F100AET which bogs down under hard acceleration? no waterskiing :(

[Frankiez]

I have a Yamaha F100A -99 outboard with carburetors. It runs great during idle or high speed. However, when I tried to do waterskiing the engine stalled when throttle stick was turned on full at a fast pace. It only worked when throttle was used gradually. Propeller is 13.2*21 aluminium.

It just does not respond under hard acceleration as I would expect.

Does the engine has a accelerator pump, is that part 43? 1999 F100TLRX Yamaha Outboard CARBURETOR 1 Diagram and Parts (names are wrong, 43 should be "diaphragm assy 2").

Are the carbs clogged (I have used carb cleaner solvent)? I suspect no, since there is no problem during idle or fast run?

Where is the problem? Accerelator pump (if any) gone or carbs are out of sync?

[TownsendsFJR1300]

Boy, that parts fisch is messed up. Part #42 looks like a vacuum brake of some sort, not an acceleration pump...

(1)What RPM is your engine at wide open throttle with no skier? If its propped for too low an RPM @ WOT, it'll really show with a skier, especially getting started...

(2) Nailing it for a water skier would put a bunch of load on the engine, and if the carbs were borderline dirty, pulling a skier I would think show up any clogged issues...

How old is the fuel, has it been sitting for awhile?

I would drain the float bowls first and catch what comes out. Maybe a flush with the primer bulb... You may get by with a strong dose Of Yamaha's RingFree, I would try that before pulling the carbs.

[Frankiez]

Fuel is fresh.

I have to test that rpm thing.

So, there is no acceration pump on that outboard?

[TownsendsFJR1300]

I don't see one on the parts fisch...

You don't have a tachometer on board?

[rodbolt17]

that dash pot IS the accelerator pump.

if you have had the carbs off they MUST be correctly synched with a 4 channel manometer.
no other way to do it.
there is a check valve that must be working and installed correctly.

this setup uses that 14 mile or so high colum of air to move fuel at rapid throttle opening.

remember that is the reason why fuel moves in a carbed motor.
as the throttle is rapidly opened intake vacum drops rapidly.
once the air pressure is about equal on both sides of the venture fuel quits flowing the engine gets lean and stalls and or backfires.

on this setup the diaphragm actually lowers the air pressure in the fuel bowl causing it to flow more fuel from the main nozzle.

pretty simple if one thinks about it.

[boscoe99]

that dash pot IS the accelerator pump.

if you have had the carbs off they MUST be correctly synched with a 4 channel manometer.
no other way to do it.
there is a check valve that must be working and installed correctly.

this setup uses that 14 mile or so high colum of air to move fuel at rapid throttle opening.

remember that is the reason why fuel moves in a carbed motor.
as the throttle is rapidly opened intake pressure increases rapidly.
once the air pressure is about equal on both sides of the venture fuel quits flowing the engine gets lean and stalls and or backfires.

on this setup the diaphragm actually lowers the air pressure in the fuel bowl causing it to flow more fuel from the main nozzle.

pretty simple if one thinks about it.

Is the air column 14.7 miles high?

Ever heard of the 14 mile high club? 14 times 5280 feet.

[Frankiez]

Finally I could confirm (So as you said) that it is a accerelator pump. It was in the repair manual.

I have a 4 channel manometer and I can check the sync. However, check Valve was mentioned and what was the part number for that?

The repair manual (clymer manual) says that sync procedure should be performed on water? Yamaha Shop manual does not require that which indicates that it could be done on land with Mickey mouse flaps.