While we are talking about four strokes I should mention some of the features of the Walbro WT-456 as it is really a great little carb

It has a High Speed nozzle and check valve assembly in the venturi. This helps when you suddenly chop the throttle. Many engines will try to die on you when you chop the throttle but with this valve, these carbs do not do this.

A real rarity for Walbros is that this carb actually has an accelerator pump believe it or not

This carb also has a Choke.

It is not a very big venturi at 6.5 mm so is ideal for the four strokes up to probably a 150 size and should have excellent throttle response

This is at M&D

<table cellspacing="0" cellpadding="3" border="0" width="95%"> <tbody> <tr valign="top"> <td align="left" valign="middle">WL-WT-456</td> <td align="center" width="55" valign="middle"><input type="hidden" value="WL-WT-456" name="mv_order_item" /> </td> <td align="center" width="40%" valign="middle">WT456/WT-456 WALBRO CARBURETOR PART WT456/WT-456
CARB</td> <td align="center" valign="middle">$41.00</td> </tr> </tbody></table>

Thank you very much.

Sincerely,

SPACEWORM/Richard

I did more reading in the service manual from walbro. I can have a metering problem ,since the metering hole to atmosfere is UP and on the side where proppelor pushes the air. I have an Idea how to fix that, Imay have to do a cleaning and blowing on the carby, After I got the gas in and I took the pump plate out , Ifound some fine aluminum on it.
Now ...How I can drop a 1000 RPM's on idle, from 3000 to 2000.

I drew my set-up, any diffrent ideas?

TK
Adrian

It should work.

That is how a Honda GX 31 manifold is from the factory. It works fine.
motorhd

Hey, Adrian. A couple brief comments and questions. From your pictures, it looks like you've hooked up a fuel tube to that extra tube stub that comes with the WT456, and I see it's full of fuel, too. What are you doing with that? On my Saito 150/wt456 conversion I have this blocked off with a cap and it works fine. I think that's a tank return line for carbs with a primer bulb, which you don't have (going from memory here folks...). As long as your choke is working you should get plenty of fuel to start the engine.

Eventually, those black reed valves give up. If you're not having issues now, you will. Get the teflon impregnated glass one on order now, via a rebuild kit for that carb. The blue mylar version works too.

Regarding your suggestion to reorient to horizontal the metering hole; On my engine, the metering hole is DOWN, like your's. And it works fine. Just to make sure we're talking about the same thing, the metering hole (to ambient) is the little hole in the metal cover (4 screws) on the side of the carb opposite the pump cap (1 screw). It's purpose is to provide a reference pressure to the diaphragm below that regulates how much fuel is available to the needle valves upon vacuum demand inside the venturi. If any ram effects from relative wind inside a cowled installation are present, the pressure on the reference port can rise, leading to a rich condition.

Outside the cowl, out in the open, and protected behind the cylinder head, it's doubtful you're having metering problems based on this hole pointing down. Now, I don't know what you mean when you say your metering hole is "UP". Your pic shows it down I think. Is that an old picture you posted earlier? Even your sketch shows the metering hole down. But in the sketch, you refer to your "new idea" of the "pulse pump", too. This adds to confusion over what you are really talking about reorienting. Pulse pump? or metering hole, as in the text?

Regardless, don't go to too much work to reorient the entire carb as my opinion it's doubtfull the position is affecting your engine. Is there either sealer, or a gasket on both side of the carb spacer? If it won't run at idle, it should also be almost impossible to start by hand. Is it? When you choke it before applying spark, is the carb a lttle wet? it should be, especially with the carb pointed down. Is one of your idle ports blocked? If all simple fixes fail, blow it out with an airhose to make sure (carb disassembled). This is so dumb as to not be worth mentioning, but your pic shows the external idle set screw engaged with the throttle plate. Back that screw off. It may be limiting your idle low speed.

"I'll try to post the pics of the counter-spring this weekend. "

[/quote]


Hi. Is the "counter-spring" you refer to use to counter the existing throttle return spring? I just slip or snip the little hook off of the stock return spring and leave it in place to act as a spacer. Pros and cons of each approach?? TIA
[/quote]

Spaceworm: I usually pull the whole spring out. I determined the spacer effect isn't necessary because the throttle plate, as it's closing, recenters itself in the venturi.

However, even with this return spring gone, there is STILL spring pressure being exerted on the throttle by the accelerator pump spring. This is internal to the carb, so you can't really see it until you take the throttle axle out.

My counterspring is designed to counteract that remaining spring force. Many people don't know about this, because most Walbros don't have an accelerator pump.

Pull Up Now,

On the schetch, on new Ideea for the pulse I want to try to drill the insulator plate in the middle of the tickhness from one side untill the the middle of intake hole for the carb.and then one more hole on the side to communicate with pulse hole on the carb...like an "L" I want to eliminate the other hole in the intake and the tygon tube.think of the L with the long bar West and short one South. I guess now you get the idea if you look again at the schetch.
The Primer tube that you mentionated that is full with gas ...I use it to pull gas trough Carby . It does not go anywere is caped OFF.
The Metering (4 Screws) is oriented UP behind the cylinder. I think to JB weld a 1/8 tube to that hole and run a tygon tube to eliminate any ...wind.
The cab has the original Gasket between carby and Insulator plate, to seal the intake tube,insulator and top plate I use a O ring that it gets compressed between Top plate and Insulator and tights around the O ring around the tube. That should do it.
I do not know what you refering to:<div id="TixyyLink" style="border-right: medium none; border-top: medium none; overflow: hidden; border-left: medium none; color: #000000; border-bottom: medium none; background-color: transparent; text-align: left; text-decoration: none">"<u>Eventually, those black reed valves give up</u>. If you're not having issues now, you will. Get the teflon impregnated glass one on order now, via a rebuild kit for that carb. The blue mylar version works too."
If you got those...please give me a link. How low your engine is Idle?
When I got off the 1 Screw cover(pump side) after I drew some fuel I seen some aluminum shavings ....like from manufacturing. I guess the Carby may be also have some clough areas.
I will teare it a part and clean it. soon that I will have some time.

Thank You

Adrian



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Here's a belated response to ROTCCAPT's request for a picture of the Stearman with it's Saito 150 (WT456-1) gas conversion showing the throttle helper spring to counteract the constant servo pulling by the accelerator pump spring. Sharp folks out there will figure out this is a compromise at best because at idle, the accelerator pump spring is more relaxed just when the helper spring's force it at it's maximum. Likewise, when the throttle is a full and the accelerator pump spring is at maximum force, the helper spring is unfortunately relaxed. HOWEVER, I fly at mid throttle a lot with this powerful setup, so at that point there is benefit to the servo.

What I have done, I moved the spring to the 3rd hole to make it easy to actionate by the servo.

OK, now I see what you're saying about the metering hole orientation. I looked at your pics more closely. The metering plate is facing FORWARD, not really up. Maybe the hole is on the upper portion of that 4-screw plate...that's true. But the plate is facing the prop blast.

So.......why not just rotate the carb around 180 degrees? Maybe that's what you're saying, I don't know.

The black reed valves are part of that black "rubber" diaphragm that the pulse helper spring pushes against. It's under the 1-screw cover. The fuel attacks it and once it wrinkles, the carb won't pump anymore.

My engine idles at 1400-1800 RPM.

My personal opinion is your current pulse tube rig should work. Didn't you say when you pull off the pulse tube the engine died? Next time, use needle nosed pliers to pinch it and see if it dies. Don't pull the line offof course the engine will die then. You've destroyed it's vacuum by doing that. If the engine dies by pinching it, your vacuum rig works fine and no more work to reroute that tube using your L concept will be necessary.

</div>

well i have not touched the engine all week i have been busy at work and have had no time maybe some time this week

pullup, what is that attached to the choke shaft my plan was a length of brass tubing soldered to the existing shaft and putting a handle on it

Well, that structure attached to the choke about which you asked, is part of a choke operating lever. Two parts to it; the part you asked about is a home made female 1/4" hex. At the bottom of the hole is glued one of those super strong neodemium magnets. There is a hole in the cowl that lines up with this hex-tube. Once the cowl is installed, I insert the mating part, a handle (shown in these new pics) which incorporates a piece of allen wrench stock. The magnet holds it in strongly, even during flight. It's an easy way to take the cowl on and off without a lot of hassle reattaching a choke lever.

Interesting idea. How did you make the internal hex?

AV8TOR

I made a crude broach, using the following process. I stuck a piece of aluminum stock in a lathe, and drilled out a hole the same size as was the hex, across the flats (the smaller dimension). Then, I cut off a piece of allen wrench, used a torch to heat up the tip and hit it with a hammer to swell the end. After cooling, I ground it sharp. Then, I put that piece, swelled end out, in the lathe's tailstock chuck and repeatedly rammed it against the tube material. About 5 hits later, it hit depth, making a female cut hex. A crude broach. I torched and hit the cutting tool so that the hex hole would be bigger than the allen wrench that was to mate. I didn't want too tight a fit.

Another update,

I think something was wrong with my WT 456, it will not adjust. I had around a WA120 and I said to give it a try. What I did, I took the spring for pump from the 456 and without making a hole in the pump cover, I just stik it under the membrane, close the carby and span the motor. I did not prime ...nothing. When I span the motor I was able to see how the fuel got to the carb and engine started. It holds a real nice Idle around 1800 , it can go down to 1550-1600 but a bit shaky.On high I got top RPM with Evolution 16/6 8600 RPM. Transition is not that smooth, I have to go progresive on acceleration. If I ritchen the low it does better on mid range. And the setup instructions from Walbro for adjustment work like the book say.Why the Wt 456 did not want to ?
Any way I ordered on ebay another 456 to try it out again. ThisWA 120 has a 7.89 ventury if I remember right. How this...ventury afects the engine. How would you know what to get. does the wentury influence the fuel consumption.
It is any other Walbro carb there with acceleration pump close to this 6.5- 8 mm ventury?

Thank you
Adrian

Love to help you out, but there are limits to what can be accomplished verbally, over a forum. At a certain point, one must be there in personto spot unusual situations that can cause problems. For my money, I don't think the reed valves were sealing. If you had a closeup camera, some pics of the components would help. The "membrane" you refer to is probably the pump diaphragm. Not a big deal, but it helps if everyone, as much as possible, uses common terms on here. It avoids lengthy misunderstandings. In the case of the WT456, the reed valves (they look like little flaps) are punched from the same little sheet as the pump diaphragm. Was yours BLACK on the WT456? I don't think the venturi size is the issue here. Now, you said you put the negative-pulse-spring UNDER the "membrane". That is not the right place. It goes BETWEEN the pump cover and the diaphragm. Not under it. Hope this helps, even if just a little.

Thank you,

Sorry ,on membrane I was refering to pump diafragm (1 bolt cover) and I got it wrong, when I sayaboutthe spring,I put it between the cover and pump diafragm exactly like on wt 456.
I was thinking that little flaps may be a problem (reed valves, that is the way you call them? I did not know that. ) and not sealing on to the little holes to create the pumping. I bought a new repair kit KW10 . The pump diafragm was Black color, I ask early before if that is the right one, I seen here that blue was mentionated and I seen a pic with a tanish transparet one.
What color I shoul use use?

Thank you
Adrian</p>

Those little flapper valves cut into the pump diaphragm I always called them check valves. They act as one way valves and are common to all reciprocating pumps

I think either tan (Teflon) or blue (acetate) will work and be ressistant to the ethanol in gasoline. The acetate one is said to pump less than ther teflon, but still is said to be ok for our use in the small engines.

I've run all three in my 50cc'ers and can't tell any difference at all. The black rubberized one holds up OK on E10 fuel but does get a little stiff after about a year or so (I assume from the ethanol in the fuel). I've never worn out a "Tan" Teflon one or the "Blue" Acetate one. I have a couple of carbs with the synthetic materials and they seem as good as the first day I put them in; both the blue and the tan.

Thought you guys would like to see Saito 150 gas conversion #2....first run. Walbro was balky at first, so I just set them at the factory 1-1/4 turns out and you can see the results.

This conversion's hall sensor and magnet are a little different than the first one. This was made by CH Ignition. I like the vertical concept for the hall sensor bracket. The magnet is mounted parallel to the crankshaft in the ring, which is adjustable (timing) because it's only held on by a couple of setscrews. Good job CH! Just make the sensor bracket a little shorter for Saito and it'll be PERFECT! The bracket wouldn't fit the engine unless I placed two washers UNDER the bracket. Otherwise, it hung down too far and hit the front bearing housing. The sensor is held onto the bracket only by JB Weld. Working so far.

The good part is this setup is getting 8500RPM with an APC 13x8 prop (pattern). Seemed like it had a lot of compression when working with this engine on the bench, so I guess I'm not that surprised.

Here's a couple videos:

http://www.youtube.com/user/ripfree#p/a/u/1/FYL2JSwNCzc

http://www.youtube.com/watch?v=9EC1rSYJgj0


EDIT 7/10/2010:
A sharp reader spotted the fact that 8500rpm was slow for a 13x8 prop. Good catch. It was a late-night typo. The prop is a 16x7 pattern APC.

Sounds good, try to get another video on...daylight and get the sensor part . what carb? wt 465?

Adrian

Adrian,

The carb is a used WT456 purchased used for $20 on Ebay.

Here's some pics that show that sensor mounting bracket. Unfortunately, with the viewing angle, you can't see the two washers under the mounting screw that were needed to keep the sensor off the bearing housing. Couldn't just file down the aluminum because it was the actual hall sensor that would have touched first.

Too bad the video is kind of dark. Probably won't be another one....that water has already passed under the bridge so to speak.

Am I reading that correct? An APC 13x8? 8500 seems a bit low. I have an ST G-90 that would turn that prop 1000rpm more than that.