Troy Bilt TB475ss Trimmer wont accelerate past half throttle

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  #1  
Old 08-21-09, 05:49 AM
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Troy Bilt TB475ss Trimmer wont accelerate past half throttle

Hi,
I have a Troy Bilt 4 cycle trimmer that was running fine. I put it up one week, when I started it the next week it cranked fine, and will accelerate up to about half throttle. Past that, it dies like you switched it off. It does not have a lot of time on it. Nevertheless, i installed a new carb kit (the carb looked spotless) new plug, checked fuel filter, checked muffler, and installed new plug. Same deal, cranks on first pull but will not reach WOT. Can a coil or ignition module as they are called allow it to run but fail at higher RPM's? that is about all I can think of. Any help appreciated.
 
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  #2  
Old 08-21-09, 06:03 AM
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That kind of thing is usually fuel, although it can be airflow = exhaust plugged, dirty air filter.

I would make sure you have new fuel, then look for adjustment screws on the carburetor. When you find them, don't bother the one that stops the throttle (idle speed). Just turn it/them about 1/8 turn in or out while trying the throttle and see if that makes any difference. Make sure you remember where they started before you changed them.
 
  #3  
Old 08-21-09, 07:12 AM
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The 4 cycle carb has no adjustment screws except for idle.
Again, it was a sudden thing too, not like a slowly worsening problem.
 
  #4  
Old 08-21-09, 08:07 AM
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The fuel filter, located in the fuel tank, may be the culprit. Disconnect the fuel filter line at the carburetor. Gently blow into the line, if it requires any effort to blow through the line replace the fuel filter.

Troy-Bilt (MTD) filter with fuel line is Part Number 791-182353.

The other possibility is the valves are out of adjustment. If the valves are too tight, compression will be high (125 PSI) and the engine cannot breath properly.

From the Service Manual:

Valve Adjustment

1. To adjust the valves remove the valve cover with a T-25 driver.

2. Rotate the crank shaft to bring the piston to top dead center of the compression stroke (valves closed).

Use the starter rope to turn the crank shaft.
Use a probe in the spark plug hole to track the piston position.

3. The valve clearance for this engine is .003- .006 (.08-.15 mm) for both valves.

4. Check the valve lash by placing a feeler gauge between the rocker and the valve stem. To adjust the valve loosen or tighten the fulcrum nut with a 8mm wrench until there is a slight drag on the feeler gauge when you pull it out.

5. Inspect the gasket that the valve cover sits on for damage. If it is damaged or compressed replace it.

6. Install the valve cover.
 
  #5  
Old 08-21-09, 09:27 AM
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Without mixture adjustments you might look the choke over to make sure it's fully off.

An all position carb like that would have a pulse port coming over from the crank case. I would check to make sure it's clear.

When this started did the idle speed change any? If it stepped up you may have picked up a vacuum leak.
 
  #6  
Old 09-07-09, 10:56 AM
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First off let me say to the moderators,thank you for the help you have provided me in the past.Now to the matter at hand,I worked on this very same model trimmer for a friend of mine,it seemed like a carb problem,tried a rebuild.no help.tried new fuel filter,no help.adjusted valves,cleared flame trap on muffler,tried "new" carb no help.new spark plug no help.tested compression ckd good.disassembled eng to ck for anything broken or missing,no trouble found.the only thing I did not replace was the ignition coil.some folks say it either works or It does not.I never got the trimmer to work correct.I called troybuilt at the customer sevice line they said they were not aware of any complaints about this model.I did alot of research on line and found many people with this very same problem.Most returned them for an exchange,one person was told by the repair shop they were not sure what was wrong but they would replace parts till its fixed.My friend opted to buy a new trimmer than to try a coil.Please post if you get the trimmer working again I'd love to know what you find out.And one last thing the key on the fly wheel was not sheared and the timing was spot on.I spent alot of time on this machine and got nowhere.
 
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