# 4 cycle engine problems



## deaconjim

I need help with my Troy Bilt weed eater motor. It has been working fine all day, and I picked it up again to do a little more trimming around the barn. It will start, and run fine at idle, but as soon as I open the throttle past about a 1/4, it stalls out. 

The manual suggests either bad fuel (that isn't the problem), grass binding the head (it's turning free), or a clogged spark arrester (took it apart and cleaned it). The fourth option was a faulty carb, but it went from running great to this all at once, so I'm doubtful on that. 

Any suggestions?


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## james dilley

Whats the Plug look like??? Any chance the Air mix is off? Could the Electronics be going out??? That would be the only thing I can think of.


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## deaconjim

james dilley said:


> Whats the Plug look like??? Any chance the Air mix is off? Could the Electronics be going out??? That would be the only thing I can think of.


I haven't checked the plug yet, it got dark before I got that far. I didn't go there at first because it runs fine at idle. I suppose the air mix could be off, but it was fine a couple of hours earlier, so it shouldn't have changed. 

I'm not sure what electronics it might have, but that is always a possibility. I don't know what to check to find out though, the manual doesn't make any mention of them, and aside from what's in the manual, I'm lost on small engines.


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## Rocky Fields

Hey.

Make sure the air filter is clean enuff. If it is dirty, it will bog when you give it the gas because it's not getting enuff air. Sometimes you can leave the filter material out for testing purposes and then gun it to see if it makes a difference.

Be careful with the fuel mix...too much oil is a no-no.

RF


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## Rocky Fields

oops...retract oil mix comment...missed seeing it's a four cycle


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## deaconjim

Rocky Fields said:


> Hey.
> 
> Make sure the air filter is clean enuff. If it is dirty, it will bog when you give it the gas because it's not getting enuff air. Sometimes you can leave the filter material out for testing purposes and then gun it to see if it makes a difference.
> 
> Be careful with the fuel mix...too much oil is a no-no.
> 
> RF


I actually cleaned the air filter yesterday when I first started using it, but I checked it again today to be sure it hadn't clogged again. I tried running it with the carb open with the same results.

I got the 4 cycle specifically so I wouldn't have to mess with the oil mixing. I can fill both mowers and the weed eater from the same gas can, and I love it. I will have to say that this has been the best weed eater I've ever had, and that thought ran through my head just before it started giving me trouble.


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## Beeman

Not familiar with a 4 stroke weedeater. Does it have a fuel filter? Most weedeater fuel filters are attached to the gas line in the fuel tank. Find the fuel/air mix screws. Turn each one in to bottom it and count exactly haw far you turn them to LIGHTLY bottom them. This way you have a baseline to return to. Then open them up an extra 1/2 to 1 turn and try it as you might have a little piece of something blocking the fuel.


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## deaconjim

Beeman said:


> Not familiar with a 4 stroke weedeater. Does it have a fuel filter? Most weedeater fuel filters are attached to the gas line in the fuel tank. Find the fuel/air mix screws. Turn each one in to bottom it and count exactly haw far you turn them to LIGHTLY bottom them. This way you have a baseline to return to. Then open them up an extra 1/2 to 1 turn and try it as you might have a little piece of something blocking the fuel.


No fuel filter. I've looked for the fuel mix screws on the carb, but all I can find is the idle speed adjustment screw. I'll have to dig a little deeper for them. The manual just says to take it to an authorized repair shop for carburator adjustments.

I'm thinking that running it at idle with some carb cleaner in the fuel might help.


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## Rocky Fields

Hey.

Have you checked to make sure choke isn't partially on?

Is the primer bulb filled with fuel and no air when you prime it?

It might kill at high speed if your 4 cycle crankcase is low on oil causing overheating...

RF


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## Rocky Fields

Jim,

Visit this link: http://forum.doityourself.com/showthread.php?t=302806

This guy had a problem somewhat similiar in part to yours. Scroll down to near the thread bottom and he claims it to be a flywheel problem...

RF


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## deaconjim

I talked to customer support at MTD today (it was great to talk to someone at customer support with a southern accent), and they agreed with the 'varnish in the carb' diagnosis. ("My husband had the same problem with ours. I thank you've hit it right on the head.") They also confirmed that there are no adjustments to be made on the carb. I'll try running some carb cleaner through it tomorrow, and if that doesn't work, I guess I'll have to resort to spending 40 bucks on a new carburator.


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## barelahh

deaconjim said:


> I talked to customer support at MTD today (it was great to talk to someone at customer support with a southern accent), and they agreed with the 'varnish in the carb' diagnosis. ("My husband had the same problem with ours. I thank you've hit it right on the head.") They also confirmed that there are no adjustments to be made on the carb. I'll try running some carb cleaner through it tomorrow, and if that doesn't work, I guess I'll have to resort to spending 40 bucks on a new carburator.


Before i would spend 40 bucks on a new carb i would pull it off disassemble it as much as you can and clean it by soaking in carb cleaner. Then blow out all the holes and slide a thin wire through the holes in it to clean out the varnish.


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## Cabin Fever

Jim, I agree with Barelahh. Whenever I have a carburator problem with a 4-cycle, I take it off the engine. Break the carb down into parts. Wash all the parts with carb cleaner. Spray carb cleaner into all of the orifices and needles. Then put the car back together and on the engine. It works perfect every time! In these situations, I had no idea what caused the problem. All I know is, a good cleaning cured the problem.


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## deaconjim

barelahh said:


> Before i would spend 40 bucks on a new carb i would pull it off disassemble it as much as you can and clean it by soaking in carb cleaner. Then blow out all the holes and slide a thin wire through the holes in it to clean out the varnish.





Cabin Fever said:


> Jim, I agree with Barelahh. Whenever I have a carburator problem with a 4-cycle, I take it off the engine. Break the carb down into parts. Wash all the parts with carb cleaner. Spray carb cleaner into all of the orifices and needles. Then put the car back together and on the engine. It works perfect every time! In these situations, I had no idea what caused the problem. All I know is, a good cleaning cured the problem.


I think I might give that a try today. I'll let you know how it works out. Thanks for the help everybody.


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## MELOC

be careful with that wire. you probably have a very delicate diaphram in there somewhere and you don't want to puncture it.


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## raymilosh

if there's no fuel filter, then anything in the gas tank entering the carb will immediately clog it, causing the symptoms you mentioned...from fine to suddenly not OK...starving for fuel.
there is typically at least a fuel screen inside the carbeurator under a flat square plate held on by four very small screws. It is shaped like a basin and is about as big around as a pencil erasor. Pluck it out out of its recess with a pocket knife. Look at it carefully. if there is trash in it, clean it and replace it. It's the first line of defense for keeping trash out of the carb so it is the first place to get clogged. 
good luck.


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## Beeman

Adjustment screws might be under plugs to prevent "tampering" with the factory clean air approved setting.
A good wire for cleaning is a guitar string.


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## BRYAN

Having read thru all of these, I will give you my opinion, for what its worth. If your engine is fairly recent manufacture it will have neither idle or high speed adjustments. Almost all of these engines have fixed jets these days. It sounds very much like the high speed jet is blocked. If you decide to clean, proceed with caution and remember how it came apart. Be very careful not to enlarge the hole in these jets, as that will ruin it. Very likely you will find loose material around the pickup tube and in the bowl, since the problem started suddenly. Varnish and gunk take time to form. Also go light on the carb cleaner if its plastic, as well as on any gaskets. Good luck. (Oh yeah, that was a southern ******* accent you heard here)

P.S. raymilosh is correct about the fuel filter issue, if there is a fuel line to put one in, its cheap insurance against problems.


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## deaconjim

Sorry I haven't updated this. I took the carb apart and cleaned it. Found some chunks of varnish and other trash inside. After putting everything back together, it ran great for about 5 minutes, and acted like it was out of gas. 

Found the rotten fuel line broken off in the tank. I fished it out (along with the pickup filter that the parts list didn't include), cleaned the varnish out of the tank and replaced the line and the filter. Put everything back together and it ran fine as long as I kept the choke about 3/4 closed. The fuel line I put on was 3/32", and it could be that I should have used 1/8". 

The next morning, I tried to start it again and now it's back to the original problem.

Did I ever mention the fact that I absolutely hate weedeaters?


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## raymilosh

i imagine there are pieces of rotten fuel line that have made their way back into the carb, causing the same problems. 
To fix it in a way that it stays fixed, replace the fuel line and the filter in the tank, blow out the fuel line and remove and blow out the ports in the carb and put it back together. Without the filter in the tank, every single speck in the tank will make its way to the carb and clog it. It'll make you crazy.


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