LX172 Hard to Start

I have changed carburetor, spark plug, ignitor, coil, fuel pump. Checked the flywheel key. The only way I can get it started is with starting fluid. Once started, it will run all day. If I shut if off for only a short time, it will restart with no problem.

Sounds like choke not closing completely at cold start up. Try to choke by hand and see if it helps.

Hard to start says nothing decsride exactly what is happening from the instant the key hits the s position.
What do you see , hear feel & smell
How does the engine react, spins quick, spind slow spins then stops then spins then stops

He already said it only starts with the help of extra fuel upfront and that it runs fine afterwards. That negates a whole slew of other potential issues.

This is either choke not closing when necessary, or a weak fuel pump. Take it from someone who's been there: a weak fuel pump on one of these will let it run like a top all day long except when starting cold, because it won't have enough power to pull up from the line and over to the carb.

But you replaced that, so we'll assume the new one's not defective and was installed correctly. Remove the air cleaner and verify the choke plate closes to "mostly" when the lever's all the way up in the choke position. If it does, suspect the new fuel pump.

And if neither the choke nor fuel pump is the problem, the mower cannot be fixed whatsoever and must be trashed. Don't read that last sentence.

And the first sign of excessive valve lash is an engine that will not start cold in the morning right out of the shed but once hot and the gap closes a little will start & run all day.
However the cranking will be a little lumpy.

If the mower was on the workshop floor & it could be seen, heard & smelled they it could be diagnosed in 2 minutes flat.
However all we have to go on is words on a screen and as you should know, the first step is to rule out what it is not.


So very low compression from a sticking valve or worn rings will allow the engine to crank too fast but be difficult to start
And of course too much valve lash will make it crank lumpy as will a faulty decompressor or worn cam.

A leaking head gasket will also make the mower difficult to start but allow it to run fine once started.

In each & every one of these cases a shot of starting fluid will allow the engine to start, as will a choke that is not fully closing as you have already suggested which could very well be the actual problem.

When you go through the list of things that Deckeda has done in his original post the only thing missing was checking the valve lash.
So assuming that everything he replaced was actually good that does not leave much.

And as a "cute' example I had a Murray with a 17Hp intek.
The customer would ring me early in the morning and tell me "it wont start, I ,have cranked it till the battery has gone flat "
I would turn up several hours latter, hook up the jumper pack & it would fire right up.
So after cold one for payment ( he & his very large family are all very good customers ) I would be off to the next house call.
Next morning, same thing.
Now when I say early, I mean crack of dawn type early & the mower lives in a steel shed out back.
After a 1/2 dozen of these , I took had a loaner come available , so swapped the mowers & took it back for a service.
The valve lash was massive, the cam was worn almost round and the exhaust valve was just about burned from the edge to the stem.
When I asked him about the lumpy cranking in the morning he said he thought it was "normal" as the mower had always done it from new.