Help With Jetting 140 hp carbs for an 85 hp V4 Johnson

[Spybot]

Hi all new to this forum i need some help on jetting 140 carbs to fit a 85hp

I know that they will fit ( I have to sort out the choke/primer )
I have been told that they may run rich.
Which Jetting do i use ??
think the idle jet is the air jet so to lean her out do i move up one number?
Do i leave her as she is?
Do i take out the 140s and Jet her as an 85 ?
The carb size is 1 5/16" think the standard was 1"
I will look at adding reed stuffers once i get my new ccms sport reeds so hopefully a nice wee fast boat.

[filthy phill]

your asking a lot to use the 140 carbs on a 85hp.
so many differences in the motors.
what year carbs are they from and what year is the 85hp ?

[Spybot]

The engine is a 1980 the carbs i think are 78. They have choke plates I will change them to primer.
I will be putting in some ccm reeds and the Reed stuffers. The guys at ccm said they would work but probably will run rich, So i know i will need to lean them out. What i need to know is what way do i go with the idle jet. Up or down ???

[filthy phill]

dont forget this is probably a smaller cc motor than the 140 !!!
I had a 1980 85hp and that was smaller capacity than the 140hp fo rsure even though according to numbersit should of been same diameter piston, it definitely was not..
I have seen a lot of people trying to uprate the 85hp and not get a great amount more, maybe 5 to 10hp.
it is not just a carb thing, its exhaust tuner ,exhaust chamber at the back, porting, heads, stuffing blocks plus a lot of machining.
the 85hp I had was nothing like a 140 when you started having a good look into it.

what is the number/letters on the little disc on the top of the motor ?

[Spybot]

I know whats involved in the transformation. I just want a wee bit more power out of engine just now as i have the stuff ready for the winter strip down and build (which will be documented on here) Engine number J85TLCSA

[ClayT]

dont forget this is probably a smaller cc motor than the 140 !!!...

That was my thought. Going from 1" to 1-5/16" venturies just about doubles the volume. That's going to tank the intake velocity.

[Spybot]

dont forget this is probably a smaller cc motor than the 140 !!!



Both engines are 99.6 cubic inches and use the same pistons, cranks.

[Spybot]

That was my thought. Going from 1" to 1-5/16" venturies just about doubles the volume. That's going to tank the intake velocity.

Should i add the ccm reeds and stuff the reed blocks before i change the carbs ?
on the point of reeds is it best to polish the surface of the cadges ?

[filthy phill]

I too thought about polishing the reed housing and getting them like mirrors as I used to do on car intakes.
But I have read up a bit about this and it seems that a smooth satin type finish is best ?????
Reeds will not give more power, they will just give better idle and smoother running motor and will not destroy the block if they break up.
although saying that, if a bit gets into a ring groove destruction WILL take place to a point.
Metal reeds are stronger by a long way, just not as good for idle as some of the performance reeds like those from ccm .

[Spybot]

I dont know about the satin type finish i know what you mean by it but i would think the mirror like will be best. As smooth as glass almost. How about the intake manifold and the carb throats ? should they be left as is to create some turbulence or should these be smoothed out ?
How about the exhaust manifold ? I would reckon that should be as smooth as possible to stop carbon build up or am i wrong ?

[filthy phill]

yes the exhaust would be better the smoother you can get it, the front intake on carb could also be mirror finish, But once the fuel starts going through the carbs its a
case of turbulence thats needed to keep everything as a mist.
if you make the read intake like a mirror, there is more chance of the oil in the fuel sticking to this finish ?

I also asked about completely polishing the inlet manifold like a mirror and got told I would lose power and overall engine smoothness, I was gutted as just got some nice
small polishing mops for this very job ha ha but glad I did not go ahead and make it ultra smooth.
here is a video by a bloke who knows his stuff big time to explain about it better than I can.

https://www.youtube.com/watch?v=GwtquXIAOrk

[JohnsonM50]

Should i add the ccm reeds and stuff the reed blocks before i change the carbs ?
on the point of reeds is it best to polish the surface of the cadges ?
I don't know much about specifics but from experimental experience I can say trying the reeds with the 85 carbs is your best bet & most likely success. Sure you might have to re-jet the 85's but you were going to have to do that anyhow. As far as the 140 using bigger ventury's there's got to be a compensating factor- porting, exhaust tuner, timing, reeds, etc. If you go to BRP catalogues you might find some answers, part #'s & expandable exploded view. In the past I tried 115 carbs/reeds on an 85hp V4 they bolted up ok but didn't run well. Later i adapted a 115 2barrel carb to a 35hp twin. It ran but was too much. I switched to an 85 carb & got it working well. In the end tho it achieved more mid range power but was 1mph slower than than my best modified single barrel carb made for the 35. It's always a stretch to try this stuff & not easy to improve upon what's already been engineered to work well but.. can be done.

[JohnsonM50]

I dont know about the satin type finish i know what you mean by it but i would think the mirror like will be best. As smooth as glass almost. How about the intake manifold and the carb throats ? should they be left as is to create some turbulence or should these be smoothed out ?
How about the exhaust manifold ? I would reckon that should be as smooth as possible to stop carbon build up or am i wrong ?
If I've learn't anything in building RaT motors & racing it's that what seems 'should be' often is not. My best guess is you want turbulence on the intake side because it can aid in mixing the fuel & air. By the time it's exhaust tho you just want it gone, turbulence won't matter. Keep in mind there's more physical resistance than just parts, it's also got pressure & thermal barriers to overcome. Clearing out casting chaff might do a little but making it shiny probably won't help.