does anyone want to buy an engine. Anyone have any other thoughts….pulling what hair I have left out on this one

Everyone always thinks it just has to be the carburetor when an engine misbehaves. That's not always the case, and I think you've covered that in this instance. Can you rig up a pressure check as I outlined? Do you have another ignition to try? If shipping both ways wasn't so expensive, I would say send it to me and I'd have a look at it. If you really are ready to "chuck it in the trash", I'll take it! :)

AV8TOR

Time for a little more drastic measures me thinks. Like swapping some parts out or sending it to a pro. The fact it does well at higher RPM would generally make one believe the carb is getting and pumping plenty of fuel. Same on the ignition. Generally if they run at all, they'll start screwing up, for whatever reason, at higher rpm.

With no further clues, my best guesses would be some kind of vacuum leak, or a near complete failure/blockage in the carb's low speed circuit.

If unable to swap parts because this was my only gasser, I'd be tempted to contact Valley View to see if they might be willing to look at it.

If the crankshaft is pressed together, it may have twisted in the crash. The counterweights can rotate on the crankpin/rod journal, a lot easier than you might imagine. Seen it happen just using a piston stop to tighten prop mounts or collets. That sudden stop may have "re-indexed" the crankshaft halves. I always remove the cylinder & use a wood block between the counterweight & the crankcase. Block the counterweight on the same side of the crank pin as what is being tightened. If the timing is mysteriously off after a crash, a twisted crank is the likely suspect, IMO. I have spot welded crank pins to counterweights on my favorite/best running engines to help them remain healthy through the stuff we subject them to.

The DLE 20 is a caneilever crank engine and the whole crank assembly (single counterweight and main shaft) is one piece. Only the crankpin is a press in piece. Twisting not really an issue here though the hub locating key could shear I guess.

http://www.rcuniverse.com/forum/atta...mentid=2160362

Thanx for that info. Not being familiar with dle's, I learned something ;) Hopefully my post will be helpful to some on press together crankshafts. Very true on the crank key, worth checking out!

Yes, Zenoah's and a very few other engines still use "real" crankshafts. Nothing wrong with the cantilever cranks though for most applications. They work quite well and save quite a bit of weight.

As you suggest, it takes very little to block the low speed fuel passages. The usual problem is a speck of sealer they use on the welch plugs in the carb housing. This was more common in years past though. I haven't seen any sealer present on any of the newer Walbro or Walbro clone carbs though it still may be present and out of sight.

I prefer brake clean over carb cleaners as the solvents are less aggressive and less apt to damage any rubber parts if present. Brake clean is cheaper also. Some of the new spray cleaners designed for cleaning EFI throttle plate assemblies are also advertised as being rubber / plastic safe so this would be acceptable. av8tor, I know you mentioned the carb cleaner issue, I just added some possible substitutes. Like many solvents, carb cleaners may have been neutered by the EPA these days and they my be rubber safe. I just don't take a chance on them as there are other alternatives.