tinsink

I could use some help as I am new to gas/glow conversion engines. I have a Poulan 25 cc from a weed trimmer. I am converting it to gas/glow. It has a diaphram fuel pump looks to be powered by the crankcase pressure. It also has 2 lines from the tank to the carb. It is a Zama Carb. Is this set up with a feed and return line? There is one line larger in diamaeter than the other. I don't think it is for pressurizing the tank. Further there does not seem to be a vent line to atmosphere from the tank and I can't find a vent hole in the tank, maybe I don't know where to look. Anyway, when I set up the tank in the plane should I run muffler pressure or just vent to atmosphere and let the pump do the pressurizing.

Antique

My Feedback: (4)

There is no pressurizing anywhere...The larger line in the carb is the fuel inlet, the other is for a remote primer bulb....Close it completely....The fuel system is a line from the clunk in the tank to the carb, and a vent to atmosphere in the top of the tank....
The carb has a pump function that pulls fuel from the tank....The tank location is optional, the carb will pull fuel from anywhere in the plane regardless of height...

av8tor1977

My Feedback: (6)

This has nothing to do with how it installs in the airplane, but just for your curiosity. The vent in the tank on the original installation is usually a tiny rubber flapper valve in the fuel tank cap itself.

AV8TOR

rangerfredbob

My Feedback: (13)

for the in plane vent line, have it wrap around the fuel tank at least once to keep fuel from spilling if you tip it over in the pits to do something... and have it exit outside the plane somewhere

tinsink

thank you all for the information. I will cap off the primer bulb line. I assume I just leave the primer bulb where it is. Do I keep the choke or get rid of it and simply put my finger over the inlet to draw fuel as in a glow Engine?

By the way, I purchased a couple of glow plug/spark plug adaptors and I am not impressed with the design. It has no place to grip it with a plier or wrench in order to remove or tighten the adaptor into the engine. I had to file flats into the outer diameter. Further, the glow plug sits flush with the top of the adaptor, it is way up inside the threaded section for the plug. i.e. it does not sit where the spark plug sits. This lowers compression and puts the heating element in an isolated area away from the cylinder making a bad situation for heat at the idle. I'm going to make my own the next time and I may have to make one if this doesn't work out. But they were only $8.00. Oh well.

aero nut

tinsink buy the one from horizon hobby the brand is Zenoha and they are very well made!

av8tor1977

My Feedback: (6)

Yes, the one from Horizon is better. Also, yes, leave the primer bulb on and just ignore it. In your case, I would leave the choke on the carb. In cooler weather in Conneticut you will probably find that the engine will like to run at half choke for a while to warm up, at least on the first start of the day. Further, engines running Gas/Glow take a bit longer to warm up as they inherently run cooler than straight gasoline engines.

That is something for everyone to remember as well when tuning your engine. Make sure it is fully warmed up before adjusting, and that can take a little while, even in the summer.

AV8TOR

tinsink

The Horizon adapter looks much better, however, I don't know if the plug actually recesses into the adapter or if it rests at the same level as the other ones. My goal is to place the glow element in the cylinder at the same location as the spark gap. This should help with the low end idle. Further, I think that in order to make this happed I will have to create a tool to tighten the plug. The tool will have to be just barely larger than the major diameter of the glow plug. this is required because the recessed hole needed in the top of the adapter must be just larger than the plug diameter to insure sufficient material for the outer thread casing.
If anyone knows of such a tool please let me know as I do not want to reinvent the wheel.

av8tor1977

My Feedback: (6)

The Horizon/Zenoah adapter places the glow plug in approximately the same position as the spark plug as you want it to be. (And as it should be.)

A standard glow plug wrench will JUST fit, but it's tight and it doesn't fully engage the hex. I just use a 1/4" drive socket, ground down on the outside to fit the recess.

Another way to do it is to make your own adapter out of an old spark plug. It's a bit tricky as the shell gets pretty thin as you mention, but I've made a number of them. After gutting the plug, I braze the end shut, drill out the internal recess for socket access, mill the braze flat in the recess for the glow plug, and then drill and tap it for the glow plug. All in all a lot of work for a part that's available for 10 bucks... You will also need a special tap, as glow plugs are a somewhat rare 1/4" x 32 thread...

AV8TOR

hollbrow

You guys sure that a glow plug is 1/4-32 ??? The ones I have look to be 1/4-24 thread.
32 TPI sounds awfully fine. I will have to locate my thread gauge.

av8tor1977

My Feedback: (6)

Hmmm, I could have messed that up; and it could be 1/4" x 24. I am not at home to double check for you. I do know it is not the more common 1/4" x 20, nor 1/4" x 28....

Do you have a thread gauge to check?

AV8TOR

hollbrow

I think that 1/4-32 is correct- I dug through a bunch of stuff and came up with my thread gauge- and that is what fits the closest.
One thing that led me to question is that I have one of those cheap 'glow plug wrench' things that looks like a little tire lug wrench- it has threaded spots to store spare glow plugs in the handle of it- I tried a 1/4-24 tap on those threads and it threaded right in with a good fit- felt 'right'- but when I threaded my glow plug adapter that I made with the 1/4-24 tap, the glow plug feels 'wrong' in it.

I think it's one of those situations where it is very close- but not exactly it. That was a trial adapter anyhow- I'm just experimenting with trying to come up with the best way to make a few of them- I'm gonna order a 1/4-32 tap and try again.

Anyone know where I can buy a 14mm die to thread the 'spark plug' end of an adapter? Or know the correct change gears for a mini lathe to turn the threads?

I haven't had the greatest luck starting with a spark plug- by the time I get the porcelain insulator cracked out of it- it looks like I beat it with a hammer- which I did.

Anyone know a good way to remove the porcelain?

av8tor1977

My Feedback: (6)

First, wear eye protection.

Then lay the plug on the flat of your vise, or an anvil, and smash the porcelin part of the plug above the plug shell.

Then firmly mount the plug in your vise with the electrodes pointing up. Bend/break off the ground electrode. Take a punch, and carefully tap the center electrode down out of the porcelin. Then lay the plug on one of the flats of the hex on the flat of your vise or an anvil again, and give it a good rap with the hammer, but not hard enough to damage the shell. Do this on several of the flats, but once again not hard enough to make a mess of the metal plug shell. This will usually crack/loosen the porcelin inside the shell, but only after the center electrode has already been removed.

Then mount the plug in the vise again, and keep tapping on the porcelin in different places with a punch and it will break up and fall out.

Once again, it's really all a lot of work for a part you can buy for $10.00....

captinjohn

yup...1/4 x 32 is glow plug threads!

tinsink

FYI
I ran the engine with a 2 stroke plug and 40:1 fuel. It runs OK. Battery stays on the plug with this setup. I have not had time to adjust the high and low idle but I will tell you that through suggestions on other threads I opened hi and low adjustments 1/2 turn before starting. I am off a lot. The engine ran and would accelerate at half choke only. Once the choke was opened full it would not accelerate or stay running at WOT. I believe it is too lien. I will open the high and run it again. By the way, the highest rpm at this seting was 6100. I think I can do much better when tuned. I am using a 16X8 Master Airscrew Classic. Further, the low idle would only go to 3400 rpm. Obviously I will close the low adjustment somewhat. I am shooting for 1800 rpm at idle. After I get some time with a good range of prop speed and acceleration I will remove the stock muffler (very heavy) and replace it with a Bison style muffler. This will be basically an open exhaust, maybe I'll put some steel wool in it. I will adjust the hi and low again and go to the next step- to put a four stroke plug and a good adapter in it and then try some fuel to get it to run without the glow battery. I'm thinking 4 parts gas to 1 part glow with 18% oil and 15% nitro.

av8tor1977

My Feedback: (6)

Save yourself a lot of grief and experimenting and read the Gas/Glow thread here:

http://www.rcuniverse.com/forum/m_12...page_80/tm.htm

AV8TOR