1972 mercury 1150 low rpm?

[74sidewinder]

I believe I found the problem. I was checking at what throttle position the engine starts to bog/ won’t accelerate anymore, it would happen as soon as the throttle plates begin to open which seemed weird to me. I found a post saying “if the mixture screws aren’t set properly the carbs won’t switch to the high speed circuit”. I went back to check my mixture screw setting and they were all around 1 turn and even one at 3/4 of a turn :\ I don’t know how I set them that low could have sworn they were all at 1.5. Anyways I was also reading they usually end up in the 2 - 2.5 turns out range. I set mine to 2 turns out, ran it on muffs and it revs up great in neutral, I took the prop off and ran it in a barrel for a few seconds to see if I could get past 3000 rpms and it was great, got up to 5K, and I quickly brought it down to idle ( didn’t want to damage anything ) I’ve never seen the engine rev this high so I think I’m in the clear. Redid a compression test to make sure nothing was damaged by running lean but everything checks out. Will be heading back to the lake in a week and a half to give the boat hopefully one last test.

Just wanted to to post my findings to help someone else if they were having a similar issue. Glad I found the water intrusion that is fixed now as well. Thanks

 

[Chris1956]

When the idle mixtures are set too lean, you usually cannot get anything above idle, in gear She will either stall or simply bog. I have never seen it, but I guess 2 of the carbs could be set rich enough to accelerate, with the other 1 set way too lean to accelerate. Maybe that is what you have?

Setting the idle mixtures richer is the first step, and I hope it works out for you. I would recommend that you start at 1-1/2 turns open and try to accelerate. If she bogs, open the top carb 1/8 turn and try again. If still bog open mid carb 1/8 turn and retest. Then open bottom carb 1/8 turn and retest. Then repeat process top to bottom, testing after each adjustment.

I think you will find that top carb needs to be a bit richer than mid carb, and bottom carb set a bit leaner than mid carb to run fast and smooth.

BTW - mix up some fresh 50::1 fuel to do the tuning. it makes a difference.

 

[74sidewinder]

Thanks I got fresh gas in it, will try that when I head out to the lake next. The top 2 carbs were set roughly the same but the bottom carb was only about 3/4 of a turn out maybe a bit less. I’m sure this is my problem, will post my final results once the lake test is complete

 

[74sidewinder]

Update. Still no luck won’t pass 3000rpm, back to trying to figure this thing out. I have narrowed the problem to as soon as the butterfly’s start to open the boat won’t accelerate no more. The engine sounds the same, speed stays the same, doesn’t chug or anything just nothing else happens. I can open the butterfly’s fully but the engine stays at 3k. I 100% have spark on all cylinders through the rpm range, no water intrusion, great compression, I’m thinking it must be a carb issue.

In neutral the engine will rev fine just not under load. I assume as the butterfly’s begin to open up that’s when the carbs switch to high speed?? I’m thinking is it possible all 3 carbs high speed circuits are clogged? The link and sync is correct, the mixture is correct it idles good and accelerates great to 3k then hits a wall and won’t go further. I’m going to take apart the carb and give them a really good cleaning and recheck the fuel pumps. I also have no fuel filter only the ones on top of the carbs. Should I be running an in-line filter before or after the hand pump?

 

[racerone]

They all rev " great " in neutral.----Checked the reed valves ??---Your location ?

 

[Chris1956]

Those banjo filters on the carbs can get clogged. Recommend you check them for debris. In addition, open the hex bolts on the base of the carbs and see if fuel run out as you pump the primer bulb.

It is a good idea to run an inline filter before the motor. Make sure the fuel line and filter are at least 5/16" ID.

Pump the primer bulb when you want to accelerate. If she then takes off, the fuel pump is the suspect. You have dual fuel pumps?

 

[74sidewinder]

Located in caledon, Ontario, Canada.
I have not checked reeds I’m hoping I can see them with my boroscope once the carbs are off. Engine is in a test barrel with no prop on, with the engine in gear it will rev past 5k no problem ( essentially neutral cause no load ) with the control in neutral it will rev to 3k.

I will I’ll check all the fuel items tonight once I get into it. And yes the 72 model year has 2 diaphragm fuel pumps I guess you call them on the side on the power head, which I rebuilt this past winter.

 

[jimmbo]

Keep revving it, and you won't have worry about it soon.

What is the max timing set at, and what is the Pickup timing? Check to see if the spark is dropping on some cylinders as the timing advances, use an inductive timing light

 

[74sidewinder]

Lol I know bad things can happen quick, only did it once for a split second for testing purposes. Checked reeds they’re all there and not broken. Fuel line is all 5/16 at the carbs and fuel pumps and 3/8 from the tank.

There was was quite a bit of debris on the banjo fittings on the bottom 2 carbs. Opened the hex bolts and fuel came out of all 3 carbs. Didn’t have much timing to fully go through the carbs gonna soak them and blow out all the passages, reset float height as well

As timing advances no cylinder looses spark, checked with an inline spark tester as well as a timing light. Primary pick up is set at 5* btdc, max timing is at 20* btdc

 

[Chris1956]

Do yourself a favor and replace all carb gaskets, inlet needles and seats, plus floats, when you clean the carbs

If the floats are the original foam ones, alcohol will dissolve them. In the floats are the newer hard plastic, check them for cracks.

Just a note, There is nothing special happening in the carbs at 3000 RPM. If you can get past 1200 RPM, the main jets are working. A limit of 3000RPM sounds like a cylinder is still not firing at high speed, or she is overpropped.

There is a way to test high speed cylinder firing. The method is crude. You start with new spark plugs, or clean ones. You run the boat at high speed and kill the motor still at high speed, safely of course. Now you pull the spark plugs and compare them for color and especially water.

 

[74sidewinder]

Rebuilt the carbs, one of the floats were set too low fixed that. All the floats are new as well as needles and seats. Took the boat to the lake today, After fixing the carbs and putting fresh plugs there was no change. Did a high speed run for a few minutes straight and pulled all 6 plugs, all looked good except cylinder 3 and 4 which were soaked with fuel and water, I believe there is still water intrusion on those cylinders. Ran the boat for a few minutes longer than took it home. I removed the plugs once I got home and there was flash rust on cylinder 3 and 4.

I took the exhaust covers back off to see if something went wrong on the install, did notice one spots were water was getting into the exhaust. I didn’t put any sealer or silicone on the gaskets before installing, I think I should have put some on. They are also oem quicksilver/ mercury gaskets orange in colour, was also reading of black glossy ones which has silicone built into them. I don’t believe I got those ones though. Anyway I can use a light coating of silicone to seal the covers and baffle?

 

[jimmbo]

Pull the plug wires and see if performance drops even more. If none, then that cylinder was just hitching a ride

 

[74sidewinder]

I did when I was out on the lake would drop the rpm a bit but not much change when 3 or 4 was pulled, it would make the isle sloppy but the max rpm was still around 3k

 

[Chris1956]

Most don't recommend silicone on Merc gaskets, however, I think you are desperate enough to try it.

Just a note, Cylinders 3 and 4 share a carb. Is there any possibility it is flooding? I think that a longshot, because it is real hard to flood that motor, but worth a look.

 

[74sidewinder]

I don’t think it’s flooding, I siliconed the gaskets with ‘the right stuff’ and it seems to run better. I noticed no water coming out of the centre exhaust port but there was a large amazing of water coming out before. Not sure if this is normal or not picture is attached. Taking the boat out this weekend and will retest and hopefully everything will be good.

 

[Chris1956]

Those square ports are exhaust relief. Water will exit them whenever backpressure is on prop exhaust, say at idle in neutral.