# no high speed power after warm up



## tjohn2 (Nov 30, 2007)

I've got a Chinese DuroPower backpack blower that looses power after 10-15 minutes. Easy start. Compression feels good. Plug is nice even tan. If throttle is kept open it dies. If throttle is released when power is going down, goes back to ok idle. A 1/4 minute at idle and I get high power for 10-15 seconds, then power starts reducing and if I hold the throttle open it will die. Air cleaner is fine and so is spark arrester. A bit of fuel wetness on the sides of the tube between the air filter and the carb intake? No carb adj. screws, low or high. Only 1 year old so I don't think it's the diaphram. Fuel mix is the specified 25:1 of 2 cycle oil. This one has really got me going as it repeatedly runs fine for 15 minutes from cold. Oh, and the good news - parts currently no longer available nor service manual - but it came with a full set of gaskets and a spare plug.


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## 30yearTech (Sep 14, 2006)

I would check the fuel tank or cap for a plugged vent. I would also check the condition of the fuel filter and fuel lines, a partially restricted filter or soft fuel lines can collapse when running for awhile and restrict fuel supply. 

There is also the possibility of an air leak somewhere in the crankcase that may get worse as the engine heats up.


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## tjohn2 (Nov 30, 2007)

Did try loosening the fuel filler cap so that's not it. I will try to see if there's a fuel filter, tank is buried between the air filter assembly and the backrest. Note that the blower worked fine all last fall and for a number of days cleanup this fall. I'm wondering if some crud could have been sucked into the carb passages going to the high speed jet. Without a carb type or exploded drawing I'm playing this by ear. Gasket between carb and engine is well seated. Could there be enough carbon buildup in the exhaust ports after one season's use to cause the problem?


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## 30yearTech (Sep 14, 2006)

There is always a possibility that there may be some restriction in the exhaust, but this will usually cause a problem all the time, not only after it has run for awhile.

It could be an air leak that develops when the engine heats up and something may distort a little.


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## tjohn2 (Nov 30, 2007)

Many thanks for your help. I didn't think through that restricted exhaust would show the problem from start up. Maybe temperature warpage in the crankcase reed valve, if it has one, allowing blowback towards the carb? That might account for the small amount of fuel coating the tube between air filter and carb. I will also check for other external leakage around the engine. Ever see blowback through a reed valve before? Also, what American carbs use a cylindrical rotating throttle? Perhaps this is a copy of an American carb. I've been looking on the web for exploded dwgs but haven't found anything useful.


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## 30yearTech (Sep 14, 2006)

Yes, reed valve designs do tend to "spit" fuel back up through the carburetor when running, this is not unusual. 

Check the walbro carburetor site they have several rotary valve carburetor designs mostly the WY series, the carburetor on your unit is most likely a clone but may actually be a branded carburetor, if it is it should have the mfg name on it.


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## tjohn2 (Nov 30, 2007)

Thanks again, 30yearTech. Pulled carb off and with magnifying glass got WALBRO WKY-175A (I'm a 45 year tech, eyes not so good anymore). No idle screw, no air adjust; all plugged it appears. And, this model not listed anywhere - models jump from WYK-174-1 to 176-1; and there's a ~100 other WYK models. Probably an OEM for the mfgr. All gaskets down to the engine cylinder are clean and tight. And no reed before piston. No real carbon anywhere yet. I'm just about down to replacing the fuel line to see if that works but it will be a bear, threaded around all over the place.


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## tjohn2 (Nov 30, 2007)

Another thought, in your experience could it be the ignition module giving up at high rpm after it gets hot? I discounted it because it immediately goes to smooth idle when I release the throttle. Thanks.


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## 30yearTech (Sep 14, 2006)

Not likely that the ignition module would cause this type of problem


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## geogrubb (Jul 28, 2006)

After reading all the posts I vote for bad fuel lines. Have a good one. Geo


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## tjohn2 (Nov 30, 2007)

Well, I replaced the fuel line and checked the fuel filter which was clean. Thought I had it solved - this time it took about 20 minutes before it would start loosing power. Same symptom, 10-15 seconds at idle gets me 10-15 seconds of power, then I have to release the throttle or it dies. And it does act like a fuel problem as it doesn't miss at high rpm, just slows down. I'm thinking either rebuild the carb next or replace it with a Walbro WYK-17n series that has adjusting screws. All the rebuild kits for the WYK-17n series have the same part number. Any further advice or educated guesses? And thanks again for your suggestions.


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## glenjudy (Aug 26, 2006)

Maybe worth a try to send your original post to DuroPower on their website 'support' or 'contact us' and see what their take is, they say they will respond within 24 hrs, be worth a try.
I have no idea how the backpack blowers are constructed, but, would there be any parasitic load commence after it's good and warmed up, like, is impeller/fan connected directly to end of crank, or, is there a clutch involved, any gearing involved with fan etc. ??
I notice on Walbro site that the WYK-174 has 10.5mm venturi whereas, the 176 has 15mm venturi, if you're thinking about replacing carb, make sure of comparable venturi size.
just some ideas,
thanks,


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## tjohn2 (Nov 30, 2007)

Spent a little more time with it this afternoon. (It's cold here near Chicago.) It will run at high speed for a minute or so, but I always get the power loss eventually. Dies if throttle is held open; settles down and idles fine if throttle is released. Spin it up and it looses power within 15 seconds to a minute.


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## tjohn2 (Nov 30, 2007)

Blower fan is direct drive, just attached to the engine shaft. I talked with DuroPower and they say that they no longer have any support from their Chinese supplier; no service manual available; no parts. Thanks for the reminder about the venturi diameter. I'll measure the carb to get the size.


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## tjohn2 (Nov 30, 2007)

I tried looking on the Walbro site and I can't find any listings for the individual specs for the WKY series carbs. glenjudy mentioned there were various venturi/throat sizes. Does anyone know where I can find the specs for individual models? Thanks.


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## glenjudy (Aug 26, 2006)

Go here:
http://wem.walbro.com/walbro/
enter WYK-174 in upper box, click Go
you'll see as result, WYK-174-1 in left box, click on it.
2nd item in table on right is venturi size.
go back and do same on WYK-176.
and, you're right, Walbro has no results for WYK-175(A)
hope this helps,
thanks,


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## tjohn2 (Nov 30, 2007)

Thanks glenjudy, found it. I hope it doesn't come down to buying a carb to see it that's the problem. I hate troubleshooting by replacing parts. Gets expensive, and sometimes no solution. ;-)


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## tjohn2 (Nov 30, 2007)

Spoke with a tech that told me there is a small fuel filter screen within the carb, that when partially blocked can display this symptom on this model carb. So the carb wants a rebuild and replacement of this filter which is in the rebuild kit.


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## 30yearTech (Sep 14, 2006)

Let us know if thats it. I would be surprised if this filter screen is causing the problem, as the engine requires a richer mix when cold and will run leaner after warmed up. If this filter is clogged it should cause a lean condition all the time, not just when it's warmed up. Complete cleaning and carburetor kit may take care of it, a dirty or sticking high speed check valve in the carburetor can certainly cause this type of problem.


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