What is the difference in Johnson outboard fuel pumps

[Intoodeeep]

I have a Johnson 1978 235 I am building. I am using carbs and electronics from an 1988 175. I have fuels pumps with the Bottom pump part numbers 328-781 on the front with another # 393648. The Top pump part # is 343462 and the other # on it is a 438559. The original fuel pumps that i was using was 328781 but I could not get a rebuild kit that would work for it and not leak. So whats the deal with all these different fuel pumps? Will these pumps work?

 

[emdsapmgr]

First of all, OMC never intended that these V6 pumps be overhauled. They have never made overhaul kits for them, and suggest that you need just replace them in kind. I'd be very careful when using various pumps on this engine. It has a need for lots of fuel and you just don't want to get the wrong size (wrong part number pump on this engine. Religiously follow the part numbers the factory suggests.) Latest pumps have new internal bladders which will handle today's ethanol fuels.) The upper pump supercession goes like this: 388554-393868-393870. The bottom pump supercession goes like this: 388555-438559. What you will find is that both pumps supercede to a 438559 pump. The upper pump number 393870 is actually a pump "kit" which includes the special j-hose that goes between the two pumps and a second 438559 pump.

 

[Intoodeeep]

So basically I need to go ahead and order a second 438559 Pump. I plan on running stainless steel fuel lines. Worse case scenario I have a J hose and perhaps a second one. I guess to clarify I ordered a gasket kit because I knew it was leaking. I need to check the part numbers of what I ordered again and send it back if need be to get the right stuff. I think this motor blew on account of multiple possible reasons. Fuel issues being related to the 175 carbs and possibly even the wrong fuel pumps. Either could have done it. And this doesn't even take into account that there may have been an internal water leak in the exhaust housing from a bad gasket or who knows what. I would love to run across this guy I got this motor from and claims he rebuilt it and knew what he was doing. I have been told these 1988 175 carbs should do fine. I have to look up my old notes but I believe there is some jetting variances between the three carbs. Oddly enough if memory recalls right it was usually the bottom 5th or 6th cylinder that was notorious for going bad on these motors. The amount of black oily goop that was caked inside the inner exhaust manifold on the side of the motor that blew was amazing. It had to have prevented things from working right. So I wonder if these bottom cylinders need more or less fuel. I would think more, but wonder if all this left over oil is from the other cylinders running down and collecting at the bottom. Thanks for the help. I have a few other threads on here. I will see if I can figure the photo bucket thing out to post a bunch of pictures since things on here are still really iffy.

 

[Intoodeeep]

Ok, Looking at the part number 393648 which is my current lower fuel pump, the part supersedes to 438559 as well. So I should be ok. Just need to change the gasket on it right?

 

[emdsapmgr]

The 1988 175 carbs should be fine. Your block is a small bore 149 cubic inch version. The 1988 175 is a 160 cubic inch detuned big bore (235) version. You should get plenty of fuel. These engines do seem to accumulate a lot of carbon. That's not a good thing-on a long-term basis. I'd run a can of engine tuner through it on an annual basis and use the XD50 Bombardier engine oil exclusively-which has the Carbon Guard additive already in it. Also, run premium fuel only. A few of the OMC V6 engines did run different jetting on the lower cylinders, but I think it was only on the Xtra long shaft engines. Maybe on the loopers.

 

[racerone]

Repair kits / diaphragms are available.--Just need to look for them !

 

[Intoodeeep]

So if the jetting is different, should I leave it the same or make it the same as the other two carbs? Also, do you think I still need to look at charting the high speed jets and increase the jetting sizes to make sure I am not running too lean?

 

[emdsapmgr]

Be careful comparing jet sizes in carbs. Your 78 235 used two jets, plug a fuel pullover jet. The XP/GT small bore engines used a low speed, mid jet and a high speed jet. The innards/passages are different, so I'd be careful making jet comparisons between carb years. Best to run the XP/GT carbs, then tweak their high speed jets. Test by running short distance runs of 1/3 mile or less, then a high rpm throttle chop. Pull a couple of plugs. This will show you what is going on with the plugs and jetting.

 

[Intoodeeep]

Just to clarify a high speed throttle chop, running at WOT and then cutting the throttle to neutral and shutting the engine off right? Why not just kill the engine at wide open throttle?

 

[emdsapmgr]

If you just shut off the key switch, the boat's movement through the water will continue to turn the prop and spin the crank. Add'l fuel will enter the combusion chamber and can affect the plug readings. So, pull the engine into neutral immediately after turning the key off when running at WOT.

 

[Intoodeeep]

What should I look for when checking the plugs? What do I want to see and not what to see?

 

[Intoodeeep]

Besides the question above, When I ran the previous motor I remember running the 61c high speed jets and it seem to run well. I ran 64c and if i remember correctly it ran really bad. I was thinking of getting a set of 62c and trying those once i get this motor up and running. Thoughts? Also do I need to go through at least part of the break in process first before doing short high speed test runs?