Sabo lawnmower with Briggs & Stratton engine won't start when warm
- Thread starter Raiden
- Start date
What Slomo is saying is you need the piston to be at Top Dead Center when you check the valve lash. This is SOP for lash inspection. I assumed to found a good instructional video somewhere that walked you through all of it? When he said heel, he mean the cam is in it's dwell. At TDC both cams are in their dwell. The slight motion you see on the exhaust valve is the compression release function. That is normal at very low RPM. At normal running speeds it will not happen. When you say lapped, I assume you meant you removed some material from the valve stem to meet the lash spec? When people say lapping a valve, they generally mean the seat of the valve on the head side. Not the stem side, where it meets the lifter(or tappet) depending on your preferred terminology. If you did it all correctly you should be fine. Double check your valve lash at TDC before you install the head. What are you measuring for valve lash on the exhaust and intake now?
Thanks. I understand it now. I made sure to set it at Top Dead Center.
I have a clearance of about 0.006 for the intake valve and 0.0098 for the exhaust valve. The clearance on the exhaust valve ended up being a bit too large. I thought I had actually done a pretty good job grinding it down by hand—getting the clearance to around 0.0075. But wanting to ensure the angle was exactly 90 degrees, I took it to an engine reconditioning shop to have just a tiny bit more ground off. Unfortunately, the guy was too quick, and a bit too much material was removed. I hope it’s still within the acceptable limit.
I’ve put it back together since then. The lawnmower started right up on the first pull, even though I didn't pull very hard. It ran well, too. I mowed for about 25 minutes afterward, turning it off and on again a few times in between. It worked without any issues.
But an hour later, it wouldn't start again. I gave up on it at that point.
Five hours later, it started up again with no problems.
I can't quite make sense of it.
The spark plug, ignition coil, and carburetor are new, and the valves are clean and adjusted.
There’s really nothing else you can do, is there?
I have a clearance of about 0.006 for the intake valve and 0.0098 for the exhaust valve. The clearance on the exhaust valve ended up being a bit too large. I thought I had actually done a pretty good job grinding it down by hand—getting the clearance to around 0.0075. But wanting to ensure the angle was exactly 90 degrees, I took it to an engine reconditioning shop to have just a tiny bit more ground off. Unfortunately, the guy was too quick, and a bit too much material was removed. I hope it’s still within the acceptable limit.
I’ve put it back together since then. The lawnmower started right up on the first pull, even though I didn't pull very hard. It ran well, too. I mowed for about 25 minutes afterward, turning it off and on again a few times in between. It worked without any issues.
But an hour later, it wouldn't start again. I gave up on it at that point.
Five hours later, it started up again with no problems.
I can't quite make sense of it.
The spark plug, ignition coil, and carburetor are new, and the valves are clean and adjusted.
There’s really nothing else you can do, is there?
WOW, talk about cholesterol my gosh. She is or was packed full of carbon. Never seen one THAT bad. Must of over filled the oil all the time or did a lot of tipping.
Your thermostatic lever off the muffler is all bent up. One of the other guys gave you a PERFECT set of instructions on how to set all this autochoke stuff up.
No wonder she won't start with all that carbon plugging up the intake port and who knows about the exhaust port.
THIS is EXACTLY why ALL engines require DE-CARBONING after say 5-7 years of use.
No wonder she won't start with all that carbon plugging up the intake port and who knows about the exhaust port.
THIS is EXACTLY why ALL engines require DE-CARBONING after say 5-7 years of use.
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What Slomo is saying is correct. It sounded like you have already cleaned all of that out.? Right? If not go back and do it. Otherwise test the choke feature fully. Remove the air filter and air box case. The choke plate should be visible. It should be closed when cold. Run it like that for a bit.(do not cut grass just let it sit so you do not pull dirt in to the engine. After about ~30 seconds stop the engine. Observe where the choke plate is when it is off. if should be partially open. Try to restart it. If it does not start you need more choke. i.e. the plate needs to be closed more. If it runs , keep it going for about 30 more seconds. Stop and repeat the observations. Keep doing this and see if you can repeat the no start issue. If you do have a no start, note where the throttle plate is. You need to adjust the lever to provide ore choke. With a hot engine it should be fully open. You can observe the choke slowly close as everything cools. It could take a while if at running temperatures. If it is not moving freely it can hang up. It has been described earlier how to adjust it. After all you have done, it seems like this is un left for full confirmation. However it does not mean the problem is not else where. You are methodically confirming systems to be working as they should or not. Again you may want to go back and confirm everything else. Like having good gas, good consistent spark. No debris in the carb. etc. You will figure it out. You are very determined and have stick to it drive. more than most.
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