I just put together A 42 cc poulan with A new Frank Bowman ring and A 13.MM carb put it on the test stand and I could not even get it to pop let alone fire and run.I changed glow plug and carb even sprayed some starter fluid in it check the glow driver but with no luck so I took it back apart and measured the ring gap with the new ring and it was .018" which I think is way to much.
So the question is is it A scrap engine or can it be saved?

Well, yeah, .018" is way too much gap. The cylinder must be really worn if you received the correct ring. The stock spec is around .003" or so, but Frank actually recomends a gap of zero. An option would be to send the piston and cylinder to Frank and see if he thinks a custom made ring would save the engine or if it is just plain worn out.

If you have a compression gauge, anything under about 70 lbs. of compression makes a two stroke engine tough to start.

AV8TOR

My Echo 21.2 has 120psi. I would check compression second, after looking for good spark. Then if you have both of those, start looking at fuel.

If you just bolted on a brand new aftermarket muffler make sure the exhaust tubes are drilled !!!! Don't ask me why I am bringing it up though !! ha ha

Yeah, 120 is a good number. 70 lbs. is a minimum to even try to start up and run basically. Power would be way down...

AV8TOR

The engine in my post "engine did run goo...but then" had 105 LBS of compression ... but after just 8 oz of Gas/glow , it has a lot more compression now! Capt,n

Well I came up with another engine it is A 40 cc poulan. I took all the things off of my 42 cc and installed them on the 40 and it started and ran good. idles good and revs good so the glow and the muffler was not the problem and also used the same carb.The only thing I didn't like was when I removed the glow driver it did lose A few RPMs ?
Thanks guys I'm putting this on A road runner and will try to fly it Sunday all the guys At the Field are waiting on me because they have never seen A gas/glow run so its all up to me to show these guys all about it and I could have never done it with out you guys and this forum.So thanks to all.

Well, good deal that you got a setup going. The guys at the field are going to be very surprised.

My Poulan 42cc on Gas/Glow also drops a few rpms when I remove the glow heat. That is usually an indication that an engine could use a bit more nitro, but mine runs so good I just don't worry about it and go fly. If you are not using a four stroke plug, it would help to do so.

Let us know how it goes at the field!
AV8TOR

I see the Gas/Glow thread in the forum and plan on reading into it, though it is HUGE and will take a long time for me to extract the needed information, but could you guys help me out by summing up what I need to do to turn my Echo 21.2 into a Gas/Glow. I want to use this engine this way. Thanks.

pretty simple really, get a glow plug adapter, a 4 stroke glow plug, some premium gasoline, some 10% oil 10% nitro glow fuel (usually marketed for big super tigre engines, Omega's is "Super T"). Mix 1 part nitro to 2 parts premium gas. you want the fuel tank set up for gas, a walbro carb (zama's aren't as friendly with alky) and run it...

Perfect, Thanks a ton. I will do just that. I'll post up when I get it done.

Yes I'm running the type f plug. Thanks
Harold

Well We maiden ed the road runner with my 40 cc poulan and the guys at the Field woke right up when they seen how easy it started and how good it ran The only problem I had was it keep wanting to run back wards but I could throttle it way down and gas it and it would cough and start running the right way.Also for some reason I wasn't getting full throttle.I think it needs A little more carb adjustment and possible a bigger out let on the muffler (I only have two 1/2" out lets on it)but all in all it was neat to get it running and fly my chain saw engine.The plane cost me $20.00 the engine A case of beer and the fun we had was priceless.
Thanks Harold

Congrats! Yeah, it sure is fun to watch the looks on peoples faces when you show them one of these Gas/Glow engines...

AV8TOR

What do you guys think about the muffler? as I said it has two 1/2" out lets,is this enough or do I need more?I don't know yet how much my road runner weighs but it sure didn't lite up the sky but it did fly it good.
Thanks
Harold

I would say two 1/2" outlets are a touch too small for that size engine for optimum performance. If noise isn't a problem, I would add more outlet. However, you also mentioned that you weren't sure you were getting full throttle, or maybe the mixture wasn't quite right at full throttle??

Before I installed my little twin cylinder job on my Giant Stik, I had my Gas/Glow Poulan 42cc on it. It is fairly heavy, with heavy duty servos, a smoke system, large tires, etc. With the Poulan, it would roll about 30 feet on takeoff. I could then pull it into a 45 degree climb while doing a roll at about 20 feet off the ground, and then I could pull it vertical. It would then just keep going until I couldn't see it anymore!

Another thing is the prop pitch speed. Many, if not most of us transitioned to gas engines after flying glow powered planes. The glow engines tend to rev a good bit higher than their gasoline counterparts. So consequently when you go to gasoline engines, you have to use more pitch in the prop along with a bit smaller diameter than "normal" to achieve similar performance. A lot of guys (to me) seem to over prop their gas engines. I ran an 18 x 8 prop on my 42cc engine, which many would consider way too small. However, I really liked it's performance. I like to "wing" my engines a little higher rpms than most, but they seem to like it. Keep in mind though, that I don't fly 3D, and I do enjoy a plane that I can cruise around with at half throttle, and nail it for some blazing speed and/or conventional aerobatics when I care to do so.

AV8TOR

I havent read that thread in ages but when myself,av8tor,and a lot of others oposted there if i remember right the first 20 pages or less are the most important.Most basics are there.Dont need to read the whole thing.A lot of the thread was a lot,lots of people testing,ect..and posting results and thoughts.Rangerfredbob said it all in a paragraph.try a 10-11mm carb.That is one long thread just like the [dont forget echo thread].Those 2 threads truly belong to a lot of people here on RCU and i personally thank everyone who participated.Ive learned and accomplished a lot.

Well I have A 13.5 mm carb and I'm running A 18-6 prop I rework the throttle linkage and now I'm getting full throttle but haven't had the chance to try it out again its raining to day.
Some where on here was A really good thread on carb adjustment but I couldn't find it. maybe it needs to be readjusted?I will go back and read those pages again.
Thanks guys I will post some pictures of the engine.also the vent for the diagram was pointing toward the prop and I had not soldered a tube in it yet and run it to the fuse I have since finished that task.

does any one know where the link is to the carb adjustment? I did A search but did not find it .thanks

http://www.prestwich.ndirect.co.uk/walbrocarbs.htm
http://tech.flygsw.org/walbro_tuneup.htm
Try these 2,the bottom would probably be the better one to save to your hard drive.

Thanks for the carb info that will really help.I got to fly the road runner again today and it ran great.I did some work on the throttle. I replaced the linkage on the bell crank and that made it a lot more stable and I now have A full throttle.I noticed at full throttle it had A little putting noisy? I guess that would mean it is to rich? and that I would have to open up the high speed needle A bit more?
Thanks Harold

forgot to mention I weighed the plane to day it weighs 14pounds 10 oz. and has the 40 cc poulan on it.
Harold

If engine seems rich...turn the Hi speed needle in (clockwise) to lean it out. Just a tad at a time. When top RPM is reached ..turn it a little the other way to drop the RPM about 100+ Sounds like your getting there. Capt,n

Thanks Captain for the info.The engine that I have looked like it was brand new and not run that much and when I took it apart I found that the carb manifold was loose and the gasket was blow out,so I'm sure that was the reason for getting rid of it. So maybe this engine isn't even broken in all the way yet?Just A thought.
Thanks to all
Harold