Homelite trimmer carb adjustments

Hi again. Have a Homelite SX-135 trimmer that was given to me. Wouldn't start, but I took the carb apart, cleaned it and replaced the plug. It starts now and runs ok, but it seems to bog off of idle. It idles fine and runs fine at wide open. What are the rough settings for the high and low screws? I'm pretty sure I read that the high should be around 1 3/4 turns out, but what about the low? Thanks.

 

Hello John!

1 to 1 1/2 turns out is usually where I start on the H screw. If it idles fine and bogs when you try to increase throttle, then try adjusting the H screw both ways to find which way you need to go to get it to pick up rpm like it should. It should not hesitate to throttle up. Adjust it until you get it screaming fast, then back the H screw out just until it begins to "flutter" a little and you're set.

 

Thanks Cheese. OK, I'll try and adjust the H screw again. I had it at 1 3/4 out to start. What should the L screw be set at? You don't think the problem is the L screw setting?

 

Humm, it has been my experience that the low speed adjustment has more
influence in the problem you indicated. The low speed adjustment is adjusted
by screwing the adjust out while the motor is running until it starts to miss
and then turn the screw in until it starts to miss again and then adjust mid-
range between the two positions. Then adjust the high speed at
full throttle doing much the same. Adjust the screw out until poor running and
then adjust back the other way until poor running and then set the screw
mid-range between the two. You don't want to set the high speed to the
maximum speed as it will build up heat and cause damage. If anything,
adjust the low speed a little more to the rich site of the adjustment range.
Or adjust the low speed adjustment by tweaking to get the smooth transition
between idle and high speed.

Otoe

 

You may well have an emissions-compliant carburetor and if so, and depending on the carb manufacturer, these adjustments will be much more than the afformentioned suggestions. If you are not familiar with what a compliant engines' carburetor adjustment screws look like then you will have difficulty knowing if in fact you have one or not. Lets assume you don't know. If you have a Walbro carb, the adjustments will be 2.5 turns out on the High and 1.5 out on the Low. If you have a Zama, the High will be out 4.5 turns and 1.5 on the Low. Any lag in throttle-up will be related to the High needle adjustment. In other words, you have a lean condition when the throttle is cracked and thereby need to richen the adjustment. Try these initial adjustments, allow the engine to warm up for a couple minutes and give the engine a go. If you do not have a compliant carb, then these will obviously too rich. But at least you have a place to start.

 

Thanks for the replies guys. Well, I fiddled around with it last night and got it running pretty well. It idles great and doesn't bog off idle anymore. Doesn't seem to scream up top as much now, but I'll fine tune it some more after I record where the screws are set now. It seemed to get better after adjusting the H screw a little. Puey, Its definitely a Walbro carb on it. No doubt about that. Gonna try the 2.5H/1.5L settings next chance I get. You guys are always a big help. Thanks.

 

I have a homelite ST 175 with a Zama carb.

I have to toggle between choke and run and keep the throttle trigger at full to get it to run. it runs for a short time then will die. I assume the carb needs adjustment..the screws have a colored plastic cover with a slot in them, one white and one red.. 1) do I need a special tool to adjust them and 2) I assume the red is the high speed, and 3) is the 1.5 low(white) and 4.5 high(red) a correct place to start?

 

1.5 and 2.5 will work. You may have to remove the plastic limiter caps.

 

thanks. I will give that a try.