I bought a couple weed eaters to fix up as I have been repairing small engines as a hobby for the past couple months. However, these 2 have me stumped and both have the same issue. One is a GT-225 and the other is a SRM-225. On both if them I have drained and put fresh fuel in, replaced both fuel tubes (supply and return), Cleaned the carb, replaced primer bulb, New fuel filter, new air filter, cleaned the spark arrestor, replaced and gapped the spark plug to .025", cleaned the ignition coil and set the gap to .014". After a few pulls of the recoil starter the spark plug is soaked with fuel. I then hooked up a spark tester and I have spark going to the spark plug. I tested the resistance of the coil and it came out to about .250. I also adjusted the carb to be more lean on startup and still no dice. So I have Spark, Air, and Fuel. What am I missing?
Thanks,
Cory
#2
sgkent
Are they two stroke with the oil and fuel mixture 50:1, and the zama carb? I find that on those the fuel pump diaphragm that sits under the carb goes bad. It costs as much almost for a carb kit as a new carb if it is that type engine. I was getting about six months to a year on them with the fuel here, and then started draining the gas each time I used them and running them dry, which gives me about 2 years, sometimes up to 4. I think the flaps that allow the carb to pull fuel properly fail.
Timing
The flywheel should have a key cast in it
These can shear & put the timing off
Put some lines on the flywheel with a paint pen against some sort of marker corresponding to TDC & 1/4 either side of it
Ground the spark plug & hook a timing light up to the spark plug wire
This way the units will rotate easy
use a drill to spin the flywheel in the right direction and see where the flywheel ( thus piston ) is when the light flashes .
I will check the timing when I get the chance, will any timing light work or is there a certain one I need? Also yes they are both 2 stroke with the zama carb.
#5
sgkent
buy a couple new zama carbs [$12 to $13+/-] each usually unless you buy one in a zama box $30), with the correct part number and see if that doesn't fix it. Usually the problem with them not working is the gasket that goes against the engine and has the flaps that are fuel pump valves. That diaphragm/gasket also warps where the spring sits against it. I have not found a source for that specific gasket by itself, there a couple folks on ebay who sell like 3 - 5 kits in a package at a reasonable price but I don't know the quality. The primer bulb can be replaced also. Also get some fuel line or kits because some of the stuff sold swells and won't stay on the carb right once you pull it off. What quality kits I have found cost almost as much as a new carb. I've been thru this with my leaf blower, hedger, and a mantis tiller about 10 - 12 times now. It started when the fuels changed here in California. Same symptoms as you have. Getting the right fuel to air mixture and a stable mixture will be impossible if it is the same issue. It will die at idle, fall over at certain RPM's, start cold but not hot or vs versa etc. When that diaphragm/gasket is replaced it will run right for a season or more depending on the fuel and if you drain it and run it out between uses. If the engine has clutch springs, they break sometimes too.
The wet plugs may be oil. Remember that these are 50:1 mix.
#6
StarTech
Try inducing some fuel into the cylinder to see if it will even hit.
Most these uses the Zama RB-K93 carburetor which use the RB-188 repair kit. Some of newest are using a clone Zama carburetor.
#7
Hammermechanicman
Remove the carbs and the plugs and pull the rope about 20 times to clear the crankcase and cylinder. Insall spark plug spray a small amount of starting fluid in the intake opening and try to start. If it hits a runs a few seconds you have a carb problem. If it doesn't hit you either have a spark, timing or compression issue. If it doesn't hit pull the muffler and check cylinder for scoring.
I don’t believe it is a carb issue because I have tried a quick shot of starter fluid and it didn’t hit. Also I have dried the spark plug numerous times and after every attempt it is soaked with fuel. I am using 50:1 mix. But I am newer to this so I could be wrong. Any advice on what timing light to get? And where should the piston be when the light flashes?
I will check the timing when I get the chance, will any timing light work or is there a certain one I need? Also yes they are both 2 stroke with the zama carb.
I don’t believe it is a carb issue because I have tried a quick shot of starter fluid and it didn’t hit. Also I have dried the spark plug numerous times and after every attempt it is soaked with fuel. I am using 50:1 mix. But I am newer to this so I could be wrong. Any advice on what timing light to get? And where should the piston be when the light flashes?
Something to check for is flooding of the bottom end of the engine w/ fuel, which would make it too rich to fire. Enough fuel in the bottom end can make it hard to crank over, or even cause a hydraulic lock w/ the plug in. Fuel can saturate the air filter and be discharged from the muffler when the engine is pulled over. The plug will be wet when it is pulled to check it. If flooding is suspected, orient the engine so the spark plug hole points down and pull the engine over to discharge the excess fuel out of the plug hole until fuel stops coming out. The cause might be a problem w/ the carb flooding the engine, or the fuel tank cap might not be venting. If the fuel cap doesn't vent, pressure can build in the tank when the fuel warms, and fuel will be forced through the carb into the engine.
#11
StarTech
Would not hurt to do a compression test. If it is below 100 psi with the throttle held open then the PNC is worn out. Flooding with a known good carburetor is usually a sign of weak compression, clogged spark arrester, or ignition problems. But even a stiff metering diaphragm can cause flooding.
#12
Hammermechanicman
The only time i have seen incorrect spark timing on a string trimmer is when someone put the wrong coil on or a cheap aftermarket one. If the trimmer has the original coil i doubt it has incorrect timing. That leaves fuel and compression. Pulling the muffler and a flashlight to look at the piston and cylinder would go a long way in checking compression along with checking all crankcase screws. A can of starting fluid will solve the fuel question.
#13
StarTech
For me I have seen it happen with non clutched models where the flywheel key gets sheared.
But when you have the non invasive test tools, you save time by checking things using them. This why I use the compression tester and pressure/vac tester. Usually if the compression is low I do pull the muffler and check the PNC to confirm damage. If damaged I call it and return the unit to the customer as not feasible to repair.
When I first started working on two cycles I did a lot unnecessary disassembly work but now I can usually tell the causes with 15 minutes using the test tools. Sometimes it takes longer to get the tools out then actual troubleshooting.
Even the Echo trimmers here that uses plated cylinders, the plating will wear through easily especially under commercial use. The SRM-225 here at the Nursery customer usually only make it two years before being worn out where a Stihl lasts much longer.
I would pull the mufflers and clean all the carbon out of the entire exhaust side of the engine. Clean is clean is clean is to clean.
Remove the window screen, EPA, US Forestry spark arrester and throw it in the trash. Unless you are trimming in a forest that is. Not really needed for a home owner.
Most likely you have a carb issue.
#15
Hammermechanicman
The average joe probably doesn't have a spark tester, compression tester or a pressure and vac tester. I was trying to give the OP some things to diagnose and not guess without special tools. I have seen more than one 2 stroke with good compression but had scoring and wouldn't run properly or not at all
Timing
The flywheel should have a key cast in it
These can shear & put the timing off
Put some lines on the flywheel with a paint pen against some sort of marker corresponding to TDC & 1/4 either side of it
Ground the spark plug & hook a timing light up to the spark plug wire
This way the units will rotate easy
use a drill to spin the flywheel in the right direction and see where the flywheel ( thus piston ) is when the light flashes .
