Craftsman/Briggs & Stratton surging won't start

First of this is what I have:
Craftsman Lawn Tractor model 917.270812 with a Briggs & Stratton model 42E707 type 2631-E1 code 9905035B engine.

Here's the problem:
The tractor had been running fine for years then for no apparent (at least to me) reason it started surging at Idle and low RPMs. At higher RPMs it would smooth out. At idle it would smooth out if you choked it a little. OK so it was running a little lean. I made a mental note (not a good idea for me) to remove and clean out the carb. I was too busy and never got around to it - ah heck all I had to do was pull the choke out a little - right.

Well finally it just wouldn't start at all. It would turn over like a champ but wouldn't fire up.

The battery had a full charge and YES it had gas in it. LOL!

I checked for spark at the plugs and there was.

Thought it wasn't getting gas to the carb so I checked the fuel lines and filter and they're good.
So maybe a bad fuel pump? I pulled the fuel line off the pump and gas flowed out the end of the fuel line at the pump end. This was checked after checking the fuel lines so they were empty of fuel so pump must be working.

I put a little gas down the throat of the carb (didn't have starter fluid) and it fired right up and ran great until it ran out of the gas I'd poured in so that eliminated a possible electrical problem.

So now I finally got around to doing that long awaited carb cleaning. I pulled the carb off and disassembled the carb and fuel pump. Cleaned out everything. I've had this unit since the 1990s and there was hardly and debris in the bowl. This was it's first cleaning too. Ran small copper wire through the jets and any small orifices and used compressed air to blow everything out. I reassembled everything and reinstalled the carb.

With a full charge on the battery it turned over like a champ but it still would not start. Nothing changed. It'll turn over but not start at all. Got starter fluid now so I gave it a shot and it momentarily ran until it ran out of the starter fluid. With the carb still installed I pulled the top of the carb off to see if it was getting gas. The bowl had plenty of gas in it so the pump was working fine. So electrical is fine and it's getting gas to and into the carb but that's as far as it gets.

So.... I must not have done a good enough cleaning or it's a bad gasket/internal leak? Any Ideas. The carb is the one that has four screws that hold the fuel pump on. It's not the three screw version. Before I throw money at a carb gasket kit is there a problem area on these carbs that frequently cause this type of problem? I know the kits aren't that expensive but its the down time waiting for the kit that's the problem. If there is a problem area in these carbs that I need to re-clean I can get to that right away.

Your help/advice is appreciated!

Most surging is caused by a lean running condition. Are you sure you set the float level properly when you rebuilt the carb. The other thing I would be checking is valve clearance, which may be the cause of your starting problem.

Rivets said:

Most surging is caused by a lean running condition. Are you sure you set the float level properly when you rebuilt the carb. The other thing I would be checking is valve clearance, which may be the cause of your starting problem.

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Like Rivets stated ..... check your valve adjustments / (clearances ) Believe it or not !!! ..:thumbsup:

Rivets said:

Most surging is caused by a lean running condition. Are you sure you set the float level properly when you rebuilt the carb. The other thing I would be checking is valve clearance, which may be the cause of your starting problem.

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I was aware that a lean mixture causes surging as stated in my post. It would smooth out when I pulled the choke out a little. I didn't rebuild the carb. I just tried to do a thorough cleaning thinking there was a blockage somewhere. All settings were left the same. Float and needle were free and working ok and I paid, what I thought was, close attention to cleaning the jets.

As stated in my post I could get it to start and run by by-passing the carb. I poured a little gas down the throat and later used starter fluid. It started right up and ran properly so I don't understand how adjusting the valves would have any impact.

As stated it appears I failed to get the carb completely clean or the carb has developed an internal leak. Are you aware if these carbs are prone to internal leaks or if there are particularly difficult areas in the carb that need additional attention?

Said the heck with it and ordered a carb rebuild kit. Looks like the kit includes the parts for the pump as well. We'll see.

Most common cause of a lean running condition is a float level drop. You have a 17 year old engine. The Viton needle tip or seat will expand over time, causing the float to close off the fuel flow to the float bowl too soon. This will reduce the amount of fuel available in the float bowl, resulting in a lean running condition. When you change the choke position, you are making a richer mxture, which will smooth out the engine running condition. Many times it has nothing to do with the jets.

Rivets said:

Most common cause of a lean running condition is a float level drop. You have a 17 year old engine. The Viton needle tip or seat will expand over time, causing the float to close off the fuel flow to the float bowl too soon. This will reduce the amount of fuel available in the float bowl, resulting in a lean running condition. When you change the choke position, you are making a richer mxture, which will smooth out the engine running condition. Many times it has nothing to do with the jets.

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Thanks for the input Rivets! Good point. When i install the rebuild kit ill keep it in mind. I should get the kit sometime next week. Ill let you know how it works out. Will also check for vacuum leaks between head and carb.

If you have not torn into your carb let me suggest trying to geterdone with a choke setting. If you have a partial blockage and setting the choke helps then you are good to go until the problem worsens. The choke adjusts the fuel-to-air mixture and should be richer if slightly choked. That might not be the case in-your situation and you may be getting closer to normal by partial choking. If the engine smooth's out and is constant try running a cleaner mix in fuel tank for a bit. I like Seafoam but there are others such as STP, etc. You may save yourself added work. I use cleaner in all my engines at varying times (per engine) and never have starting or operating problems. For instance I will use cleaner in my touring bike about every 4-5 tanks, where as in motor home I add it every other tank. It also cleans up the engine and improves valve operation, especially if mucked up.

Well, carb kit arrived. I disassembled the carb and gave it another thorough cleaning. JMS180, thanks again for the carb link. It was really helpful! I reassembled the carb and installed it. Not wanting to take any chances I decided to clean out the fuel lines and fuel tank. I had to remove the main body to get to the tank. I drained the gas in the tank into a clean bucket and jumping Jehosaphat! Guess what I found? See the picture below. I don’t know how in the heck it even ran at all. The picture shows a small layer of gas floating on top of a lot, and I mean a lot of water!

I suspect the water has entered over a long period of time through the gas cap. The seat while in the down position covers the gas cap. Because of rain I have made a habit of flipping the seat forward so that it stays dry. Who wants to ride a tractor with SWAMP BUTT pants right?

Bottom line is while I had the body off I pressure washed everything of and did a lube job. Also took engine cleaner to the engine area. Looks purdy now! I also changed the fuel filter to a good quality clear one so I can do a visual check occasionally. I put fresh gas into it and it started right up and purred like a kitten - both cylinders firing like a clock. Problem solved!!!!! Still can’t figure out why it didn’t want to run on water.

P.S. I want to sincerely thank everyone for taking the time to help me out. You have a great forum here!!!

And no those aren’t pollywogs in the bottle. Just debris that fell in the bucket. LOL!

AND we thank you for letting us know the outcome of your issue... yeah it sure would be nice
IF they did run on water !! ...:thumbsup: ...Boobala