I'm thinking that if I have a diaphram/pumping carb. and using a starter, do I need/want a choke? It's a 3W-50 in a World Models Extra300, mounted inverted, and I'm building it for someone who has no large gas engine experience (I don't have much) and we don't want to flood it, or maybe hydraulic it...Won't just using the electric starter eliminate the need for the choke? If I had to just hand prop it, then I'd seriously consider using it , but...It should start and warm up O.K. w/o it shouldn't it? Thanks.

You will probably be able to get by with out a choke when using an electric starter. If you will choke the engine with the ignition switch on, it will not flood as easy. It will try to run, but wont and then you can turn off the choke and fire it up.
Besides, what if the starter quits due to a dead battery or something?

doubt it would start without a choke. How about a fuel squeeze bottle with a piece of brass tubing on it. Someone should come out with a primer kit with a rubber bulb, somewhat like they use on the chainsaws and weed eaters, then you wouldn't need a choke. Used to make them for snowmachines.

Most people have 10 of them.....fingers. Just place your finger in the carb opening on the walbro card and turn the prop until you feel or smell the fuel on it.
I have the airlow inlet tube on my gas engines to keep more gas going into the carb,I use a cork in the inlet to get the prime.


David

Thanks guys...It's going to be a long and dificult reach to use my finger inside the cowl tho The 3W has a rear carb (Tillotson) and it looks like I'm gonna have to use a servo to actuate the choke. The guy I'm building it for doesn't want to see any choke wire sticking out anywhere, but getting the servo hooked up is gonna be a pain...Guess I'll just have to bite the bullet so to speak, and work out the details, maybe w/ a bell-crank or sumpthin'...

You can get by without a choke, if you solder a nipple to the steel diaphragm cover. That is the carb's pressure regulating part. Put a tube on it, and blow on it whilst starting. Now the carb will pump fuel into the engine like an injection system.
During the warm-up, blow as required.
I had a Quadra equipped that way, and it worked very well with the cylinder in 6 o-clock position (carb horizontal)

A friend set-up his ZDZ 40 with a linkage on the choke that he acceses through one of the front air intakes with a pair of hemostats. You cant see it at all but it works well, except when it comes disconnected .

The engine WILL start with an electric starter without benefit of choking the engine. Been here done this. Remember, the carbs fuel pump operates on crankcase pressure pulses, turning the engine over with a starter will provide sufficient pulses to bring fuel up.

starter motors on big gassers ?
whee- sounds a bit dangerous to me .
I prefer a simple servo/choke setup -

once you learn the engine - uo can typically flip the prop with choke on - then as soon as it burps - flick the tx switch and the choke opens and the engine runs
Once I got used to this - I was hooked - it is so easy -
here is another choke:
fella walks up to a lady on 7th Ave and flashes her .
She looks him in the eye and says
"you call THAT a lining?

Damn, even with 10 of them, I sure would hate to have to take the damn cowl off each time I tried to start it. And if it took to long to put the cowl back on, would it loose prime so that I'd have to do it over again?

Seriously, I'd put a choke on it, and power it via a servo for easier starting if the carb is in the cowl or is hard to access the choke lever. This can then also act as a secondary kill method should the throttle linkage foul.

I put the choke servo on my snap roll switch (since I never use it for snaps). I hold the button in while flipping the prop (choke on). As soon as it pops, I let go of the snap switch (choke off) and it just keeps on running. It saves me from putting my hands in the prop for the three or four extra flips after it pops to get it running. And the more time my hand is out of the prop arc is a plus in my book. Its simple, fast, and safer IMHO.

Thanks a lot for all the replys guys...I spent some time studying the situation and last night I figured it out. I mounted a servo to the top of the engine mt. box, above the front of the tank, and used a bell-crank. It works great...I guess after all the previous work, I was getting a little tired of farting around with things (gettin a little lazy?) The push rod runs foreward from the servo to a 180 deg. bell-crank, then back to the choke arm on the carb. Thanks again! Tom.

Did you mount the servo far enough away to prevent ignition interference feed back to the receiver?

I hope so... It's about 4-5" away from the module, and I have the wires seperated as far apart as possable...If I run into interferance problems, can I install an electronic "choke" in the wires to squelch it? Or am I gonna have to find a new home for the module??? What's the rule of thumb for this sorta thing?

Try it and see if it works, most likely it won't be a problem.

Ther are alternatives such as optical isolators and fiber-optic isolators in the event you have a problem. Chokes won't help!

Just choking?

Ba-dum-bump (rim shot) But seriously folks...Thanks a lot for your help guys...It's almost ready to fly, so we'll know soon if we get any interferance. Thanks for the tip on the opto isolator Mike. Are some Rx's more or less succeptable than others to ign. interferance? I've been told that Hitec supreme 8ch. rx's are a little better in that respect? That's what we're using...

Do a range check with the engine running and without the engine running and see the difference before you fly it Shouldn't be more than 10% difference.

DavidM. I used your cork idea today. I have a G38 (scale job) who's carb is without a choke. The cork worked great! I got 8 for two bucks, so even I can afford to lose one or two. Wonderful clarity of thought in your problem solving. Thanks.

Did anyone try squirting a little gas into the exhaust? With a fuel bulb and a short length of gas line you can insert the hose into the exhaust up to the piston and squirt it easily. Works for me!