Choke problems

This relates to a 4-cycle engine on a lawn tractor. It will only run in the “full choke” position. Any ideas as to solving this problem?

Thank you.

Have you checked anything so far?
Have you looked at the owners’ manual?

Thanks for your reply and questions. Gasoline and air filter are clean, owners manual is no help - it is an Intek engine – a Briggs and Stratton product. I also notice that gasoline is apparently getting past the carb and into the crankcase. I’ve taken it to two shops, they have not been able to diagnose it or fix it.

I’ll try to do some research into how the crankcase in those engines is ventilated. The only two paths I can figure to get from the fuel delivery system to the oil is either past the piston via a scored cylinder or through a crankcase ventilation system.

Thanks again for your interest and reply. I will appreciate whatever you can find. I do not think there are many hours on the engine - I bought it used, but it is fairly new – and the seller was a farily careful guy, so I don’t think he ran it without proper oil, etc.

I couldn’t find exactly what I was seeking, but I found this small engine troubleshooting and repair site. Perhaps it’ll help.

How do you know that? Did you drain the oil? If you took it to two repair shop for small engines and they couldn’t figure it out . . . you went to the wrong shops. These engines are bone simple, and the carb & choke system is equally as simple. Since I can’t see it from here I assume that your oil is full of gasoline because your choke isn’t operating properly. Fully open? I would say fully closed (choke all the way closed) to dump gas into the crankcase. Is it smoking during operation? (black & sooty, rich running) ? Rocketman

I had a Echo Leaf Blower that would only run with the choke on. I finally took it apart and it turned out to be a rotten fuel line from the tank to the carb. Once the leaky fuel line was replaced the blower ran fine. It’s a long shot but worth checking.

The gas is not getting properly drawn into the air as it flows through the carb. I would check the fuel lines and maybe there is a fuel filter. Also, check the gas tank to see if there is junk in it. Partially clogged lines or a clogged carb jet causes starvation of fuel, and only the extra vacuum generated by mostly closing the choke will suck enough through to keep it running. You might have to take the carb out and rebuild it or at least clean it thoroughly. Another possibility is that the carb is loose and air is getting sucked into the intake through the gasket between the carb and the block.

I wonder if you have a broken valve spring. Does the engine feel like it has good compression? If you have an electric start, remove the spark plug and crank it over with your thumb over the spark plug hole. If you have a manual start, you should be able to feel resistance as you slowly pull the cord with the spark plug installed. I had a broken valve spring on a small engine and it wouldn’t run unless the choke was closed. A bad valve spring would allow an overly rich mixture to dilute the oil in the crankcase.

This is a great reference, thank you for sending the link. I will take a look. I appreciate your help.

Thank you for your response and suggestion. I’ll look at the fuel line.

The broken valve spring seems like a possibilty, and I’ll try the compression test you suggest. Thanks for your reply and ideas.

Thanks for your reply and ideas, I will check on all those possibilities.

Thank you for your response and ideas. Yes, the black smoke is often there and I agree, the full choke position is the closed position and could be the reason gasoline is getting into the crankcase.