Briggs 5.75 hp engine on pushmower wont start

[bwestbrook]

I have a yard machines push mower with a 5.75 briggs engine that will not start. I have cleaned the carb and put a new kit in. I have repaired tons of these with this same problem. It is usually the main jet. There is plenty of fuel flow to carb and carb bowl is full. Primer bulb works and will push fuel into the carb venturi. But mower will not start. Yes I would say spark. But when you spray carb cleaner into the carb it will fire up and die after it burns that off. Then I thought maybe weak spark.
The two differences I see are with the fuel from the primer bulb isnt going as far into the carb and then the difference of ignition point of gasoline versus carb cleaner. any help would be appreciated. Sorry for rambling.

 

[EngineMan]

What type of carb is fitted to you're engine.

 

[bwestbrook]

Model type code
12H802-3306-B3

 

[pugaltitude]

Coils dont usually give weak spark, only spark or no spark.
Is the spark plug working under compression conditions?
Is the engine sucking the fuel in. Try little oil down plug hole.
Usually its always carb on a model 12.
Manifold cracked?
Valves not seating?

 

[bwestbrook]

It acts like it isn't sucking the fuel in. That is the best way to explain it. But wasn't sure how to verify that or what would cause it.

 

[pugaltitude]

Usually bad starting on a primer is the gasket not sealing properly which dosent push fuel into carb but as you say you spray carb cleaner then it rules out primer as it runs then cuts out.

Could just be that when you spray cleaner through carb its going into cylinder and running which then could be rings or valve not closing all the way.

 

[bwestbrook]

It has 110 psi compression. I put some oil in spark plug hole and it did not help with pulling fuel into cylinder. It will run as long as I spray carb cleaner into carb. It is just not getting fuel for some reason but plenty of fuel in bowl, bowl vent is clear, main jet (bowl screw) is clear, and emulsion tube all spotless.

 

[EngineMan]

Was the photo taken before or after cleaning, looks if it could do with a clean again..!
Have you got good compression..?
Check to see you have good seal on gasket between carb and engine, you maybe down on vacuum..!
If you have spark and compression it has to be fuel..! (not being pulled in)
Do you have item 163 upside down (just a thought) it can happen and are the hole's in the gasket free (vacuum hole)

 

[pugaltitude]

When the carb is fitted does it flex up and down as if the manifold is cracked? it could be drawing air instead of fuel

The compression test shows rings are sealing but im still thinking valves.
With plug fitted and blade fitted does the engine turn freely like no compression or is there a bounce to it.
This kind of checks valves seating or head gasket.
This is where a leakdown test comes into its own and you get a result in minutes.

 

[bwestbrook]

yeah I wish I had the setup for a leakdown test.
When rope is pulled it has good bounce.
Carb is mounted good. Gasket is good. No movement.