Do not hone the cylinder, it could ruin it. Take the cylinder off and inspect it, the piston and ring. You should be able to see the problem easily, if you need help interpreting the condition of your parts you might take some pictures and post them. You could just throw a new top end on and be done for just under $100, parts are in stock. But with only 3-1/2 gallons through it I would assume it should still beunder the warranty offered by all authorized DLdealers.</p>

Like he said. A stuck ring is really easy to see. Maybe even a defective ring from the start?

I am getting ready to hook up all the linkage for the motor . Does everyone remove the return spring on the throttle ? Is it extra strain on the servo to leave it on ?

A friend told me to get some carbon rod with Ti ends . So I got 4-40 carbon rod with Ti ends to glue on .I was told not to use a metal rod cause of transfer of vibration and signal to the servo . But whats the diff. with a stiff carbon rod . Key word "CARBON" . I have nylon balllink connectors I was gana use too . What are all you using to link the throttle to the servo ?? I got a HS-5625mg for the throttle servo . I am questioning my friends advice cause he has gone through throttle servos so he must be doing something wrong . He unhooks the throttle return spring and I think he uses a standard analog MG servo .

Edit:
Also does anyone replace the throttle arm on the carb with something else ?My HS-7955 servos came with 1" alum. arms that could work but I would have to modify it somehow so it won't slip on shaft . I haven't figured anything out on that yet other that making a mold somehow to fit in arms spline area .

All you had to do was look up the page a little ways. The push rod doesn't realy matter use what you want I have used golden rod. steel pushrod and my last setup was 2-56 threaded rod with carbon tube epoxied over the rod. with 2-56 ball links. Snip the hook off but leave the spring in.

Remove the 4 screws that retain the cylinder. Carefully pull the cylinder up from the case. You may need to use a very slight twisting motion for the cylinder to break loose from the gasket. Try not to tear the gasket, and do not press on the piston ring during the cylinder removal. Once the cylinder has been removed use a paper towel to block off the open case top. Then view the piston and ring. If the ring has stiuck it will have done so on the exhaust port side of the piston. Easy to see because it will be flush with the side of the piston while it will be sticking out from the opposite side of the piston. If it appears struck, apply light pressure to the side sticking out. Any resistance of the ring to pop out the other side means there is a carbon build up around the ring and groove. Carefully remove the ring without bending it upwards. They are brittle and will break easily if forced to bend. Carefully clean the top of the ring groove, the top of the ring, using an exacto knife, and the back of the ring using an exacto knife. Flush debris away with a can of WD 40 and a spray tube. The best tool you can have to clean the ring groove is a broken ring but I don't expect you'll have one of those around. Be creative but don't gouge the ring land (top or bottom) with a tool while cleaning away carbon.

Reassemble by first getting everything wet on the piston and inside the cylinder with some ore mix oil. Be sure to get some on the roller bearings at the carnk and the piston wrist pin. If you have the tools, the torque spec for the head screws is 35-40 inch pounds. If not just slightly more than snug tight is close. Don't white knuckle the hex wrench because you'll strip the threads out of the case. Tighten the screws like you would the lug nuts on a car tire. Cross pattern.

I have a DL 50...it was running fine the first 2 gallons when I was using the Fuji oil fuel mixture.  After changing to the Zenoah oil fuel mixture, I been having  a very hard time starting the engine.  The engine would sound like it back fires with a loud sound coming out of the muffer and that is it.  It will not start.  Has anyone had or seen  this  problem before?</p>

Richen up the low needle. It's possible that it's lean after the oil switch. If that's not it check your timing.

Thanks Joe ap,</p>

What do I need to do to check the timing?  Thanks</p>

You will need a piston stop or a good wood doweland a degree wheel to check the timing, but if you have not messed with the hall sensor there should be no need to check it, if the engine ran ok before. By chance have you checked the ign batterys?

That's why Ialmost didn't suggest checking the timing. If it ran before then it may just be a lean low needle. Hard starting and backfiring are lean low needle settings. They are alsoignition problems. What voltage are you running on the ignition? More than 4.8V packs can burn these things up.

See the bottom of the following web page for timing instructions.

http://www.ch-ignitions.com/CHinst.html


Timing degree wheel.
http://www.ch-ignitions.com/timing.html

Muah, running one at 5.8v 200+ flights zero issues. Rated 4.8-6v means more something like max 6.x for a short duration on a fully charged 5S NiMh.

4.8-6 volts, no more, no less, no problems. A fully charged 5 cell pack can be over 7 volts.</p>

You can run anything you want. Doesn't matter to me. I only run 4-cell NiMh.

Good for you But you claimed the DL50 iginition can die feeding it over 4.8v which is incorrect. The ignition module of the DL is an RC-EXL v2 that works fine up to 7 volts so also on an unregulated 2S A123 6.6v <u>if you keep the rpm below 8000</u>. The manufacturer however recommends using a diode which I did. Either the 400x or 500x series is fine and brings the voltage down to 5.8-6v depending on the load/rpm.

4.8v input voltage gives an output voltage of 12kV
6v in, 14.1kV out
7v in, 16kV out.

So yes, a higher voltages gives a hotter spark.

My understanding of capacitive discharge ignition is that the muliplication of input voltage by an a fixed transformer ratio to get the output is not so.  Rather it is energy in joules that get transferred to create spark, and not simply voltage. </p>

The output voltage decays very rapidly.  The capacitor that dumps the charge also has an impedance that is rpm (frequency) dependent.  In other words, supplying a higher input voltage only provides a 'slightly' hotter spark.</p>

Does your carby have the longer arm installed? (ie the yellow composite ones that comes with the engine, or bolt a hitec servo arm or similar to it) if you are just using the small metal arm that is fitted on the carby you will have very little resolution, and a slight movement of the servo will give a large movement on the carby if you get my drift.

Throttle curve as mentioned is a good idea also to help smooth things out a bit too.

Cheers

Scott.
[/quote]

Dude , i'm gana call you Einstein from now on . Thats cool stuff there . Thanks

Thanks Paul , Yeh if I would have looked back about 10 posts dlenginesaustrailia had those picks too . Thats a good setup .

thnks

You said it yourself. The transformer has a certain ratio. Higher input voltage equals higher output voltage. Almost linear since the efficiency drops a bit (8% at 7v compared to 4.8v), see RC-EXL manual.

I have been running A123's on the rcexl ignition for two years now with no problems.

mstam1971what do you mean if you keep it below 8000rpm?? I know my engine unloads to more than that in the air at WOT

Max 8000rpm is the manufacturer's recommendation if the ignition runs at 7v. So you should be fine (obviously). I believe tha max allowed rpm for the DL is 9000. At that rpm a regulator or diode is a must.

Gotcha

Anything more than 5 volts is just wasted in heat. It's not needed.

There's only about 8% loss in efficiency over 4.8v at 7v. 5v is absolutely more than fine. For my EF Exra I just wanted troublefree batteries that have a consistent voltage and can be charged fast. Answer = A123. I don't want a mix of NiMh and A123's in my planes. 1100mah A123 ignition is good for 8 flights, 2300mah Rx 5.9 flights. I rarely do more than 5 and if it happens I can balance charge them through the charge receptacle at 4 amps. Especially on the Rx, NiMH can vary in output voltage. A123's stay at 3.3v up to 98% discharge. The new gen Hitec digital servos can deal w/ up to 7.4 volts.

It may not be needed but when those of us use A123 batteries then its nice to have all the batteries the same.

Untill the instructs say its ok to use more than 6 volts i'm going to stay with the 4 cell packs, at the moment I'm useing a 1400 MA 4 cell that holds up great I made myself from ni-cads batterys. I run the plane on A123's and I can't see what the big deal is if they don't match the Ign batteries unless you try to charge them with the wrong settings, but I take my batteries out before I charge so I doubt that will happen. I had a new 1800MA 5 cell Ni-MI pack that I wanted to use in this last plane but I wasn't to sure when I saw the 4.8-6 volts on the side of the Ign box.,also the instructions says not to run over 6 volts.  Like Jody said a 5 cell can go way over 6 volts at full charge so why take a chance on letting the smoke out of a good working ign box.</p>