JIMARRINGTON

I just replaced a walbro carb on a Quadra 35. The old carb did not have a choke. The new one is an 11mm walbro carb with a choke. This is my first gas engine and I have no idea what the initial needle settings should be or how to adjust it afterward. Any advice? By just playing around with it on a test stand, I did get it to run some but did not really know what I was doing.

Thanks
Jim

warbird lover

Hi Jim

There is a good article at the following site that might help you.

http://prme.nl/forum/viewtopic.php?t=10


Warbird lover

ram3500-RCU

My Feedback: (221)

I like to start with about 1 1/4 turns on both needles.

Starting.............Choke on, switch on, full throttle on the radio (this is important), prop till it fires (it will stop because of the choke), choke off, throttle set to idle, prop till it starts.

Keep it running and let it warm up a minute or so (you can not adjust a cold engine). Now, I run it on full and lean it for maximum RPM, then richen it 300 RPMs or so (about 1/8 turn rich), then idle for a few seconds. If it slowly sags, the idle is rich, adjust for a smooth constant idle. Now advance smartly, if it hesitates, you are too lean on the idle. Make all your adjustments no more than 1/8 turn at a time, of you will be chasing it all over the place. If you hear it barking in the midrange, nean out the top end a little till you have smooth transition and no detonation in the middle.

Keep in mind that adjustments will likely be needed with different props, large temperature changes, and type of oil used. But from here, all these adjustments are minor. Gas is the bomb. You will like it once you figure all this out.

Rcpilot

My Feedback: (78)

I tune as most guys do. High end first. Richen 300RPM.

On the low end, I am a bit different.

High end is tuned:
Back down to 1/2 throttle-- listen for burbling
No burbling? Back down ONE click. Listen for burbling.
No burbling? Back down ONE click. Listen for burbling.

Burbling? Shut it down and lean the low end just a TEENY bit. Less than the thickness of a screwdriver--just a tick.

Now start and run to full throttle. Back down to 1/2 throttle.

Back it down ONE click. Listen.
No burbling? Back it down ONE click.

Keep backing it down ONE click at a time and note the position of your TX throttle stick when it starts to burble. Shut it down and lean the low end a teeny bit.

Start it up and run to full throttle.
Back it down to 1/2 throttle. Listen

You keep backing it down one click and when it burbles, shut it down and lean the low end.

It takes 1/2 hr to do it like this. But, eventually, you'll get the low end leaned out so it will idle from 1/2 throttle all the way down to slow idle without a single burble or hiccup.

Now let it idle for 1 or 2 SOLID minutes at idle. Advance throttle in a smooth manner--no "flicking" the throttle stick. Thats for rookies. Just run it up to full throttle smoothly. If it will transition up to full throttle after it just idled for a full 2 minutes--then it's done. Go fly it.

If it hesitates, you might have gone just a tick too lean. Richen it up 1/16th turn on the low end and repeat--let it idle 2 minutes and advance throttle smoothly.

A guy in Pueblo, named Tony, taught me this. It works on most every gasser I've ever touched.

ram3500-RCU

My Feedback: (221)

Good post and sounds very thorough. You are right about small increments. I see a lot of guys trying to adjust them as if they were working on their 4-strokes. Very frustrating when done this way.

pe reivers

RCpilet,
Because the low needle is active from idle right up to full throttle, but the H-needle is active at full bore only, it is better to start tuning at idle, then High. Back to final idle again, and final High.
That way, once the H-needle is set for best performance and backed off slightly, you are 80% in tune.

The rest is fine-tuning according to your system for which you need to fly as well. This will get the Idle/High ratio just right.

JIMARRINGTON

Having trouble getting it to run. I started with the needles set both at 2 full turns out. With choke on, it will start and run for a few seconds then choke down. Turn off the choke and it will start with throttle open full and run at full rpm for about a second or two then die. Will not fire again until choked. Then same procedure. So to me it sounded like it is not getting enough fuel. I jockeyed needles back and forth for a while same results. I opened both needles up to 3 full turns total then same choke procedure then with choke off, it ran for about a minute and a half again at full throttle. Just long enough for me to pick up my tach and take some base readings. With a MAS 18x10 I got arount 8k rpm then the motor died and back to the same as above. I also noticed that there is a plastic ring under the flywheel that seems to turn at times. Does not seem to affect running though.

Any suggestions?


Thanks
Jim

pe reivers

How new is that carb? If it is an old new one, the rubber membranes may have hardened and it will pump nor regulate.
However, I suspect that the carb housing pulse hole does not line up with the pulse hole in the carb manifold all the way down into the crankcase. Also tha gasket may be damaged such, that pumping pulses cannot reach the carb.
For good measure, check the internal fuel strainer for cleanliness (underneath the cast carb cover). If dirty, improve your fuel filtering.

JIMARRINGTON

Pe,

You were right. What clued me into the problem was the statement that someone would flip the prop until the fuel came up from the tank. Mine would not pull fuel from the tank without using the spring starter. So I got to looking at the carb mount. What I found was that the new carb did not line up properly with the notches on the intake manifold. Pulled the whole thing off and took a razor blade and trimmed the notches until the carb fit properly. Screwed the whole thing back on and hand flipped the prop. Now it will pick up fuel from the tank with just hand flipping the prop. Keep in mind that I have it mounted inverted on a test stand. Also, just a pushrod run to the trottle and there is not an idle stop on the carb. Anyway, with the 3 turn settings, she fired on the first flip with the choke on and ran for a second or two. Turned off choke and and she stared and ran on the 3rd or 4th try. Ran and ran. Only had about a 1/4 tank of fuel in my tank so it didn't take long to run it all out. Refilled the tank and away we go again.

This time I stared checking throttle response and idle. Hard to set a low idle as I am operating the throttle by hand. If I close the throttle all the way, the engine will die. I like it this way, that way I can set the idle with the transmitter when in a plane and can kill it with the transmitter throttle kill switch. The 3 turns on both needles were pretty close. A tad rich on low end as it would start burbling at 1/2 throttle or less. So leaned the low end 1/8 turn and richened the high end 1/8. Started her up again. Running real reliably now.

Think I am pretty close now as with the MAS 18x10, I can get about 1800 on idle and 7200-7300 top side with just a little burble just under half throttle with perfect transition. Does his sound about right for this motor? If my calculations are correct, this ought to pull the Midwest Texan I am restoring fairly nicely.

Thanks for the input guys.

Jim

pe reivers

Advise:
for the first tuning stages, leave the idle stop screw in place and switch off the ignition to stop the engine. It makes setting up the engine so much easier, especially the idle adjustments.

sodbuster 1

The plastic ring you see spinning behind the flywheel is a points dust cover that is NOT supposed to spin. There's a molded tab on it that should locate inside a notch in the cranckase casting to keep it from spinning. You can get a replacement from B&B Specialties just do a search on the web. Dicks been around for a loooooooooong time and knows anything there ever was to know about Quadras.

Flypaper 2

Usually the Q 35 runs an 18-8 and the Q 42 runs the 18-10 ..But.

arobatx

Pe has a good point....I've started with the high and I've started with the low. If you are careful and remember that the low circuit affects the mixture throughout the range, you'll succeed. I know many folks will set the high for max rpm minus a bit, then tune the low as lean as possible while maintaining a nice smooth transition, but then never return to the top to retune. This often leaves them LEAN on the top end. And unfortunately, these are the same folks that haven't yet learned the benefit of proper cooling. These two problems make a short life of your engine. Please don't forget to go back and forth between the high and low ends, several times if need be, until you are confident.

Chad