Raw gas in Tecumseh crankcase breather

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  #1  
Old 12-06-04, 05:53 PM
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Question Raw gas in Tecumseh crankcase breather

I have a Tecumseh H60 755 06R, Ser.# 002RD (last digit D may be 0) on my Troy-Bilt tiller that starts easily and seems to run perfectly for a short period of time but then dies. I adjusted the carburator float thinking the float was sticking, but that made no difference. The engine still starts easily and runs fine for a short period then dies. I then discovered raw gas with a tinge of oil in the crankcase breather. I plan to disassemble the engine, but since I am new to this, only rebuilding an old Brigss and Stratton engine years ago, I would like to know what some of you really good mechanics think may be the source of my problem. I'm guessing a problem with the intake valve but I don't know what I'm doing.
Does anyone have an idea where I should expect to find the problem and/or what I should do when I tear this engine down?

I thank you in advance for your assistance.

Respectfully,
Dan
 
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Old 12-06-04, 10:04 PM
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Before you try anything look at the breather itself. There should be a diaphram type check valve inside. The check valve keeps the crankcase from drawing in outside air when the piston is coming up on the compression or exhaust stroke. When the piston comes down any blowby or air inside the crankcase should be pushed down the tube to the carb and sent back to the combustion chamber. Inspect the diaphram to make sure it's not cracked and there's no holes in it.

Try disconnecting the tubing between the crankcase breather and the carb. Run the engine and see if you are getting any raw gas in the breather. You should plug the hole in the carb where you disconnected the tube before running. You might be getting some gas into the breather if the intake valve guide was totally trashed. I suppose you could also be getting some gas if you had bad piston rings. Since you say you can easily start the engine I'm assuming that cylinder compression is 100 psi or better. That should mean the rings are good. Disconnecting the line to the carb will eliminate or confirm the carb as the source of the raw gas.
 
  #3  
Old 12-06-04, 11:28 PM
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Check the oil. Is it too full, smell like gas, and/or thin? If so, the carb is leaking gas into the crankcase when the engine is not running.
 
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Old 12-07-04, 02:55 AM
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Thanks for rapid responses

Thanks guys for the rapid responses. In the next couple of days, when I'm able, I'll check those things and let you know what happens.
 
  #5  
Old 12-11-04, 02:33 PM
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No luck yet

Originally Posted by jughead
Try disconnecting the tubing between the crankcase breather and the carb. Run the engine and see if you are getting any raw gas in the breather. You should plug the hole in the carb where you disconnected the tube before running. You might be getting some gas into the breather if the intake valve guide was totally trashed. I suppose you could also be getting some gas if you had bad piston rings. Since you say you can easily start the engine I'm assuming that cylinder compression is 100 psi or better. That should mean the rings are good. Disconnecting the line to the carb will eliminate or confirm the carb as the source of the raw gas.
The engine would not even fire with the breather tube disconnected and the hole for it from the carb plugged. I reconnected the tube and engine starts easily, and runs for a second or two then dies same as before.
 
  #6  
Old 12-11-04, 03:26 PM
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Cool....Your simple test reveals that what little gas is available is coming from the carb. If I were there in front of the engine I might try starten'er up. Then, just before she dies I would try a quick spritz of carb cleaner right into the carb throat. If she keeps runnin' for another second or two that will tell you a bit more about what might be wrong. At the moment it's clear that the engine compression is probably fine. You know that the ignition system and timing is good or you wouldn't get a start at all. It's reasonable to assume that you won't find much wrong with the valves. Keep the wrenchs in the tool drawer until you have a good look at the fuel system and carb. On many small engines it's possible to carefully take the carb apart while keeping the float bowl down. The idea is to take the float bowl off the carb without spilling all the gas to see how much gas is in there. That way you might be able to tell if your carb is flooding or starving for fuel. If it's starving look for a fuel line obstruction (filter??) or for rust in the tank. Make sure the tank vent is in good order. A real full float bowl would mean that the needle valve isn't working or the float isn't (floating that is). One of the biggest complaints in this forum is problems with carbs. Mostly it's from leaving untreated gas in the engine too long and letting the fuel vanish inside some of the very small passages inside the carb. When that happens your only choice is to take the carb apart. I have used a torch tip cleaner to probe & clean small carb passages with good success. My guess is that you will find your problems somewhere in the fuel tank, fuel line, fuel filter, or in the carb. Post back if you have any further comments or questions after you've had a go at inspecting those things.
 
  #7  
Old 12-11-04, 04:17 PM
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Smile Thanks!

Thanks jughead!

That is very helpful. I did get the tiller from a lady who had it sitting up for a couple of years in a shed. First things I did was change the gas and oil and It ran fine for a couple of hours then the problem began. I added a fuel filter and a shutoff valve to the fuel line when I first started having the problem, then adjusted the float, but that didn't change things. Probably the fuel varnish you mentioned is the culprit.

I'll check the needle valve and ports then reassess the float again later. I'll let you know how it goes, but it may be a while before I have time to do it.

I guess I'll have to settle with using the wrenches on an old B&S 5HP that's locked up.


Thanks again!!!
Respectfully,
Dan
 
  #8  
Old 12-11-04, 09:05 PM
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Makes perfect sense. When you put fresh gas in the tank that gas acted like a solvent and shook loose the gunk accumulated in the fuel system. The gunk was mobilized by the flow of gas. Those semi solid particles won't make it through the small passages in the fuel filter or the carb. That's where the obstructions will be. Take apart the carb, fuel line, and filter. Inspect the tank and carefully clean everything as necessary and I'll bet your problems will be solved. Good luck.
 
  #9  
Old 01-29-05, 04:26 PM
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Smile Thanks to everyone!

Thanks to everyone who offered me advice concerning this thread!

After removing the carb, taking it apart and cleaning it, I re-installed it and the engine runs just fine now. Thanks for the advice that saved me from doing extra and unnecessary work.

Respectfully,
whome? aka Dan
 
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