carb and intake qustion

ironcross79 · Feb 9, 2012

hi just looking for some input on a 1990 20hp johnson my qustion is that the part number on the carb says its for this year and hp for this motor but looking down the barrel of the carb and i can see that the intake is way smaller so i took the carb off and its a inch smaller so is this right or wrong ?

JB · Feb 9, 2012

Re: carb and intake qustion

Howdy, Ironcross.

Welcome to iboats.

Please reword your post so it becomes clear what you are talking about. "It" does not identify any part that is 1" smaller than what?

steelespike · Feb 9, 2012

Re: carb and intake qustion

I think you may be overlooking the venturi in the carb I would be surprised if the venturi is much bigger that about an inch.
I don't see how the intake could be an inch smaller.
I suppose they may have made the intake small as a restrictor while using a carb perhaps used for a 25 as well as the 20.
If you look up parts for the 20 and the bigger motors you may see a difference or similarity.
Maybe the intake is the only thing different. Someone may be alpong with more info.

boobie · Feb 9, 2012

Re: carb and intake qustion

Back in those days OMC did have some mixed up carbs on those mtrs. You may want to verify the #'s on shop.evinrude.com. What's the throat size of the carb ??

ironcross79 · Feb 10, 2012

Re: carb and intake qustion

sorry guys the intake opening is about a inch smaller then the carb opening but the part number for the carb matches the year and hp of the motor so shouldn t both be the same size openings

boobie · Feb 10, 2012

Re: carb and intake qustion

What is the size of the hole in the intake manifold and the size of the venturi in the carb ???

ironcross79 · Feb 12, 2012

Re: carb and intake qustion

the intake hole is 1/2 inch and the barrel of the carb is 1 1/4 inch and in side the barrel of the carb theres a ridge thing its 3/4 of a inch round

JB · Feb 13, 2012

Re: carb and intake qustion

Hmmmmm. Sounds like a 3/4" venturi, about right for 20HP. But I am mystified by a 1/2" intake hole. Is the 1/2" hole leading to the reeds??

ironcross79 · Feb 13, 2012

Re: carb and intake qustion

soon as u take the carb off the intake and theres the 1/2 hole in the intake i allways thought the carb and intake had the same size openings its got me confused

cyclops2 · Feb 13, 2012

Re: carb and intake qustion

She is only 21 years old and somebody DIYed her already.

RIP

Take ALL the parts to a dealer / service department. They will see what someone did & tell you the bad news.

MAKE SURE THE ADVICE IS FREE. Then buy.

boobie · Feb 13, 2012

Re: carb and intake qustion

The hole in the intake manifold for a 20 hp for that yr was 3/4 " and the venturi was 7/8 ". Now I don't know what you have???

the machinist · Feb 13, 2012

Re: carb and intake qustion

I have recently ran into about the same thing if I understand the above correctly. A reader from Europe of my 9.9/15hp "Ramblings" sent me a photo of a "restrictor plate" that was between the carb & manifold of a 1989 GT10 model. This was apparently a 15hp that had this plate restricting the hp to something lower (10hp?)

Our guess was that these motors were a cheap method of lowering HP to pass or get the motor into a smaller HP rating for restricted waters ???

Maybe this has some bearing here also. What exactly does the ID plate say, model code etc. ?

ironcross79 · Feb 13, 2012

Re: carb and intake qustion

id is J20CRLESB ps ill try to get some pic`s of what i got the intake looks factory never touched with a diy grinder

boobie · Feb 13, 2012

Re: carb and intake qustion

Not to doubt you, but are you positive it's 1/2 " ??

ironcross79 · Feb 13, 2012

Re: carb and intake qustion

yup took the carb off and measured it its got me stumped but tomorrow im going to try ta get a few pic's of it

the machinist · Feb 13, 2012

Re: carb and intake qustion

Got to figure out how to post a photo I guess as I have one of the restrictor plate mentioned above.

ironcross79 · Feb 14, 2012

Re: carb and intake qustion

thank guys for all the input at this point the intake is got to be died out or just going to pick up a new one and carb

ironcross79 · Feb 20, 2012

Re: carb and intake qustion

hi agian i found a used 35hp intake and carb now to put it on so is there eny other mods gotta be done to my motor ????

tx1961whaler · Feb 20, 2012

Re: carb and intake qustion

Not really. You can go to marineengine.com and compare the 20hp and 35hp motors to see if there is anything different in the midsection.

carb and intake qustion

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