soarrich

My Feedback: (98)

If you wanted to you could screw the H needle all the way in, start the engine, then by adjusting the L needle get a pretty good tune on the carb between idle and 3500 rpm. You can get the engine to run from idle to almost max rpm on only the L needle, it would just be overly rich on the low end.

The way I tune a new engine is to turn both needles out 2 turns, start the engine and then using the radio get the engine to run 3500 rpm. I then lean the L needle, as you do that the rpms will go up. When the engine gets to 4000 rpm I use the radio to throttle back to 3500 rpm. I keep doing that until the rpms don't climb when adjusting the L needle. I then open the throttle wide open and adjust the H needle to max rpm. Now I put the engine to fast idle with the radio, wait 5 seconds then pop the throttle open, if it stumbles then speeds up I lean the L a 1/16Th of a turn. The L needle is usually slightly lean though and the engine either dies or just accelerates poorly so I richen the L until it accelerates nicely. The two sounds are very close unlike a nitro engine which it's easy to tell which it is, so on the gasser I'll richen first and see if it improves or not. After I've got the transition right I richen the H needle, then retune for max rpm. You have to remember the L needle affects the top end, so if you peak the top then lean the L the top end will be lean. The whole process takes about two minutes at most.

On the MT62, G62 clone, I can get it to idle at 1500 rpm with a 23a Xoar, but that's way to low to be of use. I have a Futaba 9C so I use the end point adjustment to have the engine fast idle at 22~2300 rpm, then using the idle-down setting have the engine idle at 17~1800 rpm for landing. I assign the switch on the top of the radio over the throttle to the idle-down. When I'm going to land I flip the switch to get the lower rpm. I also assign the engine kill feature which I always put on the D switch, D for dead.

karolh

I am certaintly going to give your method a try and see how it pans out.

Karol

JoeAirPort

My Feedback: (41)

There are many paths to a good tune. And his is certainly as good as any. I can usually hear the low end 4 stroking as clear as day so the low end is easy for me. I just keep leaning the low needle until most of that 4-stroking goes away. If I lean all of it out it's usually too lean. I usually test the transition to make sure it's not too lean. This probably gets me close to the same result as soarich on the low needle. The peak RPM is a little more difficult since it's hard to keep the screw driver on the high needle while it's screaming. It's hard to even get the screw drive on there. I still have a bit to learn about tuning an engine but I can usally get them to run pretty well.

I liked soarich's the tip about leaning the high needle just until it stops gaining RPM. That's something I'd like to try. I'd be willing to bet that's very close to where you'd want to run it.

soarrich

My Feedback: (98)

Two cures for this:

I took a carb int the LHS and found a brass tube that JUST slides over the needle's head, then I cut a piece that was about 1/4" longer than my screwdriver's shaft. Using Goop on the last 1/2" of the screwdrivers shaft I glued the brass tube onto the screw driver. You just slide the brass tube over the needle's head and tune away until you leave it in the grass somewhere.[:@]

A short piece of large fuel tubing can be slipped over one needle's head to hold the screwdriver in place on most Walbro carbs.

JoeAirPort

My Feedback: (41)

I like the brass tubing idea better. I tried the fuel tubing and it was hard to get the tubing over the needle...it was probably the wrong size tubing. But the brass tube idea sounds like it would be easy to slip over the needle...then finding the slot is a matter of twisting the screw driver either way till it catches. I bet that would work well.

Thanks

captinjohn

soarrich, After you complete expanation of the 3500RPM, I will give that a try. Sounds like another good way. It may depend on how good the carb is also, as far as pop off on needle inlet ...ect is working. My favorite tool for adjusting is a long allen wrench I made with a T handle. I solder the head off allen screws on end of needles. It is possible to reach through a very small hole in a cowl and fine tune if need be. The T part on handle is good to refer to how far you turn needle. Try it once. Best Regards capt,n

dditch

I had made adjustments about a week ago. I thought I was still a bit rich on the low end. If I let it idle for a while, when I punched it, the rpms would increase slowly like it was rich. The high end was turned in at the beginning of peak RPM. I decided last night to put the cowl on. (the ajustments int he 2nd sentance were w/ the cowl off.
Today at lunch (only time to fly lately) I took it to the field w/the Cowl on. When I had it at idle and punched it, it would immediatly die unless I dropped the throttle stick back down. With the cowl on, I can't adjust w/ it running. I shut it down and gave it 1/8 turn rich on the low end. Better, but needed more. 1/8 more rich on the low end. After that, it was better, A little more warm up and it was ok. was running out of my lunch time so after 9 years of the plane sitting in the basement, I took it up and flew it one flight. It was definitly in need of tunning still and I still need to follow "somebody's" procedure. The question I have is does the cowl make that much of a difference that the idle setting might have changed or maybe I missed something I did to the needles since I last ran it up?

Below are photos of the bird w/ the Cowl on.

pe reivers

Late post, but read this:
http://www.prme.nl/forum/viewtopic.php?t=205
It explains why the mixture changes, and ho to cure it.

dditch

Thanks,
Actually great timing. I just finished changing all my fuel lines for the spring and will be starting it up in the comming weeks.

thx

pe reivers

To get all info from Walbro, you can download their manuals at
http://wem.walbro.com/distributors/servicemanuals/
The servicemanual is great help

AA5BY

Karol, I think I follow what Soarich is saying and it fits the scenario of the acetate pump we recently talked about. With the acetate pump, I detuned from a high rpm of 8300 to 7900 but the engine still overheated after a few minutes and sagged. With the teflon pump it could be tuned to max rpm and ran cool enough to hold the crankcase after a ten minute run. The explanation seems to be that there is fuel overhead to lube and cool even at full rpms if the pump is supplying good pressure. With the acetate pump, there must not have been any fuel overhead because of inadequate pumping.

karolh

You have got it figured out quite right as the acetate type diaphram would now be my very last choice of materials both for pumping ability and durability, as the teflon type also seems to be quite compatable to ethanol blended gas.

Karol