Lureman

Ok guys I'm ready to buy my carbs for my 3 conversions Homelite25cc , weedeater/ poulan 25cc and a ryobi 31cc I guess what I'm looking from you guys is the model carbs you are running on your engines, also what would happen if a 11mm ,12mm and 13mm carb would be put on these????? Thanks Lureman

Rcpilot

My Feedback: (78)

Bigger carbs only work if you can get the engine to move enough air through them.

You can try and dump more gas in the engine with a bigger carb--but it won't work unless you can get the engine to pump harder. Just putting a bigger carb on it--does not make it pump harder.

You might need to raise the compression. You may need a better ring--get a better seal--less blowby--more compression.

You can bend the reed limiter out a bit. This will allow the reed to open more and put in more gas--but there's a point of diminishing return somewhere.

When you run a bigger carb-the vaccum on the carb goes DOWN. You need vacuum--or air velocity through the carb to make it work right. A bigger hole--bigger bore--will lower the vacuum unless you can get the RPMs up high enough to pull the same amount of vacuum, or more, through the bigger carb. Lower the vacuum on the carb--and it won't work right. You could end up beating your head against the wall unless you do something else to increase the power as well.

I'm not saying that nobody ever put a bigger carb on a weedie and made it run better. But it's uncharted territory and it's all guesswork.

davewallace

My Feedback: (29)

Hi Lureman,
This isn't uncharted territory. The three engine models mentioned will respond well to a 10 to 11mm Walbro or Zama carb. The insulator/manifold bore needs to match the throttle bore of the carb for the biggest improvement. Of the three the weedeater is the only one that may need a 9 or 10mm carb, because some of them have rather small ports. The Ryobi already has a 5/8" intake. The Homelites and Weedeater manifolds need to be bored out. It is usually necessary to install a external pulse hose to the crankcase for the carb pump on these. Do a RCU conversion forum search on carbs, there is a ton of posts on this.

Dave

mikenlapaz

Another way to get more air thru the carb is to reduce the load on the engine a little. An 18" prop creates a 254 s.i. column of air while a 17" has only 227 s.i., roughly a 10% ruduction which should allow more rpms thus more/better air flow thru engine. The thrust will be less but offset by the rpm increase.



I use a Walbro 167-A 11mm venturi (with primer bulb) on a 21cc Echo Spad trainer 17-6 APC. 12# AUW
Chris has a thread on his plane @ http://spadworld.net/forum/ search for : 22cc Echo Powered "trainer"
Also have same carb on Ryobi31, and Homelite 25

Lureman

Thx Guys for the info I'm learning alot . Ok my next ? is can I use any walbro or zama 11mm carb or are they jetted for different engines. I have a listing of carbs from www.prestwich.ndirect.co.uk/walbrocarbs.htm Take alook and plz get back to me. thx Lureman

davewallace

My Feedback: (29)

Hi,
Just shop for a good deal on Ebay, RCU classifieds or contact Wackerengines.com, poco242 on RCU. You want a 28 cast into the venturi inlet for a 11mm Wallbro carb. The number is in 64ths fot the venturi diameter. That is the narrow throat area.

Dave

mikenlapaz

I use Walbros as I have not had any luck so far in finding a source for diaphram and rebuild kits for Zama carbs. The last time I tried to get ingo from Zama website I found it lacking in all respects. Walbro on the other hand, took some getting use to but lost of info available. If anyone has a good link to real info for Zama, please share. (It has been over a year since I tried Zama site. ) [ edit Just visited the new, to me, zama site what an improvement.]

Just one way into Walbro site: http://wem.walbro.com/walbro/family.asp

Living in a limited shopping area, and knowing carbs need parts replaced periodically to function correctly, I go with Walbro.

Rcpilot

My Feedback: (78)

I called Walbro yesterday. They are sending me a "service manual" so that I can learn how to tinker with these carbs.

The goped guys re-work the pop off pressure springs and some of the other internals that we don't usually mess with.

Most of us just slap a carb on and if the engine starts and runs--we figure, "Good enough."

These goped guys know all the little intricacies of the guts on the walbros. They get them to flow better and their engines end up really cranking out a lot more power than with a stock--unmolested--carb.

I have a shoebox full of carbs, so I'm gonna start working on them and see if I can get anymore out of them. I'll post procedures and results if I find anything worthwhile.

Antique

My Feedback: (4)

Looking forward to your results.

Flypaper 2

Mike :
try your small motor repair shop for carb kits. When I was in the business I sold jobber carb kits for Walbro, Zama ,Tillotson and a couple of others for around five bucks for any of them as the same company made the kits for all of them. Quality was as good as original. RC: you'll have to get a pop-off pressure gauge if you're going to play with the spring, otherwise your just guessing. When you go to a bigger carb, you're running lower vacuum in the carb so you need to run lower pop-off pressure as there isn't enough vacuum to pull it off properly.

Rcpilot

My Feedback: (78)

I know that I'll need some specialized tools in order to work on the internals of the Walbros. I just don't know what kind yet. Obviously, I'll need the pop-off pressure gauge, but other than that, I haven't a clue.

I'm hoping that this service manual Walbro is sending me will get in-depth and really tell you how to tweak these things. The woman I talked to at Walbro was going to just send me a basic user guide--but I told her that I wanted the technical stuff, so she said that she'd send the "big book". She said something about changing jet sizes--but I don't think she was a service tech. I might very well have to change jet sizes for my altitude and performance expectations. I just won't know untill I read the book and gather the necessary tools to work on them.

If a guy could replace a few $5 parts in a Walbro and get an additional 500RPM out of a G62--I'd be really tickled. The goped guys say that it's possible to get an additional 2000--3500RPM from their G62 engines--just by messing with the carb. But, you gotta consider that they are running gear reduction of some kind. There's less low-end load on the engine. They run their engines up in the 12,000RPM range and more. I imagine that once you break that 9000--10,000RPM band--then those last few thousand R's come a bit easier, simply because thats where the engine is really making lots of power and it's up in the torque curve.

With our engines loaded up down in the 7000-8000RPM range, it might be hard to coax additional RPM out of the engine. It's not really running up in the peak of the powerband--so your fighting just to GET it up to 9000RPM. But I would think that if you could get a G62 to swing up in the 8500--9000RPM range--then carb mods would be more effective.

But, this is not a G62 thread. It's about Walbro carb. I plan to read the book and do some tinkering. I have a G62 here and I know what it turns with XYZ prop at this altitude. I'll just put different carbs on it and tach it for baseline RPM. Then I'll tear into the carbs and make a modification. Put it back on the engine with same XYZ prop and tach it again.

ryan@ddm

If you are looking to see significant performance gains on your G62 by simply tweaking the stock HDA-48 carburetor, you're headed down a road with little upside. The G62 has a TON of potential, but most of it is lost inside the engine, not up front with the carb. Proper porting (or, if you are feeling more agressive, the addition of a cylinder reed intake and proper reed porting) will allow you to add a significant power improvement throughout the RPM range, and quite a few more RPM's on top...

Rcpilot

My Feedback: (78)

While I don't doubt your knowledge or intentions, there is a guy that I talked to that claims he wins lots of go-cart races with modified carbs and stock engines.

He does some kind of deal where he bores out the carb and adjusts the pop-off pressures. He wouldn't tell me exactly what he was doing--said it was to complicated to try and describe it over the phone. Had he described what he was doing to the carb--well he may as well have been talking to Homer Simpson, as I have no knowledge of the internal workings of these carbs. But, he did offer to send me one of his modified carbs free of charge. If I like it, then I can keep it and pay him for it. If I don't like it--then just return it.

IMO--it never hurts to experiment. Nobody ever learned anything by taking things for face value and not questioning the "why" and "what if".

ryan@ddm

Of course. I'm not suggesting that you shouldn't experiment or learn more. I'm merely passing along the information that in stock form, the HDA-48 has a sufficiently large venturi, adequate internal metering and jetting, and an appropriate pop-off pressure when used on the G62.

In the end, I assume you are most interested in seeing higher operating RPM's out of your G62, and increasing the power your engine generates along the way. The G62 is part of a family of Zenoah 'angle-plug' motors (starting down in the 23cc range with models like the G23LH, moving into moderate cc's with models such as the G43L, etc). These engines are designed and tuned for extremely high reliability at the expense of performance - reflecting their primary uses in industrial applications. Modifying the port timing, switching to a reed intake, or installing a complete billet head with a straight-plug combustion chamber are all steps back toward real performance - and when properly done, will not negatively impact reliability

Antique

My Feedback: (4)

Not to be a wet blanket, but we have been running stock G62 engines in our AT6 racers for 13 years...I am the tech inspector at the races, responsible for checking the winning engines after the races...I'm sure the pilots have tried everything in the book to get more rpm from an otherwise stock engine...While I don't tear down the carbs to check for internal mods, it''s almost a sure thing that someone has tried everything possible...They have been running the same for all the 13 years..I defy anyone to change only the carb and make more power and/or rpm, it can't be done..The amount of fuel going through the carb determines the rpm, and a stock carb will flow more than enough to do that....
Improvements in the speed of our planes have come from better props and smoother airplanes, not from anything done to the carb..No other mods to the engine are allowed, they must be completely stock, no metal added or removed, no thinner base gaskets, different spark plugs, etc.....
FWIW, I tried a Trevor Simpson reed on an otherwise stock G62...Beautiful piece of workmanship..Without internal mods to the engine there was NO improvement....

ryan@ddm

Yep, without reed porting the performance gain will be negligible.

chris6414

My Feedback: (10)

WT-499 and Methanol? Strip the ignition, get a glow adapter and mix Methanol with some Cool Power 15% nitro to get about 4-7%oil content and you have a capable G62. Increase in cost is about .50 a gallon down here.

av8tor1977

My Feedback: (6)

Ah the magical, mythical "SUPER CARBURETOR." This urban legend has been around since the day after the internal combustion engine was invented I believe. Will it ever die???

Even high tech computer controlled fuel injection will not give any more horsepower than a properly sized and jetted carb. (Sometimes it will give a slightly better torque curve due to more accurate fuel metering, but no free horsepower!)

AV8TOR

Prop Nut

My Feedback: (3)

There is a "Super Carb" out there, it is just masquerading as a mild mannered reporter named Carb Kent.

Lureman

Thats a good one Prop Nut

ernest2

where can i find a good but cheap carb for my stock 25cc homie? walbro 167 is a bit expensive for me. anybody has any extra carb? will buying a used carb ok?

Lureman

ernst Go on e-bay thats were I'm finding mine pal Clay

teddywilk

My Feedback: (10)

IM INTERESTED IN MORE INFO ON THIS REED INTAKE YOU SPEAK OF. IM WORKING ON A 25 TORE AND WANT TO US SOME KIND OF REED VALVE. CAN YOU POINT ME TO A SITE WITH INFO ON THIS?
FARMER TED