1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

[espdeepblu]

Been looking for answers and a pile of new parts hasn't helped yet. So I turn to all of you for some further advice, I'm out of bullets.

The Problem: At low to mid throttle, the engine runs great. Fires up every time, doesn't misfire, skip, or anything else that might lead one to believe there is a mechanical problem with the engine. But as the throttle is slowly increased, at about 60% the engine acts as if it is losing fuel. That is, the rpms slow down and unless the throttle is reduced, the engine will stall. IF, the primer bulb is pumped while the boat is underway at the higher throttle condition, the rpms will pick back up and the boat will remain running, but eventually it returns to the "starved" condition and it has to be pumped by hand again to restore the power.

We've tried all kinds of troubleshooting to identify the problem with no luck. Here is a list of things we have replaced: the fuel lines, the fuel/water separator, the fuel filter, the VRO fuel pump, the primer bulb, rebuilt all 6 carburators, changed all 6 plugs and wires, the throttle and shift cables, the water pump, and the radio (not that we think that one would help).

What I'm looking for is some ideas on what we might try next. Its frustrating that it only occurs at 30 MPH and higher and operates so well in the driveway and at low rpms.

Any insight someone might offer would be greatly appreciated.
Graham

 

[Faztbullet]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

You have a air leak in fuel supply, it can be from the plastic fitting in cowl where fuel/oil lines come in, connections at primer bulb and tank, a goofy acting anti-siphon valve in tank withdrawal fitting or a air leak at air motor on VRO.. Run it on a shop tank to test the above, also is VRO/OMS new or used?

 

[espdeepblu]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

You have a air leak in fuel supply, it can be from the plastic fitting in cowl where fuel/oil lines come in, connections at primer bulb and tank, a goofy acting anti-siphon valve in tank withdrawal fitting or a air leak at air motor on VRO.. Run it on a shop tank to test the above, also is VRO/OMS new or used?

The VRO is new. is there a test for the anit-siphon valve in the tank? I'm not sure what goofy would look like.

Thanks for the reply, this gives us another place to look for sure.

 

[espdeepblu]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

The VRO is new. is there a test for the anit-siphon valve in the tank? I'm not sure what goofy would look like.

Thanks for the reply, this gives us another place to look for sure.

Well, so much for that test. The anti siphon valve was removed and gues what, no spring, no ball. We disconnected the fuel system and connected a spare tank directly to the engine. Still no better, above 3000 rpms, bogs down and tries to stall. The probelm has to be in the engine.

Any ideas about an engine problem that might cause the problem?:blue:

 

[Chris1956]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

Fuel lines and primer bulb must be 3/8" ID. Remove the water seperator from the fuel system for testing to eliminate that issue. Bypass all quick-connect fittings to eliminate that issue. Check/clean the Pulse limiter near the OMS2 pump. Post back.

 

[espdeepblu]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

Fuel line and primer bumb are all 3/8" ID from tank to the cowling. Inside the motor the line seems smaller, maybe 1/2" but i cant read the text on it clearly. We bypassed everything with a small portable tank, used the fuel line through the cowling. Same result.

Pulse limiter looks clean but I'm not sure how to "check" it for proper operation. I read on another post you could turn the red arrow to up instead of down on the fuel system while at full throttle and if it takes off, them it would be a problem with the high speed jets in the carbs. I dont know what that red thing does but it sounds liek another troubleshooting option. Maybe the high speed jets are not big enough?

I really appreciate the help, I'd hate to have to sink her.

 

[bob johnson]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

Fuel line and primer bumb are all 3/8" ID from tank to the cowling. Inside the motor the line seems smaller, maybe 1/2" but i cant read the text on it clearly. We bypassed everything with a small portable tank, used the fuel line through the cowling. Same result.

Pulse limiter looks clean but I'm not sure how to "check" it for proper operation. I read on another post you could turn the red arrow to up instead of down on the fuel system while at full throttle and if it takes off, them it would be a problem with the high speed jets in the carbs. I dont know what that red thing does but it sounds liek another troubleshooting option. Maybe the high speed jets are not big enough?

I really appreciate the help, I'd hate to have to sink her.

wouldnt you rather have my $1000 than sink her?? then Ill have your headache!...

tricky situation.....one problem is , ( and I have been on both ends of this) is that anyone trying to help you has to assume you did any fix or check 100%...then they go from there.....but the case maybe be that it ends up being somethign you THOUGHT you took care of.


it definately seems to be a fuel delivery problem.....usually that is an easy fix, but you just have to be dilligent in your checks and what you have established as GOOD TO GO..and then work down the line...there are so many places where restrictions or air can get in....

since the primer bulb goes soft...id rule out anything in the carbs or after....( as in maybe a manifold leak)...the red lever is for your primer...the lever is a shut off valve.....and the fuel to that primer hosuing is pressureized by the primer bulb, just like the fuel going to the fuel comopnent bracket assy.....when you hit the primer button( push in the key) you open the door on the other side and gas squirts directly into the manifold...bypassing the carbs.... if you turn the lever up.... you open the door and now it will flow gas diredtly into the manifold constantly as long as the primer bulb is pressureized....( you would not want this to happen very long...or while running, as it might flood the cylinders...( the gas needs to go through the carbs for proper ratio mixing...).....i havent had my ocean runners long enough and luckily havent had all the isses there can be to have experienced every possible problem...but as i think of all those lines and parts....it is easy to think something is being over looked...I become and expert in all the problems i solve on my motors!! defacto!! youll be a much more experienced once you find this gremlin....is the oil dissconnected??? is it possible that the is a cracked piece somewhere.... I had a similar issue....and finally said screew this and went to replace the pump and found that the hose that goes from the pump to the pulse fitting was split!!!....i just replaced the hose and everything was fine...good luck


bob

 

[espdeepblu]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

Hmm... hose from the pulse fitting leaking. Hadn't thought about that one. And now that I am, I wonder about the pulse fitting itself - any chance IT could be the problem and how would you test it to know for sure?

I can't keep driving around at 30 mph, I got passed but a pontoon boat yesterday while troubleshooting this problem. Talk about embarasssing.

 

[espdeepblu]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

well no leak in the pulse hose. I guess I should have thought about that a little more - it runs fine at 3000 rpms and below, just higher and it dies. A bad pulse hose or limiter would have affected all rpm ranges wouldn't it?

Like you said, must be something so simple yet so hard to find.

 

[bob johnson]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

well no leak in the pulse hose. I guess I should have thought about that a little more - it runs fine at 3000 rpms and below, just higher and it dies. A bad pulse hose or limiter would have affected all rpm ranges wouldn't it?

Like you said, must be something so simple yet so hard to find.

i am looking in the book now and for loss of WOT rpm...one of the things it says is: PULSE hose restricted or leaking.. it also says for : plugged pulse fitting.

another dealing with carbs..is this: restricted fuel distribution manifold( where ever that is)
another is flat valve stuck closed, stuck open, float improperly adjusted, float valve installed improperly...there are more... you really need to get a manual

bob

 

[espdeepblu]

Re: 1996 Johnson 150hp Ocean Runner - Almost dies at high throttle

i have the seloc manual for it, but cant find anything like that described in the this one. What book are you finding such valuable insight in? Thansk for the help, i will certainly check all those things again.