52 cc tuning pros!!!
05-27-2006 | 11:57 PM
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From: Port Edwards,
WI
52 cc tuning pros!!!
I have a slightly used 3.2 Sachs style engine on my WH Edge. It has a lot of power, but blubbers at mid range. If I roll to inverted as it is blubbering, it instantly goes away. It totally clears up. Roll back to right side up and it blubbers again. I can lean it to the max on high and low needles and it still does this. Does anyone have suggestions? Thanks!
05-28-2006 | 12:03 AM
#2
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RE: 52 cc tuning problem
Wow I am starting to see a pattern in low end problems on these gassers. Some of the DA-50's do this too. Some people say it's an air flow problem in the cowling that changes when you go inverted. I know one guy that said his never went away regardless of all the fixes he tried (diaphragm vent routed inside fuse, carb plate, etc).
05-28-2006 | 12:10 AM
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From: Port Edwards,
WI
RE: 52 cc tuning problem
I had someone else say it could be an air flow problem, but I can't see how the air could flow differently because it's inverted. I can't get it to blubber at all inverted at any RPM. I must be missing something somewhere.
05-28-2006 | 06:47 PM
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From: Calgary, AB, CANADA
RE: 52 cc tuning problem
ORIGINAL: marzo91
I had someone else say it could be an air flow problem, but I can't see how the air could flow differently because it's inverted. I can't get it to blubber at all inverted at any RPM. I must be missing something somewhere.
I had someone else say it could be an air flow problem, but I can't see how the air could flow differently because it's inverted. I can't get it to blubber at all inverted at any RPM. I must be missing something somewhere.
What else could cause this sort of thing? The engine doesn't know or care if it's right side up or upside down, and neither does the carb. Yes, there are things that **COULD** cause this other than airflow changes, but the most likely cause is the one you should be eliminating first.
HTH
Jim
05-28-2006 | 11:57 PM
#6
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RE: 52 cc tuning problem
ORIGINAL: Icebird
I guess a little understanding of how an airplane flies would really help here. All planes require a slight angle of attack in order to produce lift. When you are inverted, the angle is going to be different than it would be if you were right side up. This change in attitude causes the air pressure within the cowl to change. The change is even more apparent when you don't have enough air exit for the cowl, and end up building pressure inside the cowl.
What else could cause this sort of thing? The engine doesn't know or care if it's right side up or upside down, and neither does the carb. Yes, there are things that **COULD** cause this other than airflow changes, but the most likely cause is the one you should be eliminating first.
HTH
Jim
ORIGINAL: marzo91
I had someone else say it could be an air flow problem, but I can't see how the air could flow differently because it's inverted. I can't get it to blubber at all inverted at any RPM. I must be missing something somewhere.
I had someone else say it could be an air flow problem, but I can't see how the air could flow differently because it's inverted. I can't get it to blubber at all inverted at any RPM. I must be missing something somewhere.
What else could cause this sort of thing? The engine doesn't know or care if it's right side up or upside down, and neither does the carb. Yes, there are things that **COULD** cause this other than airflow changes, but the most likely cause is the one you should be eliminating first.
HTH
Jim
05-29-2006 | 08:11 AM
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From: Goodyear, AZ
RE: 52 cc tuning problem
I have a profile that does this, either on a knife edge or an abrupt change in pitch. The metering diaphragm cover on the carb has the hose going into the fuselage, so as far as I'm concerned, it is a air flow problem over the velocity stack. The stack is set with the tall side facing forward, with the tall side facing rear, there is no way to maintain power on a knife edge where the carb facing down.
If someone has a solution, let's here it.
If someone has a solution, let's here it.
05-29-2006 | 04:11 PM
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From: metropolis, ANTARCTICA
RE: 52 cc tuning problem
get rid of the stack if you are using the tube into the fuse it shoud be OK. Stacks, unless designed for THE engine really don't contribute. One size fits all doesn't work. Here is something to try if the plane isn't to big. It takes two people. One to hold the plane in different attitudes at different throttle settings and see what happens. It isn't easy but you might find some thing.
As for the carb, it is a pumper and no matter what angle the engine is will not matter,ergo it has to be air flow. you might also put a dam in front of the venturi. In all my years I have not had to resort to any of these possible solutions. Must live right.
As for the carb, it is a pumper and no matter what angle the engine is will not matter,ergo it has to be air flow. you might also put a dam in front of the venturi. In all my years I have not had to resort to any of these possible solutions. Must live right.
05-29-2006 | 06:30 PM
#9
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RE: 52 cc tuning problem
You also have to remember that not everybody gets their planes into inverted harriers near idle so it all depends on the right conditions for the problem to surface. It's hard to believe an air flow problem can surface at almost zero air speed. I'd like to turn mine upside down at idle with the help of three people at the field. That would be a good test.
05-29-2006 | 06:35 PM
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From: Port Edwards,
WI
RE: 52 cc tuning problem
I built a baffle around the carb. The top piece is on top of the diaphragm cover, out to the cowl. The other piece is verticle from the top of the carb down to the cowl. Now the carb should have to draw it's air from behind this baffle. I'll try it Monday and report my results.
JoeAirPort, We'll work on this thing together. If I have any luck, you'll hear about it.
JoeAirPort, We'll work on this thing together. If I have any luck, you'll hear about it.
05-29-2006 | 08:25 PM
#11
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RE: 52 cc tuning problem
Sounds good !!!
ORIGINAL: marzo91
I built a baffle around the carb. The top piece is on top of the diaphragm cover, out to the cowl. The other piece is verticle from the top of the carb down to the cowl. Now the carb should have to draw it's air from behind this baffle. I'll try it Monday and report my results.
JoeAirPort, We'll work on this thing together. If I have any luck, you'll hear about it.
I built a baffle around the carb. The top piece is on top of the diaphragm cover, out to the cowl. The other piece is verticle from the top of the carb down to the cowl. Now the carb should have to draw it's air from behind this baffle. I'll try it Monday and report my results.
JoeAirPort, We'll work on this thing together. If I have any luck, you'll hear about it.
05-31-2006 | 03:33 PM
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From: Port Edwards,
WI
RE: 52 cc tuning problem
JoeAirPort, I had a good fellow e-mail me with a fix for the blubbering problem. I tried his fix this morning and it worked perfectly! It's simple. You need to remove the diaphragm cover on the carb to get at the needle and spring set-up. Use a small screwdriver or exacto-knife to hold down the "U" shaped part of the arm that attaches to the needle. This will keep the needle seated in the seat. Gently bend the opposite end of the arm down about a sixteenth of an inch. Mine ended up a bit lower than the machined top of the carb, after you release the needle end. This would be the end of the arm that touches the peg on the diaphragm. You'll need to reset both the high and low settings for optimum performance. Try it and let me know how it worked out. This engine has never ran this good.
P.S. I took off the baffle I built for the carb. It's not needed.
P.S. I took off the baffle I built for the carb. It's not needed.
05-31-2006 | 05:36 PM
#13
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RE: 52 cc tuning problem
You changed the pop off pressure. That's what I heard could be the problem, saw it on another thread. I guess the pop-off is set too high (or not set at all).
I guess I'm going to have to try this. I'm a little unsure of messing with the carb but in your case it sure paid off. I'll keep you posted and thanks for the update.
I guess I'm going to have to try this. I'm a little unsure of messing with the carb but in your case it sure paid off. I'll keep you posted and thanks for the update.
ORIGINAL: marzo91
JoeAirPort, I had a good fellow e-mail me with a fix for the blubbering problem. I tried his fix this morning and it worked perfectly! It's simple. You need to remove the diaphragm cover on the carb to get at the needle and spring set-up. Use a small screwdriver or exacto-knife to hold down the "U" shaped part of the arm that attaches to the needle. This will keep the needle seated in the seat. Gently bend the opposite end of the arm down about a sixteenth of an inch. Mine ended up a bit lower than the machined top of the carb, after you release the needle end. This would be the end of the arm that touches the peg on the diaphragm. You'll need to reset both the high and low settings for optimum performance. Try it and let me know how it worked out. This engine has never ran this good.
P.S. I took off the baffle I built for the carb. It's not needed.
JoeAirPort, I had a good fellow e-mail me with a fix for the blubbering problem. I tried his fix this morning and it worked perfectly! It's simple. You need to remove the diaphragm cover on the carb to get at the needle and spring set-up. Use a small screwdriver or exacto-knife to hold down the "U" shaped part of the arm that attaches to the needle. This will keep the needle seated in the seat. Gently bend the opposite end of the arm down about a sixteenth of an inch. Mine ended up a bit lower than the machined top of the carb, after you release the needle end. This would be the end of the arm that touches the peg on the diaphragm. You'll need to reset both the high and low settings for optimum performance. Try it and let me know how it worked out. This engine has never ran this good.
P.S. I took off the baffle I built for the carb. It's not needed.
05-31-2006 | 08:18 PM
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From: El Reno, OK
RE: 52 cc tuning problem
If this is truly the "fix" (and sounds like it evidently IS), then it is the absolutely best-kept-secret in the airplane gas-motor world. I've read the thread about popoff pressure, and all the Walbro testing and "calibration" info....
Do we all believe that this problem is just now surfacing after a few decades of Walbro carbs in gas planes?
Is there something else that maybe is being compensated for by making this pop-off adjustment?
Do we all believe that this problem is just now surfacing after a few decades of Walbro carbs in gas planes?
Is there something else that maybe is being compensated for by making this pop-off adjustment?
05-31-2006 | 08:43 PM
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From: Port Edwards,
WI
RE: 52 cc tuning problem
I don't know the answers to any of your questions, but I just flew a whole gallon of gas through my WH Edge today and it never blubbered once!
05-31-2006 | 09:58 PM
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From: RIDGENew York
RE: 52 cc tuning problem
This is definitly not new, I had a ZDZ 40b about 2 1/2 years ago( this was a beginners version of the regular ZDZ 40) which had a bad case of blubbering when I took off . When I would land the engine ran fine so what I had to do was set it up so lean on the ground that it was almost impossible to start just so that I could fly around sort of ok. But I still had all sorts of problems.
When i spoke to Mike Dooley at RC Showcase he emailed me directions with step by step photos of how to change the pop off pressure. Once this was done I didnt have that big of a change from ground to flight tuning, But I still had other issues so he upgraded me to a newer ZDZ 50ng for free.
About a year later a friend had a similar problem with his New 40% pw with a DA 150cc. He would fly around for about 5 minutes and then the engine would (like clockwork) go deadstick. None of the big guns at the field had a clue why and really didnt want to help him out. With my new found skills for setting up and tunning gassers wich I learned from post like this one and many other headaches I had encountered. I suggested adjusting the pop off pressure. since he was so depress and down he was willing to listen to a 1/4 scaler like i was at the time. I can remember his pressure being so rich that the carb would leak fuel while just sitting there. We lifted the little arm which allows less fuel and then put it all back together. Know with the needles out to a respectable # of turns (believe it was 1 3/4 for both) we fine tuned the carb and took her up. He had his first 35 minute flight since he purchased the plane and the engine ran and transitioned very smoothly. Afterwards he let me take a flight, my first giant scale flight ever and boy did I enjoy it.
When i spoke to Mike Dooley at RC Showcase he emailed me directions with step by step photos of how to change the pop off pressure. Once this was done I didnt have that big of a change from ground to flight tuning, But I still had other issues so he upgraded me to a newer ZDZ 50ng for free.
About a year later a friend had a similar problem with his New 40% pw with a DA 150cc. He would fly around for about 5 minutes and then the engine would (like clockwork) go deadstick. None of the big guns at the field had a clue why and really didnt want to help him out. With my new found skills for setting up and tunning gassers wich I learned from post like this one and many other headaches I had encountered. I suggested adjusting the pop off pressure. since he was so depress and down he was willing to listen to a 1/4 scaler like i was at the time. I can remember his pressure being so rich that the carb would leak fuel while just sitting there. We lifted the little arm which allows less fuel and then put it all back together. Know with the needles out to a respectable # of turns (believe it was 1 3/4 for both) we fine tuned the carb and took her up. He had his first 35 minute flight since he purchased the plane and the engine ran and transitioned very smoothly. Afterwards he let me take a flight, my first giant scale flight ever and boy did I enjoy it.
05-31-2006 | 10:15 PM
#17
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RE: 52 cc tuning problem
This web site has some info on setting pop-off pressure. I think I'll pick up the stuff at a local automotive store to check it.
http://www.geistware.com/rcmodeling/...n_pressure.htm
http://www.geistware.com/rcmodeling/...n_pressure.htm
05-31-2006 | 10:19 PM
#18
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RE: 52 cc tuning problem
Marzo91
Could you post a picture of the baffle you made around the carb? I have a DA-50 in a WH 300LX. It burbles almost exactly as you descibed your Sachs.
When flying upright and level at 1/3 throttle, the burble (or blubber) is very prominent. When I turn the plane inverted at the same throttle setting, the burble goes away completely. The carb low needle has been leaned for the best transition with high side peaked and backed off slightly. No burble on the ground.
Also, I spoke with a Rep at Desert Aircraft today. He suggested the carb plate mod. DA is also selling them now.
Thanks - Jaketab
Could you post a picture of the baffle you made around the carb? I have a DA-50 in a WH 300LX. It burbles almost exactly as you descibed your Sachs.
When flying upright and level at 1/3 throttle, the burble (or blubber) is very prominent. When I turn the plane inverted at the same throttle setting, the burble goes away completely. The carb low needle has been leaned for the best transition with high side peaked and backed off slightly. No burble on the ground.
Also, I spoke with a Rep at Desert Aircraft today. He suggested the carb plate mod. DA is also selling them now.
Thanks - Jaketab
06-02-2006 | 01:23 PM
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From: Gadsden,
AL
RE: 52 cc tuning pros!!!
Qk all,i'm the one who gave Marzo the needle setting tip to remove the barbbles from his engine. I've been flying these birds for over 30 years and from exsperience have learned that ( so called pressure in the cowl) has absolutely NO affect on the diaphram on the walbro carb. So soldering tubes over the diaphram cover hole isent doing anything to lessen pressure under the diaphram. The diaphram gets ALL its pressure from the engines crankcase and no where else! That little hole your adding the tube to is just a counter vent to allow the diaphram to be sucked down by the motor without causing a vaccum on the opposite side of the diaphram from the motors vaccum,thus not allowing the diaphram to work correctly. As for the lowering of the needle to fix the barbbling,think of it like this. All the diaphram is ,is a fuel pump! It pumps a set amount of fuel into the carb,by raising or lowering the needle tab up or down,your increasing or decreasing the fuel flow to the motor. The motors barbbling while right side up then cleaning up when inverted is caused by Gravity feeding excess fuel pass the needle seat into the motor.This is because on most gassers the diaphram is on the top when the motor is mounted with the jug aimed down.( the standard way of mounting a engine)The needle seat is on top where as in every chainsaw,weedeater and the like,the needle seat is always on the bottom. By lowering the needle seat setting,your forcing the engine to draw the fuel it requires to run,and are no longer letting gravity feed it. By doing this your removing the excess fuel feeding the motor and thus removing the barbbles.
Hope this better exsplains the barbble problem a bit more to everyone,and how easy it is to fix!
Good Luck Guy's & Gal's
have fun flying,and not worring about the DREADED DEAD STICKS!
Hope this better exsplains the barbble problem a bit more to everyone,and how easy it is to fix!
Good Luck Guy's & Gal's
have fun flying,and not worring about the DREADED DEAD STICKS!
06-02-2006 | 04:36 PM
#20
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RE: 52 cc tuning pros!!!
Jeez it's about time I see some concrete talk about this issue. Thanks a bunch abacro !!
One thing, do you think using a pressure gauge and cutting/lengthening the spring to adjust the tension is better than bending the arm? Example: set spring so pop-off pressure = 10-12 psi?
One thing, do you think using a pressure gauge and cutting/lengthening the spring to adjust the tension is better than bending the arm? Example: set spring so pop-off pressure = 10-12 psi?
ORIGINAL: abacro
Qk all,i'm the one who gave Marzo the needle setting tip to remove the barbbles from his engine. I've been flying these birds for over 30 years and from exsperience have learned that ( so called pressure in the cowl) has absolutely NO affect on the diaphram on the walbro carb. So soldering tubes over the diaphram cover hole isent doing anything to lessen pressure under the diaphram. The diaphram gets ALL its pressure from the engines crankcase and no where else! That little hole your adding the tube to is just a counter vent to allow the diaphram to be sucked down by the motor without causing a vaccum on the opposite side of the diaphram from the motors vaccum,thus not allowing the diaphram to work correctly. As for the lowering of the needle to fix the barbbling,think of it like this. All the diaphram is ,is a fuel pump! It pumps a set amount of fuel into the carb,by raising or lowering the needle tab up or down,your increasing or decreasing the fuel flow to the motor. The motors barbbling while right side up then cleaning up when inverted is caused by Gravity feeding excess fuel pass the needle seat into the motor.This is because on most gassers the diaphram is on the top when the motor is mounted with the jug aimed down.( the standard way of mounting a engine)The needle seat is on top where as in every chainsaw,weedeater and the like,the needle seat is always on the bottom. By lowering the needle seat setting,your forcing the engine to draw the fuel it requires to run,and are no longer letting gravity feed it. By doing this your removing the excess fuel feeding the motor and thus removing the barbbles.
Hope this better exsplains the barbble problem a bit more to everyone,and how easy it is to fix!
Good Luck Guy's & Gal's
have fun flying,and not worring about the DREADED DEAD STICKS!
Qk all,i'm the one who gave Marzo the needle setting tip to remove the barbbles from his engine. I've been flying these birds for over 30 years and from exsperience have learned that ( so called pressure in the cowl) has absolutely NO affect on the diaphram on the walbro carb. So soldering tubes over the diaphram cover hole isent doing anything to lessen pressure under the diaphram. The diaphram gets ALL its pressure from the engines crankcase and no where else! That little hole your adding the tube to is just a counter vent to allow the diaphram to be sucked down by the motor without causing a vaccum on the opposite side of the diaphram from the motors vaccum,thus not allowing the diaphram to work correctly. As for the lowering of the needle to fix the barbbling,think of it like this. All the diaphram is ,is a fuel pump! It pumps a set amount of fuel into the carb,by raising or lowering the needle tab up or down,your increasing or decreasing the fuel flow to the motor. The motors barbbling while right side up then cleaning up when inverted is caused by Gravity feeding excess fuel pass the needle seat into the motor.This is because on most gassers the diaphram is on the top when the motor is mounted with the jug aimed down.( the standard way of mounting a engine)The needle seat is on top where as in every chainsaw,weedeater and the like,the needle seat is always on the bottom. By lowering the needle seat setting,your forcing the engine to draw the fuel it requires to run,and are no longer letting gravity feed it. By doing this your removing the excess fuel feeding the motor and thus removing the barbbles.
Hope this better exsplains the barbble problem a bit more to everyone,and how easy it is to fix!
Good Luck Guy's & Gal's
have fun flying,and not worring about the DREADED DEAD STICKS!
06-02-2006 | 05:56 PM
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From: El Reno, OK
RE: 52 cc tuning pros!!!
Great info, except the part about the static port. If the "atmosphere" pressure didn't have an effect on overall metering, the static port ("diaphragm cover") would not have a hole in it. No need for a hole unless the pressure does "something".....
As for pressure differences on that port causing performance differences.... there is absolutely NO doubt that if the static port "hole" is positioned so that direct ram air into the cowling is directed at that hole, it *will* cause a difference in transition richness/smoothness coming up off idle in flight. That difference is then exacerbated by AOA differences to the air flow in the cowling.
ANYONE who has a BME that has had the "problem" knows EXACTLY that running that static port "hole" into a relatively-calm, atmosphere-pressure area INSIDE the fuse solves problems.
Not to dispute ANY of the other information.... as Joe sez .... "It's about time for some concrete info", so Thank you!
Just wanted to clarify the static port issue.... it has a hole because it MUST sense "atmosphere" to get correct differential across the diaphragm.
As for pressure differences on that port causing performance differences.... there is absolutely NO doubt that if the static port "hole" is positioned so that direct ram air into the cowling is directed at that hole, it *will* cause a difference in transition richness/smoothness coming up off idle in flight. That difference is then exacerbated by AOA differences to the air flow in the cowling.
ANYONE who has a BME that has had the "problem" knows EXACTLY that running that static port "hole" into a relatively-calm, atmosphere-pressure area INSIDE the fuse solves problems.
Not to dispute ANY of the other information.... as Joe sez .... "It's about time for some concrete info", so Thank you!
Just wanted to clarify the static port issue.... it has a hole because it MUST sense "atmosphere" to get correct differential across the diaphragm.
06-02-2006 | 07:33 PM
#22
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RE: 52 cc tuning pros!!!
The spring tension against the arm is the only thing controlling the mixture at 1/3 throttle. The actual pop-off pressure is difficult to predict but easy to troubleshoot and adjust. If too low the engine will four-cycle around 33%, if too high it may be difficult to get mixture rich enough anywhere. Low pop-off is more reliable if you can accept the burble.
06-02-2006 | 08:25 PM
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From: Left Coast ,
CA
RE: 52 cc tuning pros!!!
If you do a search on Google and look for Luis Salas. He is Mr. Walbro (so to speak) I learned this from RCIGN1 and have personally talked to Mr. Salas. He also has written a couple of articles on how these carbs function and how to tweak them. Unfortunately some of the information given in this thread is not correct and some is right on. I suggest everyone read these articles, then there will be no doubt.
If I can find the link I will post it.
If I can find the link I will post it.
