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Walbro WT-71 Carb?

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Old 11-15-2012, 04:27 PM
  #26
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Default RE: Walbro WT-71 Carb?

K, got the gaskets on and fuel flows beautifully thru the intake hose up to the primer bulb and back out the return line.

when i prime it off the engine am i suppose to see fuel going into the throat or does that require the pulse from the engine
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Old 11-15-2012, 05:02 PM
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Default RE: Walbro WT-71 Carb?

Vacuum from the engine opens the metering valve and makes fuel available at the venturi and along openings along one side of the throttle plate. Some of these are more airflow sensitive than others
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Old 11-15-2012, 05:37 PM
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Default RE: Walbro WT-71 Carb?

Good. those are the right ones for my WT-76 carbs. I hope they are the right ones for yours. Dan
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Old 11-16-2012, 01:09 PM
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Default RE: Walbro WT-71 Carb?

OMG! this dang carb, i hooked it up to the engine, try to prime it and no fuel is getting to the engine.

Ive checked the heat dam for clogs and its clear, ive sprayed the hole from the carb hole into the crank case and its clear

the carb will push fuel threw both intake and return line but no fuel will come out anywhere...
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Old 11-16-2012, 02:14 PM
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Default RE: Walbro WT-71 Carb?


Quote:
ORIGINAL: MetallicaJunkie

i have a wt-71 on my 3w80....im sure you know this...but you might want to make sure the metering fork is engaged on the pump.... some carbs dont have it, but this particular carb does...

what engine do you have it on?
My bet is your 3W80 uses a WJ-71, not the WT-71. The WT series does not have the fork that engages the pin on the metering diaphram. The WT series just pushes against the arm.
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Old 11-16-2012, 02:25 PM
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Default RE: Walbro WT-71 Carb?

...? the Walbro WT-71 was stock on my 25cc Homelite weed wacker engine

the wt-340 carb was from another engine i was testing but the venturi is way to small




my WT-71 is not getting any fuel out the venturi
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Old 11-16-2012, 02:31 PM
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Default RE: Walbro WT-71 Carb?


Quote:
ORIGINAL: Schizted

OMG! this dang carb, i hooked it up to the engine, try to prime it and no fuel is getting to the engine.

Ive checked the heat dam for clogs and its clear, ive sprayed the hole from the carb hole into the crank case and its clear

the carb will push fuel threw both intake and return line but no fuel will come out anywhere...
This whole thread has me confused. First, I assume from the past posts this carb has a primer pumb bulb on it. If this is correct, is it on the pump side (most common) or is it on the regulator side of the carb (rare)? If on the pump side, it can only bring fuel to the carb, it will not inject any fuel into the carb venturi. The carb still depends on having a closed choke and the vacuum from the pumping action of the piston in the engine to displace the regulator diaphram and actually suck fuel into the venturi. In short, if the piston is not going up and down, there should be no fuel flow into the venturi of the carb. If fuel could just flow freely, the engine would just flood with fuel as it would siphon from the tank anytime the carb was lower than the tank.

There are some different primer setups used on some of the Walbro carbs that will actually squirt fuel into the venturi, but these are rarely used for RC applications .... and most of the carbs that use this setup don't have choke plates in place. The primer is their only way to get fuel into the engine for starting.

At this point on your learning curve about Walbro carbs, I'd strongly suggest replacing the carb or take it to someone with a great amount of Walbro experience and have them analyze the problem.
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Old 11-16-2012, 02:51 PM
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Default RE: Walbro WT-71 Carb?

Well the primer is on the carb, it sits above the metering digaphram.
I close the choke on the engine and prime it and hand prop with no results at all.

ive also tryed rocking the prop back and forth to get the piston moving to suck in fuel no results i understand that thecarb needs a signal from the crankcase, but no fuel is flowing and the heat dam, gaskets are in working order

Im doing this as a home project and a learning experince. i would love to figure this out myself just trying to get as much information as possible from this community.
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Old 11-16-2012, 03:10 PM
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Default RE: Walbro WT-71 Carb?

Has this carb worked for you in the past? If so, how long ago? Did it sit around unused for a long period of time or was it exposed to the elements for long periods.
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Old 11-16-2012, 03:23 PM
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Default RE: Walbro WT-71 Carb?

it was a buddy's it sat in hes garage for a year or so, he said it stopped working on him and just bought a new one.

I took it apart to convert it to rc and trim the excess metal and in the process the piston had a ton of carbon on it, cleaned all that off cleaned the engine up and bought all new gaskets,fuel lines,spark plug. lubed the engine with a bit of oil before putting it back togeahter.
dont have a compression tool but id sucks on my finger hard threw the plug hole.
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Old 11-16-2012, 08:56 PM
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Default RE: Walbro WT-71 Carb?

are you getting a pulse signal from the engine? take the carb off and rotate the engine and see if you can feel the pulse from the hole in the crank case. also one other thing, how many turns out are the needles? some carbs need more than the traditional 1 1/2 turns open.
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Old 11-16-2012, 08:57 PM
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Default RE: Walbro WT-71 Carb?

what kind of engine is this? it might help us get you more help if we all know what you are using.
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Old 11-17-2012, 01:57 AM
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Default RE: Walbro WT-71 Carb?

its a homelite 25cc, and yes it sucks air in, and pushes it out of the little hole. the low is 1 1/2 turn and the high is 2 turns
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Old 11-17-2012, 06:34 AM
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Default RE: Walbro WT-71 Carb?

I'm not familiar with your particular Walbro model, but I have experienced a similar problem with Walbro carbs and found the diaphram cover to be warped or bowed. Air leakage at this critical area could be your problem. Check this and ensure it mates perfectly with the carb body. If the cover is questionable, you could resurface it on a flat surface using a fine grit sandpaper (220-400 grit). Hope this helps.
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Old 11-18-2012, 03:12 PM
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Default RE: Walbro WT-71 Carb?

Ok, Ive tried 3 diffrent carbs on this engine, one that i jsut pulled off my weed wacker it was a zama i know it works. But when i put it on the engine, prime and rock the prop back and for still no fuel in the cylinder.
It must have something to do with the engine....

Im getting a pulse from the hole in the crankcase the gaskets are all brand new and in there right positions, this might be a stupid question but could i have put the piston on backwards? i dont know what else to try
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Old 11-18-2012, 03:57 PM
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Default RE: Walbro WT-71 Carb?

Some of them have an arrow stamped on the top of the piston that points in the direction of the exhaust. Dan.
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Old 11-19-2012, 02:54 PM
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Default RE: Walbro WT-71 Carb?

IDK anymore, i put a zama carb on it that i know works and was able to get a little fuel into the cylinder by hand propping,

took it outside to really try turning her over, for 30 mins i hand propped over and over, was only able to get a tiny pop from the exhaust once, now it looks like there is no fuel in the cylinder
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Old 11-19-2012, 04:43 PM
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Default RE: Walbro WT-71 Carb?

You will be lucky to ever start a magneto ignition Homelite 25 by flipping the prop. You need an electric starter.
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Old 11-19-2012, 05:12 PM
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Default RE: Walbro WT-71 Carb?

any suggestions? and on a bit of a budget
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Old 11-19-2012, 05:32 PM
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Default RE: Walbro WT-71 Carb?

I have a couple Homelite 30's that look identical to Homelite 25's and they both run nice. One has CH ignition and the other has the original ignition.

The one with the original mageto ignition, you have to use a starter. A friend said that he thought that he could start it by hand flipping because he always started his Zenoah G-38 by hand flipping.

But he couldn't get it started.

For a while I just had a regular Tower starter and it would not turn it over. But if someone would hold the plane for me, I could hold the starter in one hand and flip the prop once with the other hand. This would give it enough speed to start turning the engine over and start it with the starter.



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Old 11-19-2012, 05:45 PM
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Default RE: Walbro WT-71 Carb?

what power source are you hooking the tower starter too?
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Old 11-19-2012, 06:02 PM
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Default RE: Walbro WT-71 Carb?

At the time I was using a 12v - 7 amp gell cell from Tower.
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Old 11-19-2012, 06:09 PM
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Default RE: Walbro WT-71 Carb?

I would stick my thumb over the carb venturi to choke the engine during starting.

The carb is a Walbro WA-167A from a Zenoah G26. It has a 11.2mm venturi and a number 28 cast into the venturi entrance.

The other Homelite has a Walbro WT-499 carb with a "27" cast into the venturi. The carb is from a Zenoah G-23 glow engine but I use gasoline.
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Old 11-19-2012, 06:26 PM
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Default RE: Walbro WT-71 Carb?

what nose cone should i be looking for... im using a 18x6 master airscrew classic
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Old 11-19-2012, 07:21 PM
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Default RE: Walbro WT-71 Carb?

In the picture is a Harry Higley 1" prop nut that has 5/16" X 24 threads
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