Walbro Carburetors - So how does this thing work

[ben_beyer]

Is there a way/tool to put in a new welch plug without buying the Walbro tools?

[carey shurley]

sure, if you have a flat end nail driver thats small enough it will work. You want to bend it enough for it to stay in, not hammer it flat

getting the original out requires some care, its pretty easy to damage the ports beneath it

As I've been quoted many times, a carb costs $35. If I suspect there's something wrong with the carb I just replace it with a known good one. If the problem stops I throw the old one away. This doesn't happen very often and you can spend HOURS trying to find the small piece of debris thats causing whatever problem you have.............IF its even a carb problem.

[ben_beyer]

Found a possible shortcut to the installation of the welch plug. My repair it came with a smaller one than necessary. So, I got a hex wrench insert and used one of smaller welch plugs to spread the load of the hammer. Just a couple light taps and it's in!

[kenobi36]

Century HWC Extreme Pro G29 has additional tube conecting the carburator to the crank case. Any idea what for is it?

[carey shurley]

yes it is a boost port for the pump diaphragm.

the intent is to ensure full pump volume even at higher RPM's

its just a vacuum pulse

[kenobi36]

I have just finished reading your carburator bible :-) Beautiful piece of work.
Now I see its connected to pulse chamber.

The tube is connected on the bottom for crankcase, maybe it changes the phasing to match pulse with intake. I wonder if the original pulse port is left opened.

[carbon02]

Guys- I found your site, via a google search for Walbro Primer not filling up after carb rebuild. If anyone has any suggestions please post. I can't get the primer bulb to pull fuel. Filter clean and the metering lever appears to be level where it should be. It could be the age of the plastic primer on this WT-220.

Anyway-- a good cheap source for rebuild kits.. About $5.00 each for the diaphrams, and $10.00 each for the rebuild kits containing hardware and gaskets is mowers4U.com These are original kits, not the aftermarket knock offs.

No I don't work there, but this small buisness in New York has shipped these kits to over 50 countries at a fair price.. Give them a day to get to your e-mail, as it's one lady Sharron running the internet store, while her husband Jeff, owns and operates a small power equipment store in New York..

[carey shurley]

The tube is connected on the bottom for crankcase, maybe it changes the phasing to match pulse with intake. I wonder if the original pulse port is left opened.

yes they are both open and working. The second line is intended as a boost pulse at high rpm

[rcguy5`]

I actually know how these carbs work now!!! Amazing and simple but a complicated way to do a simple job. The primer bulb was of most curiosity to me.

Thanks Carey

[Bustedmp]

I have a few questions about the 811 on my G20EI. I am not new to tuning engines, but the needle settings on this one are nowhere near the initial settings listed for the engine. I know most of the time these settings are just ball park settings and that adjustment is needed. But I am 1/2 to 3/4 turn in from initial on both high and low needles. I am running coleman fuel if that matters. I know the needle adjustments are touchy as well, but I can barely touch the low needle and the engine dies. I did purchase the engine used and think the needles have been screwed in too tight at one point and may have damaged the seats. I have a new carb on the way to my house to see if that makes a difference.

[carey shurley]

well good idea on swapping the carb. As you've read I keep a spare one around and use it for diagnostics

the G20's are notorius for air leaks on the intake and cranks seals. One way to test is to run the motor and spray something like WD40 around the intake, crank and case gaskets seals. If its leaking the RPM will change. Be careful though

[Bustedmp]

We had a heat wave around here today ( 29F ) and I got the new carb installed at the recommended needle settings. Took my heli out to try it out again. It ran pretty good, idled nice, responded correctly to needle adjustments. I was starting to think the coleman fuel wasn't all it's cracked up to be.

I am still a bit on the rich side running 1650 rpm with 640 woodys, just hovering around my yard a bit and a few low level climbs for about 15 minutes and I have a little over half tank of fuel left. I'm lovin it! Now I can get my gov settings figured out, but after I get rough throttle curves set up without the gov on.

[gajomac]

carley as many others have said Thank's for taking your time to Help. Thought I had my heli tuned in pretty good (thanks to your videos), But due to events in Life, it as sat for several months got it out this weekend and tried for several hours to get it to run It'll fire up and run for a few seconds and die, I've got fresh fuel and new plug no help After reading though this post I'am taking your advice again and ordering some new carbs, rather than attempt to repair for now I actually found some 30 dollar carbs, Heck I ordered 2 along with some other spare gaskets Again Thanks Carely
http://www.davesmotors.com/av643.html

[shona13]

Thanks for an excellent write up on Walbro carburettors By far the best I have seen .
Thanks.
Hutch.

[Thomasx]

Definitely a very good "tutorial"!

The only thing I was lacking was a graphical on the flow through the primer. But having had my carb apart just now, I see it just sucks fuel from the fuel reservoir and sends it all through to the return line, and in that way priming the fuel reservoir.

I noticed my primer sucks a lot of air in, but I came to the conclusion that air gets sucked in directly at the primer betwen the primer "button" and the primer base.

I have had quite some problems getting an engine to run, but tonight I installled a reed valve between the carb and the crankcase, and suddenly the engine started running just fine

Thought it was a carb issue, but clearly it wasn't

[CharlieNH]

This whole thread is just a fabulous resource and I learned more from it than from all the youtube videos of Walbro rebuilds. I happen to have a WT199A in a Homelite blower. It starts briefly easily but cannot keep going, probably after using up the gas I pumped in with the bulb. The Walbro rebuild kit I just put in came with 3 identically shaped pump diaphragms: a thick one with a sorta weave texture, a bright blue one, also plastic and a bit thinner, and then a thin rubber one. I used the thick one since it was similar to the one coming out. (But the engine ran poorly and I don't know if it was the original.) Should I try a different one, or look for a different issue? I did check that there is a clear pathway for the engine pulses to get to the outside of the diaphragm.
I would very much appreciate any advice.
Thanks.
Charlie

[fastflyer20]

The carbs we use in RC run the thin rubber style, its worth giving it a try. The blue is for alcohol.

[F-Type]

Hi

I have a GT15 engine with a walbro carb that will only run for a few seconds and then stop.

I have followed the videos on youtube by Joe Pace for 2 stroke engine fault finding and found everything to be ok by his procedures. They felt really good, but clearly didn't pinpoint quite everything

Some of the test are pressure testing of the carb, both on fuel inlet side and on return line side. Where it is checked that it holds pressure.

What I realised was that, as I understand it, none of his tests checks for any air leaks in the metering reservoir area. Just up until the needle, and after the metering reservoir.

I tried running the engine with the prime bulb part remove, in a way that I could see the membrane working. And what i noticed was that the membrane wasn't working. I could not see it move at all. So, in that case, I guess, no wonder the engine stops after a few seconds.

After the engine stopped I carefully pushed the membrane, just to feel it. And then I could see how the gasket was all primed with fuel and getting really wet.

Then I realized, normally when I pump on the primer, I get some air in there. So, now I wonder, could it be that I have a vacuum leak in the metering reservoir? And the reason the engine stops and I don't see the metering diaphragm work, is that instead of building an under pressure pulling the diaphragm in to release the inlet needle, it is sucking air through the gasket?

Does anyone know if this is a known issue that sometimes happen?

Here's a link to the videos I mentioned

https://www.youtube.com/channel/UCDo...7BLZDx_VCfn2ng

[carey shurley]

hi, I have a carburetor question

what is the number stamped on the carburetor?

I'm not aware that any version of the engine had a primer bulb on the original carburetor.

[MattJenner]

Hi Guys
What a great thread, I currently have bought a plank ( moved to the dark side) and it has a zenoah G38 with Walbro WT338,

I just could not get it to suck any fuel into the carb, this carb does not have a primer, it relies on my spinning prop, well i decided as the club member said it had never been run and has sat in garage for over 3 yrs,i took the carb apart, but made the rookie mistake of not taking a picture, it came with an insulator but i cant remember where it goes, as my engine has an elbow bend in it.
Do you know where this isolator goes ? does it fit on back of carb or go between elbow and manifold ?

Also i did a pump test after fitting new gaskets, and fine bubbles were coming out of pump side, i tightened more and that stopped leaking, but then bubbles were now coming out of pulse port, in fact all the air was as i could not get compression... so for the last week i have been scratching my head what to do...

Any help would be great.