Can't get my gas trimmer running... what am I not thinking of?

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Bret Chase

Bret Chase

Minister of Fire
Jan 15, 2013
870
Maine
I've got an old (formerly trusty) Homelite ST155 (UT-20539) that I've had for ages that I cannot get to start this year...

This is what I've done so far: Rebuilt the walbro WT carb with the full repair kit from NAPA, new primer bulb, new tygon fuel line, new fuel strainer, new DJ7Y plug.

It has spark, it has compression... and now at least the primer bulb will pump fuel. I rebuilt the carb in accordance with the walbro manual... setting both high and low needles to 1 1/4 turns out.... best I can get it to do is "fart"

what am I not thinking of? it is irking me...
 
Sometimes those things just like to be ornery. Have you tried some ether? Also, I'm not so sure on those needle settings. Might want to double check what they should be.
 
the needle settings came from the walbro manual.... I cannot for the life of me find a manual for the trimmer online.... no, I've not tried ether... yet
 
make sure you have hot spark, too. You may also have fouled the plug. Take the spark plug out, pull the rope 20 or 30 times, put spark plug back and and try to start it again.....
 
If it fires with a shot of starting fluid but not otherwise then you know its a fuel draw issue. Did you make sure to have everything spotlessly clean while rebuilding the carb? The tiniest spec of dirt in a jet could cause issues. Also double check you put all the gaskets and especially the pump diaphragm ( the one with two flappers) are in the right orientation. And check to make sure you didn't block the pulse port to the crankcase (unlikely unless you rotated the carb 180 somehow)

All else fails open the needles some more, maybe to 1 1/2 or 1 5/8 and try again.
 
I am quite versed in carb rebuilding... though I will admit it is my first trip inside a Walbro WT. they are far more complicated than the stone axe roundslides in my Skidoo.... and nearly as complicated as the 4 keihins in my bike.

I will go through it again...

I do not like being vexed by a damned weedwhacker...
 
If you put in a different needle and spring,, the pop off pressure could be too high to allow fuel in.. For what carbs cost, it's worth just getting a new carb at times...Run seafoam in your gas mix,, it will start year after year...They make a spray you can use to get it started as well... Try another plug as well..Could simply have a new bad plug...Then you'll really be searching for a problem ;) Gap the plug to specs?
 
it's the same needle and spring... the new one in the kit was twice as long as the old one.... and the original one appeared to be in good shape.

the old pump diaphragm was definitely junk.... before the rebuild... the primer bulb did nothing....

a new carb for it is $63.....
 
As former mechanic I've probably rebuilt thousands of carbs including very complex models that many mechanics would not tackle.
I gave up on rebuilding Walbros and their ilk though and just replace them now. (though I hate the thought of letting the little bastards get the better of me!)

You might want to check around on that price. That seems expensive for that carb.

Some two-strokes used to have reed valves that allowed air to flow only one way through the intake. Maybe yours does and its not working?

Clogged exhaust port?
 
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looking at the exploded diagram... it's a plain old piston controlled port engine... no reeds or rotary valve...

Maybe I should just swap in the K&B model airplane engine I've got sitting in a box on a shelf..... lol
 
semipro said:
As former mechanic I've probably rebuilt thousands of carbs including very complex models that many mechanics would not tackle.
Click to expand...

I can do pretty much any 4 stroke carb blindfolded.... though those 4 Keihins..... that requires a 6' table covered in white paper to keep track of all the parts
semipro said:
I gave up on rebuilding Walbros and their ilk though and just replace them now. (though I hate the thought of letting the little bastards get the better of me!)
Click to expand...

I completely concur!

semipro said:
You might want to check around on that price. That seems expensive for that carb.
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it seems VERY expensive to me.....
 
I admire wanting to fix it. I have one hanging on my garage wall. I should say I have three. They don't work and I don't know anyone who wants them. Every time I work on one, I just get frustrated. Went out two years ago and got another one from Sears. Starts every time. My only complaint is that they are too heavy for anymore than 15 min. I also picked up an electric one that takes the attachments. Electric one is not so heavy and works so long as I don't cut the cord off.
I recently saw an add on tv for a battery powered one that has wheels. That should help with the weight issue.
 
save$ said:
I admire wanting to fix it. I have one hanging on my garage wall. I should say I have three. They don't work and I don't know anyone who wants them. Every time I work on one, I just get frustrated. Went out two years ago and got another one from Sears. Starts every time. My only complaint is that they are too heavy for anymore than 15 min. I also picked up an electric one that takes the attachments. Electric one is not so heavy and works so long as I don't cut the cord off.
I recently saw an add on tv for a battery powered one that has wheels. That should help with the weight issue.
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I've got the homelite... and a B&D 18V that I got for my wife.......

If you find yourself oh about 60 miles south of Chelsea on the pike..... I'll take the 3 trimmers.... I like to tinker... I will not let the homelite win!
 
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A search of the ST 155 brings up some sites..
  1. (broken link removed to http://search.yahoo.com/r/_ylt=A0oG7kpngttR5mMAnJZXNyoA;_ylu=X3oDMTE0OGFodHBzBHNlYwNzcgRwb3MDMwRjb2xvA2FjMgR2dGlkA0FDQlkwOF85Nw--/SIG=12acd1nn2/EXP=1373369063/**http%3a//www.n8fan.net/en/homelite-st-155-repair-manual/)
    www.n8fan.net/en/homelite-st-155-repair-manual
    Document Size Uploader Downloads Health; Manual / Instructions / Useru0027s Guide : HOMELITE ST 155 ( HOMELITE... 1 months ago: 1.31 MB: username 280: (broken link removed) ...
 
I had a similar issue with a Ryobi weed wacker. I found a new carb on either Ebay or Amazon for $20.00. Was not worth the hassle to rebuild, took old carb off, put new carb on, done deal.
Did you try a new spark plug?
 
I didn't think of the base gasket.... I had that trouble with an old 35HP Chrysler outboard long ago...... I should have thought of that....
 
Bret Hart said:
On the engine page of this link: http://www.ereplacementparts.com/ho...tring-trimmer-parts-c-18807_20299_147677.html have a look at reference #17. An air leak can cause all kinds of issues and I've seen a few Homelites with leaks at that gasket.

Also, I don't recommend a champion plug in anything. Just had too many with problems even right out of the box. NGK is my go to plug.
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I generally don't use champion.... but it was the stock plug.... and it was at walmart during a grocery trip.. I use delco in my GM's.... NGK in everything else....

though my small engines tend to have whatever they had in it when I acquired them....
 
Bret Hart said:
On the engine page of this link: http://www.ereplacementparts.com/ho...tring-trimmer-parts-c-18807_20299_147677.html have a look at reference #17. An air leak can cause all kinds of issues and I've seen a few Homelites with leaks at that gasket.

Also, I don't recommend a champion plug in anything. Just had too many with problems even right out of the box. NGK is my go to plug.
Click to expand...

Second on the NGK plugs. They just seem to hold up better in general based on past experience. I've had more than a handful of Champion plugs go bad after a couple seasons on 2-stroke equipment.
 
Hogwildz said:
I had a similar issue with a Ryobi weed wacker. I found a new carb on either Ebay or Amazon for $20.00. Was not worth the hassle to rebuild, took old carb off, put new carb on, done deal.
Did you try a new spark plug?
Click to expand...


yes, new plug.. I will rtv the base gasket before I start looking towards ebaying a different carb....
 
Going through this right now with a Jonsered spacing saw (same as Husky 235). All the ingredients seem to be there but it won't run - all it does is give a little 'sput'. Have a coil on order, even though there is some spark at the plug. Frustrating...
 
You might want to check your exhaust ports, mufflers, spark screens for clogging.
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Try checking your spark with an inline spark tester with plug installed.

Many times the spark gets weak just from corrosion at the pick up(emery paper).
Check ground @ coil
Clean all wire connections with electroclean

Just a thought.
 
I have a similar issue. Sears 31 cc weed wacker, 2 years old. It will "pop" with the choke on, when you then move it position "2" it will catch, rev and die. If I leave it run on full choke it will chug and looks like its spitting fuel out of the carb (walbros) . I've taken the carb apart and blown out every passage and I still get the same thing. A new carb is $35 and I only paid $113 in the first place. I'd hate to pay $35 wait two weeks and have it still not work. I'm about to pitch it in the river!!!
 
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