I am having problems tuning a HT75 pole pruner. The saw seems to run best with H and L fully in, i.e. no fuel but still not running great. I posted link to video below showing the saw running and trying to adjust the H/L. I started the saw with both L/H fully in and first adjusted the idle screw to keep the engine revs up. You can hear the saw bogging down when I try to open the L or H screws. I notice there is quite a bit of fuel mix coming out of the muffler or is this normal?
Any ideas what I'm doing wrong?
PS: I have cleaned the carb twice and all looks ok. Only thing I didnt do was remove the H/L screws and blow through. The H screw has a cap limited so would be difficult to remove without hacking part of the plastic.
#2
Fish
Sounds like the needle is leaking, or you have lost a welch plug.
Here is a bulletin that discusses carb adj.
Attachments
ht75bull.pdf
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#3
Fish
Looking at your video, I would suggest you remove and inspect the muffler and screen, look for obstruction, and peek at the piston.
Also, when it is back together, while it is running, remove the air filter and see if things change drastically.
Hey, many thanks for reply. I did notice when putting the carb back together that the needle was not fully going down (if i pushed the top with my finger it would move down slightly). Can I bend the needle holder (not sure correct term) to apply more force from the spring through to the needle?
Someone before me has removed the screen completely. I have some fine wire mesh that i could cut to fit if necessary. My understanding is it's only there to prevent sparks from flying out and catching fire. I had the muffler of previously but will look again thanks.
#6
Fish
Yeah, mainly peek at the piston for damage, or it could be badly carboned over as well.
I removed the muffler and checked the piston. Couldn't see any obvious damage. Removed the carb and tried to bend the needle holder by pushing down on needle and spring at same time. I probably should have removed it first and used pliers. Removed the air filter and got the engine running and tuned up. It seemed to be running good as shown in first video. I then put the air filter back on and struggled to get it started. Removed filter again and still struggled to get started. I have an old strimmer engine. i might try and swap over the needle and holder to see if that makes a difference.
I replaced the sparg plug. That was the first problem I had to fix. Someone had pulled the spark plug boot off. I put on a new spring connector and boot cover. I struggled to get engine going and realised the spring connector was not making good contact with the wire coming from the magneto. I reconnected it and tested for continuity with multimeter. I can put back in old spark plug to see if it makes a difference. I tested both plugs previously with meter and both showed similar resistance.
#11
Fish
How did you attach the spring/thingee to the wire? It is a pain to do.
It is a bit fiddly. I took the spring connector and plug cover off an old strimmer and used that. It had two ends on the spring similar to a clothes peg. I had to line them up on the cable and squeeze trough using a pliers making sure the spring end was central on the cable so it would make contact with internal wire. I also stripped back a small bit of cable and exposed the wire on the top so I would be in contact with the spring connector.
You could but you shouldn't have to. I would clean it out first. I say this because the spring doesn't push very hard to keep the needle closed. -BUT- being a hacker that i am, you could try it but that means you can toss the general rule of thumb of 1.5\1.75 turns of the fuel mix screws, etc and have to wing it to get the right mix. Not difficult but can be frustrating- i say this from what i had to do to get current carb to work on the original FS80.
So I learned that the metering lever should be flush with the body for Zama C1Q-S159 carbs. I checked the lever which was below the body so adjusted the lever up and put back together after checking the needle was seating properly by blowing through the fuel nozzle. The engine then wouldn't start at all so I just left it at that. I later noticed fuel leaking out of the air filter while the engine was sat there. This leads me to believe that either the metering lever or diaphragm are not correct. I took out the diaphragm and had another look. I am not sure if the meter gasket is part of the diaphragm as per picture below. Zama show they are 2 separate items: http://www.zamacorp.com/tclist.html?cnum=C1Q-S157
The diaphragm also looks a little stretched but I guess this is normal as it needs to flex. I will try lower the metering level slightly to see if that makes any difference. After that I am out of ideas apart from replacing either the entire the carb or gaskets.
