mrbigg

My Feedback: (21)

I think you jet a carb leaner when the altitude increases.

altavillan

My Feedback: (1)

I want some of Eugene's weeds. Once every 10 years would be super!!!

Tired Old Man

My Feedback: (1)

I can assure you that our carbs can run effectively from sea level to above 15,000 msl without requiring an adjustment. In fact, they can go to above 20,000. I've seen it done too many times recently not to be a fact, and I know others that do it frequently. That's not saying that it wouldn't benefit from an in flight adjustment, but it''s not truly needed.

However, just for the sake of arguement, let's presume that a carb that's been adjusted on the ground, be it either rich or lean, remains at exactly the same setting in flight. Meaning it does not go richer or leaner as the plane goes faster, climbs, or descends. That condition was established before the plane left the ground. Now, if the carb had been set a little on the lean side, what would be a factual description of the event that causes the engine to sound like it was "sagging" on a climb? The reverse will do from being set too rich.

Hmmmm.

More ammo for your guys. I'm surprised there has not been more input so far. Dick, Pe, or one of you other true engine experts, feel free to jump in on the next one. I have a short business trip I have to do tomorrow. You guys are more knowledgable than me anyway.

JoeAirPort

My Feedback: (41)

Yeah Dick, tell us about how the engine RPM quickly hits it's peak RPM if it's lean and slowly climbs to peak when it's rich or just right. Sumthen like that. Huh?

bubbagates

My Feedback: (32)

I'd love to find out just how bad my interpetation has been on this subject. I do not mean that as sarcastic, I just want to be as sure as possible on this subject

I am by no means an engine expert, not even close, but I can I tune one, pretty darn good. I would love to know the reasons why I do what I do, it would make me feel lots better

And BTW, thanks to everyone for keeping this thread really civil. I was away for the last 2 days and when I saw all the email notices for this thread I almost half expected to come in and see a bit of a war going on.

I'll tell you what, if we can get a really good detailed and precise explanation on this subject and proper tuning, spark plug reading, various good explanantions on how to solve certain issues with the most common fixes, I'll ask for the admins permission to make it a sticky at the top of the forum so that we can all reference it when the question comes up again and you know it will

Tired Old Man

My Feedback: (1)

It's all about the amount of fuel available for the engine to perform work. To little and it can only do as much work as it has the fuel to sustain it. When it hit's the limit of the fuel it's been provided it cannot do anymore work. There's a cap on how much work any given engine can perform based upon gearing, propeller size, etc, but we often place limits on that amount of work well before it should occur with the needles.

3d-aholic

My Feedback: (7)

How high are you flying? Sheesh.

eugene

Well, it's not the ten year weed, but the ten year weed-eater!
My point was the simplicity of these 2 cycle gas engines.. My first gas Warbird was test flown by someone very familiar with Zenoah engines.. After the flight , He asked me if I had a small screwdriver I could use to adjust the needles... I presented him with my screwdriver, which He promptly threw 50 ft. into a weed field.. I got the point!!...after two flying seasons the needles have never been touched, and the Zenoah is pulling like a Mule in a mudhole...

rmh

stories like that warm the cockles of my heart .

Tired Old Man

My Feedback: (1)

Get 'em right once and then leave 'em alone. That method still works. So does tuning for the type of flying intended. If it's acing then tune for all out level speed and rpm with the best turning prop you can get. If you're going to be doing a lot of ups and downs, tune for the ups. Level and down take care of themselves.

chuck l

My Feedback: (17)

Hey guys, I really haven't seen an answer to my original question. Can some one please give it a try?

Chuck

"There are frequent references to tuning the high speed needle for max rpm, then richening it for a 200rpm drop. Can some one explain the reason/theory for doing this? Can you really tell any difference when flying the plane?"

Tired Old Man

My Feedback: (1)

Running peak rpm sets the stage for over heating. Few modelers set up their engines and cowls in a manner that effectively promotes decent cooling. Running back of peak keeps things a little cooler. Getting hot is why a lot of engines drop rpm on a long up line. You can still cook 'em off, but it takes a bit more work and time. Maximum power is created at peak rpm but so is maximum heat.

bob_nj

My Feedback: (62)

Here is a post from another board that has really good information in it if you take the time to read through it.
I now use this method and it's made a big difference in the way the plane flies, and how I go about tuning gassers.

[link=http://www.flyinggiants.com/forums/fg68/427-gas-engine-tuning-newbies.html]Tuning[/link]

Happy Motoring...

bob_nj

My Feedback: (62)

I guess I **** the censor gods. It's a shame as the post is useful.

edited by moderator

mistydee0

My Feedback: (103)

To bad Ralph's not around.

WRK

My Feedback: (2)

The carburetors on these engines are fairly simple and do not compensate for some engine and temperature changes, when the outside temp. goes down you need to richen a bit for max power and opposite for rising air temps.

The charecterestic of venturies ( they pull the fuel into the carb by pressure drop with moving air ) is that they are non linear with air flow which means that as the engine speed changes to a higher RPM from a lower RPM (going from the ground to unloading in the air) they go richer because the venturi pulls more fuel with increased RPM with a given needle setting, The "more fuel" that is pulled is not proportional to the added air flow through the carb but increases more than the air does so it goes a bit rich.

If venturi action was linear with air flow then the carb would not need an idle circuit and other internal compensation passages, these devices help make the carb. more linear with air flow but are not perfect.

WRK

rmh

yeh -but be careful on leaning out for high temp days --tho the air is thinner - the engine usually gets hotter and the lean mix adds to the problem
ask any old VW racer---
also if the carb is oversized to the engine - or undersized to the engine - the designed in "linearity" goes to pot -
some go very lean at full power as the bore is way oversized and the low pressure does not suck hard enough on the high speed jet.
the small ones -do the opposite - go rich
the carbs are calibrated to match various engine flow -based on pumping volume at rpm.
Now if you want some really shi-tty carbs to work on -try adjusting a set of three SU carbs on an old Healey
when the sun goes behind a cloud - they change -

BTerry

My Feedback: (8)

here is another way to post, use tinyurl.com

Anyway, here is Bob's link: http://tinyurl.com/2thejl

bob_nj

My Feedback: (62)

Thanks Mister Wizard [X(]

Did you get to look at it by chance?

BTerry

My Feedback: (8)

Yes, I think that is a good method with a LOT of useful information.

I understand why RCU won't allow linking to the **** website, and they have the right to disallow it, but it still hampers the flow of information.

edited by moderator

bob_nj

My Feedback: (62)

Glad you enjoyed it!

karolh

Amen to that.

Karol

mikenlapaz

Bob, it is a shame that moderators feel that linking good info to a thread is bad just because it is on another site. I found the thread 13 pages of it with even current comments from a guy called ? Ralph ?
His narrative sounded familar.
Protectionism has not proved beneficial in other situations.

bob_nj

My Feedback: (62)

I asked the same question in post #125 of the thread I linked to about having to adjust the needles with varying weather conditions and got a different answer.

Now I'm confused

blw

My Feedback: (3)

First of all, the moderators don't have anything to do with making filters. We do have things to do with trying to fix problems like this. I'll ask about this link and see if something can be done. There is a possibility that there were problems in the past that caused it to be filtered out, but I don't know about that.