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Johnson1999 25hp fuel pump mistake? J25RLEEB

V

valvebounce

Regular Contributor
I have fitted a new fuel pump,the ad was a bit vague,it turns out the pump is for the 75hp plus.
It fits exactly the same as the old pump.The fuel outlet nipple to the carb on the pump is a larger dia than the one on the old pump.
I changed the nipple over for the one off the old pump.
My problem is now,that the fuel filter sight glass doesn't stay full.The motor will tickover all day nice and smooth,but if I increase the revs,the fuel filter empties and the motor runs out of fuel and cuts out.
I am wondering if the higher capacity new pump isn't getting enough vacuum pressure from the 25hp engine,and really needs more vacuum pressure like it would get from a higher hp engine.
Has anybody got any idea whether my theory is correct?
I have a new primer bulb and pipework on it,and have put the fuel line pickup pipe directly into the fuel tank.
It ticks over great,but still empties the site glass when I rev it up.
I have also tried it by putting the fuel pipe directly onto the fuel filter,and cutting out the connection fitting on the engine,with the same results.
 
flyingscott said:
Is the restrictor elbow on? OMC puts a restrictor elbow on between the outlet and the carb. Is the gasket on?
Click to expand...

Sorry not quite sure where you mean.There is a brass elbow that fits in the block for the lower vacuum pipe.
It's tapered and just taps in.
The gasket is on the back of the pump.(oval shape)
When I fitted the new fuel pipe primer bulb and pipe,I had to release the filter on the pump connection to purge the air out.
It was airlocked.
 
Pumps are driven my crankcase pressure and not so much by vacuum.-----I do not understand how this pump can be " airlocked " in any way.-----Pictures of your set up ??
 
You say there is a brass elbow and the gasket is on the back of the pump. Are you running 2 vacuum sources to that pump. The restrictor elbow comes off of the pump outlet and reduces the fuel line size to the carb.
 
Yes,there are two vacuum sources to the pump.
The fuel line reduces from the fuel nipple on the pump to a smaller dia fuel pipe to the carb.
The new pump had a larger dia nipple and I swapped it for the smaller nipple off the old pump.
This carb has a feed to the primer/choke from the bowl where the drain plug normally is.There' s no T piece like on the other models.Could this pump be too big and may be causing the problem?I've stripped both pumps and they look exactly the same.
The motor ticks over no probs,but if I increase the revs,the fuel level goes right down in the site bulb.
 
On the back of the pump there is an oval gasket,with a hole in the centre,which is one source of vacuum,in the bottom of casting
there is brass nipple which is fed by a pipe from the block.
one is fed by the top cylinder,the other by the bottom cylinder .The ally casting deals with the vacuum,on the other side of the diaphragm,which is plastic is the fuel side.
 
Eliminate the block hose you can only have one pressure port!! Because the cylinders are 180 deg apart you are pressurizing the pump all the time. This does not allow the diaphragm to move back and forth as it should. It probably works at an idle because the cylinders are moving slow enough that the pump somewhat works.Or it is just leaking past the diaphragm from cylinder to cylinder and not doing anything.
 
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The engine and pump are designed to have two inlets and outlets.Each piston causes a pressure drop as it passes the pump
port,top piston to the back of pump,bottom piston to the brass elbow and pipe and into the bottom of the pump.
Dangar stu has a vid showing servicing the same pump for marine engine dot com
 
Just looked at a 1998 model.-----This pump mounts on the pulse port for top cylinder.---- And has a hose from a pulse port from the bottom cylinder going to it as well.-----So Mr Bouncer should check if the port on the back of the pump is actually open to the diaphragm !!-----Perhaps advise Dang , Dang on this as well.----I have to say it again.----These pumps use crankcase compression to operate the pump !!-----Or explain to me what the SPRING does in these pumps !!-----Valvebounce have a look at your pump again and explain the spring to me.
 
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Valvebounce... This fuel pump you're speaking of, having a problem installing it... could you insert a picture of it?

How many hose fittings does it have?
 
His pump has 3 hose fittings.----One fuel in on the filter screen cap.-------One fuel out to the carburetor.----One for pulse to the diaphragm !
 
Valvebounce... This fuel pump you're speaking of, having a problem installing it... could you insert a picture of it?

How many hose fittings does it have?
 
racerone said:
Just looked at a 1998 model.-----This pump mounts on the pulse port for top cylinder.---- And has a hose from a pulse port from the bottom cylinder going to it as well.-----So Mr Bouncer should check if the port on the back of the pump is actually open to the diaphragm !!-----Perhaps advise Dang , Dang on this as well.----I have to say it again.----These pumps use crankcase compression to operate the pump !!-----Or explain to me what the SPRING does in these pumps !!-----Valvebounce have a look at your pump again and explain the spring to me.
Click to expand...

The springs support the non return valves in the pump.They are in contact with the diaphagm
 
The big spring on one side of the diaphragm, what does it do ??----There is an opportunity to learn some basics about what PRESSURE does in this pump.
 
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The big spring returns the diaphragm after it has been subjected to pressure from the engine.
In,out flexing of the diaphragm.
I have been advised to ignore the part empty in line fuel filter and use the engine.
 
So would you agree that the + pressure compresses the big spring when piston is coming down.----Then when piston is going up the spring works to pull fuel from the tank.-----Have you determined if the pulse port from top cylinder acts on the diaphragm or not ?
 
There are two springs in the pump,they assist the diaphragm and the non return valves.Both ports work on the diaphragm.
Because the pistons are at 180 on the crank they give a double pulse.
 
Have you checked to see if the port on the back of the pump actually goes to the diiaphragm, yes or no ?----There is an opportunity for you to learn here.----I do not believe your pump gets a " double pulse "-----Not at all !!!!
 
Well, well, I looked at the pump earlier today.-----And the port at the back of the original pump on a 98 model DOES NOT go to the diaphragm.----You should STOP making assumptions here.----Look at the pump or your old pump and report back the facts.
 
I appreciate your advice,but logically,the diaphragm must have pressure pulses on it to operate.Or what is the point of having
the pressure from the ports in the first place.Try looking at the principals and specs of the pump,not just the pump itself.
 
Do yourself a favour,and click on videos and blog at the top of the page,and click on Dangar marine,he services a fuel pump by OMC on there.
 
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