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Old 02-02-2010, 02:44 PM   #1
RCEXTREMEPOWER
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Default Checking carb pop off pressure

Everybody but me might know about this site, But I found it interesting.
I think that most of the problems we are having with the carbs coming out of China might be the pop off pressure.

http://www.aerocorsair.com/id28.htm
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Old 02-03-2010, 07:45 AM   #2
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Default Re: Checking carb pop off pressure

I know the website, and to be honest I do not agree at all with the content.
Having done some experiments, I agree with Walbro who states that the pressure CAN have influence, but should not be overrated.
It should not be overrated especially in model airplane engines that drive a propeller. In a (edit typo) kart that will be required to rev up very high it will be of more importance.
Fuel pump pressure is up to 7 lbs/in2, so pop-off should be no less than 14. Below that pressure I found idle operation very lacking.
With pop-ups in excess of 30 lbs, no problem at all.
Like I said, racers may find benefit in lower pressures, but I think 14 lbs is the lower limit.

When adjusting the pressure, NEVER cut the spring like shown in the article. Instead, compress the spring and slightly heat it so it "sets" at a shorter length. Cutting the spring alters the way the spring works and lever lifting will be limited just as if the pop-off was higher.
It is not the fuel pressure that should lift the needle. It is the job of the regulating diaphragm to do that.
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Old 02-03-2010, 08:30 AM   #3
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Default Re: Checking carb pop off pressure

EXACTLY
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Old 02-03-2010, 08:33 AM   #4
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Default Re: Checking carb pop off pressure

Ok Here is why I posted the link.

I have been having a problem with new engines and there carbs.

I test run all engines before I ship them, The engines are mounted on the test stand are about 30" off the floor and I have a 2 1/2 gallon gas can with a fuel line running directly out of it.

On some engines, They will not draw fuel unless I put the gas can higher than the engine, I can do this, run the engine and then put the can back on the floor and the engine will stop drawing fuel.

If I ship out one of these thinking they are OK , Then have customers contacting me saying they will not draw fuel even with fuel tank just about level with the engine.

I have worked one for hours and finally give up, Install another new carb and problems goes away.

So my question is to anyone that can tell me why they do that. any carb worth spitting on will draw fuel 3 feet.
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Old 02-03-2010, 09:40 AM   #5
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Default Re: Checking carb pop off pressure

Perhaps this is not the right Thread to offer this opinion on, but I just can't resist. I fly gas planes only and I get around to a number of fields during the IMAC season and in Florida during the winter. I see quite a few of the Chinese "Knock Offs", most of which have Chinese Carbs. There are some exceptions but time and again I see the owners of these motors struggling with a variety of problems. They are spending more time working out problems than they are flying.
I understand the cost difference between the knock offs and the real thing, but I can't help but wonder if it's really worth it. We go to the field to have fun and enjoy flying. It's got to be really frustrating for the guys that spend thier time at the field trying to get one of these things to run right.
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Old 02-03-2010, 11:24 AM   #6
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Default Re: Checking carb pop off pressure

Quote: Originally Posted by pe reivers
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I know the website, and to be honest I do not agree at all with the content.
Having done some experiments, I agree with Walbro who states that the pressure CAN have influence, but should not be overrated.
It should not be overrated especially in model airplane engines that drive a propeller. In a cart that will be required to rev op very high it will be of more importance.
Fuel pump pressure is up to 7 lbs/in2, so pop-off should be no less than 14. Below that pressure I found idle operation very lacking.
With pop-ups in excess of 30 lbs, no problem at all.
Like I said, racers may find benefit in lower pressures, but I think 14 lbs is the lower limit.

When adjusting the pressure, NEVER cut the spring like shown in the article. Instead, compress the spring and slightly heat it so it "sets"at a shorter length. Cutting the spring alters the way the spring works and lever lifting will be limited just as if the pop-off was higher.
It is not the fuel pressure that should lift the needle. It is the job of the regulating diaphragm to do that.
Except that the web site had nothing to do with Karts. It is about the engines strapped on the backs of paraglider pilots. Personlly I think it's a good way to die but.... The site is all about Walbros and Tilotsons for aircraft and how to check and set the popoff pressure. How the heck do you get Kart and high RPM out of Paramotor? They have just a little bit more on the line than any model flier.
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Old 02-03-2010, 11:31 AM   #7
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Default Re: Checking carb pop off pressure

Pe, you're right about the spring and cutting but, I doubt if any one on the forum has a the equipment or the knowledge to properly heat and temper a spring especially after it's been plated with chrome or other. The only real choice is to go to a spring Mfg or Dist and buy the correct spring. Or just get one or ten from Walbro and test the squish.
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Old 02-03-2010, 02:33 PM   #8
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Default Re: Checking carb pop off pressure

Walbro has a wide selection of springs for the different model carbs. The hard part is indeed sshecking the pop off pressure of each one.

As far as our R/C stuff goes, the carbs that are most likely to have an issue due to pop off pressure are those with a lower pop off value. As Pe noted, once you go above 14 you're pretty much good to go. I prefer them over 25 but that rattles the cages for a lot of people. If you fly at a high altitude site you definately want a higher pop off pressure.

As for the people messing with their Chinese knock off carbs at a lot of fields, that may be because they don't know how to adjsut an engine to begin with. The inevitable rebuttal about DA owners never having to adjust theirs is not a valid arguement. Running badly is still running badly. Just because an engine runs out of the box does not mean it runs as well as it could, and every field I've been to has had every DA engine running worse than it should. So those people simply haven't bothered to try, where the knock off carb owners are at least giving it a go. Perhaps it's because they have to where the others don't, but why settle for mediocre peformance with any engine?

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Old 02-03-2010, 04:29 PM   #9
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Default Re: Checking carb pop off pressure

Chinese knock offs.........? I just had to do a little maintenance on my wee pee rototiller (Mantis) It's powered by an engine that comes from a fine Japanese company or so I thought, Kioritz. I've had the tiller for about ten years and it's still running strong! The interesting part is every part on the darn thing is stamped made in China, including the Walbro carb....... Maybe they aren't all made in Japan???? Oh yeah Walbro makes all sorts of stuff in China. Does that mean they knock off their own product? I know China is full of unscrupulous manufactures stabbing each other in the back...... I personally rather envision a bunch of Japanese techs, clad from head to toe in white working in a clean room assembling carbs but I don't think it's the way of the world anymore........ All boils down to currency and who's going to do it cheaper. And the contract goes to.......... Are the model engine mfg's buying seconds or just what ever happens to be available at the end of a real OEM production run or are they truely from a pirate company? Again we run into that QA thing and consistency.
All just food for thought.
Here's a snip from the Walbro web site.


WALBRO ENGINE MANAGEMENT IS THE PREFERRED PARTNER FOR ENGINE MANUFACTURERS.
Walbro Engine Management is the world's largest manufacturer of carburetors and a major manufacturer of ignition systems, fuel injection and air/fuel management components, and fuel storage and delivery components for engines targeted at outdoor power equipment, marine, recreational and two-wheel applications. Walbro Engine Management has facilities in the United States, Mexico, Italy, Japan, Thailand and China.

T.O.M., It's all good!
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Old 02-03-2010, 08:39 PM   #10
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Default Re: Checking carb pop off pressure

According to Luis Salas (Mr. Walbro Tech @ Walbro, thanks Ralph) and from what I have seen through experimentation of my own, the pop off pressure is not all that critical unless it is too high or too low. Changing the pop off a little usually changes the needle settings either in or out a little.
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Old 02-03-2010, 10:31 PM   #11
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Default Re: Checking carb pop off pressure

Bodofish,

Many are not aware that only a few years ago Honda was using Chinese manufacturers as sub contractors making a wide line of their Honda generators. Honda later ended those contracts but the sub contractors continued making them but used a yellow case instead of a red one. Can't remember the exact name they were sold under but most of the U.S. RV dealers were selling them for a thousand dollars or more less than the Honda named products. Honda filed suit to stop sales of those generators in the U.S. The "after market" generators are just as good as the brand name Honda product, just selling for less money.

The Chinese can and do make some very good products but I do not believe our hobby has product sales levels high enough to generate a desire by a larger and more reputable manufacturer base to step in and start making goods. My view is that we are only a small cottage industry for a few "back yard" jobbers and not found to be worth the attention required for larger companies. One fact remains, there are a very large number of people over there that will steal someone's patents and copyrights in a heartbeat. They know they are untouchable in any court, and the World Court has proven through their lack of action they will not prosecute any charges against the Chinese.

All they have to is make it cheaper than the original and they know we'll buy it. We have sown the seeds of our demise through our greed and averice, and those seeds are now rooted deep.
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Old 02-03-2010, 10:52 PM   #12
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Default Re: Checking carb pop off pressure

Have you ever thought that it may be that the fuel from the first run at the factory that was left in the carb may have gummed up the works a bit and that just by opening it up and reassembling it you are curing the problem? I had a chinese motor act the same way- wouldn't draw fuel.. I left it sitting for a week after and it started to work fine after sitting with fresh fuel in it. I noticed the g-62 on my 1/3 scale cub will do the same thing as I only fly it a couple of weekends a year. If I am planning to fly it, I will pump some fuel up into the carb it a week or so before and just let it set.

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Old 02-04-2010, 12:06 AM   #13
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Default Re: Checking carb pop off pressure

Quote: Originally Posted by Tired Old Man
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Bodofish,

Many are not aware that only a few years ago Honda was using Chinese manufacturers as sub contractors making a wide line of their Honda generators. Honda later ended those contracts but the sub contractors continued making them but used a yellow case instead of a red one. Can't remember the exact name they were sold under but most of the U.S. RV dealers were selling them for a thousand dollars or more less than the Honda named products. Honda filed suit to stop sales of those generators in the U.S. The "after market" generators are just as good as the brand name Honda product, just selling for less money.

The Chinese can and do make some very good products but I do not believe our hobby has product sales levels high enough to generate a desire by a larger and more reputable manufacturer base to step in and start making goods. My view is that we are only a small cottage industry for a few "back yard" jobbers and not found to be worth the attention required for larger companies. One fact remains, there are a very large number of people over there that will steal someone's patents and copyrights in a heartbeat. They know they are untouchable in any court, and the World Court has proven through their lack of action they will not prosecute any charges against the Chinese.

All they have to is make it cheaper than the original and they know we'll buy it. We have sown the seeds of our demise through our greed and averice, and those seeds are now rooted deep.
Absolutely agree 100%!!! Just got think'in while I was working on the little tiller and started laughing to myself about what's made where....
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Old 02-04-2010, 05:34 AM   #14
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Default Re: Checking carb pop off pressure

Quote: Originally Posted by bodofish
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Except that the web site had nothing to do with Karts. It is about the engines strapped on the backs of paraglider pilots. Personlly I think it's a good way to die but.... The site is all about Walbros and Tilotsons for aircraft and how to check and set the popoff pressure. How the heck do you get Kart and high RPM out of Paramotor? They have just a little bit more on the line than any model flier.
What exactly do you intend to say with your answer?
Read my post again! A little slower this time.
Since paraglider engines also drive a prop, they do not rev up like a Kart engine does.
If I were a para pilot, I would rather check the Engine manufacturer/Walbro maintenance manual, than that website, in that order.
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Old 02-04-2010, 07:57 AM   #15
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Default Re: Checking carb pop off pressure

Quote: Originally Posted by RTK
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According to Luis Salas (Mr. Walbro Tech @ Walbro, thanks Ralph) and from what I have seen through experimentation of my own, the pop off pressure is not all that critical unless it is too high or too low. Changing the pop off a little usually changes the needle settings either in or out a little.
Bingo. This sums up the entire thread. Thanks.
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