Question
This question was submitted to Volunteer Expert: P.K. Jones. Mr Jones asked the questions shown at the end of this email. I am unable to send the answers to him so I hereby submit them to you for forwarding or possibly providing an answer to my problem.
Question:
Dear Sir;
I recently bought (at an auction) a lawn tractor mower with 140 hours on the clock. The motor data is at the end of this letter.
Problem:
The motor starts easy, idles well, and runs OK at part throttle. However, it sputters badly during higher rpm. It also seems to run hot- the crankcase and overhead valve covers become too hot to touch!
When throttle is opened, motor has major misfires and dies as if it is running out of gas. Misfire decreases/disappears when choke is activated.
Here is a history of what I have observed and done:
1. Cold engine compression test - 160 pounds in both cylinders.
2. Removed engine fan shroud - fins very clean.
3. Installed new Champion RC12YC plugs.
4. Drained fuel tank and filled with fresh fuel and installed a new in-line fuel filter.
5. Gas tank cap vent is open.
6. Checked the in-tank filter - is good.
7. Fuel shutoff valve is good.
8. Checked fuel lines for leaks and obstructions - none.
9. Dismantled carburetor, soaked overnight in carb cleaner, and cleaned it with compressed air. Installed carburetor and used new carb to manifold gaskets.
10. Solenoid on carburetor removed.
11. Installed new fuel pump vacuum pulse hose.
12. Installed new electric fuel pump.
Engine data:
Vanguard Vertical Shaft
Model 351 777
Type 1138-E1
Code 0010 0211
Family YBSXS.5702VK 274834
Air Index of this engine - 3
Complies with 2006 CA Emission Regs
Nikki Two Barrel Carburetor #808240 621266-011
Answer:
If you choke it when it starts to sputter, will it clean up? [decreases]
Do you have an inline spark tester? [no]
This has an electric fuel pump and an impulse pump? [electric fuel pump replaced the impulse pump.]
What is the make and model of the mower? [Stiga Park Pro 20]
AnswerFirst thing I would suggest, remove 1 of the plug wires and start,
and see if it starts and behaves the same.
Next, try it on the other way around, see if it starts and/or behaves
the same.
If it acts differently on either setup, then that is a clue to the
problem.
Also, I have seen running problems on Vanguards, turned out to be the coils getting rusty and not grounding well on their mount.
Lastly, I would suggest checking the valve clearances, they should be .005 on both sides.
