1988 Johnson 110 vro v4 sputtering at idle

[Mason36]

I've got a 1988 johnson 110 vro v4, the vro is deleted and I mix the fuel. I am the second owner of this boat and just bought it a year ago. I have completely done a redone the boat and motor. The motor has a vacuum operated fuel pump on it. Compression is all good in all cylinders along with spark. I have completely redone the carbs and cleaned all the jets and ran clear fuel line so I could see if I was getting air bubbles causing the motor to run rough. The motor runs 35 mph all the time but some days it's different and will run 38 to 40 mph. The throttle and shift cables have been replaced. I've ran this boat alot. Even when the motor is warm you will still have to put into a "warm up mode" on my throttle controll every single time. But when I'm putting around idling and scanning on my graphs the engine will sputter, shake and cough acting like it's gonna die sometimes it does and sometimes not. I have no idea where to start besides that it may be out of timing and the throttle cable may need to be adjusted.

 

[flyingscott]

Do a compression test before anything. What Fuel pump are you using? Did you remove the Blue VRO Nipple and replace it with a standard brass nipple?

 

[Mason36]

I already did a compression test all cylinders have great compression. The fuel pump. Is just a typical fuel pump it's the same one that's on boats.net it's for if you delete the vro. What blue nipple are you talking about? Now the plastic piece that sends the fuel to both of the carbs broke when I tried to pull the hoses off so I built one with brass

 

[flyingscott]

What is the pulse line attached to?

 

[Mason36]

What is the pulse line attached to?

It's attached to a little plug that almost looks like a spark plug but has a nipple on it.

 

[flyingscott]

It's attached to a little plug that almost looks like a spark plug but has a nipple on it.

That is a pulse limiter and has to be removed for the fuel pump you are using. That pulse limiter is for the VRO pump only and can prevent standard pumps from working correctly. Go buy a straight brass nipple and install it. What are your compression #s? Those motors are famous for breaking the rings.

 

[Mason36]

That is a pulse limiter and has to be removed for the fuel pump you are using. That pulse limiter is for the VRO pump only and can prevent standard pumps from working correctly. Go buy a straight brass nipple and install it. What are your compression #s? Those motors are famous for breaking the rings.

I took pictures of the compression test but I can't find them. I do know that the were all 100 and up you would get different readings on different cylinders. I did find this picture of that pulse limiter.

 

[flyingscott]

That needs to be removed and replaced with a straight nipple. You also need to do another compression test. And get good quality black fuel hose clear line sucks.

 

[racerone]

??----You remove the pulse limiter and put a pipe plug there.----Then mount the correct fuel pump ( 2 nipples ) directly over the pulse port provided on the intake manifold.----I can see the spot in last picture just above the pulse limiter.-----Nice and neat that way !!

 

[racerone]

The pulse limiter is a " FLOW FUSE " designed to protect the VRO pump.

 

[Mason36]

That needs to be removed and replaced with a straight nipple. You also need to do another compression test. And get good quality black fuel hose clear line sucks.

I'll try that and hope that helps with the sputtering and coughing at low idle.
Thanks

 

[Mason36]

??----You remove the pulse limiter and put a pipe plug there.----Then mount the correct fuel pump ( 2 nipples ) directly over the pulse port provided on the intake manifold.----I can see the spot in last picture just above the pulse limiter.-----Nice and neat that way !!

The problem is the spot where the fuel pump is supposed to go is so close to the starter you can't put any hoses on the fuel pump and it pinchs the hoses that's why the fuel pump is there. Mounted on the air housing.

 

[flyingscott]

You would use a different pump for mounting there. The pulse port on the correct pump is built into it.

 

[Mason36]

??----You remove the pulse limiter and put a pipe plug there.----Then mount the correct fuel pump ( 2 nipples ) directly over the pulse port provided on the intake manifold.----I can see the spot in last picture just above the pulse limiter.-----Nice and neat that way !!

What confuses me is that the fuel pump I have is the one boat.net and when you pull it up on the internet that's the fuel pump that is supposed to go on is the one I have.

 

[flyingscott]

This would be the pump that is correct. But the one you have will work fine as long as you get rid of the pulse limiter. And get those compression #s 100 is not good for that motor.

0433387​

 

[racerone]

??--The long hose from pulse limiter to pump is not correct.-----Remember that the pump is driven by crankcase PRESSURE.and not vacuum as has been mentioned numerous times.----The correct pump as used on the 88 HP version ( same block as your 1988 model 110 HP ) and 1983 and older motors mounted right there on the intake manifold---Directly over the pulse port.----A nice neat installation.----Done it numerous times myself.----Compression should be about 120 on all 4 cylinders.-------These motors all suffer from broken piston rings.-----I would pull a cylinder head where you see about 100 PSI.----No amount of fiddling with fuel pump and carburetors will fix these if rings are the issue.----Scared to inspect by pulling the head ?----Then pull bypass cover ( 6 screws ) on cylinder with lowest reading.----Cost you a $3.00 gasket and you learn so much !

 

[Mason36]

This would be the pump that is correct. But the one you have will work fine as long as you get rid of the pulse limiter. And get those compression #s 100 is not good for that motor.

0433387​

 

[racerone]

Pull the head where you see 100 PSI -----I do not believe you will be happy with what you see in there !!

 

[Mason36]

??--The long hose from pulse limiter to pump is not correct.-----Remember that the pump is driven by crankcase PRESSURE.and not vacuum as has been mentioned numerous times.----The correct pump as used on the 88 HP version ( same block as your 1988 model 110 HP ) and 1983 and older motors mounted right there on the intake manifold---Directly over the pulse port.----A nice neat installation.----Done it numerous times myself.----Compression should be about 120 on all 4 cylinders.-------These motors all suffer from broken piston rings.-----I would pull a cylinder head where you see about 100 PSI.----No amount of fiddling with fuel pump and carburetors will fix these if rings are the issue.----Scared to inspect by pulling the head ?----Then pull bypass cover ( 6 screws ) on cylinder with lowest reading.----Cost you a $3.00 gasket and you learn so much !

Yes I get what your saying about the fuel pump. I mean I can order it it'll probably be somewhere around 30$ to 40$ for a new pump which doesn't bother me. It's a learning experience but I can't really put time and effort into this motor be I need it for tournaments and knock on wood it's always started it may be a hassle but I don't want to pull the heads to change the rings. But that's good to know that it's supposed to be around 120 psi.

 

[racerone]

Well ----I would modify the pump that you have so that it can be mounted directly over the pulse port !!!