Pruner: Won't Start

A carburetor is needed by your pruner to mix fuel and air together at a specific ratio that allows combustion. It is located underneath the air filter. To check whether it is causing your pruner not to start, first remove the air cleaner cap, and look for any obstructions in the way that could block air flow, starving the engine of oxygen. You may find this is your problem. If not, unscrew the carburetor bolts, remove the fuel lines, and then unhook the throttle cable from the carburetor linkage and pull the carburetor off. Clean the carburetor with carburetor cleaner, and use a soft-bristled brush on the inside to remove any heavily gummed up deposits. Next, check the bowl for corrosion by removing the nut on the bottom. If you observe corrosion on the bowl, a new carburetor is required. Check that fuel is present at the fuel line entering the carburetor to make sure it is receiving fuel. Reassemble onto the engine and re-check operation. If the symptom persists, follow our guide to rebuilding the carburetor under “Carburetor Kit”, elsewhere on this page.

The fuel filter is located inside the tank, and prevents debris from entering the carburetor and engine, causing damage. You can remove the fuel filter by using a hook and pulling it out of the fuel tank. From here, check to see if it is clogged, as a clogged fuel filter can stop the flow of fuel to the engine, causing your no-start symptom. A visual inspection well tells you if it’s blocked, as well as a quick blow through it.

The gasket’s job is to seal two joining pieces tightly together, sealing off air and fluids from entering areas they are not supposed to go. A damaged gasket below a carburetor will pull excess air into the cylinder, causing a no-start situation. To check this, start by removing the air filter, then loosening the carburetor bolts. Check the condition of the gasket; look for tears, or rips, or any indications of leaks. Gaskets are a one-time use, so you will have to replace it at this point regardless of its condition. Reassemble in reverse order and check to see if the symptom is fixed.

The spark plug creates the spark that ignites the fuel mixture. If it is worn or heavily damaged, it will create a weak spark or no spark at all, causing a no-start symptom. Remove the spark plug and check it for oily build up, heavy deposits, breakage, erosion, molting, or any other fouling. A normal, functional spark plug should be brown or light grey. Spark plugs should be replaced once a year as a part of normal maintenance. This is especially crucial in two-stroke engines.

Primer bulbs pull fuel through the fuel line into the carburetor by creating a vacuum. Pressing the bulb twice should pull enough fuel for a cold start up if it is functioning correctly. The first step when determining if the primer bulb is responsible is to check it for any leaks. This is easy, as you can just do a quick visual inspection. It should be noticeable; there could also be a smell of fuel or fuel dripping from it as you press it. The bulb can also pull air in if cracked, which is a problem as it disrupts the fuel/air ratio in the carb, resulting in the no-start symptom you are experiencing. It will need to be replaced if this is the case. To replace the primer bulb, simply pull it off with a pair of pliers. Next, grab a small pick and reach back into where the bulb came off, grab the clip, and pull out. Clean out the housing. Put the new clip on the primer bulb with the tabs facing out. Then use a socket that fits over the primer bulb and push into the housing, then tap gently with a rubber mallet. Make sure the metal clip is as far in as it can go without damaging the primer bulb. This could vary on different models, but all pruners will be similar.

The fuel tank holds the fuel for your pruner. If the fuel tank is cracked and has leaked all its fuel out, it will obviously need replacement, as it is useless. Here’s how it’s done. Remove the engine housing, then the grommet on the tank, then the fuel filter. The fuel filter can be taken out by inserting a hook into the tank, retrieving it, and removing the filter from the line. Remove all fuel lines from the tank, and then remove the bolts holding the tank in place. Install your new tank, re-install the lines, the grommet, and the filter. Re-install the engine housing and finally, of course, fill with fuel.

If you’re experiencing problems with your carburetor, as detailed elsewhere on this page, the carb kit contains all the parts needed to take it apart and rebuild it. The carburetor kit itself is not directly a part that will cause your symptom, obviously, but it deserves discussion here because it is a great way to restore your carburetor to new condition, preventing any problems, solving carburetor-related no-start symptoms, and keeping your engine running smoothly. Fuel that sits for a long period of time, especially when mixed with oil, has the tendency to gum up the inside of a carburetor. Simply remove the carburetor as explained under the “Carburetor” heading elsewhere on this page. Disassemble the entire carburetor, laying out all the parts on a table and making note of where they came out (taking pictures along the way is a great way to remember where things came from and how to reassemble, as there are a handful of small parts). Clean the entire carburetor housing with a carburetor cleaner and a soft-bristled brush to remove all gummed up surfaces. Once you have reassembled the carburetor, simply reinstall it. Next, set the low and high idle screws by turning them all the way until they shut off, then back off 2 turns. Start and let warm up for about a minute, then adjust. Start the with the L screw until it runs the fastest, then adjust the idle screw. Repeat and add a little more fuel. Next, at full throttle, adjust the H screw until the engine runs as you like it. This process usually takes some experience to adjust properly, so for a do it yourself-er, it may take some time.

Fuel lines take fuel from the fuel tank to the carburetor, where it is mixed with air for combustion. First, pull the fuel line off the carburetor in a gentle, twisting motion, and check that fuel is present. If no fuel is present, remove the fuel lines to check for a blockage. Some models may require you to remove a rubber grommet on the side of the tank first, where the fuel line feeds into. You can simply blow through the lines to see if they are blocked. Lines should also be replaced if they look old and weather-cracked, as they could leak and cause a fire in this condition.

The ignition module creates the electrical current that provides the spark plug with power to ignite the air/fuel mixture. To check this part, remove the housing and locate the ignition module by following the spark plug wire to it. Disconnect the 2 smaller wires to check the switch operation. To do so, check with an ohmmeter and turn the switch off and on. If you see the ohmmeter change, then the switch is good. Check the spark plug for a spark with a spark plug tester or by removing the spark plug and grounding out the end on the engine block and pulling the start rope to look for a spark. If there is no spark, then remove the bolts holding the module in place. Replace with a new module. Next, you will need to set the gap between the module and the magnets on the flywheel. You will need a feeler gauge for this, as well as the manufacturer’s specifications for your machine. If you do not have these specs, then a good general rule of thumb is to use a business card, as it is the appropriate thickness in most cases. Spin the flywheel around so that the magnets are in the direction of the module and allow the magnets to pull the module into place. Finally, tighten the bolts down and remove the business card, hook the wires back up and you’re done!