High Idle Speeds
03-24-2012, 01:15 PM
#1
High Idle Speeds
I'm curious as to how many of you guys running small gassers ( 50cc and less ) are happy with a 1400 to 1600 rpm idle settings required to keep the engine running. Personally I find this to be quite the norm with a majority of the new gasoline/ignition engines being manufactured and sold in the marketplace these days.
I have flown,rebuilt,and converted many glow and gasoline engines. All being single cylinder engines. The best engine I have converted to date is the Webra "Bully" 35cc. I convert them to Rcexl ignition and replace the original carb with a Walbro WT-540 carb. This engine will consistenty idle at a steady 1000 rpm or less without a hiccup or sputter during transition to full WOT using a 19x8 prop. I sold one of my Webra conversions here on RCU and the buyer was elated when, on the very first run, the engine idled down to 950 rpm and never quit or missed a pop.
With many modelers focusing on the peak power specs of an engine, shouldn't we also be looking at overall performance which includes the low end performance also? Especially when it comes to Scale flying? I know that many are boring holes in the sky with giant 3D planes that aren't really concerned with the idle except when they want to land.
This is my own personal observance but I find that some engines idling out at 1600 rpm is not really that good and also is a sign of poor porting design ( turbulent airflow). I have watched many pilots that have to taxi their plane off of the asphalt and on to the grass just to get them to stop rolling.
I'm not bashing one brand against another. Just wondering if any of you find the idle speeds of your gasser to be too high. In many cases the idle is set high in order to keep the engine from quitting. I understand there are many factors leading to high idle speeds such as internal mechanical resistance but I am inclined to believe that these new engines are a product of poor porting and mass marketing. Grab the money and run!
I would like to hear from any of you that has a small gasser <50cc that you are REALLY pleased with the overall performance.
Speedy
I have flown,rebuilt,and converted many glow and gasoline engines. All being single cylinder engines. The best engine I have converted to date is the Webra "Bully" 35cc. I convert them to Rcexl ignition and replace the original carb with a Walbro WT-540 carb. This engine will consistenty idle at a steady 1000 rpm or less without a hiccup or sputter during transition to full WOT using a 19x8 prop. I sold one of my Webra conversions here on RCU and the buyer was elated when, on the very first run, the engine idled down to 950 rpm and never quit or missed a pop.
With many modelers focusing on the peak power specs of an engine, shouldn't we also be looking at overall performance which includes the low end performance also? Especially when it comes to Scale flying? I know that many are boring holes in the sky with giant 3D planes that aren't really concerned with the idle except when they want to land.
This is my own personal observance but I find that some engines idling out at 1600 rpm is not really that good and also is a sign of poor porting design ( turbulent airflow). I have watched many pilots that have to taxi their plane off of the asphalt and on to the grass just to get them to stop rolling.
I'm not bashing one brand against another. Just wondering if any of you find the idle speeds of your gasser to be too high. In many cases the idle is set high in order to keep the engine from quitting. I understand there are many factors leading to high idle speeds such as internal mechanical resistance but I am inclined to believe that these new engines are a product of poor porting and mass marketing. Grab the money and run!
I would like to hear from any of you that has a small gasser <50cc that you are REALLY pleased with the overall performance.
Speedy
03-24-2012, 02:06 PM
#2
RE: High Idle Speeds
Congrats on your Bully project. I have a small bucket list of engines I wanted as a youth growing up around R/C and the Bully was one of them. The only "small" gasser I have owned was a DA 50. It was converted over to RCEXL ignition. I had never put a tach to it but was quite happy with it's overall performance including idle. The 15.25 lb airplane that it was mounted on would not roll at idle.
IMO the thing that affects idle reliability is the reed block. Most small gassers have gone the way of reed induction and a reliable idle is influenced bu reed seal. If the reeds aren't sealing on the piston downstroke then the engine is not going to idle down reliably. While I did not surface the reed block on my DA, I did replace the aluminum screws that hold the carb/block/reed cage with titanium studs. The studs were epoxied in place with JB weld. What that did was allow me to hold the whole assembly in place with a couple 10-32 lock nuts. With the screws, in order to get them tight enough to not come loose ( even with loc-tite )one usually has to tighten them enough to distort the reed block.
I now have an airplane that will be powered with a DLE 55. My plan is to resurface the reed block and use the same carb mounted studs. We will find out if it idles as well as my DA did.
IMO the thing that affects idle reliability is the reed block. Most small gassers have gone the way of reed induction and a reliable idle is influenced bu reed seal. If the reeds aren't sealing on the piston downstroke then the engine is not going to idle down reliably. While I did not surface the reed block on my DA, I did replace the aluminum screws that hold the carb/block/reed cage with titanium studs. The studs were epoxied in place with JB weld. What that did was allow me to hold the whole assembly in place with a couple 10-32 lock nuts. With the screws, in order to get them tight enough to not come loose ( even with loc-tite )one usually has to tighten them enough to distort the reed block.
I now have an airplane that will be powered with a DLE 55. My plan is to resurface the reed block and use the same carb mounted studs. We will find out if it idles as well as my DA did.
03-24-2012, 03:21 PM
#3
RE: High Idle Speeds
Speedy, I just bought a Webra Bully 35ccGlow new in box. I am on vacation in Florida. When I get back home, I plan to install a Rcexl ignition on it also. Is 28 degrees BTDC a good running set-up? I remember Antique saying the 35cc Bully to be a very good engine. That is why I bought it. Best Regards,Capt,n
03-24-2012, 03:54 PM
#4
RE: High Idle Speeds
Capt,n,
You have it correct. 28 degrees BTDC and it will pull like a horse and idle down to an astonishing "tic". I have converted 3 Webra "Bully" engines and I love them. Problem is that someone hears one run and begs me to sell it to them. I have one freshly converted and have two N.I.B. in my engine closet waiting for the conversion.
When you get ready to do yours I am willing to help. I am sick of P.O.S. Chinese engines. The Webra "Bully" converted to Rcexl ignition will spoil you. It is a real gem. I have some N.I.B. Walbro carbs that I found on the net. You are welcome to one if you want. The WT-540 is a perfect match for your "Bully".
Don't bother to mess with the Delorto carb that is on it now but keep it because it is an excellent "alky" carb for large glow engines like the ST 3250 which never ran right for anyone with the stock ST carb. I put the Delorto carb from my Webra on a O.S. 3500 and it ran great and was not starved for fuel in the least.
Florida eh??? Are the fish hitting down there or are you laying on the beach "bird watching"?
You have it correct. 28 degrees BTDC and it will pull like a horse and idle down to an astonishing "tic". I have converted 3 Webra "Bully" engines and I love them. Problem is that someone hears one run and begs me to sell it to them. I have one freshly converted and have two N.I.B. in my engine closet waiting for the conversion.
When you get ready to do yours I am willing to help. I am sick of P.O.S. Chinese engines. The Webra "Bully" converted to Rcexl ignition will spoil you. It is a real gem. I have some N.I.B. Walbro carbs that I found on the net. You are welcome to one if you want. The WT-540 is a perfect match for your "Bully".
Don't bother to mess with the Delorto carb that is on it now but keep it because it is an excellent "alky" carb for large glow engines like the ST 3250 which never ran right for anyone with the stock ST carb. I put the Delorto carb from my Webra on a O.S. 3500 and it ran great and was not starved for fuel in the least.
Florida eh??? Are the fish hitting down there or are you laying on the beach "bird watching"?
03-24-2012, 04:29 PM
#5
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RE: High Idle Speeds
I have one 55cc, two 26cc, and one 20cc. So far I am extremely happy with how these engine's run. I do not have any problem's with the idle's being high. But I am very finiky about proper prop size's, timing, and well tuned. What I notice from my observation's is most guy's generally don't pay much attention to any of those three. They are more concerned with getting airborne, and then want to complain that their motor doesn't run right.
03-24-2012, 05:11 PM
#6
RE: High Idle Speeds
I will have to agree with that observation 100%. Taking the time necessary to run-in and dial the carb in is well worth the time. The aggravation sets in when despite taking the time to tune and run an engine and it still falls short of your expectations. What make/brand are your engines that you mention?
There is a new engine being sold by Agape Racing. It is the NGH GT series of engines. It has a front rotary intake with a side/rear exhaust option and I am sure it is a non-reed style carb plus beam or radial mounting. The only true way of investigating an engine is to buy it and run it for one's self. I'm getting the itch to buy one of the 35cc's.
http://www.rcuniverse.com/market/item.cfm?itemId=832560
SPEEDY
There is a new engine being sold by Agape Racing. It is the NGH GT series of engines. It has a front rotary intake with a side/rear exhaust option and I am sure it is a non-reed style carb plus beam or radial mounting. The only true way of investigating an engine is to buy it and run it for one's self. I'm getting the itch to buy one of the 35cc's.
http://www.rcuniverse.com/market/item.cfm?itemId=832560
SPEEDY
03-24-2012, 07:18 PM
#8
RE: High Idle Speeds
Yes the Webra comes in at 3.5 lbs RTF but I compensate some of the weight by using a IBEC . The overall weight of the Webra is greater but comparring the reciprocating mass of a lighter engine is not that great and should not ( in my opinion ) cause the idle speed of the lighter engine to be double in comparrison especially if both engines are swinging identical props. Compression ratios may also come into play here.
Personally I do not see where weight, other than reciprocating mass, has any bearing on idle speed and/or top end performance other than power to weight ratio figures. I am always open to learning something new so don't be afraid to present a differing perspective.
I guess what it all boils down to is if you are willing to compromise weight for performance and what the particular application the engine is being used for if indeed the engine's weight is a factor. I firmly believe that porting,timing, and carburation are the main factors in engine performance and idle capability.
"I have learned from my mistakes.....that is why I am so darned smart!"
SPEEDY
Personally I do not see where weight, other than reciprocating mass, has any bearing on idle speed and/or top end performance other than power to weight ratio figures. I am always open to learning something new so don't be afraid to present a differing perspective.
I guess what it all boils down to is if you are willing to compromise weight for performance and what the particular application the engine is being used for if indeed the engine's weight is a factor. I firmly believe that porting,timing, and carburation are the main factors in engine performance and idle capability.
"I have learned from my mistakes.....that is why I am so darned smart!"
SPEEDY
03-25-2012, 05:08 AM
#10
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RE: High Idle Speeds
Speedy, the 55 is a DLE the other three are RCGF. My problem with the front carb is most of my build's are scale. And with that come's dummy engine's. Even without a front carb it can be tight getting the dummy in there. As far as weight goes, the only way I can see weight affecting these is by mean's of to large of a prop. If anyone would post a link for that webra bully I would like to take a look.
03-25-2012, 07:03 AM
#11
RE: High Idle Speeds
ORIGINAL: VIRGINIA MODEL BUILDERS
It would be helpful to take this procedure of honing the block through the steps of how to and with some photos and what you use tool wise
It would be helpful to take this procedure of honing the block through the steps of how to and with some photos and what you use tool wise
