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

[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.