Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

[lmuss53]

I put the boat in the water yesterday evening and idled at the dock for 5 minutes or so waiting for my brother to park the truck. I noticed a pretty big slick of unburned fuel gathering around the motor as it sat and idled.

I don't think it is a leaky hose or fitting since the ball pumps up solid without blowing anything out anywhere. I'm also quite certain it's not lower unit oil, but I will check that again today.

The motor runs fine but has bit of a hesitation when rolling the throttle on and I think it would fall on it's face if you tried to pull a skier up.

It hasn't run in about 5 years and has about 2 or 3 hours max on it since going back into service. It was winterized including fuel treatment and fogging when it was put up in '05, and I bought it in April. I'm not noticing what I would consider excessive fuel consumption although I really haven't had the boat at much speed for long. I've run about 5 or 6 gallons of fuel through it since I got it, including 3 gallons with a can of Seafoam in it.

I also have a charging problem with the tach not working and the battery only going over 11.9 volts on the voltmeter sporadically, mostly staying at 11.9 or under.

I have a good mechanic that I am in a fishing club with who is helping me work out the charging problem when we can get together on it, although he is very busy at this time of year.

I'm thinking that I need to get the carbs lined up for a rebuild as soon as possible. I'm putting this up here to see if anyone has any other ideas on this or if you think I should be looking at anything besides the carbs.

 

[clemsonfor]

Re: Unburned fuel it idle, 1990 90 hp Johnson

Re: Unburned fuel it idle, 1990 90 hp Johnson

My 90 150 had the same thing. I rebuilt 2 carbs based on a problem from the last time i rebuilt them, which was just they were not synked right. Anyway it was sheening good and i found a hose that was leaking at the intake. Fixed it and wen t to run it and it was worse, i saw a bowl gasket leaking and it turned out the bowl gasket was leaking because it was to streached and a hole was caught in the gasket on the sealing surface, basically causing an 1/8 inch of the gasket surface not to seal.

 

[Dhadley]

Re: Unburned fuel it idle, 1990 90 hp Johnson

Re: Unburned fuel it idle, 1990 90 hp Johnson

53, cleaning the carbs is a very good idea. Do that before you run it anymore.

 

[lmuss53]

Re: Unburned fuel it idle, 1990 90 hp Johnson

Re: Unburned fuel it idle, 1990 90 hp Johnson

I poked around a little under the hood tonight and noticed the yellow/gray wire on the wiring block was loose and had gotten hot enough to melt some insulation and burn the zinc off the screw turning it a rusty black. I'm probably lucky I didn't get a fire there. I gave everything else a very good going over after finding that. I tightened it back up but I'm afraid of the damage that is already done. I'll get with my mechanic friend one day this week and sort that out, but comments or advice from here is welcomed. I also noticed it has NGK plugs. I don't know how old they are but I know they sat for 5 years and most of the threads you read on here say Champions only for OMC's, so which plug do you all recommend for this '90 90hp?

 

[lmuss53]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Rectifier/regulator fixed the charging/tach issues, volt meter shows 13-14+ and tach now works.

I took the carbs off and cleaned everything and replaced the float valves and seats. I am certain all the little jets were open and clear of any debris. The carbs were actually very clean when I took them apart. I took it out to try it and the engine idled fine, but when I opened it up it pulled real strong up to about 4000 rpm and then fell on it's face. I immediately pulled the throttle back to idle. It sputtered around for a few seconds and the idle cleared up and it ran fine again. I tried it 2 or 3 times with the same result and headed back in. I tried running it up to about 3K and it ran good for a while longer but did the same thing, which makes me think it's running out of fuel on one carb. I didn't try to run it above idle after that. I'm thinking I have a float valve sticking or clogged up somewhat. Maybe I didn't get the hanger right on one of them. I set them to the directions on the Sierra kit and blew through each of them, then inverted them and they shut off like they should. The top carb did leak a little gas through the brass tubes when I first pumped the ball up but it quit after about 10 seconds, and I couldn't make it do it again.

I guess I need to pull the carbs off again and see if something is out of whack in them.

Can I check the fuel pump output without a pressure gauge?

During the rebuild I did find a hole in the line from the tank to the engine that could account for the leaking fuel at the dock. I cut about a 2 foot section of the line out and shortened the hose. Since I found a hole in the fuel line I don't trust it exactly anymore. It looks better that the one I had on with my 50 but I may try the old one to see if it makes any difference.

This is a 1985 J90TL V4 not a 1990 like I said when I started the thread, except for a little mid range stutter it ran fine before I pulled the carbs off. I pulled them because of the fuel I saw at the dock while idling. I have had it on the boat for a month or so and it has had about 15 gallons of fuel through it with no performance issues.

Any other ideas or suggestions?

 

[jonesg]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Take it out and run it until it bogs, have someone spray pre-mixed fuel into the carbs, one carb might be starving.

 

[cday]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I'm having the same trouble you are describing. I rebuilt my carbs, no change. I was wondering myself if the pump was sucking air through a leak in a line, or if the fuel pump was on it's way out. Took it out last night to play with it some more and the fuel pump died completely, lol. Guess I found my trouble.

I noticed with mine, if I was going along and the motor, "fell on it's face", I would pump the bulb on the fuel line and it would take off again.

I have to try to track down a fuel pump today. I'll let you know how I make out.

 

[lmuss53]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I think mine is one carb only, it feels like the other one keeps trying, but I didn't try it more than once or twice because of the warnings about lean and or dry cylinders getting damaged.

What is the output from the pump supposed to be, or what is the pump test procedure?

 

[lmuss53]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

The old Harley guy at works says that I set the floats too low. I did leave them about 1 or 2 degrees above level when I had them upside down. If I don't find any debris in the valves (or anywhere else) I will bend them down to level or just a hair below. Does any one know the measurement on the OMC setting gauge?

I'm kind of surprised that no one has any advice on this??? Are we gonna let the old Harley guy tell us how to fix our OMC carbs?

 

[glengold]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Old Harley guy? that's hard to compete with! As someone mentioned you can diagnose a starved cylinder by spraying a fuel/oil mix down the throat. I've never done it personally but that's what someone mentioned on this thread. I'd try what the old Harley guy said if I were you, then again, I have a boat mechanic to call when I can't figure out what's wrong!! Find out if he can make my 50 sound like a roadster, that would be sweet.

 

[glengold]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Oh yeah, I had to pump the ball to keep mine going when the fuel tank got below 3/4. I replaced all the fuel filters and that fixed it.

 

[cday]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

The old Harley guy at works says that I set the floats too low. I did leave them about 1 or 2 degrees above level when I had them upside down. If I don't find any debris in the valves (or anywhere else) I will bend them down to level or just a hair below. Does any one know the measurement on the OMC setting gauge?

I'm kind of surprised that no one has any advice on this??? Are we gonna let the old Harley guy tell us how to fix our OMC carbs?

Harley guys should know what they're talking about, owning a Harley they have lots of practice working on it, lol.

I put the new fuel pump on mine. No more "falling on it's face". Now at WOT she runs like a trooper. However, I'm still having one problem which seems similar to yours.

If I let it idle for a while, or run at low speed for a few minutes, when I roll on the throttle it bogs for a while before taking the gas. It'll probably get up to about 3000-4000 rpm and stay there for a while, you can hear that it's running rough, after a little while she'll clear up and go right back up to 4800 rpm.

If I'm running at WOT, pull it back in neutral and wait for the boat to come to a stop, then hammer on the throttle right away, it jumps out of the hole and goes to top speed no trouble.

So, it seems to me that the motor is getting to much fuel when operating at low rpms and is loading up the cylinders. It then takes a little while for her to burn off the excess gas when I hit the throttle.

If you figure it out before I do, please let me know what you did to fix it. I may try adjusting the floats as well, but right now the forecast is calling for 30 mm of rain and my boat is in the water, lol. May have to wait a day or two before I get a chance to try it.

 

[Craig-]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Harley guys should know what they're talking about, owning a Harley they have lots of practice working on it, lol.

I put the new fuel pump on mine. No more "falling on it's face". Now at WOT she runs like a trooper. However, I'm still having one problem which seems similar to yours.

If I let it idle for a while, or run at low speed for a few minutes, when I roll on the throttle it bogs for a while before taking the gas. It'll probably get up to about 3000-4000 rpm and stay there for a while, you can hear that it's running rough, after a little while she'll clear up and go right back up to 4800 rpm.

If I'm running at WOT, pull it back in neutral and wait for the boat to come to a stop, then hammer on the throttle right away, it jumps out of the hole and goes to top speed no trouble.

So, it seems to me that the motor is getting to much fuel when operating at low rpms and is loading up the cylinders. It then takes a little while for her to burn off the excess gas when I hit the throttle.

If you figure it out before I do, please let me know what you did to fix it. I may try adjusting the floats as well, but right now the forecast is calling for 30 mm of rain and my boat is in the water, lol. May have to wait a day or two before I get a chance to try it.

Doubt the floats are wrong, you may have an inlet valve not seating fully in the bowl. Decarbing might also help.

 

[cday]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I don't really think it's the floats either. What exactly do you mean by decarbing?

Both carbs were just completely rebuilt. New floats, float valves, seats, gaskets etc....... I even took out all the welch plugs and cleaned in there. Both float valves were closing properly before they went back on the boat, ie. blowing in gas line and turning carb upside down to check that they were closing fully.

Could it be that both carbs are not synchronized properly? Been trying to find a good description of how to do the link and synch but haven't had much luck.

 

[Craig-]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I don't really think it's the floats either. What exactly do you mean by decarbing?

Both carbs were just completely rebuilt. New floats, float valves, seats, gaskets etc....... I even took out all the welch plugs and cleaned in there. Both float valves were closing properly before they went back on the boat, ie. blowing in gas line and turning carb upside down to check that they were closing fully.

Could it be that both carbs are not synchronized properly? Been trying to find a good description of how to do the link and synch but haven't had much luck.

Melt the carbon soot out of it. Sea Foam.

Short explanation: If one throttle plate closes before the other, the other wont close fully causing a high idle rpm. If they close equally they will open equally throughout the rpm range but should not open past full. The ignition timing typically needs to advance slightly ahead of the throttle. You need to do it per spec for your motor, that takes a shop manual.

 

[lmuss53]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I set the carb floats per the OMC gauge and it is not any better.

I put a new complete hose and ball on, new filter, fresh gas, different tank, loosened the gas cap on the tank, capped the oil side of the pump (I thought I had found it there. ) I'm ready to move on the rebuilding the pump.

The motor will run up to speed and you think it is OK and then it just shuts down like you ran a tank out. Pump the ball and it will take off again and you can keep it going by pumping the ball continuously. I checked the vacuum/pulse hose for cracks, or holes but I will look it over real well before I get pump parts.

Now that I think about it this was doing this a little before I pulled the carbs off. Once or twice it would bog out some and then take off again.

Any other suggestions???

Can anyone point me to the rebuild kits for the fuel side of the VRO pump? My VRO is not hooked up, so I just need the fuel side kit, right? Is there a way to check the air pump motor, to see if it is the failed part of the pump?

 

[Craig-]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Late model pump has removable nipple on bottom & O-ring at filter cap.
OMC 0438616
SIERRA 18-7800

Early model pump has no removable nipple on bottom & gasket at filter cap.
OMC 0398514
SIERRA 18-7821

 

[lmuss53]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I appreciate the response Craig, but I might not have been real clear. I do have the VRO pump, it is just not mixing the fuel for me. Those look like parts for the older style ready mix pump, like on my 1979 50 hp 'Rude. I looked but I can't find a Sierra kit for the VRO pump. I guess I could go to the dealer and get OMC/BRP part$$$$$.

I have a blown parts motor at my disposal, I may pull the pump off of it and see what it does, if I can't get pump rebuild parts early tomorrow. I have some friends in from Missouri and the kids want their 'toon ride.

 

[jonesg]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

Fuel pump.

 

[Craig-]

Re: Unburned fuel at idle, not charging, no tach, 1990 90 hp Johnson

I appreciate the response Craig, but I might not have been real clear. I do have the VRO pump, it is just not mixing the fuel for me. Those look like parts for the older style ready mix pump, like on my 1979 50 hp 'Rude. I looked but I can't find a Sierra kit for the VRO pump. I guess I could go to the dealer and get OMC/BRP part$$$$$.

I have a blown parts motor at my disposal, I may pull the pump off of it and see what it does, if I can't get pump rebuild parts early tomorrow. I have some friends in from Missouri and the kids want their 'toon ride.

Sorry, no kits for VRO. I believe there is a thread on mounting just the fuel pump. I have never done it, the early VRO's gave them a bad reputation, but they are great as long as they work and save lots of wasted oil, expensive to replace though.