toothpick

Howdy all,
Ive just installed a new RCGF 100cc rear carb. motor into my Extra 260.
I went to give it its first run today and it would "pop" but not start.
Any ideas??

cheers,
toothpick

coralcape

My Feedback: (4)

Popping generally indicates a lean condition. Close the choke and crank the engine a dozen times, make sure fuel is being drawn to carb. Turn off ignition and pull the plugs. Are they wet or dry? I'm guessing dry and if so make sure the choke is fully closed. If plug is wet, check the gap. If OK try a new plug. All above assumes the ignition and fuel are OK and the battery supply for ignition is good. Good luck, red

toothpick

hey. the plugs r mounted at the top of the barrel, not the bottom like DA
it isnt lean. its popping when the choke is on and then nothing with it off.

Super08

My Feedback: (2)

Can you see that it is drawing fuel into the carb? I know I have had a couple of engines that were a bear to start the first time as they wouldn't draw fuel up to the carb. I had to remove the fuel line off the carb blow in the vent and then put the line back on while pinching the line to keep fuel in it. Then I had to give it a good shot of fuel into the throat of the carb to get it to fire. Once it fired for the first time and got fuel into the carb it was good. For some reason some carbs just don't want to suck fuel until the inside of the carb is wet with fuel.

Don't know if this is your problem, but it is worth a try.

toothpick

Ok thanks for that. Ill giv it a shot tomorrow and tell you how it goes.

Rcpilot

My Feedback: (78)

Prime the carb. I've outlined the procedure several times in this forum. Try a search for carb priming.

Tired Old Man

My Feedback: (1)

Top plugs, bottom plugs, they all get wet if you get some gas into the jug. The RCGF 100 likes to start on the "wet" side. At least mine do. The fact that it's getting to pop means the carb is working so the rest of it is simply technique. Listen to Rcpilot and give it a shot of prime if you can access the carb. If using the stock 14mm plug use a .025" plug gap.

cfaw10

I worked on a Chinese 25cc a few weeks ago with the same problem. I checked fuel lines, carb, plug, ign. timing, even swapped out the ign. battery and then the carb. Finally, I swapped out the ignition module and it ran like a top. It was firing when I hand turned the engine to check the timing, but when trying to start it, all I could get was a few pops.

toothpick

OK,
Ive 'shot primed' the carb and still only getting a "pop" with the choke on and a couple pops with it off.

aussiesteve

Hey Toothpick
Call steve on (86) 137 257 54406

You may need to remove the carb and re-seal it around the carb with some red silicone loctite.


yours is an earlier RCGF 100cc

Super08

My Feedback: (2)

Either that or the pulse port is plugged......it can be so many things.

toothpick

Ok, Ive just been outside and played with it some more.
Its not sucking fuel from the tank.
The plugs are getting wet, but i suspect only from the shots i put straight into the carb.

Super08

My Feedback: (2)

Two things you can try

Check and see how many turns your screws are out.
Remove the screws and drip some fuel into the screw holes a couple of times and give it some time to work its way into the carb.
Replace the screws and it should wet the carb enough to get it to suck fuel.


Another way that has worked for me is to hook the fuel pump you use to fill the tank to the vent line.
Pump fuel into the vent line and pressurize the tank.
Loosen the line going to the carb until fuel starts to come out of it.
Ignition off
full throttle
choke on
give it about 10 or 15 fast flips.
remove pump from vent line
try and start engine like normal.

aussiesteve

Excellent procedures Super08

He's trying that as we speak - I just had a long talk with him about it. He is a "younger person".

It seems it is just a difficulty getting that first prime.
At least, I hope that is all it is

The earlier ones can be a real mongrel to get that first prime. Partly because the factory was test running them and leaving them full of fuel in the carb. They have since changed that procedure.

Rcpilot

My Feedback: (78)

"Shot priming" is NOT what I was talking about in my first post. Shot priming by squirting fuel directly into the venturi does nothing to wet the diaphragms. Makes the engine pop a couple times. But it won't prime the carb. Apparently nobody used the search function.


Super08 described the priming technique I was referring too. [sm=thumbs_up.gif]

toothpick

Ok guys i got it going.
it goes very very very nicely.
Thanks to super08 for his suggestions.

happy flying all

aussiesteve

Well done guys
I LOVE RCU

Ok - I'll tell you the full story now

Toothpick is my son

He couldn't get hold of me because I was in transit from there to here so he did the BEST thing - he asked for the world of experience that you guys are.

You guys hit the nail right on the head for him

Thanks 100000000 percent - he just had to get that very first prime going.

Super08

My Feedback: (2)

Great to hear he got it going.

saab93aero

hi guys i was reading how you guys have solved this problem ...... i am running through the same thing now ... mine runs untill the gas tank gets un presurized and then it dies... i dont want to take my plane up untill i get it right on ground .... now my engine is a ryobi 31cc weed eater engine converted by me ..... and i still cant get it to run.... thanks for your help , Ray

Super08

My Feedback: (2)

I am no pro, but it sounds like the diaphragm is shot in your carb that pumps the fuel.

aussiesteve

Yep

you mention the tank is "pressurised". You should have a vent to atmosphere and a line to the carb - are you trying to use exhaust pressure to feed the fuel?

If the tank vent is clear, I would consider the fuel diaphragm this is the most likely place to start- possibly the needle height in the carb too.

Check for leaks around the carb mounting and crankcase - these could appear when the engine warms up - use a good sealing compound.

Start again with the tuning - start at 2 turns out on each needle and adjust in small increments

Tired Old Man

My Feedback: (1)

Do not pressurize the tank on a gasser!

panioul

Hello! I have problem with an old engine too. I cannot start it. Fuel is drown to the carb and if I remove the plug it is also wet. I replaced the spark plug and checked for a spark but I only saw sparks a couple of times. I assuming that the ignition has problem (It is the old style, not electronic, it is like Zenoah 38). If the ignition coil has problem how can I fix it?

Ram Jet

I assume that you have an egine with a magneto. The first thing to check is your plug. If you have a new plug try that and if you consistantly get a blue/white spark across the electrodes you should have solved the problem. Then make sure your points are gapped to manufacturer's specification. Clean the points with a clean cotton cloth dipped in lacquer thinner or any quick evaporating solvent. Even fresh gasoline (with no oil added) will work. If there is still no reliable consistant spark it's probably your coil. If you have an ohm meter you could check the primary coil windings for proper resistance - I wouldn't know the proper value. If you get an infinite resistance reading on you ohm meter the coil windings are open and the coil is bad and need replacing. If the coil checks out OK there is possibly a bad condensor. Condensors hardly ever fail but are cheap and easy to replace.

Good luck,
Bill