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hardwatergrampa

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you seem to know a lot about the johnsons so maybe you can help i got this motor about 5 years ago have run it every year but last took it out this year and it would run and stall well i took the pump apart and it had what looked like a pin hole in the dyeaphram could not find any info on the motor as to what year it is i went to nappa and we matched up a rebuild kit bench tested the pump seems to be put togather right put it on the motor same thing runs a few min then the the inline pump buld goes limp motor stalls so i would think its not picking up fuel took the carb off and rebuilt it changed the hose cuplins it got so it runs about ten mins now ckeck the tank vent as well any ideas and what year do you think this 4 hp motor is i was thinking late 70 early 80 the guy i got it from cant remember thanks for any help

MVC-313F.jpg
 
You say it bought you more time between stalls when you changed the hose couplings? Just a hunch, but I think your hose or tank is guilty here. If it is the same hose you had for 5 years, and if the previous owner had it for a bit before that, I would say it is definitely ready to be replaced. If out in the elements, they don't last much more than 2 or 3 seasons. I think you probably have a tiny air leak somewhere in your fuel hose near your tank. The motor will pull fuel for a while, but as it pulls, more and more air enters the hose. Pretty soon it gets to where the amount of air equals that of the fuel, and it starts sucking air, and stalls. Your primer bulb still gets hard because it pulls a lot faster than the motor. The motor probably pulls about equal to the amount of air that will fit through the whole, but the bulb will pull a lot faster, so it is getting mostly fuel, and very little air, and thereby will get hard. Your best bet is probably to get a new fuel hose and see what that changes. Also, check where the fuel fitting goes into the tank (plastic tank I presume). Sometimes they don't have thread sealing tape (can't remember name) from the factory, and after a few years, you need to unscrew the fitting, and seal it.

As far as the years go, I would say late 60s early 70s. Get me the model number off the transom clamp, and I will get you the exact year.
 
thanks for the input bassboy i have already changed the hoses even with the new one it acted the same i have 2 tanks and the motor runs the same on eather tank however i will try putting some threadtape on the fittings to see if that helps cant give any # for the motor i think it had one of those stick-on # tags and its not there the only # i could find on this motor were on the lower unit thats why i asked if you had any idea those # were 314791 but i think they are just casting # i was gonna try changing the plug but cant see where this would help on a fuel problum and there burning an almost white color
 
Lemme ask this. How well is it pumping water? If it isn't pumping enough to cool the engine, it may be overheating, which would shut it down like that.

If that isn't the case, check for an exhaust leak. It may be filling the cowl with exhaust, and when it runs out of clean air to burn, it chokes on the already burned air, and stalls. Running the motor with the cowl off, and a fan blowing air over the motor should determine this.

Check those two (probably in that order), and get back to me.

Now, as far as the year goes, there should be the number on another spot of the motor.
Somewhere on the powerhead, there is a round thing that looks like a freeze plug. It is about the size of a quarter. There should be the model and or serial number stamped in that plug. No telling where they put it. On a '75 40 horse 'rude, they put it on the top of the block, in easy view, but on my '88 4 deluxe, it is down behind a whole bunch of wires right under a coil.
 
bb1 thanks again iam gonna look for the # s maybe you have something with the poor cooling idea i did notice the screens on the water intake were kinda pluged and cleaned them yesterday but havent tried the motor out after doing it ill try the motor again and let you know maybe i should change the water in the 55 gal drum it kinda grungy from testing motors and working on them thanks
 
Because we only have your serial number, it is getting a little tough here. I don't yet own the correct books that list what year a certain serial number is. Looking into getting some, but don't yet have them. Now, I have talked with a couple people who have these books, but the books of these people only go to 1964. They are guessing 1969 - 1971. I do know of one more person who might know, so let me get back to you.
 
once again thanks and to up date you on the motor tried it yeasterday when i got home i think the pluged intake screens might have been the problum the motor ran for 15 min and then i shut it down :mrgreen:
 

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