Johnson 90 made 140 running rich

Hello gentlemen I have a bit of a long winded question but here it goes. About a year ago my 84 johnson 90 developed a water leak in the lower starboard cylinder. I took the head off to discover that the block had erroded in one spot and my only option (that i know of) was to get a new block. The motor had been rebuilt less than 100 hrs before this so i opted to reuse my pistons and crank while all other wear parts were replaced. I wasn't confident in my ability to assemble the motor from scratch so i paid a knowlgeable local mechanic ( who also got me the new block from his parts yard) to build the powerhead. while doing this he offered to turn the motor from a 90/115 into a 140 with the upgraded carbs and exhaust housing. The block was machined to fit the stuffers for the 140 exhaust and it was bored 30 over to match my pistons. I dont however know what motor this block was originally from as he pulled it out of his parts yard. I have been running the motor for about 6 months now and it constanly fouls the plugs. the carbs are jetted to what the manual says a 78 140 (which is what the carbs came off of)should be. I'm running a 25 idle and a 65c main. I have been told conflicting reports about the 115 block being the same as a 140. Is it possible that i will need to run smaller jets because the ports on the 115 block are smaller than the 140?? Another possible problem is my thermostats are stuck open. I dont think he replaced them as it wasnt discussed when we made the deal. When i first start my motor on muffs it immediately starts dumping water out of the return vents and exhaust. Is this normal? I also have a shudder when trying to get on a plane around 2000-3000 rpms. This motor is on a 17 ft alum bass and has no trouble getting it up on plane and it tops out just over 50 mph . I will say it runs awsome once opened up and i am hitting 10mph more top speed than with the 90! It just has a terrible time idleing and at lower speeds. If i clean the plugs it will run fine for a while then start loading up after a while and soon it will barely idle. Pease help I love this motor and i know it should be running better than this!

Re: Johnson 90 made 140 running rich

Well I may have found the issue and it wasn't a rich cond but one cyl was running lean. Disected my carbs and found one of my idle air bleeds was not able to seat properly. With a little dremel work I managed to get it ground down smooth. I guess the warmer the engine got the worse the lean cond would get making me think it was fouling the plugs. I'm off to the water today to see how she does.

Re: Johnson 90 made 140 running rich

What spark plugs are you using?

Re: Johnson 90 made 140 running rich

I am running L77JC4 plugs. Is there something hotter that I can run?? I tested it on the water yesterday and it appears to be the two bottom cyls that are not firing properly. Carbs where both just off and cleaned. Floats where set properly and the needles and seats are new. The two bottom plugs looked wetter than the top.

Re: Johnson 90 made 140 running rich

Hotter plugs is not the best answer. As you stated, the bottom 2 are not firing correctly. That's what needs to be fixed. We need to determine if it's not "firing" correctly from too much fuel or from weak spark. Too much fuel seems the most logical answer since the bottom carb controls both bottom cylinders. If the fuel pump diaphram was leaking only #4 would be running rich or flooding. Both coils or coil wires could be weak but it's kinda unusual for both to be weak but not impossible. How's the compression?

Re: Johnson 90 made 140 running rich

Ok here's what i have found so far I'm not to sure that it is a case of running rich and fouling the plugs anymore. I think this maybe an electrical issue. There is a small fuse by the starter its the old glass tube only 4 amps is the one that was in there. Well someone wrapped it in tin foil at some point and the reason is it keeps blowing! The fuse blows when the motor starts. I've also found that my tach has stopped working in the last two runs. The "miss fire" I'm feeling is from idle up to about 2000-3000 rpms and is very inconsistant but is always there. it never seems worse or better no matter how i run the motor which is why i feel this maybe electrical. Compression is an even 105 on all cyl. coils are putting out 300 volts . What should i check next and why is the fuse blowing ?

Re: Johnson 90 made 140 running rich

The fuse should be a 20 amp. It won't cause a miss. Put in the correct amp fuse and let us know what happens.

Re: Johnson 90 made 140 running rich

Well the 20 amp fuse isn't blowing so I guess I don't have a short in the system. The motor still doesn't run right though. One other thing that seems strange to me is that when u run the motor on muffs and rev it with the high idle it wants to keep reving even after u drop the idle lever. Is this normal or is this evidence of a vacuum leak? Could a crankcase leak be causing the motor to run poorly at idle but run fine at high rpms?