Changing jets to make more HP

[DKennimer]

E150TRLCNM 1982

Someone told me that I can change the jets out on the carb to make this 150 a 175... is this true???

 

[Outsider]

Re: Changing jets to make more HP

I'm betting 'no'. Let us know what you find out ...

 

[JB]

Re: Changing jets to make more HP

No, no and no.

 

[DKennimer]

Re: Changing jets to make more HP

Kinda what I figured, he said that he had done it before, but the kind of guy that is hard to believe... Don't think I'll risk my engine that runs just fine.

 

[Dhadley]

Re: Changing jets to make more HP

That year OMC used the same powerhead for the 150 and 175. Same intake, same ignition, midsection and gearcase. There was a slight difference in carb throat sizes. The 175 was rated at a slightly higher rpm. Both should be propped out at 5800 for the longest life but one was rated at a slightly different rpm. You can fool around with carbs but unless you have a performance hull you'll probably never see an ounce worth of difference.

You could try a set of XP/GT heads, that will make a difference especially if you have a hull that responds to small torque increases.

Since the 150 and 175 are so close (that vintage) you could almost say you have a 175 now.

 

[kenmyfam]

Re: Changing jets to make more HP

Let me think .......Leave it alone !!!!
My 2 cents.

 

[DKennimer]

Re: Changing jets to make more HP

hahahaha!!! I'll leave it alone Kenny. Just thought if it was that easy than my little 18.5 ft skeeter would be a little less far behind than the other guys, but 60 is fast enough for now.

 

[emdsapmgr]

Re: Changing jets to make more HP

Yours is a base 150 model. If you increase the main jet size to put more fuel in the engine, but don't put any more air in at the same time, the engine will overfuel, bog and won't run well. The 150S (XP/GT) models used the 1 5/16" throat 175 carbs. These larger-throated carbs permit more air and more fuel.

 

[Livewire]

Re: Changing jets to make more HP

Here is my 2 cents?

With the price of gas as it is and the fuel mileage that one gets with an older model carbed motor, why in the world would you want to send more gas through it?

I have a 1988 GT 200, on a 1994 Stratos 201 Pro XL, I get to run as fast as I care to, the only thing is now I can?t afford to hardly start the thing up. But it looks good setting in the back yard.

 

[F_R]

Re: Changing jets to make more HP

Changing jets to get more power is one of the worst old wives tales there is. It actually can cause damage to the motor. Besides, it doesn't work. As somebody has already said, an engine needs a specific ratio of fuel to air in order to run properly. Changing one without changing the other upsets that ratio. The amount of air is determined by the cubic inches displacement of the engine and RPM. Carburetors are designed to match that displacement. The engineers that built the motor were very well paid to figure all that out.

 

[DKennimer]

Re: Changing jets to make more HP

Thanks guys. I WON"T CHANGE ANYTHING!!!

 

[coolguy147]

Re: Changing jets to make more HP

im going to be one of those engineers when i grow up

 

[bob johnson]

Re: Changing jets to make more HP

Changing jets to get more power is one of the worst old wives tales there is. It actually can cause damage to the motor. Besides, it doesn't work. As somebody has already said, an engine needs a specific ratio of fuel to air in order to run properly. Changing one without changing the other upsets that ratio. The amount of air is determined by the cubic inches displacement of the engine and RPM. Carburetors are designed to match that displacement. The engineers that built the motor were very well paid to figure all that out.

well that throws me for a loop.... because i have two motors that seem to defy that logic...

they both are V4 60 degree looper motors based on the eagle block of the mid 90's and later.

the 90 and the 115 hp use the exact same short block..

same bore , same stroke.. same cubic inches... they differ in the carbeuration and the head volume.

the bore in the carb is much bigger on the 115 than the 90...makes sense more air...

but it is going into the same CUBIC inches...

but..on top of that the head in the LOWER HP has more volume...so..

that should translate into less compression..i have had the heads side by side here at work and the 90 hp is about .08" deeper in the chamber than the 115..

makes sense the 115 is taking MORE air into the same size area..theoretically and compressing it into and even smaller chamber..

it is possible the displacement is different, evebn the cubic inches are the same??

because of the heads combustion chamber volume??

I wonder if the timing is different...I dont have the book in front of me..

but all else on those motors seem to interchange except the carb and head to still be seperate motors.

I say that because I an rebuilding my 90 and have a set of 115 hp heads and the carbs adn throttle bodies from a 115...that i plan to install on the rebuild..



love to hear more.


I always wonder if the design of the 2 stroke, makes compression theroies way way different than 4 strokes


bob

 

[Cofe]

Re: Changing jets to make more HP

2 cycle motors rev real high stock.
When you hop one up all you are doing is making it get to the highest rpm. faster.
But what good is hopping up your motor if your prop is in cavitation?

If you think your 2 stroke outboard is the same as a car motor guess again.
Cars are on pavement, ........boats are on water. There is a lot of "slippage" to be determined by boat weight, keel form, and trim height.

So let's get a Jet Boat and do it right...... It's hard to put drag slicks on a ob.

 

[Craig-]

Re: Changing jets to make more HP

You could feed it some NO2 along with the larger jets if you have the need for speed, but I wouldn't. You'd need a really big bottle.

 

[Cofe]

Re: Changing jets to make more HP

LOL That big bottle would come in handy to have something to grab onto to float yourself to shore......LOFL....

 

[emdsapmgr]

Re: Changing jets to make more HP

You can bolt larger-throated carbs on a stock small hp engine to increase horsepower. It is very possible that in order to get them to run correctly-that you will need to rejet the carbs downward. If you put high compression heads on later, you will have to jet up somewhat in order to keep the engine (cool) from running lean. Gets to the point where you will have to be able to read the plugs of the engine to make absolutely sure you have the right fuel to air ratio going into the powerhead. Takes a lot of high speed runs and charting to know where you are going. Purchasing an assortment of various jet sizes is not cheap, either.

 

[F_R]

Re: Changing jets to make more HP

bob, no matter what, the displacement and compression ratio was taken into consideration when the engineers designed it.

OK, now with all that in mind, you can take an engine of XX size and restrict the airflow by SMALLER carburetor, reeds, or whatever, which will decrease the horsepower. That is exactly what they do in some cases, such as the difference between the 5 and 6hp of the 1960's. Same powerhead, but the 5hp has a little carb not much bigger than the 3hp. BUT, and it is a major But, but the jets are still sized to match the airflow through the carb venturi. It's all related, jets, airflow, compression, rpm, etc. True, in that particular case you could probably put a 6hp carb on it and restore it back to 6hp.

While on the same thought, if an engine is already tweaked to get maximum horses out of it, putting a BIGGER carburetor on it will probably actually result in loss of horsepower, because there isn't sufficient airflow (air velocity) through it. Even if top end is ok, mid range will probably suffer. I recently experimented with just that. In my case, top end was ok but it wouldn't idle worth beans. Neither was off-idle. After spending about two weeks in determination, I gave up and put the original carburetor back on it.

 

[Dhadley]

Re: Changing jets to make more HP

The 90 and 115 60* loopers have different port timing although they are based on the same block, The 149 cid (non XP/GT) 150 and 175s have the same port timing. Two completely different scenarios.

 

[bob johnson]

Re: Changing jets to make more HP

The 90 and 115 60* loopers have different port timing although they are based on the same block, The 149 cid (non XP/GT) 150 and 175s have the same port timing. Two completely different scenarios.

so if I put 1996 115 hp carbs and throttle bodies, and 1996 115 heads on my 1997 90 hp block and adjust the timing to 115 specs......I wont have a 115 hp motor????

because that si what I am about to try....when I rebuild this motor.


bob