lohnson 140 bubble back on a Johnson 115

[coolbri70]

Re: lohnson 140 bubble back on a Johnson 115

Has anyone here taken the bubble back exhaust plate from a late 70s Johnson 140 and installed it on a late 70s 115 Johnson? If so what was involved in re jetting the carbs and was you happy with the end performance?

I have never done this, but this is the 2nd thread I've read tonite that has me thinking that I could easily get more ponies out of my 79 85hp crossflow:facepalm: planting the seeds that have the wheels turning

 

[V153]

Re: lohnson 140 bubble back on a Johnson 115

I have never done this, but this is the 2nd thread I've read tonite that has me thinking that I could easily get more ponies out of my 79 85hp crossflow:facepalm: planting the seeds that have the wheels turning

Oh just go ahead'n do it. Promise yer motor won't blow up ...

 

[wayneo99]

Re: lohnson 140 bubble back on a Johnson 115

Im no expert but here is what I have done and found, my 1979 85hp needed a rebuild. I found that the block was a very small ported design and small carbs 1 inch throats.
I went with a rebuild 115. stock carbs 1 3/16 no filler blocks in the intake and a flat back exhaust. much more power than my 85.
what i did notice betwenn the 3 blocks is the 85 had smaller intake and exhaust ports, the 115 were larger but nat as large as a 140 bubble back intake and exhaust ports.

i went with the 115 flat back because it was easier and i had all the parts on hand.
I could add the filler blocks but dont feel like taking it apart. same thing with the 140 carbs at 1/5/16 or 3/8 i cant remember.
you could use the high compression heads if you can find them. but beware of burning a piston if she runs lean.

the bubble back conversion in a nut shell was to involved and i wanted a simple reliable system.

I bet a 140 would be a screamer if done right.. good luck.

 

[emdsapmgr]

Re: lohnson 140 bubble back on a Johnson 115

On a V4 the rubber intake filler blocks are worth 3-5 hp (on a 140.) The 1 3/16" carbs became stock on the (86 and up) prop-rated 90. The 1 5/16" carbs first came out on the 135's. Many of the 140's came with the 1 3/8" carbs. I run a ported 79 85 hp block. Intake filler blocks and 74 135 carbs. The 135 stock carbs overfueled a bit, so I had to drop the main jet size slightly. All in all- it hauls.

 

[1983 ercoa 21']

Re: lohnson 140 bubble back on a Johnson 115

Alot of good information here . I'm surprised I haven't heard anything about timing.
everything I have read so far isn't much different than a car motor but I also realize that a tuned exhaust plays a big part on two stroke's and what about reed valves?

 

[emdsapmgr]

Re: lohnson 140 bubble back on a Johnson 115

The engine comes with metal reeds. You can upgrade them to composite aftermarket reeds. They will improve idling and midrange acceleration. You might even pickup up a couple of hundred rpm's on top end.