99 40 hp johnson mods

**Kevodaniel** · 02-06-2014

Dose anybody have and info bout making a 40 a 50 or 55hp I know the carbs and reed cages are different I'm not sure about the head or exhaust I put 50 hp jets and boysen reeds in it and I'm not sure if the jets hurt or helped me it's on a 1648 weldbuilt with a 4in jackplate just got it put together only had it out one time so not much testing time thanks for any info

**Kevodaniel** · 02-06-2014

I've also heard of adjusting the timing to get a little hp

**Lil' Blue Rude** · 02-08-2014

the 40hp and 50hp carbs have different size throats so you can't just add 50hp jets and be the same.

**omcstratos** · 02-08-2014

You need to get the big bore 40 carbs, 50hp carbs, or 2 of the 75hp carbs. Also if you can find a 2cyl 60, they will work also. The 60hp had timing set at 20 or 21 degrees. I think my 50 specs says 19 degrees.

Remove the carb airbox to get another 150 rpms and jet accordingly. Once you do this and let more airflow in, you will need to open up the exhaust tuner or get a 50hp one.

**Fastjeff57** · 02-09-2014

..."Remove the carb airbox to get another 150 rpms"

Has anyone done this while running with the stock hood in place? From what I've seen, of motors with one carb per cylinder, there's a nasty reversion layer of gas mist that forms ahead of the carbs at certain speeds. (The airbox contains it for safety.) Of course, with the hood off it's no problem.

The reason I'm asking is that I'm in the process of building 3 carb Merc triple that MUST retain its hood (long story).

Jeff

**Kevodaniel** · 02-09-2014

How would you open the exhaust tuner I not wanting to take the power head off to put a 50 tuner in I've heard of drilling some bigger holes were the exhaust come out above the cavitation plate

**Kevodaniel** · 02-09-2014

My 40 says 18 degrees on timing I might turn it to 20 degree

**omcstratos** · 02-09-2014

Originally Posted by Kevodaniel

How would you open the exhaust tuner I not wanting to take the power head off to put a 50 tuner in I've heard of drilling some bigger holes were the exhaust come out above the cavitation plate

You have to pull the powerhead and modify the tuner. Drilling the midsection is different. The easiest thing to do is buy a 50hp one.

**Jonboat** · 02-09-2014

so would carbs off a sst60 3cycl work? me and kevodaniel looked at them today and seem to be a bolt on swap but with bigger bore..we are trying to get this 1642 weldbuilt in the 40's