Wednesday, May 26, 2021

Plugged Up Carb

  It doesn't happen often but I had a repair come back with the complaint the unit still didn't run right. In the past I've been pretty rough on myself if this happens but this being an intermittent type of problem I decided to give myself a break and just learn from it. 

 Husqvarna offers a commercial handheld blower thats been out for a few years now. The ones we've sold have mostly been to homeowners and the units have held up well. What I'm saying is that I haven't had to work on them much. When this blower came in the complaint was that it had a big bog when trying to throttle up. Sure enough I found that the carb was loose, ordered new gaskets, and put it back together. The unit ran fine and the bog was gone.

 A week later it came back. It had run fine for a while but then the problem started again. The first thing I checked was if the carb was still tight and it was. Now is where the second guessing starts. Was the loose carb even part of the problem? What about the rest of the fuel system? How about the ignition? I performed some tests but in the back of my mind I knew this thing had an air leak and I wanted to pressure test it.

 To pressure test a 2 cycle engine you need to seal off the intake and exhaust. Then air gets pumped in maybe through the spark plug hole with an adapter like in the first pic. Sealing the intake would require a special block off tool that I didn't have. I was prepared to order the factory tool till I discovered there wasn't one and in fact the tech manual was all wrong on performing the procedure. I called Husky tech to discuss this and he directed me to page 64 that showed the (wrong) procedure. I told him not to believe everything he reads on the internet and that the offered procedure was wrong. He connected me with a level 3 tech. I wonder how many levels they have? 


 Our level 3 guy was pretty sharp and when I explained the situation he quickly agreed that the provided testing solution was impossible. He also discovered there wasn't a special block off plate to perform the test. He then admitted that they often don't even use the factory tools and just take an old carb and fill it with silicon then bolt it on to block the intake. "Do you have an old carb the same style"? I laughed  and told him there was a 5 gallon bucket full of carbs right behind me and he laughed and said he knew there would be. I guess a lot of dealers hoard old carbs and now my single 5 gallon bucket full seems, well, inadequate. 

 As you can see in the top picture I found a matching carb and filled it with silicon. In the bottom pic I've bolted it to the engine and am performing the pressure test. I squirted some Mr. Bubbles around all the seals, gaskets and mating surfaces and found a large air leak. This leak is along an air passage between the engine and carb and provides a pulse that runs the fuel pump in the carb. With a leak this size its easy to see why the unit didn't run right. This leak is also right where I replaced a gasket the first time which explains the limited good run time. See what happened was that the loose carb must have vibrated enough against that plastic intake manifold to deform it. This is something I couldn't see the first time but is quite clear now that I've torn the thing down farther. 

 A lesson learned. You can't become an experienced mechanic without these types of experiences. Lets just try to keep them to a minimum during the busy season.


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