Small Engine Problems? Ask an Engine Mechanic for Answers ASAP
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If the pulse pump is working at all, it is flowing enough fuel.
I have never seen one flow enough fuel at idle, but not at full throttle.
Your problem is most likely in a dirty or sticking float needle.
Even is a carb looks spotless, it is usually the source of the problem.
Another thing that is a possibility is the valves.
If they are misadjusted, it is possible that they are causing this.
The valves should be set as follows:
The filter should have fuel in it, but it will not be full.
You will typically see it be between 1/3 and 1/2 full.
There is one other possibility here.
If the crankcase is building up too much pressure, it will place a severe load on the engine.
Try cleaning the breather assemblies and adjusting the valves to try and reduce crankcase pressure.
Have you done a compression check and cylinder leakdown test to see if you have bad rings?
Engine compression is 88/90psi
Valve adjustment on both heads checked and is ok
Pump inlet vacuum is 1.6"Hg instead of 2.6"Hg min.
I checked and cleaned breather assembly.
Checked pump inlet vacuum again with no change.
I cannot visibly see anything wrong with the pump inlet vacuum tube. What would you do? This engine has under 150hrs on it.
Compression is good.
To be honest, if this were my engine, I would install an electric fuel pump with a pressure of 2-2.5 psi max.
But the book fix would be to do a cylinder leakdown test to see if exhaust is leaking past the rings, causing the low vacuum.
If it checked out good, I would replace both the pulse line and the fuel pump.
On a cylinder leakdown test, the spark plugs are removed, and a special tool called a leakdown tester is installed in the spark plug hole.
The cylinder is then pressurized with air.
The guages on the leakdown tester will measure how much pressure is lost, and how fast it loses it.
The source of a leak is determined by where the air is escaping.
If it is bad rings, you will hear the air escaping into the crankcase.
If it is a bad intake valve, you will hear the air escaping through the carburetor.
If it is a bad exhaust valve, you will hear the air escaping through the muffler.