Help starting 3w 75
Have same problem as Lowpass 202 .Seem to have to prime forever,20 30 flicks still nothing,all systems are good battery,switch ignition just back from 3w for check all ok, just cannot get fuel into engine, there is fuel in lines up to carb,but does not seem to get pulled through carb into engine ,this is a motor with only 6 flights on it, has been standing for a year.
My back and arm cannot take any more it should not take all this effort,have not been able to fly my last 2 outings to the field,and am getting fed up with this, PLEASE HELP

Same problem. So, did you pull the reed block out and eveything looks good?

Hi rcdude
Yes pulled out reed valve, looked ok,but really dont know how it should look.Will not put in model till i have this sorted,sick of turning up at the field and not getting to fly.

It`s frustrating isn`t it?!
Well, it think I figured out my problem, It finally set the engine and a jar with some gas on my citchen table and did some research.
The latest problems seem to have been my own ignorance, just didn`t understand the engine.
First of, I have been draining my tank after every flyingsession whitch of course allso will empty the feed line. When you choke the engine by cranking the prop by hand there is very little pumping going on, seems the pump wont work on that low prequency. So what you want to do is rock the prop back and forth between compressions as fast as you can by the spinner, that makes for much better priming and will fill the fuelline in when you do it about 50 times. If you allready have fuel in the line I would try 15 or 20 times, it`s still a lot easier than cranking the prop all the way around.
If that doesn`t help, check your reeds either by blowing air into the exshoust port with the piston at bottom dead center or by rocking the propp back and forth and listen for the valves to open and close.

Good luck, hope this helps!

Best wishes for the new year and the new engine
"the bonehead formerly known as Lowpass"

glad all is well now

rcdude7
what do you look for in the reeds?

For all of who have trouble getting the engine to draw fuel. Use a three-line tank. One line goes from the felt clunk to the carb (no breaks, no T, no filler, no chance for an air leak). One line is the fill/drain that goes to the bottom of the tank. One line is the vent (at the top of tank). After you are done flying, just drain the tank. The feed line to the carb stays full of gasoline because the diaphragm pump makes a seal. When you go to start the engine, gas is already in the carb and in the line - easy choking and the diaphragm pumps better when wet with gas.

It should NOT take that many flips to draw fuel from a tank, through two feet of tubing, to the carb. My 3W 100 with Tillotson carb takes about 5 flips. I suspect there is another problem:

1) when the choke is closed, it should be totally closed. If it is cracked open, the fuel draw will be poor.
2) if the diaphragms in the carburetor are stiff or leaking, the pumping action will be much reduced. this is a fairly easy DIY repair.
3) If the screen in the carburetor is clogged, this will reduce in low fuel flow. Also an easy DIY repair

I have dismanteled carb, blew into carb through fuel nipple, air goes through no prob.On checking pump diaphram it is flexible and no damage,this is a motor with 1hr run time, so all looks to be ok

When you blow into a gas carb where the fuel normally goes, you should NOT be able to blow any air into the carb. A properly working gas carb will not allow anything to pass through it (air or fuel) unless it has at least 10 or 20 psf (not possible with lung power). The carb has a regulator that prevents fuel from flowing unless there is a vacuum from the venturi. I think you may have found a problem here. The regulator is on the side of the carb opposite of where the fuel comes in. It is characterized by a metal cover with a hole in it. remove this cover to expose a teeter-totter device with a small needle going in to a hole. the spring on the teeter-totter holds the needle valve tightly in the hole. No fuel or air can pass thru this valve unless the teeter-totter is activated. the teeter-totter is activated by a diaphragm that is sucked down by the venturi.

Im sorry i meant i had blown intodismantaled carb to check if clogged, if i blw into carb and push diaphram through hole in carb then air passes through

Now you have me a bit confused, the choke will never close completely because there is a round cutout in the disk that provides a small opening even when the choke is closed. Other than that it seems to close well.
The screen seems good and the diaphragme is undamaged. Hard to tell how flexible it should be as I have no experience with this..

I`m running an alkylate gasoline whitch comes ready mixed with 2% oil, dont know if you know it but i know many pilots in Norway use it with no problem. I was thinking there is an off chance that this gas along with some long periods of not using the engine might effect the diaphragme or something.

It sure sounds like turbokalli and I have the exact same problem.

Lowpass,
its for sure we have the same problem, had troulble from the start but i did manage to get it to run and was ok but always difficult to start.I am looking foward to sorting out this problem to get in some flying,but will not put back in airframe until sorted.
By the way on my brison i filled the hole in my choke disc with solder,I use electric starter to prime that motor then when i feel it loosen up i switch on ignition and away she goes,50cc. Not poss with my 3w-75 starter not powerfull enough,shouldnt have to do that anyway, looking foward to SWITCH ON IGNITION FLIP MOTOR 3 OR 4 TIMES WHEN IT FIRES TAKE CHOKE OFF ,FLICK AGAIN AND ENGINE FIRES UP, at least thats what they say in the instructions.

OK, thanks for the clarification about blowing air through the carb. Sounds like everything is OK here. With the carb assembled, air passes only when the diaphragm is pushed in. Good. Earlier I suggested to make sure that the choke is fully closed. Most choke butterflies have a hole drilled in them to allow some air to pass. So all I mean is to make sure the choke is as fully closed as it is designed to be. If you use a choke servo, it could be adjusted so that it is almost closed but still cracked open a little. If you use your finger to close the choke, usually, they snap into the fully closed position pretty easily.

One of my buddies had a bunch of "lint" on the carb inlet screen. (this was a zdz 80). It was hard to start (50 flips required) , but somewhat surprisingly would run reasonably well once started. I think you have something similar going on. Is the plumbing from the tank to the carb confirmed to be free flowing? No valves, filters, etc? How about air leaks in the crankcase or carburetor fitting? Air leaks will cause poor fuel draw.

Again, my experience with my Tillotson carb is that every flip of the engine (with throttle cracked open and choke closed) will bring up a few inches of fuel in the tubing. After 4 or 5 flips the engines fires and quits (because of the choke being closed). Sounds like in your setup, there is very little fuel being drawn on each flip of the prop. Can you see this happening?

I have an in line fuel filter from fuel tank to carb,this is reccomended by 3w,after 20 flips i have fuel in the line,just does not draw through carb, going to contact 3w today

Do you have the fuel line on the right nipple on the carb?

Some carbs have 2 nipples coming out. 1 for pressure pulses from the engine. And 1 for fuel.

If you hooked your fuel/clunk line up to the nipple thats reserved for pressure pulses--that could explain the problem.

Not sure if your carb is designed like this or not. Some carbs just have a hole in the base and take the pressure pulses from the cylinder through a machined hole.

Did you take the carb off? Did you put it back on the right way?

If you took it off--and it has the little machined hole in the base for the pressure pulses---then the hole needs to line up with the hole in the reed block or cylinder to get the proper pulses.

There is only 1 fuel nipple,I reasembled the carb exactly as i dismanteled it, as far as i can see evreything is ok have done complete check on complete set up , fuel tank and lines ,ignition system,including battery and switch harness,just no fuel draw into engine.

I am going flying now. I will watch the fuel line after starting with an empty tank. I believe the fuel will draw completely from the tank to the carburetor (about 18 inches) in 4 or 5 flips of the prop. I will report back later today. Yours is taking 20 flips just to get fuel through the fuel line.

My 3W 100 pops after only 5 flips. I use a "T" in the fuel line between the tank and carburetor. So the fuel line between the "T" and the engine generally holds fuel for a while. If your line is completely empty from the tank to the carb, perhaps it is normal for it to take 20 flips to draw fuel to the carb.

Man oh man, just temporarily open your low needle a turn and then try and start the motor. If it's been sitting for awhile then this is the easiest thing to try unless you like pulling reeds, carbs, tanks, clunks and on and on. If the motor was running fine before it will run fine again.

Not to rub too much salt in the wound--but...............





















You could always sell it and buy another engine.[X(]

Just kidding. Hope you get it figured out.

For those still checking this thread:

I had all the same troubles you describe here. I just replaced a broken Reed Valve Cage and put in new Reeds. When I was putting it back together, I noticed there is no gasket between the motor and the phenolic block that the carb mounts on. There is a passage thru that interface that I believe puts the vacuum pulse on the fuel pump diaphram.

Well, I looked at it closely, and it sure doesn't look like it seals very well. Not only might you be loosing some of the vacuum to the pump, but you may also be pulling a leak into the intake. I sealed mine with a very thin painting of Pematex Silicone Gasket Sealer for good measure.

I'll tell you this... After all the troubles I have had flipping my ***** off trying to start this thing, and having to constantly resort to priming, my troubles are gone! I put it all back together, flipped it 10-12 times (it was all totally dry after disassembly) to get fuel pulled up, turned on the ignition, varroom! Choke off, second flip it started.

After that, I started it 14-15 times adjusting the needles. Started every time within two flips without choking. I am now convinced that I was either leaking air into the intake at the block, or not making enough vacuum to the pump, or probably both. It is sweet now. Cold starts, 2-3 flips with the choke on, blappppp... choke off, starts withing 2 flips every time!.