Hopefully one of you great guys can relate to this problem. Having been flying for almost 34 years have seen only one similiar situation, and would like some opinions on solving this one, if you have had experience like it. This engine has about a gallon and a half through it now, and I let it break in on the rich side as always, while flying it, and she has been good in that she has never died on me yet. The problem is this , and I am strongly wondering if its the fuel pump problem as this is the version with the pump... When I set the top end on the ground, around 9200, max rpm. she will always be rich in the air. Not to mention the fact , we are not to max out on the ground, most people 200 to 300 on rich side is supposed to be about right. Well if you did that, she would be extremely rich in the air. So, basically I have never attained a normal setting in the air, she is always rich. Also good transitions on the ground always produce sloppy rich transitions in the air. Idle mixture is fine on ground (using pinch test ) about 200rpm on rich side...
My years of experience with engines, were that if anything, they would go lean in the air, but never ok on the ground and rich in the air.
Now this is my first Webra running a fuel pump. You guys thinking of a pump adjustment problem or what ???

Sounds like the effect of a short pipe. You did not mention what exhaust system you were using.

Effect of a tuned pipe set too short - in brief. The pipe set too short will try to 'force' the engine to get on the pipe while on the ground. You get a false-peak rpm. (pipes not only boost, but the function as a governor/regulator of sorts). When in the air, the engine happily unloads up into the pipe's true tuned rpm band.... and now no longer on the edge, the engine settles down, the pipe works properly, fuel delivery improves, and the engine will go slightly rich.

How do you fix this..... 1) make the pipe a tad longer 2) drop the prop size a bit

Something to consider. Not exactly sure if this applies to your situation.

Bob

If you are not running a pipe or tunned muffler per Bob then there is a fair likelihood you are under proped. Very often enines that are under proped will go rich when they unload in the air. Try a prop with 2 inches more pitch and you should be able to tell right away. I wouldn't try an inch more diameter because there is a good chance it will unload the same way as your current prop.

Denis

Another posibility

I haven't run the new pumped webra120 but I have 3 of the old webra120s. Webra uses the taper on the idle needle to control the mid range mixture. I have generally found the mid range would be too rich unless the idle needle was set very lean (right at peak) if the tank was located at about 1/2 inche below the spray bar. With a pump tank hight shouldn't matter but the idle needle still may be something you have to screw with.

Denis

I think you may be so right. YES I have a MAC pipe (non muffled 15cc.) and std. header. I just got through talking to MAC'S about the tunning problems, she was less open faced instead of more on the first run. IE: without cutting the pipe. I made one 1/4 inch cut and gained 250rpm. Made another cut and lost a lot. Mac's said the pipe may not have even been long enough from the get go. WOW, I think you may have pinned it.

Thanks,
Charlie

Reply to bob27s

I have since put a Scimitar wood 16 X 6 and rpm jumped to 10,700. This was without changing the pipe length anymore. I realize I should start over to establish a new point, open faced, then pipe, etc. but you know what, I have so much power now, who needs too, lol. Airplane can actually be launched vertically as I have done this in the past, but not with this one. I just feel its capable. The 16X6 actually slows the airplane, but still pulls vertically as well. Just want to say thanks again bob.

Charlie,

Happy to be of some help.

Sounds like that prop got you right in the sweet spot for where everything is set now. Keep note of the length for reference in the future.... provides a baseline from which to go up and down on rpm.

Enjoy the aircraft.

Hi Bob,

Looks like I'm back to my same old problem again. You were most helpful last time, so I thought I would give it another try. This is the Webra 1.20 with integral pump, we concluded last time my problem was too short of a headder with the tuned pipe. Well I thought I had solved everything by using that Scimitar 16 X 6 which gave a lot more rpm, because its really a smaller (narrow) compared to the Zinger Pro's if you compare them.
I tried to go back to my Zinger 16-6 or even 16-8 and the same problem. You have to set extremely lean on the ground, then even just running down the runnway she starts going rich. Also rich naturally in air. I have to set sinfully lean on ground to get a descent run in the air. NOW, the pipe length I extended back to the original length I had cut off which was only 1/2 inch total. Did this by extending the rubber coupler. Because you had concluded before that the pipe was too short. MAC doesn't offer a longer pipe length. Help, what can I do with this thing.
The reason I wanted to leave the Scimitar prop, was not good vertical, when I do get a descent air run with the Zinger, it performs much stronger I found. So if we ever got it to run right I know the Zinger Pro 16-6 or 8 would be a great prop for the engine.
Help Bob ???

I also forgot to ask you,
If I want maximum airspeed what prop, and if I want maximum vertical (forgetting speed), what prop?

At least you are on the right track here

One quick fix,

get ahold of some of the same diameter aluminum header tubing. Cut a straight piece about a 1.5" long to use as an extension. Stuff that inside of a longer piece of coupling material (3.75" long?), and place the assembly inline between the pipe and header. Clamped in place, it should work well enough for flying. Keep the gaps fairly small between the pipes. Fly it that way with the heavier props.

Once you know that length works, get a hold of Johnson Headers, and he can make what ever size you require. That will get you back to a one-piece header.

Also... in general
FAST = smaller diameter + higher pitch
Vertical = larger diameter + lower pitch

What aircraft is it installed in ??

Thanks again Bob,

Its installed in an Ultra Stik Light, weighint 10lbs 7ozs.
Bob I just got hold of a NIB MDS 1.48 ! Which will outperform the Webra or this MDS ???

Thanks Again,
Charlie

I have not run the MDS 1.48, but my money would probably be on the Webra.


Just for goofs, try the APC 16x4 W on that webra of yours (They are kinda expensive, maybe borrow one ).

I like the APC 17/6N on my Webra, but it doesn't have a tuned exhaust and is only pulling around an 8lb airplane.

Just out of curiosity, what muffler are you using, and on the APC 17-6, what rpm do you get out of it.

Thanks,
Charlie

Oh yea, "Never met an engine you didn't like", what about the MDS 1.48? I just happened to acquire one of them?

The MDS 1.48 is a great engine, it's actually a 1.52, it should turn a 16x8 Mejslik at about 9,400 on 5% nitro. Also the Bisson mufflers for the Webra fit the MDS.

So thats probably a tad bit stronger than my Webra 1.20, even with the tuned pipe ?
Since the exhaust are the same, how do you think the MDS will do with the tuned pipe from the Webra on it? Should out perform the Webra a little then? Thinking of trying it on the same plane I have the Webra on right now...

Thanks,
Charlie

I am using a Slimline pitts style muffler. It turns 8800 needled for flight. I never ran or saw run an MDS 148 but I dearly love my ST2300s (1.40). And they are stronger than the Webra 120. They do wonders for my Balsa Nova in the Avatar at 10lbs 10ozs.
Denis

Mr M this sounds much like my GMS 120 problem. The GMS is based on the Webra and has the same Dykes ring design. Not sure about the carb tho. How is the mid range on your Webra? Mine goes way rich despite running fine at idle. On my first flight it went very rich after take off much like your problem Ground running confirmed the problem. Djlyons comments on the Webra carb using the low end nedle to control the mid range sounds like it may be a fix with my motor. BTW, have you tached your Webra with an APC 16x6. The GMS gets 9100 rpm with 5% nitro.

My mid range goes rich too, is your GMS on a pump?

No pump on the GMS, just wide bore fuel tubing and muffler pressure. A friend had a problem with his pumped OS 160. He has since taken the pump off and runs successfully with a similar set up to mine. We are using giant scale fuelers too.

Funny, I have the exact same rich midrange problem with both my GMS 1.20 and Webra 1.20 (bisson pitts muffler and perry pump). My solution was to take off the perry pump, run the low end needle very lean and use muffler pressure alone. Runs pretty good but now I'm going lean when hovering since I'm only using muffler pressure. I just bought a cline regulator for the webra 1.20 to see if that would clear up all my problems. I'll test it tomorrow.

I have had great success with the cline regulators on other engines, lets hope.

I am running pitts style mufflers on 2 of my 3 older Webra 120s and of course that effects how they run. Both turn a 16/6 apc in the high 9s. I've never run a GMS 120 but I've picked them up and fondled them at MECOA in Monrovia. Definitely look like a Webra copy but I didn't look at the carb that close.

I normally adjust my idle for best good transition to full power after a few seconds of idle. This normally leaves them a bit rich. But that's OK as long as they don't load up in the mid range. This doesn't seem to be lean enough for my Webras. What I do is lean them some more and then start flying. If they still load in the mid range I land and turn them in a half screw driver width at a time till they clean up. This seems to work for me.

Denis