1984 Mercury 150 hp XR2 rough idle

Hello guys. Sorry my first post is a question. I have tried to search the archives and such but can't find a problem similar to mine, so here we go.

I bought a busted bass boat hull with the above motor. Upon purchase/preview the motor was run with a water hose. Starts great and fast, but has a rough idle and runs rough........smokes like a mosquito killing machine. This motor is/was and oil injection. He (guy I bought from) claims the injection unit went out and he had a mechanic remove the unit and plug the proper holes. He says he mixes the oil/gas to a 50/1 ratio. Ok, makes since I have heard of this being done. Motor had good spark and firing on all 6 cyls. Good compression and equal on all cyls. Motor seemed to be sound and it was a great deal, so I bought it.

I'm now at the house trying to figure out the rough run/idle and heavy smoke. I removed the gas tanks from the boat, removed all the old gas and replaced with premium gas at a 50/1 ratio. Runs a little better, but not much improvement. Replaced all the spark plugs. Helped but still rough and heavy smoke. "He" claims the carbs had recently been rebuilt, but I take this with a grain of salt. This model has no carb adjustment scews, factory set with no means of adjustment, or so my research shows and I can't find any screw adjustment.

I have enough knowledge to be dangerous. I think it is running super rich which is causing the smoke and rough running. Could this be the problem? My next step is to remove and clean carbs, reinstall and hope for the best.

Any help or guidance from any of you mechanic types.

Thanks in advance.

Check the recirc valves as if stopped up will make it run rich at idle and file 13 the advance box...

Thanks for the reply. I don't understand "check the recirc valves". Is this in the carbs? Also "file 13 the advance box". Is this a timing issue?

Again, thanks for the reply and help.

Follow the wee hoses to the intake manifold to find the valves.--------If there is an idle stabilizer in the wiring harness you might want to remove it.

Before you do all of this. Drop the boat in the water and see how it runs. The carbs are set up to run at idle with back pressure from the water that the BOAT is sitting in.

Posting a serial number helps.

Thanks for the guidance guys. It's the holidays so I will be checking the above items Monday.

I can't put the boat in the water because the transom is busted. I mean busted. I was scared to even tow the boat home for fear of the motor falling off. It is still on the boat with the motor sitting in a large barrel of water. I can put the motor in gear for a short time and then it spills out the water.

Here's what I have checked and replaced. The oil injection unit/pump has been removed. Previous owner claims a boat mechanic removed the unit and he started mixing gas at 50-1 ration and had no problems. The boat (as he claims) has only sat for about 3 months. I removed all the old gas and replace with premium and mixed at 50-1 ratio. I have run about 3 gallons of fresh gas through the motor. I replaced all 6 plugs. I have no tester for spark except the "eyeball" test. During the day, it has a sharp blue spark at about 1/2 inch from plug. I tried the same test at night and it seems to be an excellent spark. While motor is running, removing a plug wire at a time causes the motor to miss. I also think the spark is good because the first time I tried, my pliers had a hole in the plastic grip and it "let me know". The compression is 100 on all cylinders but one and it is 102. I removed all spark plugs when checking compression. I checked the fuel pump by removing a fuel line and it seems to be strong. I have a kit for it and will rebuild it Monday.

It has a strong "piss". "He" claims the impeller was replaced recently also. I removed the thermostats and checked them in a pot of water and they seem to be working. I had one new thermostat and it was installed along with one old. I will get a new for the other side. While I had the thermostats out, I reinstalled covers and started motor. It would piss about 10 ft straight out, so I figure the impeller is good for now. With the thermostat back in, it still has a strong steam and is warm, but not hot. The impeller will be replaced when I get it running smooth.

The motor starts fast when you turn the key. Probably just a few seconds and it is running at idle speed. It idles rough and smokes heavily. If the throttle is increased, it is still rough but there is more smoke. I can run the rpms about 2500 for 10-15 seconds and everything disappears in a huge cloud of smoke.

I will be back with more updates next week.

Thanks again for the guidance and suggestions.

It may be possible the two air jets are backwards causing a over rich condition?

Click to expand...

1st there is not enough vent bowl jets to swap and the bigger jets would make it lean not rich....The WH series carbs the smaller the jet the richer the mixture. Pull the recir hoses off the valves under the carbs with a long set of needle nose pliers while running, the spray emitting for it should be a fine mist. If its thick,solid or dribbles out, the valve needs cleaning or replaced...

Need to post serial number as the XR2 had a enrichener.... no choke plates.If its a 1984 is not a Xr2 as theXr2 did not com out till late 1985 and early 1986..

Checking back in and going over my "to do list" tomorrow. Thanks again for my info.

faztbullet, I was told XR2 but have no idea. The serial number is 06481086 and is titled a 1984.

Hope you guys have a fabulous week.

Just a plain Jane 150.....

Good morning. Sorry for being late getting back to you guys with updates, life got in the way.

Thanks to all for the guidance. I live in a small town and we have one main boat mechanic. I have asked him questions in the past. Sometimes he is great with answers and sometimes his answer is “bring it down and let me charge you some money. More on this in a moment.

Faztbullet could you help me understand your first post “Check the recirc valves as if stopped up will make it run rich at idle and file 13 the advance box”? I don’t what/where the valves are located or the advance box.

I started with the fuel pump rebuild since I had a kit for it. The previous owner “claimed” this and carbs had been rebuilt. The pump looked great and did show signs of a recent rebuild. Since I had the parts, so I used them for the re-install. Since I was right there, I thought I would remove the top carb for inspection. It was very clean, no varnish, gunk, and also showed signs of a recent overhaul. I didn’t have any kits, so I cleaned all the jets, orifices, etc. using tip cleaners and air. I also did the other two and found the same results. One thing that did stand out was the main jets for the bowl vent were missing. ALL of them, 2 per x 3 equals 6 jets missing. I noticed this when doing the top carb so I took the disassembled carb with me to the local boat mechanic. (see above comment). He has been in business for 30-40 years so I figured a 1984 would be his thing. He looked it over and commented they were not needed. I replied with “why did Mercury install them if not needed”. So be it. Being an old automotive mechanic, I thought back to car carbs that had a bowl vent tube not metered. So I went with his comment and reinstalled the carbs. To test his theory, I placed duct tape over the openings of where the jets install. It ran the same with duct tape or no duct tape. Is/was he correct? IDK.



Maybe there was something small in the carbs I didn’t noticed during the disassembling and reinstall. The motor now is a little better with smoke at idle, but still produces a lot of smoke at speeds above idle. It still runs rough at any speeds including idle. I’m going with the assumption the mechanic that removed the oil injection unit knew what he was doing, because I haven’t a clue.

I think it was somewhere in this thread that a “bleed line” diagram was posted. I checked my lines with this diagram and they are the same with one exception. It didn’t showing anything off cylinder #2 and I have one. I have tried to modify the original so excuse my lacking of computer skills. Does this diagram makes sense?


(it should say "choke plate thangy" I think that is what it's called)

I think someone has played with the timing on this motor, so that is my next task. Check timing and correct if wrong.

Once again, thanks for the help and thanks in advance for any other guidance

It not unusual for someone to remove the bowl vent jets and will not effect engine operation. The recirc valves are on the manifold plate that carbs are mounted to and where the small hoses attach. These feed puddled fuel from reed block to a cylinder to prevent bogging/idle problems.Pull the hoses off under the carbs and check(earlier post) and diagram looks correct. The idle stabilizer is a black box about size of pack of cigarettes that will be mounted either on plate above carbs or above a cylinder head, it will have a red/white/blk wires that attach to switchbox and this needs to disabled/removed.

I finally had some spare time so I found and disconnected the idle stabilizer. It didn't make any difference to the problem. The motor ran the same connected or disconnected.

I removed and checked 5 recirc valves from manifold. The all seemed to work, blowing from the manifold outward, and the screens were clean. I sprayed a little cleaner in each one and reinstalled. With the motor running, I pulled one hose and it seemed to be more than a “mist”. It was a mist with some heavy drops of fuel. I thought it was spitting a fair amount of fuel out. I then removed all 5 hoses and the motor seemed to a little better, but fuel was spraying all over the motor, so I killed the motor. About 1 minute of run time, the motor and everywhere was wet from fuel. I cleaned up the mess, reinstalled hoses.

I isolated the choke to see if it was adding fuel, but it seems to be working properly.

My question. Is it getting to much fuel (carb problem) and this is causing an excessive amount to be sprayed back out of the valves?

Thanks again in advance for the help.