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



## Bret Chase (Jul 7, 2013)

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...


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## Backwoods Savage (Jul 7, 2013)

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.


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## Bret Chase (Jul 7, 2013)

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


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## ScotO (Jul 7, 2013)

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.....


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## jharkin (Jul 8, 2013)

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.


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## Bret Chase (Jul 8, 2013)

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...


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## charly (Jul 8, 2013)

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?


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## Bret Chase (Jul 8, 2013)

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.....


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## semipro (Jul 8, 2013)

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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## Bret Chase (Jul 8, 2013)

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


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## Bret Chase (Jul 8, 2013)

semipro said:


> As former mechanic I've probably rebuilt thousands of carbs including very complex models that many mechanics would not tackle.


 
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!)


 
I completely concur!



semipro said:


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


 
it seems VERY expensive to me.....


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## save$ (Jul 8, 2013)

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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## Bret Chase (Jul 8, 2013)

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.


 

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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## charly (Jul 8, 2013)

Maybe try to start it while holding the throttle open?


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## charly (Jul 8, 2013)

A search of the ST 155 brings up some sites..  

*Homelite St 155 Repair Manual Downloads*
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: www.turfparts ...


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## Hogwildz (Jul 10, 2013)

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?


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## Bret Hart (Jul 10, 2013)

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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## Bret Chase (Jul 10, 2013)

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....


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## Bret Chase (Jul 10, 2013)

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.


 


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....


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## TMonter (Jul 11, 2013)

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.


 
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.


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## Bret Chase (Jul 11, 2013)

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?


 

yes, new plug.. I will rtv the base gasket before I start looking towards ebaying a different carb....


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## maple1 (Jul 12, 2013)

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...


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## semipro (Jul 12, 2013)

You might want to check your exhaust ports, mufflers, spark screens for clogging.


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## NE WOOD BURNER (Jul 12, 2013)

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.


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## Bad Wolf (Jul 13, 2013)

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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## oldspark (Jul 13, 2013)

Bad Wolf, sounds like it could be crank seals, sorry I see it is only 2 years old so crank seals last way longer then that, sure sounds like it is not pulling the gas in like its supposed to.


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## Bad Wolf (Jul 13, 2013)

oldspark said:


> Bad Wolf, sounds like it could be crank seals, sorry I see it is only 2 years old so crank seals last way longer then that, sure sounds like it is not pulling the gas in like its supposed to.


 
Just checked with the Sears store and I bought it April 2012!  So they are getting it back!


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## MasterMech (Jul 13, 2013)

Bad Wolf said:


> 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


That sounds a lot like a plugged exhaust.  Not the only thing that it could be but it's having trouble breathing and all the "ins" are clear......


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## Clarkbug (Jul 29, 2013)

When you rebuilt the carb, did you pull the welch plug to clean out those passages as well?  If possible, do you have an ultrasonic cleaner to put the carb in?  Any chance that when the fuel lines were getting re-connected you have one swapped to the wrong port?


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## maple1 (Jul 29, 2013)

Our Jonsered is still dead, with new coil.

Looking real close at the flywheel end, there might be some play in a bearing too.

I think it lost a crank seal - even with not getting any gas it all, it should give more than a one-stroke 'sput' with a squirt of fuel in the carb throat. A leak down tester is on my list of things to get anyway, but not sure when that is going to happen - this one might be going to the dealer.


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## Clarkbug (Jul 29, 2013)

maple1 said:


> Our Jonsered is still dead, with new coil.
> 
> Looking real close at the flywheel end, there might be some play in a bearing too.
> 
> I think it lost a crank seal - even with not getting any gas it all, it should give more than a one-stroke 'sput' with a squirt of fuel in the carb throat. A leak down tester is on my list of things to get anyway, but not sure when that is going to happen - this one might be going to the dealer.


 
Maple,

Might be worth posting a new thread in the "Gear" section to try and get some more views/advice. 

Since you are feeling some possible play in the flywheel, any chance it sheared a flywheel key and you are detecting some play there?  Put it out of time enough to cause your issue?  Any chance that some of the wires connected to the kill switch is grounding out and causing the issue?


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## Bret Chase (Jul 29, 2013)

Clarkbug said:


> When you rebuilt the carb, did you pull the welch plug to clean out those passages as well? If possible, do you have an ultrasonic cleaner to put the carb in? Any chance that when the fuel lines were getting re-connected you have one swapped to the wrong port?


 

Yes, I pulled the welch plug, no I don't have an utrasonic cleaner.  The fuel line can only be hooked up one way


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## MasterMech (Jul 30, 2013)

Bret Chase said:


> Yes, I pulled the welch plug, no I don't have an utrasonic cleaner. The fuel line can only be hooked up one way


 

A shot in the dark here, but drop a teaspoon of oil in the cylinder and try again.  If it fires up then you most definetly have a compression issue.  Another long shot is to make sure the carb is receiving an impulse signal from the crankcase.  Wouldn't be the first time I've seen a gasket in a rebuild kit that's missing a critical hole or two.


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## maple1 (Jul 30, 2013)

Clarkbug said:


> Maple,
> 
> Might be worth posting a new thread in the "Gear" section to try and get some more views/advice.
> 
> Since you are feeling some possible play in the flywheel, any chance it sheared a flywheel key and you are detecting some play there? Put it out of time enough to cause your issue? Any chance that some of the wires connected to the kill switch is grounding out and causing the issue?


 
The possible play in the end of the crank was noticed when we pulled the flywheel off to check the key. Key was OK, so timing should be good. Lots of fire at the plug too. Seems to be lots of compression. No seepage behind the flywheel. I've never had a bush saw apart, haven't searched for a manual yet. Just the hours wasted so far chasing this thing is telling us we should have taken it to the dealer to start with (they're decent). I can handle the 'simple' stuff, usually (fuel & carbs etc.) - but the patience has been all used up on this one I think.

Might be time for a new saw anyway ...


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