Re: Difference between 84 Johnson 90hp and 140hp
Your 90 is a 90 and will pretty much stay that way. Adding "bigger" carbs will make it run like crap.
Last winter I had the opportunity to dig into several 1980s era crossflows and got to set parts side by each and compare. The 140 block is quite different and unless you're into some heavy machine work, it is better to simply find a 140 powerhead and start with that, rather than try to make your 90 a 140. For starters, the carbs are indeed bigger on the 140. To make use of this, the intake and exhaust ports on the 140 are much larger - what goes in, must come out. The 140 also has an added exhaust tuner (often referred to as a bubble-back), which also requires a modification to the block to fit.
The GT/XP 100 and 115 blocks have the 140 porting with the 90hp style flat-back exhaust, and can be a good starter block if you can't find a 140 block. You still have to modify for the exhaust, but it's much easier to do than porting. I've got one on my winter-to-do project list...
- Scott
