ST-145 is driving me nuts!

[rowdy235]

Hey guys,

I've been working on getting about 2/3 of an acre of blackberries and tall grass cleared and as a result my ST-145 has been seeing quite a bit of runtime, and honestly I think I'm more tired than the trimmer! Ever since I got it its been a little temperamental. Last year I rebuilt the carburetor and it seemed all my issues were resolved, of course that didn't last very long....

So starting cold all is good. Full choke starts within 2 pulls. Take choke off, allow a couple mins to warm up and you're good to go. However once you've cut for about 10-15 minutes, it starts to act like its running lean. If you put the choke on a bit, clears up. Can tweak the high speed jet and get it back to running good, but only for about another 10-15 minutes, at which point same thing happens.

If you shut it off for any length of time (even just to refuel), it'll be super rich after restarting until you lean back out to (you guessed it) where it was to begin with.

So far I've been through the carburetor completely twice. Both times was cleaned with ultrasonic cleaner and all passages with compressed air. Gaskets are new. Fuel tank, fuel filter, fuel hoses are new.

Everything points toward a fuel issue but I don't understand what it could be at this point. I don't think ignition is to blame since you can seem to get it running better by tweaking the carb and messing with the choke. Maybe crank seals? Honestly at this point I'm about ready to retire this one lol

[sweepleader]

I would check all the hoses to make sure they are OK, no cracks, no looseness on the nipples. I would also try looking for vacuum leaks all over by running the engine till it starts to lean out. Then I would spray some carb cleaner around carefully. If there is a gasket that is leaking air when hot, the carb cleaner will provide more "fuel" and richen up the mix a little. You need to be careful not to get the carb cleaner or fumes in the intake or you will mess up the test. It just takes a tiny squirt right on a gasket joint or hose connection. The engine will speed up if idling or smooth out at higher speeds.

[onlyhomelites]

That style trimmer has the crankcase gasket & cover assembly that should be visible from the back of the trimmer. Check the screws for tightness and the gasket for leakage. I've had a number of this style of engine develope a serious air leak at this location. The leak usually shows up as the unit has fully warmed, as you are describing.

[blythkd]

Nov 22, 2019 21:57:37 GMT -5 onlyhomelites said:

That style trimmer has the crankcase gasket & cover assembly that should be visible from the back of the trimmer. Check the screws for tightness and the gasket for leakage. I've had a number of this style of engine develope a serious air leak at this location. The leak usually shows up as the unit has fully warmed, as you are describing.

I wondered about that.  I mean the only 3 places you could have an air leak on these are the rear cover, the crank seal and the intake.  I just wasn't sure if an air leak would "develop" as the engine warms up.  Sounds like it's a common problem.  I haven't touched one of these style trimmers since I gave my 385 flying lessons out in the yard one day years ago.

The one thing I used to run into on this style of trimmer routinely was the muffler outlet plugged with mud from a mud dauber, which are absolutely nuts around here in the summer time.  It has nothing to do with the issue on this post, just thought I would get it out there in print.  Maybe it's been posted before, idk.

I'll be interested to see what's wrong on this one.

[rowdy235]

Thanks for the suggestions guys. I’m gonna probably be tinkering in Monday, so stay tuned!

[rowdy235]

I was able to get a little tinkering done today. Did as suggested and ran until started to act up, then got the carb cleaner out. I really didn't notice much of a change anywhere but I may have have noticed a very slight difference when spraying around the rear crankcase cover.

As usual for one of my projects, the gasket HM-98767A is NLA. Would you guys lean toward making a gasket or silicone? I have both, just wanting ideas on what would be best here.

[blythkd]

I guess your gasket came apart? I'd probably cut a gasket and seal it. I found some stuff that I like better than the normal blue rtv. Last summer on my Duramax rebuild I bought some AC Delco RTV Engine Sealant and fell in love with it. I like it better as a stand alone gasket maker. It's gray, thicker and stickier than normal rtv. Oh I about forgot, it's not cheap.

Hope you figure this thing out.

[onlyhomelites]

Whaddya mean it's not available? www.leonschainsawpartsandrepair.com/store/p6401/NOS_Homelite__HBC-18%2C_HBC-28%2C_HBC-30%2C_HLT-15%2F16%2F18%2F28%2C_K100%2C_K300%2C_ST-155%2C_ST-165%2C_ST-175%2C_ST-185%2C_ST-275%2C_ST-285%2C_ST-385_String_Trimmer_Cylinder_Gasket_98767-A.html

[chainsawlady]

Nov 26, 2019 7:05:47 GMT -5 blythkd said:

I guess your gasket came apart? I'd probably cut a gasket and seal it. I found some stuff that I like better than the normal blue rtv. Last summer on my Duramax rebuild I bought some AC Delco RTV Engine Sealant and fell in love with it. I like it better as a stand alone gasket maker. It's gray, thicker and stickier than normal rtv. Oh I about forgot, it's not cheap.

Hope you figure this thing out.

I just checked my inventory at the house and it says I have 12 -0 98767-A gaskets. Price is 93 cents. If they are still there how many do you want. chainsawlady

[rowdy235]

Well shoot, guess I didn't look in the right places! Will be getting one on order after the holiday.

[rowdy235]

Had another “fun” day with the ST145 today.

Realized I forgot to order the new gasket but seemed simple enough, so just cut a new one out of some gasket material. When I removed the old one it seemed fine, so I really don’t think that was the issue.

Since I had been tinkering a lot I went ahead and set the carb back to original settings l. Got it fired up easy enough and trimmed along my driveway to get it warmed up. Once warm I made some adjustments to the carb and had it running pretty good.

I then went cutting some heavier stuff and for about the first 15 minutes all was good, I was actually starting to believe I may have got the upper hand. Then, out of the blue, it completely died on me. I was able to get it started back up but wouldn’t rev up. Richened the hi about 1/4 turn and had it revving up again, kept on cutting but it was apparent at this time there were issues.

I would say about every 2 minutes it would change how it was running it would be fine and then all of a sudden seem lean. I’d let it idle for 15 sec then when reviving back up was clearly rich. I tried to avoid making any more changes but didn’t run it lean for too long either.

I headed back to the shop and sprayed carb cleaner in all the usual places with no change. Turning the unit on end to test the seals didn’t change anything either. Everything I know about engines tells me it’s got an intermittent air leak somewhere but I can’t find it for the life of me.

I think I’m going to pull the exhaust next and take a look at the piston and cylinder. However since this is a newer unit and a cheap one at that, I’m not willing to put a bunch of money into it, may be time to size up a replacement.

[edju1958]

This is one reason why I haven't messed with a string trimmer in over 20 yrs.They're just too damned tempermental.The only one I had was a Homelite that I bought at Central Tractor in about 1990.I went to using RoundUp in 1999 & haven't looked back.I only have to spray RoundUp twice/yr.as opposed to getting the string trimmer fired up every week & hope the bump feed for the nylon string still worked.Whoever invented the string trimmer had good intentions,but good intentions never did much in my book.

                                                       Ed

[rowdy235]

lol Ed, you captured my attitude today perfectly.

Truthfully I really only need the trimmer for trimming around my driveway, yard, and field. Not ideal place for roundup unfortunately. Any heavy stuff I’ll grab my dr trimmer.

I gave up on the bump and fed heads years ago, the manual heads are easy to load and work just as well in my opinion. I like one called the pivotrim, it’s simple but effective.

My folks have a Tanaka trimmer that’s probably 30 years old and runs like new, had never even replaced the spark plug til a couple years ago. Some people get all the luck lol