Briggs and Stratton riding lawnmower won't start

I've posted extensively on a comparable site, but they probably think I'm an idiot now, as nothing suggested seems to be working.

I have a Craftsman LT1000 with a Briggs and Stratton engine, Family: ybsxs.5012vp 274826 Model: 31c707

Taking it all the way back to the beginning: Performance was weak at times while mowing. It was suggested to clean the carb, which I did, and it worked great for a while after.

After winter, it continued to work decent, but had a little trouble starting. Starter fluid usually did the trick, but after an hour or so, it would die. After a brief rest, it would start again to finish the job. This happened during spring cutting. Then it started happening after 30 minutes of cutting, and wouldn't start again unless I gave it a much longer break.

At first, it seemed like a fuel issue: I cleaned the gas tank, loosened the cap, replaced the fuel line, installed a filter and fuel shut-off, cleaned the carburetor several times, replaced the gaskets.

Afterwards, it would again run pretty good and strong for a little while, then it would sputter and die after 20-30 minutes of mowing. the next day it might start for a little while and then sputter and die.

Then it wouldn't start at all unless I poured a little gas down the elbow intake. It would then run until the fuel burned off. I cleaned the carb again,confirmed fuel solenoid was working, tested several ways and it was definitely getting fuel but still wasn't starting without the extra gas in the intake. But it still wouldn't run for any significant length of time.

Now it doesn't start at all. It was suggested that it might have been the ignition coil. I replaced it. I have confirmed the spark plug is getting good spark, and it still won't start even with a shot of starter fluid. (It does occasionally backfire.) The spark plug looked slightly dark like it may have had a little oil on it, but I'm not certain of this. I checked the flywheel key, and it's good. I also figured out there was too much compression, and I adjusted the valve clearances. It didn't seem to help, so I tightened them up a bit more. (A suggestion by a youtube repairman donyboy) This also didn't help compression issue. Maybe I went too tight, but he suggested it.

So this is where I'm at. It's still not starting up. What else can I try?

 

I have had a couple jobs go just like this also. One recently on a Craftsman MER.
I am betting on the fuel solenoid, or its power source. In all cases I could confirm the solenoid was working in the run position. For some reason a new one another good used one still somehow was the problem.
I have a solenoid with the plunger cut off that I keep for testing now.

I had at one time found a thread size and used a standard bolt like some of the Walbros did, but I forget what size.

 

When you try to normally start, is some fuel on spark plug? If bone dry put a little fuel or a squirt of starting fluid into cylinder. Then try starting. Also have you replaced spark plug?

 

I have a Craftsman LT1000 with a Briggs and Stratton engine, Family: ybsxs.5012vp 274826 Model: 31c707

After extensive trial and error in exploring why my mower wouldn't start, it was suggested that I check the cylinder head "You have what sounds like a valve seat or guide movement! Explains the starting issue also, not uncommon on this engine. You need to remove cylinder head. Bet the head gasket is blown also anyway. I think you will find the issue with the guide moved in head allowing valve to stick open some."

So I've taken the head off...to me, things look fine, but do you see any issues? I'll be replacing the gasket, but while I have it open, I'd like to make any other repairs necessary...thanks!

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I finally got around to looking at this mower again.... Yes, I replaced the spark plug, and injected starter fluid in the cylinder head. It still wouldn't start, even after verifying the spark plug was sparking...strange, I know...

 

Aaaack! Don't start a new thread. We have to go back and forth to get all the information. I'll ask the moderator to merge them.
He will also suggest you clean the head for a good gasket fit. It looks as if there was a blow out of some sort on the bottom of the picture where the gasket grid is not pronounced.

 

Remove the valves and make sure the seats are both tight and not loose.

 

What are your valve clearances now? Your valve seats aren't coming loose or there would be bright metal showing where they meet the aluminum head. These things aren't that complicated so lets start back at square one and find what got overlooked.

 

Valve clearances are currently at .003

Steps I have taken thus far (after each step, it either ran for a little while and then stopped, or didn't start at all, so I tried something new):

1. Cleaned carburetor
2. Cleaned gas tank, loosened cap, replaced air filter
3. Replaced fuel line, installed new filter and fuel shut-off
4. Cleaned carburetor, replaced gaskets, checked needle and float

At this point, it ran for a couple weeks fairly decent but then started to sputter and die. Then it wouldn't start without fuel dripped into the elbow. But then it would die after fuel burned off.

5. Cleaned carburetor
6. Verified fuel solenoid was working
7. Verified carb bowl was getting fuel

At this point, the engine quit starting even with fuel or starting fluid down the elbow.

8. Replaced ignition coil
9. Verified spark plug getting spark
10. Verified flywheel key was intact
11. Squirted starter fluid directly into cylinder

At this point engine still would not fire even with starter fluid

12. Determined there was a compression issue
13. Replaced spark plug and verified getting spark (even though other one was working)
14. Adjusted valve clearances to .006

At this point engine still would not fire, but would backfire with starter fluid when I quit trying to start it

15. Still compression
16. Adjusted valve clearance to .004
17. Still compression
18. Adjusted valve clearance to .003

At this point engine still would not fire, but like before, would backfire with starter fluid when I quit trying to start it

19. Removed cylinder head

This is where I'm at. I know I'm going to replace the head gasket, but I'm not sure if there's anything else I should look at before putting it back together...It was speculated that there was guide movement allowing valves to stick open, but I'm not sure if this is the same as the valve seat which Cheese has said looked fine...

Thanks ya'll

 

Okay, after checking the flywheel key, it completely stopped cranking up. Did you put oil or grease where the flywheel goes? I think your flywheel key that was not sheared is sheared now. Either it got oil or grease on it or it didn't get tightened well enough.

 

You indicated that your valve clearances are at 0.003". Is that for both valves. The spec for your motor is 0.003" to 0.005" for the intake and and 0.005" to 0.007" for the exhaust valve.

Perhaps your exhaust valve clearance is too narrow causing the valve to stay slightly open causing a loss in your compression. Could also be happening on the intake valve as well, however that is where your compression release is so a little tightness there can add some benefit but there is no reason to have your exhaust valve so tight.

Open up both clearances and as long as the motor at least spins you know that the compression release is working.

 

It will run with those clearances as long as they were set with the engine in the correct position.

 

thanks guys. both clearances are at .003...when I put the cylinder head back on, I'll adjust the exhaust valve to .005 and see if it helps...

I'll check the key again. If it's intact, is there something in particular I need to do when putting it back together?

 

Cheese, Optsy, and others...

Update, I checked the flywheel key, and it was fine.

while I had the head off, I tried this valve seat leak test...

https://www.youtube.com/watch?v=yqMslJOf5W8[/QUOTE]

it did not leak like in this video. However, both sides did leak (more on the intake), but very very slowly... it didn't show up for probably 10-15 minutes or so...It's been over an hour, and there's still gas sitting on top of the chamber. Are they not supposed to leak at all? Or is a very slow drip ok? if not, can you reference a diy to fix them? (I don't have a seat cutter.)

Is there anything else I need to check while I have the head open?

 

I wouldn't worry about it, it sounds like they are seating well enough. A problem area will leak gas rather quickly. Let's see what happens when you get it back together.

 

Well, I put it all back together, and it still doesn't start...I dont get it...very close to throwing in the towel...

 

Take the fuel line off and plug it so it doesn't leak, let the engine sit a while, then try to start it without the fuel line connected. If nothing, then with the throttle open and no choke, shoot some starting fluid in it while cranking and see if it tries or backfires or what and post the results.