# YardMachine Trimmer



## nbpt100 (Jun 1, 2015)

I was given a Yard Machine (MTD) 31cc string trimmer with a bad Carb. The Model number on the machine is worn off so I can't get anything. The number on the Carb is WT682A. I can only find a Walbro WT682-1. Can anyone tell me if this is effectively the same or a good substitute part for my machine?


----------



## finaprint (Jan 29, 2006)

Probably. 

I should point out that most 'bad carbs' are nothing of the kind but people here seem to think you get them fixed cheaper by replacing them only. I personally pretty much never had that problem and even on cars, we tended to WANT the original carb when I worked garage as it is by far the one most likely to be metered correctly for the application. 

The only thing we ever replaced a carb over was dead worn out throttle shaft holes and heavy corrosion that affected multiple fuel circuits. Anything else was fixable. 

I have never had the need to change a lawn equipment carb on anything but that's just me.


----------



## nbpt100 (Jun 1, 2015)

There are a lot of factors. Here are just some. When you look at the price of a new aftermarket carb vs. a rebuilt kit it can often be just a couple of dollars difference.
Some two cycle carbs have check valves that are not serviceable. They are in the block and when the rubber fails it is trash. Some mfg suggest to not use carb cleaner as it can damage the check valve. Blowing high pressure air in to the orifices can damage them too.

I have been just plain at my witts end on cleaning and rebuilding some 2 cycle carbs. For 12 to 20 bucks it is worth getting a new one and move on. Sometimes I have luck and can clean them out and all is well.

In my case on this post, one of the jet screws is just plain missing. Try to find just that part.


----------



## geogrubb (Jul 28, 2006)

The Walbro site only lists the WT-682-1 on its price list there is no 682A so I would say they are the same. Have a good one. Geo


----------



## finaprint (Jan 29, 2006)

They tell you not to clean say hydraulic rubber brake parts with solvents too but I have done it more than once, some of the gummy deposits on brake parts can only be removed with a solvent that has some VOC in it. The trick is that when the part shrivels out of shape you let it sit 2-3 days and then when the VOC that shriveled it up evaps out of the rubber the part is often good as new again. If of course you look at the part right after putting it in a solvent you will think the part is bad. I myself tend to use fuel as a cleaner, more economical and I do it outside, I do not smoke either. That pretty much clarifies if the part is bad due to VOC as the fuel is what the part is exposed to in normal use. Any damage after that is usually due to ethanol content.

Carb cleaner simply has more VOC (acetone or xylene or other) than fuel, which itself swells any true rubber part up, it is just built into the part to expect a certain small amount of swell. More VOC and part swells more, let it sit and part back to normal other than older rubber can end up a bit harder or firmer as the VOC also removed a small amount of necessary oil the rubber has in it. The brake fluid or fuel puts the flexibility right back into the part and I've used them in cars for years after doing that. Yes, even on brakes, I don't hesitate to put my life on my work. . 

One reason I may not use a replacement carb is like I said, the original already proved itself out by running correctly at least at some point and the metering valves they use in those are so finicky even a brand new one can be off enough to not run right as the usual setting method of a gauge there sometimes does not work, the valve works based on spring force vs. vacuum too and the setting tool does not really take that into effect at all. Even the engine condition (ability to pull down vacuum) can make the OEM setting wrong. I've messed with them to alter the valve position less than .005" before to get one right and no way can you get that close using the usual setting tool, you are splitting hair there. The valve has to be just right as it sets up the entire fuel map window around the main jet to then meter perfectly. Yes, the jet is settable but if the underlying fuel is not there or too much then you can set the jet all day long and anywhere you want and still performance throughout the rpm range will not be dead right. That setting is often the reason why so many give up when they think they have cleaned or renewed everything yet the device still does not run right. 

The big thing in repair for cash is the time element, you have no time to allot for parts shrinking back to normal but if you do it on your own a great way to get things back to working right and for a long time. The need for speed in responding to the customer is what drives at least 50% of all parts sales, I used to work parts as well and I commonly fix most things without 2/3 of the parts many others use but I have the time to do so.

Just some thoughts from somebody who pretty much learned all out of the box and I don't really fit in with many repair methods, I generally can repair for 1/10 of the common assumed price and often more. 

Yours and do as you will, we all have parameters determining how we must go about doing things.


----------



## finaprint (Jan 29, 2006)

Ever MADE a mixture adjusting screw? BTDT. The hardest part is finding the correct threaded shaft to make one from. I've even added a complete new adjustable fuel/air circuit in the carb that was not there before to fit a specific need. Chainsaw that had no provison for high speed adjustment, I added it.


----------

