valid carb tuning technique
08-28-2011 | 01:03 AM
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From: Athens, GREECE
valid carb tuning technique
i'm new to gas engines and i'm reading/watching videos on how to tune the carb right.
the thing is i can't see the difference from slightly rich and slightly lean.......mostly on the low speed needle.... sound stupid i know,but i don't have any reference other than the videos on youtube.
then i came across this post,seems easier but completely different than the "usual guidlines".... but i'm not sure if it is OK to do it this way.
what do you think?
With the engine warm, adjust the high speed screw for maximum revs.
Then reduce revs and hold the throttle steady close to 2000rpm and then adjust low speed screw for maximum revs at that throttle setting.
Let the engine idle.
Then adjust, as necessary the slow speed screw to give smooth transition from idle to max revs.
Repeat if required.
Final settings should ideally within ½ turn of initial setting.
08-28-2011 | 02:52 AM
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From: FrederickMD
RE: valid carb tuning technique
That's the way I do it, and it works every time. The only thing I do a little differently is on the high speed needle, find the drop off point both rich and lean, and then set it between those two points.
Brad
Brad
08-28-2011 | 05:19 AM
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From: Crowley,
TX
RE: valid carb tuning technique
Interesting variation om Walbro tuning from "GringoPete" at BP Hobbies.
ORIGINAL: gringopete
<div style=''margin: 0in 0in 10pt''><span style=''line-height: 115%; font-size: 10pt''>I'll see if I can answer a couple of questions here.
Hope this helps everyone in the tuning and troubleshooting their engines. The following applies to just about any engine that uses a Walbro type carb.
... here is the easiest way to set the needles on the engines.
1) Start by turning out both the high and low needles 1 5/8 to 1 3/4 turns.
2) Go full throttle and peak the high end with the high speed needle valve. When the engine sags you have gone too far. Back the needle off 1 hour or 1/12 of at turn.
3) Go full throttle and peak the engine using the low speed needle valve. When the engine sags back off the low end needle 1 hour or 1/12 of a turn. That’s right peak the engine using the low end needle. The reason for this is that the engine gets fuel from both needles once the engine comes off of idle.
4) Bring the engine down to idle. Adjust the low end rpm idle with the trim on your transmitter. The engine should not need any adjustment at this point.
The engine at this point should be almost perfect. It should transition from low to High speed without any burps. If the engine does not run good after this setup look for an air leek, bad reed valve or carb diaphragm.</span></div>
<div style=''margin: 0in 0in 10pt''><span style=''line-height: 115%; font-size: 10pt''>I'll see if I can answer a couple of questions here.
Hope this helps everyone in the tuning and troubleshooting their engines. The following applies to just about any engine that uses a Walbro type carb.
... here is the easiest way to set the needles on the engines.
1) Start by turning out both the high and low needles 1 5/8 to 1 3/4 turns.
2) Go full throttle and peak the high end with the high speed needle valve. When the engine sags you have gone too far. Back the needle off 1 hour or 1/12 of at turn.
3) Go full throttle and peak the engine using the low speed needle valve. When the engine sags back off the low end needle 1 hour or 1/12 of a turn. That’s right peak the engine using the low end needle. The reason for this is that the engine gets fuel from both needles once the engine comes off of idle.
4) Bring the engine down to idle. Adjust the low end rpm idle with the trim on your transmitter. The engine should not need any adjustment at this point.
The engine at this point should be almost perfect. It should transition from low to High speed without any burps. If the engine does not run good after this setup look for an air leek, bad reed valve or carb diaphragm.</span></div>
08-28-2011 | 03:42 PM
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From: La Porte,
IN
RE: valid carb tuning technique
ORIGINAL: tdriver
i'm new to gas engines and i'm reading/watching videos on how to tune the carb right.
the thing is i can't see the difference from slightly rich and slightly lean.......mostly on the low speed needle.... sound stupid i know,but i don't have any reference other than the videos on youtube.
With the engine warm, adjust the high speed screw for maximum revs.
Then reduce revs and hold the throttle steady close to 2000rpm and then adjust low speed screw for maximum revs at that throttle setting.
Let the engine idle.
Then adjust, as necessary the slow speed screw to give smooth transition from idle to max revs.
Repeat if required.
i'm new to gas engines and i'm reading/watching videos on how to tune the carb right.
the thing is i can't see the difference from slightly rich and slightly lean.......mostly on the low speed needle.... sound stupid i know,but i don't have any reference other than the videos on youtube.
With the engine warm, adjust the high speed screw for maximum revs.
Then reduce revs and hold the throttle steady close to 2000rpm and then adjust low speed screw for maximum revs at that throttle setting.
Let the engine idle.
Then adjust, as necessary the slow speed screw to give smooth transition from idle to max revs.
Repeat if required.
Look at it like this;
Your wiper blade on your car goes so far to the left & so far to the right which is an arc.
Transfer that idea to our LS/HS needles and when you get them close to being correct,
you have an arc of so far to the left ( it becomes rich) and so far to the right (it becomes lean)
Do your setting of the LS/HS needles AFTER it's fully warmed up, and apply the above to what
you quoted, and you'll get it very, very close.
Some fine tuning may be needed after you make several flights.
Don't get worried too much about a tad bit of mid range gurgling.
Some is not a bad thing.
There's 2 pdf type files in this msg on how to tune, download them from this msg;
http://www.rcuniverse.com/forum/fb.asp?m=10293852
08-29-2011 | 05:25 AM
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From: Valencia, SPAIN
RE: valid carb tuning technique
As another newbie to gassers.. also be ware of the people who ay they can tune your engine in your club.
i'Ve had mine flying fine, as in not a perfect mix but no deadsticks... then somebody will say that sounds "xxxxxx" i can fix that.
It always ends up with deadsticks and that person running away!
just take your time and try to tune by your flying experience! and if its going well.. just leave it be while you get used to gassers!
reliable is more important to me than a perfect tune!
i'Ve had mine flying fine, as in not a perfect mix but no deadsticks... then somebody will say that sounds "xxxxxx" i can fix that.
It always ends up with deadsticks and that person running away!
just take your time and try to tune by your flying experience! and if its going well.. just leave it be while you get used to gassers!
reliable is more important to me than a perfect tune!
08-29-2011 | 07:53 AM
#6
RE: valid carb tuning technique
I'm also new to gassers and I have come to realise that the recommended starting point on Walbro type carbs is not quite cast in stone. Be prepared to open both needles as is necessary to get the engine running. I have had the experience where opening up the high needle as much as 2 1/2 and the low 2 turns out was necessary to start the engine.
DaleD<br type="_moz" />
DaleD<br type="_moz" />
08-29-2011 | 09:20 AM
#7
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RE: valid carb tuning technique
If you have a Walbro carb that requires opening over 1-3/4 to 2 turns on either needle to get the engine started you have either a bad carb or other issues in play. I have yet to see a Walbro carb that fits engines up to 150-170cc that would not start an engine with both needles at 1-1/2 turns open. Would the engine run good enough to fly? Almost never with any size engine but the idea is to get an engine started and then tune accordingly.
In reply to another post, if your engine is running fine, is not over heating, provides the power you need, and has good throttle response, why would you let someone mess with it?
No two engines are the same, just are no two carbs the same. Follow that up with propellers. Slight variations will always be present, which requires differences in needle positions from one user to the next. This does not include weather and elevation deltas which impact tuning further. That is why any engine tuning guideline that places hard limits/turn values on what to do will be wrong. Some engines will have a burbal no matter what an owner does. That is generally attributed to design issues.
The process can be easy or difficult, and what it will be is up to the user. If you are one that gets hung up on a number you will have a very hard time of tuning an engine.
In reply to another post, if your engine is running fine, is not over heating, provides the power you need, and has good throttle response, why would you let someone mess with it?
No two engines are the same, just are no two carbs the same. Follow that up with propellers. Slight variations will always be present, which requires differences in needle positions from one user to the next. This does not include weather and elevation deltas which impact tuning further. That is why any engine tuning guideline that places hard limits/turn values on what to do will be wrong. Some engines will have a burbal no matter what an owner does. That is generally attributed to design issues.
The process can be easy or difficult, and what it will be is up to the user. If you are one that gets hung up on a number you will have a very hard time of tuning an engine.
08-29-2011 | 10:57 AM
#9
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RE: valid carb tuning technique
It's about (I think) finding a way to avoid reading an entire thread devoted to gas engine newbies and making things easier for them. Why read all that stuff when a single question can be posted in a "stand alone" thread that 50 people will reply to, each having a different answer. Of course having 50 different answers only generated more questions and answered none. The last question ever (if ever?) asked is the one requesting the experience and success level of the person providing the answer.
What's in the sticky works so that's where people should go first.
What's in the sticky works so that's where people should go first.
08-29-2011 | 11:11 AM
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From: Egg Harbor City,
NJ
RE: valid carb tuning technique
I imagine it would help RCU spacewise to not have so many,maybe have a vote with moderators so far into a thread as to remove it if enough info on question asked is givin or directed in accordance. OH! The pro,s an cons of the modern R/C gas engine!
08-29-2011 | 12:53 PM
#13
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RE: valid carb tuning technique
Not trying to promote an arguement but when you read answers to questions you should be asking yourself "What qualifies this individual to respond with an answer?", "What does the respondant know about the subject matter?", "Is that answer correct?" "What differentiates this answer from the 10 or 30 others, and why might it be correct?. Those are just the basics.
I'm definately not going to request RCU to censure posts due to supreme level of redundancy, but I will hope that each individual asking a question understands that just because they got an answer did not make it right. I "read it on the internet and it must therefore be so" only tells you how gullible you are. It does not imply any level of correctness.
This particulr thread is a good example. There is nothing new to be learned about tuning a small gas two stroke. However, there is a multitude of ways to confuse the issue and promote methods that make the process more difficult than it needs to be.
Ralph,
I know you're right, but I refuse to quit trying. That refusal to give up has made the company I work for many millions of dollars but it took a lot of forehead banging before it happened. The same process is in play here but it should ultimately be easier. Most of the people here don't have "m.e." after their name.
I'm definately not going to request RCU to censure posts due to supreme level of redundancy, but I will hope that each individual asking a question understands that just because they got an answer did not make it right. I "read it on the internet and it must therefore be so" only tells you how gullible you are. It does not imply any level of correctness.
This particulr thread is a good example. There is nothing new to be learned about tuning a small gas two stroke. However, there is a multitude of ways to confuse the issue and promote methods that make the process more difficult than it needs to be.
Ralph,
I know you're right, but I refuse to quit trying. That refusal to give up has made the company I work for many millions of dollars but it took a lot of forehead banging before it happened. The same process is in play here but it should ultimately be easier. Most of the people here don't have "m.e." after their name.
08-29-2011 | 01:35 PM
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From: San Tan Valley,
AZ
RE: valid carb tuning technique
One question I have that I don't find an answer in the sticky is what tool do you use the tune those needles while the engine is running? A screwdriver doesn't work too well for me. It keeps slipping off the screw with all that vibration. And its dangerous being close to the prop.
08-29-2011 | 01:44 PM
#15
RE: valid carb tuning technique
ORIGINAL: dirtybird
One question I have that I don't find an answer in the sticky is what tool do you use the tune those needles while the engine is running? A screwdriver doesn't work too well for me. It keeps slipping off the screw with all that vibration. And its dangerous being close to the prop.
One question I have that I don't find an answer in the sticky is what tool do you use the tune those needles while the engine is running? A screwdriver doesn't work too well for me. It keeps slipping off the screw with all that vibration. And its dangerous being close to the prop.
08-29-2011 | 01:55 PM
#16
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RE: valid carb tuning technique
Unfortuantely the answer is still "a screw driver". If you have Parkinson's it gets a little easier if the condition has progressed to a level where the palsy is at a higher frequency than the engine vibrations. Yea, I know that wasn't nice, just a crude attempt at some humor....
A screwdriver with a blade thickness that fits the slot, having a blade width that is much wider than the screw, and a long shank is still the best I'be been able to come up with outside of making modifications to the tuning screws. There was a firm at another site that was developing hex head carb needles but I don't know how that project finally fleshed out.
A screwdriver with a blade thickness that fits the slot, having a blade width that is much wider than the screw, and a long shank is still the best I'be been able to come up with outside of making modifications to the tuning screws. There was a firm at another site that was developing hex head carb needles but I don't know how that project finally fleshed out.
08-29-2011 | 02:34 PM
#17
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RE: valid carb tuning technique
The low speed needle usually isn't so tough, because at idle the engine doesn't usually have the high frequency vibration that makes it tough to keep the screwdriver located properly. So I leave the low speed needle alone. But on the high speed needle, I often solder on a piece of brass tubing with the end flattened so I can get ahold of it with my fingers or a needle nose pliers and do the adjustment. Sometimes on my cowled airplanes, I also do the brass tube needle valve mod, but instead of flattening the end, I drill it and insert a short piece of music wire soldered in. Then I have a long screwdriver I made with a slotted tube welded on the end that goes through the cowl and solidly engages the modified needle valve. Works great.
AV8TOR
AV8TOR
08-29-2011 | 05:27 PM
#19
RE: valid carb tuning technique
ORIGINAL: dirtybird
One question I have that I don't find an answer in the sticky is what tool do you use the tune those needles while the engine is running? A screwdriver doesn't work too well for me. It keeps slipping off the screw with all that vibration. And its dangerous being close to the prop.
One question I have that I don't find an answer in the sticky is what tool do you use the tune those needles while the engine is running? A screwdriver doesn't work too well for me. It keeps slipping off the screw with all that vibration. And its dangerous being close to the prop.
08-30-2011 | 08:06 AM
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From: San Tan Valley,
AZ
RE: valid carb tuning technique
ORIGINAL: Antique
A long brass tube that just fits over the needle with a pin soldered straighe across about 1/4 inch in works...
A long brass tube that just fits over the needle with a pin soldered straighe across about 1/4 inch in works...
I would think someone would be selling something like it. I bet you could get $10 for it.
08-30-2011 | 09:44 AM
#24
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RE: valid carb tuning technique
Only took me a few minutes to make the custom screwdriver, only takes me a minute or so to modifiy the high speed needle. Then it's "cake" to adjust the carb. On my cowled engines, I make a small hole in the cowling for access to the needle. Then I put a rubber grommet in the hole. I can put the screwdriver into position before I start the engine. I then start the engine, make the adjustment with ease, and it's done. The screwdriver stays in place until I pull it out. When I am adjusting an engine with the cowl off, I don't even need the screwdriver as the modified needle is easy to manipulate by hand.
Works for me!
AV8TOR
Works for me!
AV8TOR
