Johnson 1988 50 HP ex-VRO Fuel Pump Question

[Dale Meyer]

I bought this motor new in 1988. I had VRO bypassed by a reputable boat sales/repair place in about 2002. I had major engine overhaul 2004 after a relative failed to use 50:1 mixed fuel. So since the rebuild the engine has run well until a month ago. Then it would want to quit at or near wot after about 30 seconds. It would run indefinitely at lower throttle. Then it stopped running at all. I replaced the aftermarket filter/water separator. I removed the in-line fuel fuel filter. Fuel is getting from the tank to the carbs with no restriction. So I bought a new Sierra 18-7352 pump. Now I am new to this, so when I went to install the new pump I found the pump was mounted to the intake plenum with no connection whatsoever to the proper location on the crankcase. So how in the @*/## has this motor ever run? Has anyone ever seen such a situation? I'll try to post some photos. Having difficulty posting images from this Android tablet. My email is dgmcrm@yahoo.com if anyone wants a photo of this situation.

 

[oldboat1]

Welcome to the forum, D.M. The pump mounting was probably fine, particularly since it worked for 14(?) years. I would just mount the new one the same way. The pulse to operate the pump is accessed through the middle hole in the back, between the bolts. Use the gasket (new one if you have it, otherwise reuse the old one). A little gasket sealer doesn't hurt if you have it, otherwise can use it dry. Don't use silicone sealant as that will end up leaking.

Keep the old pump. It may be the pump diaphragm is torn or has a hole in it, and the standard fix would be to replace the diaphragm (fuel pump kit, similar to a carburetor kit).

Anyway, hope your issue was fuel pump related (good chance), and this takes care of it. Will say as a kind of caveat, that your engine should start if you are indeed getting fuel through to the carb when priming -- would not continue to run with a bad fuel pump, or not well. Good luck with the fix -- hope you post results.

(You might want to edit your post and delete your email address, btw. We can reach you via a private message here.)

 

[flyingscott]

Which pump did get do you have a 2 or 3 port pump

 

[Dale Meyer]

I probably did not make it clear that the port on the fuel pump that is supposed to be exposed to pulsating pressure from the crankcase is connected to nothing but the atmosphere! The pump is simply attached to the intake plenum physically. There is no obvious source of energy that could make the fuel pump diaphragm pulsate to pump fuel to the carbs! That is the mystery. How could this pump ever have functioned to keep the carbs fed properly.

 

[Dale Meyer]

Which pump did get do you have a 2 or 3 port pump

The Sierra 18-7352 is the pump with one fuel intake and one fuel outlet, the non VRO pump. There is a flange for mounting on the engine block to receive pressure pulsations from the engine to cause the pump diaphragm to operate. But like I said in a previous post "I probably did not make it clear that the port on the fuel pump that is supposed to be exposed to pulsating pressure from the crankcase is connected to nothing but the atmosphere! The pump is simply attached to the intake plenum physically. There is no obvious source of energy that could make the fuel pump diaphragm pulsate to pump fuel to the carbs! That is the mystery. How could this pump ever have functioned to keep the carbs fed properly."

 

[flyingscott]

If you have the 2 port pump just mount it to the block over the pulse hole and put the in and out hoses on. The pump you took off was probably a 3 port so it uses the pulse line from where the VRO plugged in. That is probably the difference.

 

[Dale Meyer]

If you have the 2 port pump just mount it to the block over the pulse hole and put the in and out hoses on. The pump you took off was probably a 3 port so it uses the pulse line from where the VRO plugged in. That is probably the difference.

You are correct that the old pump was a three port pump. The VRO function was disabled in about 2002. I will relocate the new two port pump to the proper location on the engine block/crankcase and see what happens. I might need to alter some of the fuel line lengths to do so. I might not have said so earlier, but the engine runs OK if the carb bowls are filled by manual priming.

 

[Baylinerchuck]

I had to remove the VRO pump and oil lines totally from my 87 90hp Johnson. I ordered an 88 non-VRO pump, (since they only made VRO in 87) and it bolted to the block without issue. The fuel lines from the fuel connector and to the carbs needed to be modified and rerouted. It's been running like a champ for two years now. I never trust oil injection in any two stroke and prefer to mix it myself.

 

[flyingscott]

If it mounts over the old vro pulse hole you are fine. If it mounts somewhere else you will need to plug the VRO pulse line port

 

[oldboat1]

Circling back -- see flyingscott better covered your issue (old pump a different model). I guess the 2002 installer probably used the pulse limiter nipple for a pulse source, and maybe it's possible the limiter valve has since gotten carboned up (i.e., current problem wasn't the fuel pump itself). A moot point, in any case, as you will move the location to the block using the new pump. If nothing else, it should be a more compact installation (might be a good time to replace fuel lines when changing the configuration -- good opportunity to do that.) Hope you post results.

 

[Dale Meyer]

Today I replaced the old VRO pump with the non-VRO two-port pump made by Sierra. I replaced the suction and discharge fuel hoses. The new pump is mounted on the engine block at the location it was designed for. It is a neater, more compact installation than original. My fuel tanks are OEM original tanks which I recently overhauled, replacing the o-rings at the fuel connection on top of the tank as well as the rotten rubber gaskets on the filler caps. The priming bulb builds pressure on the system until it becomes hard to compress any further. All that said, what are the results? The engine took about 20 seconds of cranking to start using the procedure in the Johnson manual which states that the ignition key is to be depressed while starting in order to activate the electric priming solenoid. The engine started and ran for about 30 seconds. After that it would only kick enough to disengage the Bendix. I pulled the pump discharge line and watched it pump gas/oil mixture into a reservoir. I might have flooded the engine, so I took the opportunity to pull the plugs and crank the engine to verify spark. Spark OK, but I have cleaned the plugs, which really did not look bad; no carbon buildup. It started to get dark, so I grilled some fish and got something to drink.

Please, any thoughts on further troubleshooting would be appreciated. In short, nothing I did today made any difference.

 

[Dale Meyer]

Here is the latest: I tried again to start the motor and no luck. Now it won't even kick to drop the Bendix down. I verified the priming system is working and the electric solenoid valve is not leaking through. What I discovered is that I have another problem. The throttle controls at the console (startup lever and forward-reverse throttle lever) don't move the butterfly valves on the carburetors. There is no motion whatsoever when the throttle levers are moved. It's got to be something in the control box.

Any thoughts on opening up the control box to see what is wrong? I feel I should stay out of it because special tools probably required?

 

[jakedaawg]

Did you plug the old pulse limiter hole? This must be done. It has nothing to do with your control issue though.

Disconnect cable from throttle linkage. Move fast idle lever. Does cable move?

 

[oldboat1]

The standard response on suspected cable or box issues is to make sure the linkages at the motor work. Disconnect the remote cables at the motor, and manually operate both throttle and shift at the motor.

The cranking issue you describe, however, might be a neutral safety switch in the box (connects via the wire harness). The switch is normally operated by the lever position -- so may want to move the lever back and forth a bit around the neutral detent while trying to crank. (That would have nothing directly to do with operation of the cables.) Put the motor in neutral manually (at the motor), and set it to idle at the motor. The lower unit needs to be sunk in water or on muffs when cranking.

Your thread started with a fuel pump replacement, but you may need to do other basic testing (compression, spark). I would start with a compression test to see what you have, once you can get the motor to crank. Clean all electrical connections and make sure the battery is charged, then try cranking while moving the remote lever around the neutral detent. Wipe a little bit of grease on the shaft at the bendix gear.

 

[Dale Meyer]

The standard response on suspected cable or box issues is to make sure the linkages at the motor work. Disconnect the remote cables at the motor, and manually operate both throttle and shift at the motor.

The cranking issue you describe, however, might be a neutral safety switch in the box (connects via the wire harness). The switch is normally operated by the lever position -- so may want to move the lever back and forth a bit around the neutral detent while trying to crank. (That would have nothing directly to do with operation of the cables.) Put the motor in neutral manually (at the motor), and set it to idle at the motor. The lower unit needs to be sunk in water or on muffs when cranking.

Your thread started with a fuel pump replacement, but you may need to do other basic testing (compression, spark). I would start with a compression test to see what you have, once you can get the motor to crank. Clean all electrical connections and make sure the battery is charged, then try cranking while moving the remote lever around the neutral detent. Wipe a little bit of grease on the shaft at the bendix gear.

Quick reply to some of your suggestions: I checked compression before I ordered the new fuel pump. Top cylinder is 140 psi; bottom is 120 psi. This motor has had one major overhaul after a relative ran it on straight gasoline because he forgot I told him to mix 50:1. The motor cranks with no problem. Battery is OK. Spark is strong. Plugs are clean.

I have not yet disconnected the remote cables from the gearbox and throttle controls. I will do that and post the results.

I recall the last few times I started this engine this summer, when it did start and run at idle it was very smoky. Now I think it might have been a throttle position problem that was not bad enough to prevent starting but was starting very rich

 

[oldboat1]

Shoot. You might try replacing the head gasket, resurfacing the head cover in the process. See if that restores some compression on the lower cylinder.

 

[flyingscott]

Was there a new gasket with the fuel pump to go between the block and the pump.

 

[Dale Meyer]

I disconnected the throttle cable at the engine. I was able to make the startup lever move by pulling/pushing on the fitting at the engine end of the cable. After doing that I found that now the startup lever and main throttle lever were functional when they absolutely were not earlier. I reconnected the engine end of the cable and tested function of the levers from the console. Throttle control was OK, and where earlier both butterfly valves were nearly closed they were open a greater amount when the startup lever was raised.

After about twenty seconds of cranking the engine fired and ran but kept shutting down. I increased idle speed by turning the wheel on the throttle cable and was able keep the engine running. I shut down and restarted several times. I ran the boat around the cove at slow speed, shut down and started up. Then when I had more room I increased speed until I got to wot. After about 20 seconds or so the engine rpm dropped suddenly as if it was running out of fuel (seee my first post) . I decreased throttle and then tried to return to wot but rpm remained low and would not increase.

I put the boat in the boathouse. I won't be able to work on it any more for about five days.

There are still problems. I should not have had to "adjust" the thumbwheel on the throttle cable. The engine idles very rough, although even when brand new it idled roughly. I still have the wot problem I started with. But it is running now and four days ago it was not.

 

[Dale Meyer]

Shoot. You might try replacing the head gasket, resurfacing the head cover in the process. See if that restores some compression on the lower cylinder.

What would you consider good/ acceptable compression?

 

[Dale Meyer]

Was there a new gasket with the fuel pump to go between the block and the pump.

Yes.