B&S 30hp Vanguard, Rough Under Load, Backfires and Dies

B&S 30hp Vanguard in a Ferris is2000z, the engine runs fine at idle, as soon as I add any load to the machine (remove parking brake or engage blades) it starts to idle roughly. At first it seemed like one of the safety switches in the seat wasn't making good connection or something, however, I have eliminated that as a possibility.

The problem has gotten progressively worse. If I add more load by driving the machine, the engine runs worse until it breaks up enough that it is backfiring, if I continue to keep the load up the engine will die. I can reduce the load it runs better, if I return to a stopped position with parking brake on the idle returns to normal and it will run fine. Basically, any time there is load placed on the engine it breaks up.

I have replaced the spark plug and air filter, oil is good.

Suggestions?

Mugenlude said:

B&S 30hp Vanguard in a Ferris is2000z, the engine runs fine at idle, as soon as I add any load to the machine (remove parking brake or engage blades) it starts to idle roughly. At first it seemed like one of the safety switches in the seat wasn't making good connection or something, however, I have eliminated that as a possibility.

The problem has gotten progressively worse. If I add more load by driving the machine, the engine runs worse until it breaks up enough that it is backfiring, if I continue to keep the load up the engine will die. I can reduce the load it runs better, if I return to a stopped position with parking brake on the idle returns to normal and it will run fine. Basically, any time there is load placed on the engine it breaks up.

I have replaced the spark plug and air filter, oil is good.

Suggestions?

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I would start with cleaning the carburetor.

Cleaned the carb tonight, zero change.

Mugenlude said:

Cleaned the carb tonight, zero change.

Click to expand...

Post model/type number.

See if there is spark on both cylinders. It could only be running on 1 cylinder. Check valves for movement and adjust if not in spec.

Other possibilities are: Coil going bad, broken flywheel key.

I gather you eliminated the spark problem by removing the kill wires ( Both of them ) .
If not try that now. There is usually a diode in the sub loom that connects the two coils to prevent them interfearing with each other that can go bad.

That being sorted we need to eliminate either the carb or the govenor

Start the engine , make sure it is in neutral and prefferably against a wall or tree so it ain't going anywhere
move the throttle lever at the carb or govenor SLOWLY to open up the throttle.
If the engine picks up smoothly and increases revs smoothly then you have a problem with the govenor, most likely inside the engine.
I the engine acts badly as you posted then you have a problem with the fuel delivery system.

DO NOT HOLD THE GOVENOR WFO FOR MORE THAN ABOUT 30 SEC OR YOU WILL HAVE A TOTALLY DIFFERENT ENGINE PROBLEM

As you have a butterfly carb there is little reason to open the throttle butterfly more than about 2/3 to 3/4 and wide open with no load can blow the engine big time.
You can do the same test with an assistant in the seat & blades spinning, with due caution but it should not make a difference unless the timing is out
I like to put a neon in line spark tester on both plug leads just to verify that one of them is not causing the troubles.

darrinster said:

Post model/type number.

See if there is spark on both cylinders. It could only be running on 1 cylinder. Check valves for movement and adjust if not in spec.

Other possibilities are: Coil going bad, broken flywheel key.

Click to expand...

That'd be my first guess.

Sorry for the slow response I was out of town...

darrinster said:

Post model/type number.

Click to expand...

Model #276594

darrinster said:

See if there is spark on both cylinders. It could only be running on 1 cylinder.

Click to expand...

I have spark in both cylinders.

darrinster said:

Check valves for movement and adjust if not in spec.

Click to expand...

I'm not familiar with how to do this, if you could provide a link to a DIY or video I'd appreciate it.

darrinster said:

Other possibilities are: Coil going bad, broken flywheel key.

Click to expand...

Any info on how to test the coil? Replacing the flywheel key that seem pretty easy to do.

I can send you a Service Manual for your engine IF you like. Address below, put in proper format and remind me engine model number and what you want.

Walt Conner
wconner5 at frontier dot com