Small Engines (Lawn Mowers, etc.): Tecumseh carburetor problem, float bowl, gunk

Question
QUESTION: I just acquired a MTD 15.5hp mower that won’t start. The  engine is a Tecumseh OHV155-204509F.  Engine Family: YTPXS.4902AA
It isn’t getting gas into the carburetor.  The air filter is clean.  Everything in the carburetor looked clean but to be sure, I cleaned everything inside with carburetor cleaner. Gas is getting into the float bowl and I have checked everything inside the float bowl. I did replace the o-ring on the main jet. All the ports seem to be clean and open, float is ok, it has the right level of gas, and everything in the carburetor seems clean and working, but still no gas in the chamber.  The fuel shut-off solenoid is working.  I even removed it to make sure it was not the problem.
It has good spark. The engine will run for a couple of seconds when I spray gas into the carburetor.  I don’t know what the compression is supposed to be but it when I tested it, it was 90psi.  When I put a little oil into the cylinder, it was 110psi and then started to drop back to 90psi.  
Any help would be appreciated.
So that I can understand, can you explain the process of how the gas is pulled into the carburetor from the float bowl?


ANSWER: Just to be sure you do not have compression or valve problem you need to keep the engine running for a minute or two.

Use a can of starting fluid and spray dirctly into the carb to keep the engine running.


If you can keep the engine running by spraying starting fluid into the carb then you know the carb is the problem...all other components are working fine.


Let me know what you find but my bet is the carb is still the problem.

Eric

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

QUESTION: Last night, as you suggested, I was able to keep the mower running as long as I kept spraying cleaner into the carburetor.  This morning, I was surprised because I was able to keep it running as long as I kept the full choke on.  So I took the carburetor off and soaked it in Gunk cleaner for 4 hours and then blew air thru the passages.  But it didn’t seem to make any difference.  It would still only run when I kept the full choke on.
It runs pretty good with the choke on. I was able to drive it all over the yard without much problem except when I increase the speed it would run uneven.  But it runs smoothly at a slower speed.
I didn’t soak the plastic float bowl or any of the parts inside the float bowl because “Gunk cleaner” says not to use it on plastic parts. But I have cleaned these parts with just the spray cleaner and air.  What do I do now?


ANSWER: Well you know the problem is lean running carb.  Have you check all the gaskets from the air filter to carb and carb to the engine block.  If a gasket is leaking you will have a lean engine.

If those gaskets are good, the bolts are tight and you are sure there is no intake leak then the carb is still blocked up.  Last step before buying a new carb is to remove any carb welch plugs and clean the ports with a piece of small wire.  I had doing this because it is difficult to remove the welch plugs.  The manual tells you to use a metal cutting punch, with a really sharp taper, to gently remove the welch plug(s).  Easier sad than done.  If you try to use a drill bit you can easily drill too deep and ruin the carb...those welch plugs are very, very thin pieces of metal.

As for running a small piece of wire through the orfices this is a no-no as you can ream out or over-size the orfice(s).  Again, this is a last ditch effort.  I use a piece of braided automotive wire.  Just strip off a couple of inches of the wire insulation and then you have a lot of cleaning wires.  Just poke a single strand of wire through each carb orfice.

Are you blowing compressed air from an air compressor though the carburetor orfices?

Eric

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

QUESTION: I think all of the gaskets are good, but how can I tell if there is a small leak?  Are there any tricks to finding them?
Would an air leak in the float bowl gasket cause a lean engine?  The float bowl seems to be a little warped where it meets the carburetor but it is not leaking gas.  

Answer
The float bowl should not cause the problem but you need to make sure the atmoshperic vents are clean so air can enter the carb.  These vents are located on the edge of the carb throat...make sure they are clean.

Did you run wire through the orfices?

Eric