Hard cold starting - catches, then won't start again

[AMC4x4]

I'm having a weird issue with a 12 year old Craftsman YT3000 (Husqvarna) lawn tractor with a Briggs engine (331877 2371 G5). It has been getting harder and harder to start when cold until the last two seasons it's been a nightmare. Every time I run through checks for various things (air cleaner, carb linkage, etc.), it seems to start right up and I think the issue has been resolved. But next time I go to start it, I'm surprised by the hard start again.

If I put the choke on, it seems like it's going to start - it "catches" and fires up for 1-2 seconds, but then IMMEDIATELY stops and won't start again unless I let it sit for 15-20 minutes, at which time it will do the exact same thing. I can usually smell fuel at this point. Somehow, I do eventually get it to start but it takes a few tries at this. I have tried not applying the choke all the way when first trying to start it, and that worked once and then not again.

It *felt* like it was getting flooded so I did some research and replaced the old Nikki carb (original with the mower, and I read of all kinds of problems with it) with a new OEM Briggs carb. After that, it fired right up and I thought great, that's what it was finally, but the next time I went to start it, it had the same issue AGAIN. Once I get it running, it will start every time as long as the engine is hot, and it runs fine when I finally get it running.

I have replaced the spark plug, air filter, fuel filter, carb, gasoline (put new, clean in), adjusted the valves, sanded down the rusty magnet on the flywheel and checked the clearance there (it's about a business card width).

Not sure what else I need to look at. Thanks for any suggestions.

 

[Fish]

I had one brought to me with similar problems, I put in a new {good brand} spark plug, and it fixed it. Another time, the plugs were carboned over so bad that the carbon was almost touching.

 

[Fish]

If not, you should take off the valve cover, and rotate the engine by hand and observe the rocker arms, and make sure the both move the same. There was a problem with cam lobes wiping out on the cam shafts there for a while.

 

[AMC4x4]

I had one brought to me with similar problems, I put in a new {good brand} spark plug, and it fixed it. Another time, the plugs were carboned over so bad that the carbon was almost touching.

Thanks. Will try another spark plug. I bought the OEM one off the Sears site two years ago but will try another. I had read about someone talking about bent pushrod tubes so I did check when I adjusted the valves and everything seemed OK. Would they be likely to be that different when the engine is hot?

 

[Fish]

Valve adjustment just adlusts the clearance of the low part of the cam lobe and valve/rocker arm, I am talking about the tip of the lobes. The performance of the engine gets wonky if one lobe gets worn way down.

Here is a video off of youtube. Like I was saying, just remove the valve cover and watch the rocker arms as you turn the engine over by hand, see if they move about the same depth.

 

[slomo]

Threre are a few stumper like this on here under this Briggs section. Seems like the owner has covered all the bases.

Thanks. Will try another spark plug. I bought the OEM one off the Sears site two years ago but will try another. I had read about someone talking about bent pushrod tubes so I did check when I adjusted the valves and everything seemed OK. Would they be likely to be that different when the engine is hot?

So the plug is 2 years old? How about the fuel? Is it 2 years old? You said you put in a new plug. How can we help with bad info?

Go back to the basics with air, fuel, spark and compression.

Is the air filter plugged up?

Do you have good fuel flow AT the carb inlet? Can you look into the carb and rev the engine and see fuel getting sucked up from the fuel bowl into the engine?

Does your oil smell like gasoline?

Exactly HOW did you adjust the valves? What stroke specifically? Did you set the piston 1/4" INTO the bore or TDC? Not for sure on YOUR engine but some require the piston 1/4" down into the bore to set valves.

Does your carb have a pilot adjustment screw? Was the carb float level with the carb body?

Does your carb have that 12 volt solenoid on the bottom of the fuel bowl? If it does here's my trick. Remove the 12 volt wire. Remove the solenoid. Take wire cutters and cut the plunger off. Reinstall the solenoid gently. Should have fuel flow all the time now. OR make sure you have 12 volts with the key ON. Remove solenoid and turn the key off and on watching the plunger go up and down. If the plunger doesn't move, it's bad and needs replaced.

slomo

 

[AMC4x4]

So the plug is 2 years old? How about the fuel? Is it 2 years old? You said you put in a new plug. How can we help with bad info?

Sorry, I thought I had mentioned new fuel. Yes, brand new fuel. That was actually the *first* thing I thought of and changed the fuel out. Problem remained. What is the bad info? Do you need the spark plug number? I just ordered a Briggs & Stratton 591055S that is supposedly what goes with this engine and will try that next. I do not know what the spark plug gap is supposed to be, so I suppose that could be an issue as well.

Is the air filter plugged up?

No, I have removed it a number of times. It's still totally clean, as is the pre-filter.

Do you have good fuel flow AT the carb inlet? Can you look into the carb and rev the engine and see fuel getting sucked up from the fuel bowl into the engine?

I haven't looked at that, but I have a clear fuel filter and can see fuel going through it well. When the tractor is running, it runs great.

Does your oil smell like gasoline?

Just checked. No, it doesn't.

Exactly HOW did you adjust the valves? What stroke specifically? Did you set the piston 1/4" INTO the bore or TDC? Not for sure on YOUR engine but some require the piston 1/4" down into the bore to set valves.

I set at TDC as I saw on some YouTube videos. I didn't know some require the piston 1/4" down. The engine runs fine when it runs. Would that be the case if I had misadjusted the valves?

Does your carb have a pilot adjustment screw? Was the carb float level with the carb body?

No adjustments on this replacement carb except I think the idle adjustment screw. It's the OEM briggs carb # 594601.

Does your carb have that 12 volt solenoid on the bottom of the fuel bowl? If it does here's my trick. Remove the 12 volt wire. Remove the solenoid. Take wire cutters and cut the plunger off. Reinstall the solenoid gently. Should have fuel flow all the time now. OR make sure you have 12 volts with the key ON. Remove solenoid and turn the key off and on watching the plunger go up and down. If the plunger doesn't move, it's bad and needs replaced.

I will try that, but am I correct in suspecting that if this was the issue the fuel cutoff would be all the time?

Just some more info to complicate matters, today I had to mow the lawn and instead of pushing the throttle up to the choke, on a lark I just put it at max throttle before the choke linkage pushed the airway closed. The mower started right up. It surged for the first minute or so until it warmed up, but it started. I am pretty sure I have done this before and it worked sometimes, other times it didn't.

So I think the possible unknowns at this point are fuel flow at the carb inlet and possible valve misadjustment?

Again, when she runs, she runs great. Lots of power, no issues. It's getting her started sometimes that's a real PITA.