'93 Johnson 90 bogs down intermittently under load

[Montauk_78]

I'm new to the forums and have been reading through hundreds of posts, but haven't found a working solution as of yet. I have a '93 Johnson 90 V4 (Model# J90TLETS). On muffs, the engine runs well and will rev without problem. However, when I get it on the water, it will start normally and then will bog down when I give it throttle. However, at times it will randomly "catch" and stay at full throttle indefinitely. If I go over wake or the boat is bounced at all, the engine bogs down and then it picks back up and runs fine. If I come off the throttle the engine will also then bog down and if it doesn't pick back up to full throttle, it will sputter and if I do not drop it back to idle in time, it will die out completely. It is very sporadic, as sometimes it will advance to WOT after bogging a little bit and other times it will not advance past idle after many tries. Just yesterday, I found that if I go in and out of idle a couple times, eventually it will catch and get up to full throttle. I have a dashboard tachometer and it runs around 1,000 rpms at idle and around 5,000 rpms at WOT. All the fuel lines were recently replaced. The portable gas tanks are new, vents are open and intake screens are clear. Fittings, primer bulb and hose are all relatively new and marine grade. Primer bulb pumps up well and stays reasonably firm during operation - pumping the bulb while running and experiencing the problem does not help. I just replaced the entire run of fuel line hose inside the engine. All fittings seem tight with new and appropriate clamps. No noticeable leaks and no accumulation of any fluid inside the cowling. All 4 sparks plugs are brand new, as are all 4 spark plug leads. Plugs are the OMC recommended Champion plugs. The 2 carbs were just rebuilt with needle, seat, float, etc. all replaced. Float was adjusted to Seloc Manual recommendation. I even removed the core plugs before cleaning and replaced them as well. All jets on these carbs are fixed, so no adjustment is really possible with them. The boat ran fine last summer, but I did the repairs on it before running it this season and it has not been able to run consistently. I thought it might be a fuel restriction, but the boat has a VRO system that should warn me if there is a fuel restriction. I tested the VRO horn and it works fine. The new fuel hose was purchased at NAPA and is their ethanol rated fuel line. I thought maybe it might be a collapsed fuel line, as there is a tight bend where the line comes out of the fuel pump and goes to the carbs, but wouldn't the VRO alert me to this problem or does it only register problems PRIOR to fuel reaching the fuel pump? I would appreciate any advice or recommendations. Thanks in advance!

*Also, all fuel is 89 octane and every tank for the past 4 seasons has been treated with Evinrude/Johnson 2+4 Fuel Conditioner. All attempts to run it have been with fresh gas.

 

[Montauk_78]

Re: '93 Johnson 90 bogs down intermittently under load

In addition...I have read many recommendations about timing and sync. However, all I did was remove the carbs and did not mess with anything else. I left the linkages attached to each carb and simply popped the arm out of the top carb and left it attached to the bottom carb. After re-installing, I just snapped the linkage back in place. Both carbs seem to open up at the exact same time. In addition, at WOT, the little pin on each carb "butterfly" is perfectly vertical. This is, according to the SELOC manual, how it should be. Just to add that into the equation as well, so as to eliminate link and sync as a solution. However, if you can still throw off the sync inadvertently, then please let me know.


*Also, the prop is original on the engine and is still in good condition. I recently removed it and greased the splines. It does not have significant knicks in it or anything of that nature.

 

[emdsapmgr]

Re: '93 Johnson 90 bogs down intermittently under load

A couple of things to check. Your symptoms could be due to a weak fuel pump or air leak in the fuel system. When the engine acts up, have a friend constantly prime the fuel hose bulb. This will force extra fuel around the pump, direct into the carb bowls. If it runs fine while priming the bulb, consider replacing the pump. Also, The ignition could be occasionally dropping a cylinder. An inductive timing light will show the quality of the spark on each plugwire when the engine is acting up under load.

 

[Montauk_78]

Re: '93 Johnson 90 bogs down intermittently under load

I've tried pumping the bulb while running and it does not help. However, I will try and get my hands on a timing light and check the condition of the sparks during the problem. Thanks for the help.