Replace carburetor on 2005 Yamaha 9.9 4-stroke

[raptorman]

Thank you. Sorry to hear that the lighter 9.9 is not as good as the earlier model. Would like to have the manual choke, though. The electric isn't very effective. After about 10 seconds of running, it is not active. Usually have to pull the cowling and obstruct the intake horn. Would also like a lighter model. My 64 year old back has an issue with the 115 pounder. Does the 8 hp offer a high thrust option? Any word on its reliability?

[zenoahphobic]

Not wanting to confuse the OP.
Putting extra load on an engine necessitates a richer fuel to air ratio.
Contrary to what has been implied by many, carburettors are affected by changes in legs just as they are by changing gears in a car or motorcycle.
Whether a manufacture chooses not to alter the carb specification is entirely their discretion .

I like to live in a world where things are explained simply and accept the rule for ease, however I know it is also wrong. Go ask a motorcycle mechanic what he would recommend you also do when you alter sprocket sizes - jet changes! Or maybe even a change in the type or size of the carburettor! So changing the leg/ larger prop actually necessitates altering the carburettor!

[99yam40]

Changing the prop size and pitch should be counted acted by the gear ratio change.

Only way to be sure is to look up the exact same year model parts on a regular and high thrust to see what Yamaha did as far as engineering design changes

Carb itself,all of the jets,reeds,Intake, and exhaust can affect things.
Make sure you look at all of them

[cleddau1]

According to local Yamaha guru there are three carburettors for that year model. The correct one will depend on the serial number of the engine. He did not see any reason for a different carb because of the change to high thrust leg and also pointed out that the 15 hp carburettor may fit (depending on the serial number) as the powerhead is the same for the 9.9 & 15. The 9.9 being effectively a detuned 15.
Sourcing a used carb identical with the damaged one would be the cheapest option though and any possible marginal differences in power output irrelevant for the application.

[zenoahphobic]

According to local Yamaha guru there are three carburettors for that year model. The correct one will depend on the serial number of the engine. He did not see any reason for a different carb because of the change to high thrust leg and also pointed out that the 15 hp carburettor may fit (depending on the serial number) as the powerhead is the same for the 9.9 & 15. The 9.9 being effectively a detuned 15.
Sourcing a used carb identical with the damaged one would be the cheapest option though and any possible marginal differences in power output irrelevant for the application.

This 9.9 is not a detained 15; it is a Fourstroke . This mistake is often made however the point is that often carb changes are often the significant change between HP variants of the engine block.

[cleddau1]

Not sure we have been much help to Raptorman........
What about simply replacing the part that was originally damaged (using the part number stamped on it) and rebuilding?
Please keep us posted with end result of your decision.

[boscoe99]

I am confused. The OP said he converted his F9.9 to a T9.9 but then when asked about the carburetor it appears that he did not change the carburetor. That is, he dis NOT fully make the conversion. Sounds like he has an F9.9 with a T9.9 gear case installed.

He has an F9.9. If he needs a new carburetor he needs the one for his motor. The one for an F9.9. He does not have a T9.9.

[boscoe99]

Not wanting to confuse the OP.
Putting extra load on an engine necessitates a richer fuel to air ratio.
Contrary to what has been implied by many, carburettors are affected by changes in legs just as they are by changing gears in a car or motorcycle.
Whether a manufacture chooses not to alter the carb specification is entirely their discretion .

I like to live in a world where things are explained simply and accept the rule for ease, however I know it is also wrong. Go ask a motorcycle mechanic what he would recommend you also do when you alter sprocket sizes - jet changes! Or maybe even a change in the type or size of the carburettor! So changing the leg/ larger prop actually necessitates altering the carburettor!

In the vast majority of particular F versus T models the only difference is the gear case. The carburetor neither knows or cares about the lower unit. It could even be a jet pump.

Change from one pitch propeller to a different pitch (load changes) and the carburetor does not care. Start to go up or down a large swell (change in load) and the carburetor does not care. Advance or retard the throttle a bit (change in load) and the carburetor does not care.

There are many air planes with adjustable pich propellers that change the engine load as the pitch is changes. Same carburetor. It does not know or care.

[zenoahphobic]

In the vast majority of particular F versus T models the only difference is the gear case. The carburetor neither knows or cares about the lower unit. It could even be a jet pump.

Change from one pitch propeller to a different pitch (load changes) and the carburetor does not care. Start to go up or down a large swell (change in load) and the carburetor does not care. Advance or retard the throttle a bit (change in load) and the carburetor does not care.

There are many air planes with adjustable pich propellers that change the engine load as the pitch is changes. Same carburetor. It does not know or care.

The carby might not care but they do make a lot of varying noise!

Carbys are not perfect, and are sometimes as described as three systems; low medium and high. When one decreases another gradually takes over.

At those points if the load is critical then tuning needs to be done!

I have no idea whether the carby is more suitable for one application or the other two you mentioned. History has often pointed out shortcomings in the carburettor selected, a more suitable being available (but may not fit).

However difficulty in mounting and control connections, limit us to sticking with the original in outboard motor applications.

[raptorman]

There have been many replies and much discussion. Not a lot of consensus. To clarify, I have a 9.9 four-stroke that I changed the foot from a regular thrust to high thrust. Does this require a carburetor change? Part numbers for the carburetors are different for the 2005 models for regular vs. high thrust. I need to obtain a new carburetor because the original is inoperative. Is there another source for the answer? I can't find a contact number for a Yamaha technician/engineer who can answer this question.

[boscoe99]

Here is a link to the phone number for Yamaha USA. Good luck getting meaningful information. I suspect that they will say to use an F9 carburetor on an F9 and a T9 carburetor on a T9.

All the engineers are in Japan by the way. I think they would say the same.

Contact Yamaha, Request Information | Yamaha Outboards

[cleddau1]

Raptorman, if you post the serial number of your engine I can tell you which carburettors will fit.

[raptorman]

I don't have the engine or serial number close at hand. I'm pretty sure either the F model carb or T model carb will physically fit. The issue is whether or not the standard leg or high-thrust leg requires a particular carb for best operation. The serial number will be tied to an engine with a standard leg. I'm not using the standard leg.

[cleddau1]

There appear to be 3 different carbs just for the 2005 F model; cannot imagine why though; also it appears the only difference between a G9 and a G8 carb is the choke mechanism; if you contact Yamaha as advised by Boscoe the first thing they will ask you for is the engine serial number....

[boscoe99]

We learn by folks trying and seeing what works and what does not work. Try the T9 carburetor and let us know the results.

Be bold. Lead the way.