Chainsaw Repair

Quote from: brokenbudget on November 21, 2013, 04:27:13 am

what kind of problems are you guys seeing with the 164?

Saw will act like it has an intermittent air leak.  Wandering tune.  Poor idle quality.  Won't respond consistently to changes in needle settings.  Rebuild kit and long sessions in a USC didn't help my HDA-164.  Replaced it with an NOS HDA-137.  Ran fine then.  Still have the HDA-164 somewhere....

Here are a couple of vids that I did showing the high speed nozzle service for a Walbro HDA carb.  The check valve nozzle is friction fit into the cavity under the brass plug in the metering chamber.  The nozzle itself being made of brass, and slightly oversized, seals to the aluminum.  I doubt that many carbs have been serviced more than once, but if they have and you feel that the nozzle isnt fitting tight enough into its cavity, seal it will a little nail polish. 

I think you will find that the majority of problems in the HDA series is because of leaking 'mechanical type' check valve nozzles.  Symptoms are poor idle, impossible to hold tune and poor transition to rpm.  The nozzle leaks barometric pressure back into the metering chamber through which the low circuit draws bubbles or maverick air causing the lean one minute, rich next condition. 

Walbro makes the HDA with two types of nozzle seals - mechanical and capillary.  The capillary type does not leak as easily as the mechanical type and is not shown.  We will service the capillary type next.  Be careful with your high pressure air line because becoming frustrated trying to clean the mechanical seal type, you can blow the seal cap right out of the nozzle and unless you see it go wont know its even gone...     

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You may be wondering which type of check valve nozzle seal your carb has.  You can take the carb apart and look or you can go over to Walbro's website and look it up there. 

Here is a link to the HDA-164.   Walbro; http://wem.walbro.com/walbro/product2.asp?partnum=HDA-164-1&Series=HDA

Follow down the IPL to line 19, 'Nozzle Assembly Check Valve'.  If a part number is shown on this line, your carb has the mechanical seal type Walbro part 86-654. 

In contrast lets look at another HDA carb, Walbro HDA-63. 
http://wem.walbro.com/walbro/product2.asp?partnum=HDA-63-1&Series=HDA

On this IPL, there is no part number shown on line 19, but on line 50 we do see a part number for the 'Screen Check Valve'.  Then we can say that an HDA-63 uses the screen check valve instead of the mechanical check valve.  There may be other ways to tell as well, this is just one of the ways I use,