The second photo shows the starting instructions for our Troy-Bilt TB35 EC 2-cycle string trimmer. I find these instructions unnecessarily complicated, and they do not always work. No matter the condition of the engine, cold or hot, these steps are to be followed. This Instructable will show how to make a simple attachment that allows engaging full throttle during starting while the choke is also engaged, and that works far better for me.. That is impossible without the attachment I made.

Materials

Scrap of wood
Nail

Tools

Drill and bits
File
Hammer

Step 1: Factory Cams

The first photo shows two cams. One is connected to the choke shaft. The other is connected to the throttle shaft. See the second photo. As soon as the throttle control is moved in the least, the choke releases and goes to a no choke condition. Whereas the carburetor is not made by Troy-Bilt, this auto release choke is likely to exist on other makes and models, too.

Step 2: The Attachment

My attachment is a simple piece made from scrap wood and a nail. It fits over the choke lever and the nail catches the air cleaner cover so the choke cannot swivel back to the default no choke condition until the attachment has been removed. (There are two extra nail holes because I did not get the nail location right until the third try. And, I usually use a welded steel version of this attachment, but I am presenting a version that needs no welding for the benefit of those who do not have access to a welder. 3-D printing might be an option. if that is your preference and you are equipped to do it.)

Step 3: Begin Cutout for Choke Lever

The rounded part of my choke lever is 5/8” in diameter. A spade bit would work as well as a twist drill and is easier to acquire. I drilled at an angle to compensate for the angle of the choke shaft.

Step 4: Fit the Hole to the Choke Lever

I made a good guess to locate the tail of the choke lever and drilled a 1/4” hole. I used a handheld drill to chew out the basic shape of the choke lever. Some filing with a rasp was needed.

Step 5: Locate the Nail and Pre-drill

I marked the location for the nail as best I could. Notice how well the opening in the wood fits over the choke lever. As mentioned before, I guessed wrong on the nail position twice before I got it right. I drilled a hole slightly smaller than the nail so I could drive the nail without splitting the wood. (The attachment should hold the choke fully open, even after the throttle has been applied, but without stressing the choke lever.)

See the text box in the third photo for where the nail fits to keep the choke engaged.

If you wish, you can cut away excess from the piece of wood to make the attachment more pleasing to the eye, but that will not improve its function.

Step 6: Starting Procedure

The photo shows the attachment in place after a little trimming to remove excess wood. Notice the primer bulb below the wood on the back end of the carburetor.

I have never seen this engine flood. When it does not start, the reason has always been due to a lean condition. To start, I press the primer bulb three times rather than ten. (You may need to press the primer bulb a few times first to bring gasoline up to the bulb.) I set the choke and place my attachment on the choke lever. I hold the throttle fully open and pull the starter rope. The engine usually starts after three or four pulls. Let the engine warm a few seconds. Remove the attachment that locked the choke on. The engine should idle very well, but will idle even better as it warms.

The factory starting procedure says to press the priming bulb ten times even when restarting a hot engine. I simply pull the starter cord once with no choke, no throttle, and no presses of the primer bulb. The engine starts immediately.

If the engine has been stopped up to ninety minutes or more, do not prime. Just set the choke with my attachment, hold the throttle open, and pull the cord until the engine starts. It usually starts within three pulls of the cord.

A frequent complaint on these engines is difficulty starting them. People wish they had bought a more expensive make, but reviews on those models indicate the same difficulties with starting. (They probably have the same carburetor.) My attachment gives me more control over engine settings at starting and has made starting easier for me. Experience also develops some intuition about what to try when the engine does not start as expected.

NOTE: When I open the cover for the air filter, I see two screws that mount the carburetor. I have run a total of six tanks of fuel through this weed trimmer, but already one of the screw was nearly a half of a turn loose. When screws loosen, gaskets leak and the gas to air mixture changes enough that it is difficult to start the engine. Periodically tighten the carbuaretor mounting screws. Also check the screws that hold the crankcase and the cylinder together. And, the Jump Start opening for the power starter on the back of the machine is secured by two screws that also seal the crankcase. Even if you do not use the power starter option, the screws that mount the drive for the power start can loosen and cause an air leak into the crankcase. See the text box on the photo. A good clue to the presence of leaking air is the number of pulls before the engine starts. If three pulls becomes five before the engine starts, begin checking for loosened screws. Even a quarter of a turn loosened can be a problem.