Lawn tractor engine won't run without the choke

[OUCaptain]

So thats the issue. I've got a lawn tractor with a Briggs 14 hp ohv engine. It starts and runs fine with plenty of power but only if the choke is about halfway out all the time. I've changed the plug and installed new air filter. I pulled the carb, completely dissassembled it, and soaked it one of those paint cans of cleaner but no change. The only thing I haven't done is adjust the valve clearance as I don't have a spec manual. There is a small bit of clearance between the valve and rocker though. I'm at a loss. Any ideas?

Edit: tried re-tuning the mix. Richening nor leaning had any effect. It ran the best the way I found it.

Edit2:

We bought the tractor used. It didn't appear to be very well maintained which prompted the general tune up. Engine runs exactly the same as before I touched it, maybe a bit better minus the choke issue. When I began playing with mix, I wrote down the exact number of turns it was already out so I could return it to it's original position. Float was clean and moving freely. Didn't have a filter to begin with (it does now though) which is why I pulled the card and cleaned to begin with. Gaskets were in good shape and everything was reassembled perfectly(I double checked twice).

This isn't the first small engine I've worked on btw. I've been rebuilding them for about 10 years. This one just has me baffled. I'll check the muffler once it warms up a bit outside.

Thanks for the suggestions. If nothing else, it's confirming that I haven't missed anything (except whats causing the problem of course).

 

[cardiac]

Most definitely some sediment you missed in the carb. I do a a half dozen lawnmowers/tractors for the neigbors every spring. They never drain the gas or stabilize it during the winter. You need to run a welding tip cleaner through the main jet. I'm sure it will be clogged. Soaking probably didn't get it....

 

[OUCaptain]

Originally posted by: cardiac
You need to run a welding tip cleaner through the main jet. I'm sure it will be clogged. Soaking probably didn't get it....

Thanks but did exactly that. Jets and ports are completely clean as far as I can tell. The bowl was clean when first took it off, i.e. no sediment or evidence of gas sitting in it for long.

 

[M2008S]

you shouldnt have to adjust and valve clearance or whatever. id say it sounded like the mixture screw (little one with a spring) is off. just get the engine warm somehow and fiddle with it so it runs with the choke off..

but since you say you worked with it id say you messed something up when you took it apart. left something off, etc.

-take the bowl off the carb and make sure the float isnt stuck or bad, it may have a hole therefore filling with gas, fing up. might just get a new one for a couple bucks and change it neways

-double check for any loose/missing parts

-gas filter? check. it should have one in the gas line.

also make sure you have the gasket between the carb and engine, did you forget it?

some had restricter plates between the muffler and the block too. id try the other things before that though. theyre little metal plates.

try that then come back w/ edit

 

[Mulish1]

Hi folks,

Just a short note to thank those of you who put me on the right track to fix my garden tractor. I stumbled upon your site and this string that led me through stripping down the carbuerator on my craftsman tractor. It took a while for this mechanically challenged retiree, but when all was said and done, the problem was eliminated.

There happened to be some gunk (junk) that got past the fuel filter and was obstructing the flow of fuel in the needle valve at the bottom of the carbuerator bowl.

Thank you one and all,

Doug Chapman

 

[skyking]

Hi folks,

Just a short note to thank those of you who put me on the right track to fix my garden tractor. I stumbled upon your site and this string that led me through stripping down the carbuerator on my craftsman tractor. It took a while for this mechanically challenged retiree, but when all was said and done, the problem was eliminated.

There happened to be some gunk (junk) that got past the fuel filter and was obstructing the flow of fuel in the needle valve at the bottom of the carbuerator bowl.

Thank you one and all,

Doug Chapman

Welcome to the forums, Doug. I think this is the first time I've seen someone join for finding the answer to a mechanical problem here. It is better known for the computer-related information

 

[EightySix Four]

Welcome to the forums, Doug. I think this is the first time I've seen someone join for finding the answer to a mechanical problem here. It is better known for the computer-related information

I won't go near the hardware side of AT anymore. Those guys take fanboyism to the extreme.

 

[boomerang]

OU, One of the mods here was having similar problems with a full sized tractor and I suggested he had a vacuum leak. If there is a manifold that bolts to the block you may want to remove it and see if the gasket is in good shape.

However, what the mod ultimately found was that he had rust in the gas tank that was restricting the flow of gas to the carb. Without enough gas it was running lean.

Check for a vacuum leak and if not, make sure the fuel is flowing well. Could be water in the fuel filter, a pinched or collapsed fuel line, etc., too. Sounds as though you've gone through the carb pretty well. Did you need to change the float level? Do you know how to set the float level? Is it an old style brass float that has sprung a leak and now has gas in it?

 

[EightySix Four]

OU, One of the mods here was having similar problems with a full sized tractor and I suggested he had a vacuum leak. If there is a manifold that bolts to the block you may want to remove it and see if the gasket is in good shape.

However, what the mod ultimately found was that he had rust in the gas tank that was restricting the flow of gas to the carb. Without enough gas it was running lean.

Check for a vacuum leak and if not, make sure the fuel is flowing well. Could be water in the fuel filter, a pinched or collapsed fuel line, etc., too. Sounds as though you've gone through the carb pretty well. Did you need to change the float level? Do you know how to set the float level? Is it an old style brass float that has sprung a leak and now has gas in it?

Look at the date on OU's post, he's hopefully fixed it by now

 

[boomerang]

Look at the date on OU's post, he's hopefully fixed it by now

OMG, I would hope so!

 

[bourbon mo]

Look at the date on OU's post, he's hopefully fixed it by now

OMG, I would hope so!

If so , hopefully OU might give us a update on this???? And yes I see how old the last post is BUT......
I've gotta White riding mower with a 15.5 hp. Tec. eng. doing the same thing. Got to have the choke on before it will run. I have tore down the carb , replaced fuel filter & lines , spark plug,cleaned the gas tank. I also have worked on many of lawn mowers/tractors/weedeaters in my day and still run into a "head scratcher" like this. Any suggestions are welcome!!!

 

[Norm74]

If so , hopefully OU might give us a update on this???? And yes I see how old the last post is BUT......
I've gotta White riding mower with a 15.5 hp. Tec. eng. doing the same thing. Got to have the choke on before it will run. I have tore down the carb , replaced fuel filter & lines , spark plug,cleaned the gas tank. I also have worked on many of lawn mowers/tractors/weedeaters in my day and still run into a "head scratcher" like this. Any suggestions are welcome!!!

 

[Norm74]

I can see this is quite an old posting but wanted to add what I found on a Nikki model A4600 carburetor on my Generac generator. Same problem with only running with choke on and running rough. This pointed to an obstruction in the idle circuit. The idle circuit is fed from the main circuit through a small orifice directly behind the main jet. After removing the main jet it could barely be seen due to its size. It was so solidified that a small drill in a hand held chuck was needed to clear it. I hope this helps someone in the future.


Norm74... Might be a good idea to look at much newer post and leave the old ones to die in peace...

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