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-   -   Need HELP switching/repairing Walbro carb on a US Engines 41.... (http://www.rcuniverse.com/forum/giant-scale-aircraft-3d-aerobatic-110/2105099-need-help-switching-repairing-walbro-carb-us-engines-41-a.html)

aronhk_md 08-21-2004 12:11 PM

Need HELP switching/repairing Walbro carb on a US Engines 41....
 
I'm still fairly new to the sport, so I could definitely use some help from the small gas engine experts here. I bought a US Engines 41 used from a gentleman here in the marketplace, and I believe him when he says it ran for him. Unfortunately, it wouldnt run for me because it was just letting the gas pour straight through the carb at a heavy rate......non-stop from the moment I hooked up the gas line. After some searching online I came to the conclusion it might be the spring not putting enough tension on that rubber coated needle that the diaphragm moves.

I took it apart and stretched the spring a bit, put it back together, and VIOLA! No more gas pouring through, but it won't start, and now I'm thinking maybe I stretched it too much and it is not letting ANY gas in.

I also acquired a brand new carb from a 40cc chainsaw, and perhaps I can just replace the problem carb with it. The only problem is that the new carb has nipples for TWO gas lines....one slightly smaller than the other. I don't know if this second line is just an overflow going back to the tank, or what. I noticed my weedwacker has the same setup with two lines.

Can anyone tell me what I should do with the second line? Should I just block it with a short length of gas line? Should I somehow run it back to my tank? I have two brass tubes running to my fuel tank (I have never actually built a plane before, and got this one as a basket case. Being handy I have fixed everything I know of, but some of the intricacies of r/c plumbing still escape me.)

Does anyone have a good diagram of how gas lines should be run in a plane? I have been unable to locate one online.

Thanks for your help everyone.

Aron

HuskerBoy 08-21-2004 01:46 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
Any small engine shop in your area that sells weed-cutters will have rebuild kits for the Walbro. You need to take it with you since there are several model numbers they need to match. It cost about 25 to 30 per kit.
Sorry, I can't help you on the dual line versions, unless it's an overflow vent. Try simply blocking the smaller one. You need to find which brass tube goes to the clunk fuel pickup and the other is a vent at the top inside the tank and it has a line from it that drains below the cowl at the firewall.

Hooked-On-RC 08-21-2004 02:20 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
Some of the dual line carbs are for primer bulbs. Those are the little rubber domes that you press to prime the fuel to the carb. Often times they will utilize a second line.

By the sounds of it your carb diaphram needs replacing and a rebuild kit is the way to go. A local chain saw shop or small engine shop should be able to help you but take the carb with you as there a literally thousands of small walbro carbs out there. Not only do you need the model number but also the small number stamped on the side of the carb.

if possible buy a new carb as they are almost as cheap as a rebuild kit.

good luck

aronhk_md 08-21-2004 02:33 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
So the main line does not feed through the separate primer bulb on these setups? I had assumed it would. Thanks again for everyone's help. If anyone else has experience on how to use one of these two line carbs for this application it would be appreciated. The fact is I have been looking as you said to replace the carb cheaply, but have only been able to come up with these 2 fuel line versions.

aronhk_md 08-21-2004 02:34 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
I am hesitant to spend the money on the rebuild kit because I have heard rebuilding often doesnt work. Better to replace it with a new one.....or so I thought. If only I can find one.

HuskerBoy 08-21-2004 02:50 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
I've had to put in three kits and has always solved the running problems.

GreaTOne_65 08-21-2004 10:27 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
Quote:

ORIGINAL: md2b

I am hesitant to spend the money on the rebuild kit because I have heard rebuilding often doesnt work. Better to replace it with a new one.....or so I thought. If only I can find one.
md2b, you can do what ever makes you feel better, but a rebuild kit from Carquest is about $7.00. I have a Quadra 52, that seems to need a new kit every year! I blame most of the problems on the ethanol in the gas, I believe it hardens the diaphragms?! The diaphragm has four screws holding it on, make sure the lever for the needle valve is flush with the bottom of the bowl, and when you reinstall the diaphragm, put the gasket first then the diaphragm, then the cover. Set the idle needle at 1 3/4 to 2 turns open. I set the high needle with the engine running, some what dangerous I know but it's the best way to get the engine to run just right. To start it, turn on the mag, choke it til it fires, release the choke, should run on the 3rd or 4th try.

Just my .02, for all it's worth, and according to my wife about half the time it's not even worth that!! LOL!!

Dale

the-plumber 08-22-2004 06:01 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
Quote:

ORIGINAL: md2b
Does anyone have a good diagram of how gas lines should be run in a plane? I have been unable to locate one online.
Aron
The Walbro site has exploded carb diagrams online.

Surf to www.walbro.com

Select "Service And Aftermarket" button on the left.

Then use the "Browse by Walbro number" box in the upper right - stick your carb number in the box and hit Go.

All Walbro carbs have the number embossed on the carb body (somewhere).

The diagram should identify all the connections.

With the great number of configurations in the Walbro line, swapping carbs may or may not work. Best bet is to stick with the OEM carb unless you know the replacement carb will work correctly on your engine.

duanes 08-27-2004 08:14 PM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
I just got done playing with this very thing. Please forgive me if I over explain, but I will not make any assumptions.

1. The stock weedeater fuel tank has two lines. One has a short stub inside of the fuel tank. (Frequently, it is also a larger diameter). This is the vent line used to pressurize the tank.

2. The other line ussually has a clunk or weight. This is the supply line. I have also noticed that this is often a "pass through" line that just has a friction fit and goes through the tank wall.

3. If your carb setup has a separate primer bulb, the center tube is the output to the carb while the outer tube is the supply from the tank.

4. On the carb, the supply is ussually close to the recessed needle adjustments and is a straight tube. Ussually, the pressure return tube on the carb is a "bent" or "elbow" tube..

5. The supply from the tank goes to the outer connector on the primer. The center connector on the primer goes to the straight tube on the carb. The bent line on the carb connects back to the air vent (larger connector or the one that has the connector) on the tank.

Of course, if you have replaced the tank, then the supply and vent lines will be clearly known. If the fuel is supplied in reverse, fuel will come out of the exhaust port pretty easliy. While I haven't disassembled and engine/carb - it appears that the pressure is created by pulses in the exhaust and if you push fuel into this chamber, some fuel will come out of the engine in the exhaust port. However, this may also indicate a ruptered diaphram in the carb.

Again - sorry if I over simplified this, but I had a bit of a hard time finding the carb plumbing diagrams clearly shown online.

Antique 08-28-2004 09:38 AM

RE: Need HELP switching/repairing Walbro carb on a US Engines 41....
 
Wrong ! The tank is NOT pressurized with a Walbro carb. The carb has a very efficient pump built into it. The tank is simply vented outside the plane. The pump is operated by small pulses from the crankcase, not the exhaust. Usually the small tube on the carb is an excess fuel return line, we don't need and don't use this feature, just plug it off with a piece of fuel line sealed with a bolt. Rebuild kits for these carbs run from $5 to $10, well worth it.


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