A Homelite TrimLite String Trimmer

Here's a view of the ID label.

It's a machine that's been written off. It was given to me as a parts machine by the proprietor of the small engines shop that I frequent. I'll see if I can get it going.

Following are the problems I know about so far:

• The fuel uptake tube is a ruin that must be replaced. The return tube may as well be replaced too.
• I took the bump-feed spring to repair a Homelite UT 20704 string trimmer. I'm left with a kluged spring that won't work, unless I can modify it successfully. The bump-feed bumper is almost worn through.
• Compression feels abnormally high. From experience with a pocket motorbike engine, that may indicate a stiffened piston ring. We'll see.

Anyway, let's see if we have spark.

Spark Plug

It's an NGK BPMR7A, and it looks pretty fouled.

It's a 14mm plug with a 3/4" A/F (across flats) hex. Gap is 0.025". I'll clean it up and do a spark test.

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I've got spark.

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Compression Test

I did a compression test while I had the spark plug out, and the gauge registered 110 psi! That's remarkable compression for an old engine. The engine's 'pull' feels normal with the spark plug out, so I guess the piston rings are ok.

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Carburetor Removal

• Air cleaner cover off. Air filter element removed.
• Fuel uptake and return tubes slipped off their nipples. Mind/label/note which tube goes where.
• Two 10-24 hex nuts, 3/8" A/F.
• Pull off the air cleaner base. Let it dangle by the kill switch wire.
• Pull off the carburetor and unhook its throttle cable 'Z' fitting. Mind the gasket.

Embossed on the carburetor's body is "C1U 163H"; that's the body type. Etched on the carburetor's body is "H60E 5ZA"; that's the model number.

Metering Diaphragm And Needle Valve

Note the following:

• The two screws are M3 x 6mm, No.2 Phillips recess.
• The metering diaphragm gasket goes directly to the carburetor's body; the diaphragm goes to the cover.
• The metering diaphragm must be supple. Stiffened diaphragms are a common fault. A stiffened diaphragm will render the carburetor inoperative.
• Exercise extreme caution when handling the tiny spring for the needle valve. It'll take off on you in an eyeblink if you're not careful.

Primer/Fuel Pump Side

Note the following:

• The two screws are M4 x 15mm, No. 2 Phillips recess.
• The diaphragm goes directly to the carburetor's body; the gasket goes to the fuel pump block.

 Mixture Needles

A 'Pac-Man' tool works to get the needles out. Note and record the number of turns it takes to close the needles before removing them. At reassembly, set the needles as they were to get going. Odds are that further adjustment will be needed.

The shorter needle at the left above is the main jet's needle -- the one nearest the choke.

The longer needle at the right above is the idle jets' needle -- the one nearest the throttle.


Fuel Line Tubing Replacement

[The following is from my post about the Homelite UT20704, where I had the fuel tank off the engine. Fuel line tubing replacement can be done with the tank in place, though. That's how I actually did it on this TrimLite.]

The factory installs the tank's tubes by squeezing them through undersize holes. The same thing can be done in repair work; you just have to obtain the correct size of tubing.

The tubing holes in the tank are 11/64" diameter, so 3/16" O.D. tubing can be squeezed through nicely. The stuff to have is Tygon F-4040-A tubing, 3/16" O.D. x 3/32" I.D. Any small engines place should have the tubing. It's sold by the foot.

For a return tube, feed about an inch of tubing into the tank, then cut off a length outside the tank that's sufficient to reach the carburetor. It's helpful to cut the starting end of the tubing at an angle, to facilitate getting it started through the hole in the tank.

For an uptake tube, feed in tubing until it emerges from the tank's filler neck, where you can install the fuel filter, like so.

Cut the tubing end squarely and install the fuel filter. With the fuel filter in place, pull back on the tubing until the filter is back inside the tank, then cut the tube outside the tank as you did for the return line.

Label the tubes 'R' for 'Return', and 'U' for 'Uptake' with a Sharpie marker.

Bump-Feed Spring

I managed to kluge the kluge, and got the bump-feed feature to more-or-less work.

Bump-Feed Spring Update -- SATURDAY, MAY 18,2019

No, it's not working. String trimmer bump-feed mechanisms are diabolical. The only solution may be to get a complete after-market hub/reel.

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I dropped into Canadian Tire and took a look at an aftermarket hub/reel. I couldn't plainly see how the thing could possibly fit the end of the Homelite's spindle, so I gave it a pass. The bump-feed that I have could be made to work if I could just come up with a suitable spring.

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And It's Working

After an outrageous amount of mixture screw fiddling, I appear to have a working string trimmer. I'll see if I can unload it on Kijiji.

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Trouble --TUESDAY, MAY 21, 2019

Two things:

1) 'Started it up and the bump-feed hub flew apart. I have no idea how that could happen; the hub screw's thread direction is such that the hub ought not to unscrew on its own. The kluged spring that I had in the hub went God-knows-where.

2) Wide open throttle operation is erratic. It'll work for a while, then it'll start dying when the throttle is opened wide. Possibly due to a marginal metering diaphragm.

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Mystification -- FRIDAY, MAY 24, 2019

I put in a new diaphragm kit, Zama P/N GND-18, and I've still got much the same wide open throttle trouble.

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Update -- WEDNESDAY, JULY 24, 2019

I put back the original diaphragms, and set aside the new diaphragm kit for future use when it's really needed. I also cut slots in the heads of the mixture adjustment screws, so they can be turned with an ordinary screwdriver.

Bump-Feed Trimmer Head

The correct spring seems to be unavailable, and the price of a new bumper is about that of a complete after-market bump-feed trimmer head, so I decided to give an after-market bump-feed trimmer head a try. See this post for the write-up of that.

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To be continued.

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