power difference

[boatman99]

i recently switched out my 1975 9.9 evinrude carb for a same yr 15 hp carb. i didnt really notice any power increase. shouldnt i experience a signaficant power increase?

 

[Bob_VT]

Re: power difference

Probably not except with the weight loss in your wallet you might go faster........ It's been discussed and debated here before...... now you will more than likely have a thirsty 9.9

Welcome to iboats!

 

[boatman99]

Re: power difference

hey bob,thanks for responding. Im a new boater still feeling my way through. I picked up a 1975 9.9 and 15 hp,the carbs are much different in bore size.Online they are saying that carbs can be switched and a 50% power increase will be present.Is it true that both motors are the same.

 

[Silvertip]

Re: power difference

A bigger carb does no good if the manifold it mates to has the original carb bore size, or has a restrictor between it and the carb. Measure the two bores.

 

[Whoopbass]

Re: power difference

You should have gotten a very noticeable power increase on take off. Your top end will only be a few mph faster. The only thing I can think of is that your boat is light and the prior 9.9 motor didn't have a problem getting up to speed. Add some weight to your boat and you will notice the difference.
I have tested this and I know this to be the case. The biggest disagreement over the carb swap is that if you actually end up with a true 15hp motor. Probably not but its close enough and if you are pushing a heavy load its worth the investment.

 

[Fishing Dude too]

Re: power difference

Ma also hav to change reed valves to increase the hp, many times they use restictor plates on the back side to keep hp down.

 

[seahorse5]

Re: power difference

Go to www.shop.evinrude.com and look up all the years of the 9.9 and 15hp motors and compare the part numbers to find out the differences. Each year it seems there were different changes in exhaust tuning, cylinder heads, reed stops, engine blocks, carbs, etc. plus operating rpms.

 

[JB]

Re: power difference

Go buy about a dozen links of 100# chain. Replace one link with a link from 200# chain. Do you now have a 200# chain?

 

[Whoopbass]

Re: power difference

It's unheard of replacing a part or parts in a gas combustion engine and getting any type of HP gain. That's why there is no aftermarket parts available for gas engines......Oh wait a minute...............

 

[JB]

Re: power difference

It's unheard of replacing a part or parts in a gas combustion engine and getting any type of HP gain. That's why there is no aftermarket parts available for gas engines......Oh wait a minute...............

What aftermarket parts are available for 9.9 2 stroke outboards, WB?? That's what I thought.

 

[Whoopbass]

Re: power difference

Who said anything about aftermarket parts for a 9.9?
Manufacturers of aftermarket parts claim a certain percentage of HP gains for something as piddly as an air filter or a muffler. It sounds as if your stance is that a carb from a 15hp motor offers no HP gains or are you saying that you won't get exactly an additional 5.1 hp with just the carb swap alone?

 

[JB]

Re: power difference

You are the guy who brought up aftermarket parts, WB, implying that they wouldn't exist unless they work.

I am saying that modifying any engine, particularly carbed 2 strokes, can produce trivial increases in output or trivial decreases in output unless a balanced approach is taken, and that usually costs far more than just buying a bigger engine. I have modified a few 2 strokes and could probably get 25 or 30 HP from that base engine, but it would cost several kilobux and live about 5 hours.

You see, a lot of people can be convinced that they will have a 200# chain for the price of one link.