Engine stalling when you give it too much throttle on take off

[skyman2112]

Carbureted engine, PCM 351 BOSS. So far tried rebuilding original carb, then purchased another factory style carb, then replaced fuel pump and then replaced the factory ignition and finally, got a completely different brand new holley carb. Nothing every changed, Stalls when you give it too much throttle from a stand still. In cruise, accelerates fine when you give it full throttle. You can see the accelerator pump working too. Really going crazy with this one. thinking vacuum leak maybe PCV valve?

 

[kenny nunez]

Have someone watch the secondary butterfly linkage when you punch it. The linkage should not move until the engine starts to turn up. If it does move try to restrict it and see if does not bog or stumble.

 

[skyman2112]

Have someone watch the secondary butterfly linkage when you punch it. The linkage should not move until the engine starts to turn up. If it does move try to restrict it and see if does not bog or stumble.

I have not checked that cause we tried 3 different carbs with the same problem, but its worth a look. Thanks

 

[Grub54891]

Have you checked the weights inside the distributor? Sometimes they get sticky or the springs break.

 

[Scott Danforth]

have you check that the accelerator pump actually squirts when you advance the throttle?

 

[jimmbo]

Carbureted engine, PCM 351 BOSS. So far tried rebuilding original carb, then purchased another factory style carb, then replaced fuel pump and then replaced the factory ignition and finally, got a completely different brand new holley carb. Nothing every changed, Stalls when you give it too much throttle from a stand still. In cruise, accelerates fine when you give it full throttle. You can see the accelerator pump working too. Really going crazy with this one. thinking vacuum leak maybe PCV valve?

When you say "give it too much Throttle from a standstill", does that refer to how quickly you give it Throttle, or how much Throttle you give it?
Does the Stall happen the moment the extra Throttle is given, or a few seconds later?
When you "replaced the factory Ignition System", what parts were replaced?

Since the Carb, had been rebuild, and replaced twice, it is difficult to blame it.

Being a PCM Engine I will assume the Spark Advance is controlled by the Computer, not by a Mechanical Advance in the Distributor. Have you verified that the Timing does advance?

What about the Fuel Lines between the Tank, the Fuel Pump, and the Carb? Sometimes a blockage, can allow plenty of Fuel at a relatively constant flow, but chokes when there a sudden increase in demand.
Fuel Filter?
When accelerating from a standstill, the Bow of the Boat Rises, maybe that causes a change where Fuel is not able to be delivered. At speed, the bow doesn't leap up, when more power is added

 

[skyman2112]

When you say "give it too much Throttle from a standstill", does that refer to how quickly you give it Throttle, or how much Throttle you give it?
Does the Stall happen the moment the extra Throttle is given, or a few seconds later?
When you "replaced the factory Ignition System", what parts were replaced?

Since the Carb, had been rebuild, and replaced twice, it is difficult to blame it.

Being a PCM Engine I will assume the Spark Advance is controlled by the Computer, not by a Mechanical Advance in the Distributor. Have you verified that the Timing does advance?

What about the Fuel Lines between the Tank, the Fuel Pump, and the Carb? Sometimes a blockage, can allow plenty of Fuel at a relatively constant flow, but chokes when there a sudden increase in demand.
Fuel Filter?
When accelerating from a standstill, the Bow of the Boat Rises, maybe that causes a change where Fuel is not able to be delivered. At speed, the bow doesn't leap up, when more power is added

Happens almost immediately , from idle, too much throttle is referring to the amount of travel of the throttle lever. No too noticeable without a skier though.
Accelerator pump is adjusted correctly and can be seen working.
The entire ignition system was scrapped, upgraded distributor is a unilite with single coil, have not checked to see if its advancing.
Could be a soft fuel supply line collapsing but seems like it would have enough fuel in the float bowls to at least take off for a few seconds
Fuel tank is in the back so the pickup should always be covered.
Those are some great ideas. Im leaning towards a vacuum leak. It snaps your neck firewalling it at speed, and maintains 5000rpm all day long which seems hard to do without enough spark or fuel.

 

[skyman2112]

have you check that the accelerator pump actually squirts when you advance the throttle?

yeah i can see it squirting and the linkage is snug

 

[skyman2112]

Have you checked the weights inside the distributor? Sometimes they get sticky or the springs break.

the distributor is new as part of our troubleshooting project

 

[Lou C]

Ever look inside the fuel tank via the fuel tank float hole to see if there's crud in the tank?
What about the pick up tube and anti siphon valve?
I also for sure would get a hold of an advance timing light and make sure the spark is advancing as it should.
Honestly I'd rather have a simple centrifugal advance with weights and springs than electronic, unless OEM modules are readily available.

Since you've had 3 different carbs on it with same problem, look at the boat's fuel system!
look here:

HOW TO: Testing your boats fuel system.

Note, this was originally posted courtesy of Don S. Minor edits and pictures added by CaptJason A lot of you folks out there seem to be tearing into carbs quite a bit. Before you choose to open up a carb, you really need to look at what's feeding the carb first, and that is the boats fuel...

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