willig10

Up front let me state that I do not have first hand experience with this engine but it sounds to me that you are trying to get too much out of the engine too soon. In other words, by reading your post you say the engine started to sag. Were you at WOT (wide open throttle)? If so for how long? I would follow Karol's advice a few posts back as far as adjusting the high end needle to peak RPM then stop. Adjust low RPM to where you have a smooth transition from low to high then fly the airplane and adjust as required after flying. I am not a fan of prolonged running on the ground.

I hope you get it worked out.
Glenn

karolh

A new engine should not be run at WOT for any extended period of time but rather at a mid throttle setting for a few minutes then shut down and allowed to cool for proper heat cycling to take place. As Glenn suggested breaking-in an engine is best done in the air where it can get adequate cooling, just refrain from any full bore verticals and prolonged high speed runs. Tune the engine as suggested earlier and fly the model, then do any tuning adjustments that might be necessary. Also don't try for too low an idle before the engine is fully broken-in. The G20 is a great little engine and if treated properly will possibly outlast you.

Karol

Hircflyer

I was at half throttle when it started to surge up and down.....I agree with you I am not a big fan of ground runs either....I was just burning out the remainder of the tank because I had an appointment and wasn't planning to fly it...

I had set the high end by going to highest rpm and them riching up the needle....low end for best idle and accleration

karolh

Are you sure that the ignition batteries were fully charged as low battery power can give the symptoms you described.

Karol

Hircflyer

Yes, exactly what I thought...after reading CH 's instruction sheet....I charged the single cell 2100 mah li-po battery.....I was using the GT Power A6 charger....of the 2100 mah capacity the charger replaced 232 mah and shut off....so I believe the battery was good.

I dug out a couple of my old recip books from my days of working on General Aviation aircraft....as I stated in original post I replaced the stock ignition with one from CH....the stock pickup is a fixed assy however the CH pickup is adjustable....so I am thinking that I may have mis-adjusted the firing timing....a to far advanced timing could cause the engine to run hotter than normal.....which could cause the spark plug to get hot and act like a glow plug....which could explain why the engine continued to run after I shut off the ignition.....

I haven,t had a chance to recheck yet....other priorities maybe on Saturday....

Does that sound like a reasonable explanation to you?

Thanks for your reply

karolh

Having a gas engine continue to run after the ignition has been turned off indicates some big time pre-ignition, which is very unhealthy for the engine. Do a re-check of the timing bfore you attempt to run it again.

Karol

Hircflyer

Planning on it ...thanks

AA5BY

Please define continued to run after turning off ignition... did it run well or ran sputtering?

Hircflyer

It was running at half throttle when it started to suge and then slowed to less rpms than where it was previosly running. It continied to run at less rpms and would not respond to any throttle movements....the rpm was not constant it would rise and fall but never return to the higher rpm when the episode started...as I stated shutting off the ignition had no effect and engine shutdown was only accomplished by pulling the gas line from the carb.

It was not sputtering but running at reduced rpm....It also sounded as tho it was laboring....

AA5BY

A possible explanation though probably only remotely possible is that an error was made when connecting up the switch harness. If the switch harness were looped inadvertently and the battery connected direct to the ignition and the battery ran low, it would explain a lot. A G-20 will go to low throttle and not rev but remain running when the battery gets low. Of course if that is what happened, turning off the switch would have no effect.

Gasoline engines when running on other than the spark plug usually detonate because of overheating or carbon deposits glowing but when they do, they fire too early or late and without consistent timing to run smooth at any rpm.

Hircflyer

I appreciate your thoughts, however as stated, I oringinally thought the battery had run low....but when I charged it it only 235 mah had been used from the 2100 mah battery...

Antique

My Feedback: (4)

A gasser won't run with the ignition disconnected unless it's melting down inside, in which case it's no longer usable...

AA5BY

The explanation will be interesting. I was just wondering what the result of wrongfully filling a gasser with nitro glow fuel would be. Would it run but overheat and continue to run without ignition in a grossly overheated condition?

The only other thing that comes to my mind is if the switch were faulty and not opening or a capacitor were introduced in an attempt to bypass ignition noise. The wrongful use of a polarized cap would energize the ignition for a short period after the switch was opened. This might not be noticeable with the energy hungry stock ignition that would drain the cap quickly but if the ignition were changed to an RCXl unit, ignition might be provided for a short period after the switch were turned off depending of course on the value of the cap.

My apology for raising the bazarr possibilities but this is an unusual scenario.

Hircflyer

I'm with you I thought it would be toast also.....................but hey guess what?

I went to field today ....gassed up the airplane....checked the voltages on all the batteries.....went to full choke, turned on the ignition, third flip engine popped, opened choke , third flip and engine was running....

let it warm up at idle for several seconds....accelerated to full.... engine never missed a beat sooooooooooooo I figured hey why not! I taxied to runway and took off....airplane went down the runway and took off just like it was supposed to.

Ten minutes later landed, engine never missed a beat....what a great little engine...!!!

Gee! all I did was recheck the timing guess what it was close to 35 deg!.

The CH pickup mounting bracket has slots where the mounting screws attach to the engine...evidently when I set the timing the first time it must have moved when I tightened the screws down and me the big dummy didn't recheck it.

set the timing to 28 deg this time and it starts and runs perfect....

betca those cheapy other engines would have been totaled with that abuse....

Thanks to all

I hereby confirm that I will always double check my work henceforth

karolh

Make sure you continue sleeping on the side you did the night before you switched ignitions are you are one lucky so and so. Glad it seems to have turned out okay but just to be on the safe side it might be a good idea to have someone experienced in small gassers pull the jug and take a look see.

Karol

Hircflyer

Yup I think so also....I will keep a close eye on it......back in the day I replaced jugs on R 2800 engines when I worked Dc[6 aircraft....I think I can pull the jug on that little 20cc...

Thanks

karolh

How is the G20 behaving, hopefully all is well with it.

Karol

Hircflyer

Running like a fine wooden watch....no seriously it is running fine, many flights and seems to be getting stronger every flight.

karolh

Well after several gallons of 90 octane pump gas with Red Line at 40:1 my G20 timed at 28 deg. on an RC exl ignition is no closer to attaining the magical figure of 9,000 rpm spinning a Xoar 16x6 prop so many folks talk about. Not even the use of an after market side dump muffler at my club's field at sea level which gave a significant increase, much less at my home field at 3,000' has it ever happened. Only the use of a mousse can muffler and header pipe combo did it attain and exceed 9,000 rpm. I'm not complaining as the engine gives more than enough power for the models I fly and the 8,400 rpm it gives on a SPE 26 lightwweight side dump muffler is more than enough for me.

Karol

Iflyglow

My Feedback: (79)

Karolh,
Try a Piston ring from Frank Bowman like I just installed. I am also running the same ignition and timing setup as you are. I just modded the stock muffler by removing the stock baffle/pipe, and brazing in a 3/4 piece of thin wall tubing. The difference between his ring and the Stock ring is night and day. After 3/4 of a gallon of 91 octane/32:1 Penzoil Air cooled, I am getting 9,400 steady with a APC 16-6, and have seen as high as 9,480 flash on the Glow BEE tach. I will try to snap some pictures today. The compression is noticably better, than the perfectly fine stock ring, and actually felt stronger before I even ran it in comparison. The engine has a noticable thump when you turn it over now. I am sold after this last mods, and cannot believe that I waited that long to do it.

http://www.rcuniverse.com/forum/m_91...tm.htm#9107979

AA5BY

Very interesting results on the change of the ring. karol, as no doubt you know but I'll remind, all props are not created equal. Recently I compared two 16x6 props on a G-23. The wood Zinger produced 8300 and the APC 9200 with an occasional sighting of 9300. That is a 1k difference in rpm though who knows what if any thrust difference as I've not flown both props yet. Both of my G-20s run about 8900 on an APC 16x6.

karolh

Iflyglow,

My engine runs great with loads of compression so I'm not too sure that changing to a Bowman ring would make that much of a difference. What increase in rpm did you notice with just the ring change in your engine.

AA5BY,

You are so very right that all props are not created equal, as it was when I made the transition from glow to gas was when I realised the vast difference there can be in the performance of props of similar specs. On my G23 a Xoar 16x8 spins at 8,300 at my 3,000' elevation and though 300 rpm less than a similar size APC, outperforms it in flight. My G20 spins a Xoar 16x6 at 8,400 and while this figure might be down on what others achieve, my engines run very well and give more than satisfactory flight performance to my models.

It would be interesting to see how your model performs on diffent brands but similar sized props, so please keep us posted on that.

Karol

apalsson

My Feedback: (1)

I see a lot of references to 16x6 for the G20 but all seem to run in an RPM band that's higher than I prefer (over 9,000rpm)
What about a larger prop, even an 18x6, how does this engine handle those?
Does it have enough torque to drive those props properly?

Antique

My Feedback: (4)

18-6 Mejzlik 8000 or more with a non restirctive muffler....7000 feet ASL..
Don't anybody tell me they won't, I have run a FEW,

apalsson

My Feedback: (1)

Thanks Ralph,

I had a suspicion they would work fine! I just bought one of those engines for a H9 Taylorcraft and didn't like the prospect of glow-engine type prop speeds.
I might try an 18x6 Biela that I have floating around somewhere