99 40 hp johnson mods

[Kevodaniel]

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]

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

[Lil' Blue Rude]

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

[omcstratos]

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]

..."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]

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]

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

[omcstratos]

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]

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

[Jonboat]

Guess nobody knows Kevo... looks like we are forced to bolt on the sst60, and take it to Augusta Duck Boat races!!

[Kevodaniel]

Or we could put my tiller steer on that sst with that hydraulic jackplate

[Jonboat]

yeah that's what I was thinking... there sure isn't a lot of info on here about your motor wonder why?

[Powerabout]

there are 2 carb sizes for that engine, yes sst60 are the larger venturi but you will be on your own for the jetting.
The sst45 is a modified 45 ci engine that is the same as your basic design, it has the larger carbs, shaved head and a custom megaphone and adapter with reversed water flow.
All designed to suit the light tunnel boat it is used on.
Its a stock class but there are other mods for that engine, more comp would be ok and cut pistons skirt like the older 60hp

[OUTBOARDER]

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

had a stock 96 50 johnson on a 16' Carolina Skiff Ran 43mph cosistently with a 21p omc alum prop.

[Kevodaniel]

had a stock 96 50 johnson on a 16' Carolina Skiff Ran 43mph cosistently with a 21p omc alum prop.

Was your motor a large or small gearcase the it have the small gearcase and the biggest prop I found was 11.75x19 it stainless if yours is a large gearcase can I run a large gearcase prop on a small gearcase lower unit

[OUTBOARDER]

Was your motor a large or small gearcase the it have the small gearcase and the biggest prop I found was 11.75x19 it stainless if yours is a large gearcase can I run a large gearcase prop on a small gearcase lower unit

aluminum 11.25 x 21p omc on 1996 stock johnson 20" 50hp , the 11.75 x 19 ran about 40mph

[OUTBOARDER]

Was your motor a large or small gearcase the it have the small gearcase and the biggest prop I found was 11.75x19 it stainless if yours is a large gearcase can I run a large gearcase prop on a small gearcase lower unit

http://www.boatracingfacts.com/forums/showthread.php?7565-Clydes-Ride

different project with a 1985 40 converted

[Kevodaniel]

With the 12.75x15 I'm turning 5750 rpm so I think the 19p prop would be good if I I'm not satisfied I'll get it worked from my research they do not make a 21p prop for a small gearcase the biggest I found was a 19p

[thornl01]

You will be better off to go ahead & pull the powerhead & replace the tuner.

When you get this apart you will be amazed at how restrictive the internal tuna/muffler is.

get some 70/75 3cyl carbs, & 50/60 intake

you WILL have to rejet the carbs

[Kevodaniel]

You will be better off to go ahead & pull the powerhead & replace the tuner.

When you get this apart you will be amazed at how restrictive the internal tuna/muffler is.

get some 70/75 3cyl carbs, & 50/60 intake

you WILL have to rejet the carbs

I just got some 50 hp carbs and the part number on the intake is the same for the 40/50 for the preformance gain that the tuner will give it's not worth it to me to pull the power head right now maybe a later project bit thanks for the info

[OUTBOARDER]

With the 12.75x15 I'm turning 5750 rpm so I think the 19p prop would be good if I I'm not satisfied I'll get it worked from my research they do not make a 21p prop for a small gearcase the biggest I found was a 19p

Brand New OMC BRP 391014 in box. Aluminum prop 11.25" x 21 P

Fits: JOHNSON EVINRUDE - TWO CYLINDER, SMALL GEARCASE;

40HP (1984 THRU), 48HP (1987 THRU), 50HP (1975 THRU),

[Kevodaniel]

Thanks for the part number I finally found it earlier this morning I come across a stiletto triad 2 in a 11.75x19 stainless prop for $208.95 at firstchoicemarine.com

[Kevodaniel]

Did a test run today 50 hp carbs really helped out and I raised the jackplate 2in @ 6000 rpm it runs 35 now I'm just waiting on a prop I have a 12.25x15 goin to a 11.75x19 so hopefully it will break the 40 mph mark and get my rpms down to 5500

[OUTBOARDER]

Did a test run today 50 hp carbs really helped out and I raised the jackplate 2in @ 6000 rpm it runs 35 now I'm just waiting on a prop I have a 12.25x15 goin to a 11.75x19 so hopefully it will break the 40 mph mark and get my rpms down to 5500

the 21p @ 5500 was 40 mph on the carolina skiff 11% slip , rig weighd about 900 lbs.

[Kevodaniel]

Just me in the boat weights 650lbs. it done 33 mph @ 5750 rpm with a total weight of 1150 3 others in the boat

[Xpress2830]

The 40 / 50 exhaust tuners have different p / n's. Has anyone modified a 40 tuner ??

[Xpress2830]

The 40 / 50 tuners have the same p / n 's. has anyone modified a 40 tuner ??

[Lil' Blue Rude]

I've done two on the 89 up 40hp. From 89-up on both the 40hp and 50hp the tuner and the plate the powerhead bolt to are one cast piece along with the pick up for the water. So you have to cut the exhaust off leaving the water tube in tact and then weld on a new exhaust tuner. Normally a cowbell style tuner like a 45ss or a SST60 has.

[Xpress2830]

I've done two on the 89 up 40hp. From 89-up on both the 40hp and 50hp the tuner and the plate the powerhead bolt to are one cast piece along with the pick up for the water. So you have to cut the exhaust off leaving the water tube in tact and then weld on a new exhaust tuner. Normally a cowbell style tuner like a 45ss or a SST60 has.

Thanks for the info Rude. Couln't I just cut tuner just above the nipple at the bottom all way across to relieve the exhaust and call it good? Looks like alot of restriction there.Is the 50 head with reeds and carbs gonna get me close to the 50 - 55 hp window? If I not due you have a moded head that will help. I have this motor on an Alweld 1548 semi V. I want to keep the motor reliable not for racing. Thanks, Bobby...If you have a chance give me a call. 337-764-553459143

[Lil' Blue Rude]

I think by the time you get he 50hp head and plug your idle relief hole your compression will be high enough I'm not sure you'll be able to go any higher on 87 pump gas.

[Xpress2830]

I think by the time you get he 50hp head and plug your idle relief hole your compression will be high enough I'm not sure you'll be able to go any higher on 87 pump gas.

Hey rude the only holes this head has is the water jacket59160

[Lil' Blue Rude]

The idle relief holes are in the cylinder wall above the exhaust ports.