Small gas engine runs then dies

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  #1  
Old 06-21-07, 11:35 AM
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Small gas engine runs then dies

A friend gave me a really good condition Troy built rototiller. (Pony model) I havent even looked closely but I guess its got a B&G 4-5 HP motor. It has a manual choke.

It starts relatively easily (4-5 pulls) and seems to me to take a bit of time to warm up. ie, no power and babying the choke and throtle for several minutes to get a smooth, consistent idle. But maybe thats the nature of this motor. Then it runs fine

But......after about 20-25 mins of running well, it starts to surge.. run up in speed then down and keeps doing that. Then, after a few minutes of that performance it dies, not to restart. I havent checked anything yet but I am wondering if the float or something in the carb is where I ought to start ? Surely seems heat related so I am not sure where to start ?

When it cools down, it starts up again and repeats the process, so the problem is (appears ?)temp related. The reason I got tiller was a repair shop told my friend it needed new valves or something expensive ?

Any ideas would be appreciated.
 
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  #2  
Old 06-21-07, 02:10 PM
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First thing to check is the vent on the gas cap. Sounds like the vent is plugged. Try to blow thru it, if you can't it's time for a new cap (if you can't get the original opened up)
If that's not the issue, and you can blow thru the cap it could be fuel delivery or carburetion.
It would be helpful if you could post the model and type numbers, so we have an idea of what you're working with.
 
  #3  
Old 06-21-07, 05:35 PM
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RotoTiller

I meant to note the machine's got a B&S (not B&G, too fast typing) (Briggs....) engine.

I like the idea of the non-breathing gas cap, but I am not sure how that would relate to heat, or time running.

I have the original literature somewhere and I will look up the engine specs on the engine and post them.
 
  #4  
Old 06-21-07, 06:14 PM
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If the vent is mostly plugged, the gas tank will slowly, but surely pull a vacuum as the engine runs - to the point where it starves the engine of gas.... after sitting a while, the vacuum is relieved through the mostly plugged vent - and the process starts again.... Hope it's that simple....
 
  #5  
Old 06-21-07, 06:54 PM
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Try running it with the fuel cap loose for a while to see if the problem still exists, if so get a new cap, if not post model, type and code numbers and we will try to fix it. Have a good one. Geo
 
  #6  
Old 06-21-07, 07:46 PM
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This engine does not have a vent in the gas cap but through a hole in the tank mounting to the carb. The gasket that goes between the tank and the carb has a slot that accomidates the venting process through the carb. Temperature related could be ignition or valves. Check your spark when is starts to die. The cooling down before it restarts sounds like the ignition coil is opening up internally but also have seen valves that are worn and/or set to tight cause loss of compression.
 
  #7  
Old 06-22-07, 02:44 AM
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All Briggs fuel tanks vent through the fuel cap. The only difference is whether it vents through the threads of the cap or through a "drilled" vent in the center of the fuel cap. Since we don't yet know what, exactly, model series engine you have, diaphragm type carbs will vent through the center, top of the cap through the "drilled" hole and float type carbs will vent through the threads of the cap utilizing a special gasket integral to the fuel cap. However, I don't think that this is your trouble, I think you have a carburetor in need of soaking and reconditioning but to help us better help you, please post back with the engine's model, type and code numbers.
 
  #8  
Old 06-26-07, 10:29 AM
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Rototiller that dies

One of these days I will bring my glasses and a pencil to the shed and write down the tiller model number etc. However, the other afternoon I did a bit of experimenting.

Used it the other day with typical results: runs fine for 20-30 mins, after a slow warm up, then started to surge and die, surge and die. So, I took off the gas cap and low and behold it smoothed right out. I tried that several time and that seems to be the issue. I covered the gas filler hole with my hand and pretty much duplicated the problem.

I was trying to beat a thunder storm so I did not spend too much time looking but it sure seems to me that the gas cap on this rascal is a sealing type. That kind of makes sense so as to not splash any gas at all into a garden ? It has a 4 pronged T that takes a quarter turn to lock, and it seals with an O ring.

Maybe this afternoon I will get to writing down any spec info I can find on the machine. I know, even without my glasses, there are a couple of tags on the motor by the pull start rope so I can find the specs.

Thanks for all your help so far.

I do not recall if I mentioned, my friend gave this tiller to me because a repair shop told him several hundred dollars to fix.
 
  #9  
Old 06-26-07, 11:02 AM
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You might resolve the slow start up situation by running about one ounce of SeaFoam in the tank. This stuff works really well for removing the varnish build up inside the carb. It can be purchased at most automotive stores. I believe that you will see a marked difference in engine performance.
 
  #10  
Old 06-27-07, 12:34 AM
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I'm not sure what gas cap should be on this, but I don't recall ever seeing one with a T-handle on a troybilt pony. I wonder if it's not even OEM, and it apparently is not vented, or if it is, the vent isn't functioning. You need a new gas cap.
 
  #11  
Old 06-27-07, 11:43 AM
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It sounds like you have a tank with a ventless cap. The venting on this type is through the carb asm. Get the engine numbers off the shroud and we can verify it. If someone has replaced the tank to a carb that is not vented you can have this problem. I take it that there is a rectangler air filter on the carb? If you remove the filter and cover and look into the carb throat to the engine side of the choke butterfly there should be a small brass colored fitting that channels the venting to the tank for the correct carb. A local shop I know of will not work on these carbs but sells the tank and carb as a unit. Saves them time and they do not have to really trouble shot the actual problem. I got into this carb and tank real deep in 1988 with a local Shriners Parade unit and their mini car gokarts. Once we found out about the vent the problems went away on these old flat head engines.
 
  #12  
Old 06-28-07, 04:15 AM
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Rototiller that dies

Maybe today I will find 5 mins to get the engine numbers

The gas cap itself is round, the locking/screw underside mechanism is a 4 'pronged' T rather than a threaded type attachment that holds the cap in place on the tank. Sorry for that confusion.

It does have a rect - box type air filter, at least as I recall. Too many motors: throwers, blowers, mowers, whackers.

Thanks for your help so far
 
  #13  
Old 06-28-07, 10:15 PM
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You just need a new cap.

No tank vents through the carburetor. The carburetors all have bowl vents, but they don't and can't vent the tank.
 
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