What would happen if I used a bigger carb on 9.9 hp

rdhj

Petty Officer 2nd Class
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Sep 29, 2015
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I bought a carb off eBay and they said it fits the 9.9 and 15 hp suzuki models...however after getting it, i found that the throat of the carb is larger and the main jet is larger (125 instead of 110)....would I be able to use this on the 9.9 or would this deliver too much fuel and air for the size of the engine? Can it be tuned to work by changing the main jet and pilot jet size?
 

99yam40

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Sep 7, 2008
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talk to the company that sold you the carb,
tell them you need a refund or the proper carb

you need to find out what all is different between a 9.9 and a 15.
may need to change reeds or tuner (exhaust)
the motor has to be able to get more air as well as more fuel into and out of the motor to gain the extra HP
 

jimmbo

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May 24, 2004
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Thats what I figured, but is there anyway that it could be set up to work correctly or is that not possible?

If the carb has a larger throat and venturi than the 9.9 carb, it is designed for a greater amount of air to flow through it, it would also then be calibrated to flow more fuel. It may also have different off-idle calibration.
Regarding a 9.9 vs. 15hp, the two engines may share the same displacement, but that may be it. To make more power the engine has to spin faster. To do that there my be changes to the porting, intake and exhaust, either by changing the port location, port size, or different pistons, maybe all 3. Cylinder heads may be different, and in addition compression ratios too. Finally. the exhaust tuning may be different.
 

rdhj

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Sep 29, 2015
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Looking at the parts diagram, all the parts you mentioned have the same part number for both models, with the exception of the reed valve assembly...it seems like the 15 hp model has reed stoppers that are higher. would the wrong reed valve assembly cause incomplete combustion? Also, when I ran a compression test on it before, it gave me like 3 psi, so I assumed something wasn't right with my gauge...would too low a compression for the extra gas and air cause incomplete combustion? how would you make an engine spin faster? i see the two different models have a different part number for the cylinder assembly. Is this where the ports are and could be the issue. I had a marine mechanic and the guy that sold it to me tell me it should be no issue using a 15 hp carb. I don't even see 9.9 carbs for sale. Just trying to get a clue why i getting a ton of oil in the water.
 

jimmbo

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An engine is basically an air pump, reducing restrictions in the induction and exhaust systems allows it to pump more air. Being a 2 stroke, there will almost always some unburnt gas escaping out the exhaust. Most of the oil passes through unburnt to decompose in the water. If the carb is set too rich or the engine is misfiring, the amount of gas-oil in the exhaust will increased. A carb that is too big for the engine or in some cases, large carbs combined with radical port timing, can produce an engine that runs less than smoothly from off-idle through mid range.
 

rdhj

Petty Officer 2nd Class
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Sep 29, 2015
Messages
102
I just realized my motor has a throttle limiter on it that doesn't allow you to use the entire range of the cam....i'm guessing removing the limiter with the 15 carb wouldn't help fix my issue, but I'd figure Id mention it incase someone else knows better
 
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