Small Engines (Lawn Mowers, etc.): Engine no start, fire shop, carburator

Question
QUESTION: LZ-25KC60 Serial 116469 will not start.  History - caught on fire.  Shop replaced worped head and got it started but said that it needed an advance module because it wouldn't idle correctly.  The customer did not want to pay so I bought it from customer and I bought the used head from shop.  The compression is 165psi on both side after I replaced head.  I replaced the advance module along with the 2 ignition modules per Exmark dealer suggestion and I do get spark at both spark plugs.  I did get it started a few days ago and it back fired through carburator and stalled.  I found a bad hose from pump to block and I replaced it.  I can't get it started now.  When I replaced the head I noticed that I didn't install a rubber I think gromet or band of some sort but it does have the gasket.  I am wondering if I have a intake issue.  I also wonder if I could have a carburator issue.  I removed carburter and took it apart only a little to clean and blow out with compressed air.  I wonder if I need to replace carburator gaskets.  What would be the next step?  Is there any other way to test before I spend more money?  What would you suggest for me to do and in what order?  Thanks!

ANSWER: Wow, it sounds like this unit has been around a while. The serial number shows it was made in the mid 90's. If you know you have spark, the next question is, are you getting fuel? You can try putting fuel in the throat of the carburetor and seeing if it will start. If this doesn't help, you may have another problem. This could be hard to diagnose "hands off", but try this and let me know if you still have questions.

---------- FOLLOW-UP ----------

QUESTION: I did try to poor gas down the throat and it didn't start.  Your right this is going to be difficult to trouble shoot is why I am reaching out to anybody that can help.  Could a missing O-ring on the intake manifold cause this or a missing choke plate?  Is there a way to tell the difference from weak to good spark?  Thanks for you help!

Answer
Yes, if you are missing gaskets or o-rings on the intake this can be a serious problem. The engine will be getting too much air if this is the problem, also if the choke plate is missing you won't get effective choking action. The only way I can tell you to check the spark is to remove the spark plug and plug it in the wire and ground it on the engine block. You should have a bright blue spark, and if you do, try moving it away from the block and see how far away you can move it. If you can bring it away an inch and you still have a spark, you should be fine as spark goes.