'75 mercury 1150 bogging out of the hole, when heavy load

[kuehnr]

I have a '75 mercury 1150 outboard 6 cylinder, the trouble I have been having with it is, under a heavy load or pulling a tube from a stop it won't seem to come out of the hole and fire on all cylinders. If I am empty or with a couple of passengers, it will come out of the hole and get up to speed running on all cylinders. I run a mixture of 50:1 with premium fuel, I have changed the spark plugs also. I would appreciate any suggestions. I just purchased the boat not long ago, so I don't know the history on it.

 

[JB]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

Howdy kuehnr. You may be running the wrong prop for your boat under load, though under those conditions I would describe the engine as "laboring" rather than dropping cylinders. You don't mention what boat you are using, but the previous owner may have selected a prop for speed with a light load without regard to heavy loads. If that is the case, check the prop pitch (numbers stamped on the forward hub are diameterXpitch) and drop the pitch a couple of inches, ie: from 21 to 19 or 19 to 17. If you are, in fact dropping cylinders and have the right prop, look for fuel delivery that is inadequate for those conditions or marginal spark. Surf this board for advice on high load loss of power.<br /><br />Good luck.<br />JB

 

[kuehnr]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

Thanks for your comments JB, The pitch on the prop is 17 inch, it is a 17 ft fiberglass modified trihull. It is definitely dropping cylinders, I was down the lake one time and ran it for a while labouring trying to get home, when I pulled the plugs the bottom two were fine, the top four were fouled. Replaced the fouled plugs and all was fine again, with a light load. One other thing, the most trouble I had was on a mountain lake, it has happened on prairie lakes as well, but I don't think I was loaded a heavy as the mountain lake (coolers, fuel etc.) Could it be altitude affecting me?

 

[ODDD1]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

Kuehnr,cornwell is right first place to look is the propeller.with just you in the boat and not towing anything you should be getting 5500 RPM's out of the motor...if not start dropping that pitch number till you get there. every 2 inches of pitch change wiil change RPM approx 900 RPM..... when you acheive that goal and your still having probs..go after the fuel system first....this is a battery CD/distributor system...if it runs at all its usually ok

 

[opaled]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

I have the same engine from 1976... and a similar problem when trying to pull a skier out of the water. Pulling a tube seems fine though. I just bought the boat/engine. We've been out 5 or 6 times, so this is all new to me. One additional symptom. Each time we go out, the engine becomes harder to start. The first time out, the engine started after 2 or 3 revolutions. Second time out, it took about 10 seconds of cranking. Yesterday, the time to start had degraded to about 45 seconds to a minute of cranking. Once started, it runs fine. The fuel filter is brand new.

 

[kev_79]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

Make sure carbs are in sync. If they are off just a little, you won't notice much until you put some load on it. By in sync, I mean same air screw setting, butterfly's on all are completely shut at idle. Sounds like top two (or 4, depends on model) might be running a little rich

 

[Massey]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

Hi Kuehnr, I was reading your article and it just so happens that I've got the same issue with my '76 Mercury 115. I was wandering if you had solved your problem yet? My situation is continuing to get worse, and every time I take it out it's running more and more poorly. I am attempting to find your email address so I can email you directly, if you could please? My email is MasseyFamily4@aol.com Hope you were able to fix your problem, and, hope to hear from you! Thanks, Major

 

[sho305]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

I bought a '73 Merc 150 with no prop. I ordered one and it had a larger diffuser ring than Merc, and made it run very rich. Got rid of that but it still does not go as fast as it should; only 54(or less if hot out) on a light 17' at 5400 with a LaserII 20. The same with a Merc 21 but it has no lift. Laser exhaust ports get it out of the hole better and I can trim anywhere. The tach is right but the speedo could be off. I ran 50 against a jetski and he said about 55. Runs fine and been through everything. However, I think my stator is going as the battery just went dead and it has a new rectifier. Been messing with it for 2 summers now, but it was charging before.<br /><br />If you have plugs going bad it is too rich like he said or the ignition is weak for some reason. With cylinder 1-4 I would check carb adjustments first.

 

[FishermanRich]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

I have vertually the exact same problem at this moment. 115 HP 1989. Runs ok, somewhat rough at idle. When gunned it usually goes to about 1/3 speed and pops another cylinder (or two) for about 1 second in an attempt to go faster. On very rare occasion, when gunned it will make it to full speed, only to run there for about 30 or so seconds before dropping to about half and then another while (5-10 seconds) down again to 1/3 speed. <br />Put inline filter on and using High octain gas with Sea Foam - 16oz to 5 gallons. <br />I did clean gunk out of incoming fuel needle valves on top and bottom carb (center was ok) which had gas spitting out vent hole located on cover of the bowl. Bulb now pumps hard with no gas leaking/squirting out any carb. I also shot gum out through any holes I found. I poured some Sea Foam in each of the bowls. <br />Appears to be in the ignition - sparks only on 1 & 4.

 

[FishermanRich]

Re: '75 mercury 1150 bogging out of the hole, when heavy load

My 115HP Merc is a '84 in-line 6 cylinder Serial #6478920. <br />I just finished a detailed search for this topic and - What A List! Here is the summery of what I found that could be the problem(s):<br />Water in Gas, Junk in tank collecting on fuel pickup screen in the tank, Cracked fuel hoses or connections allowing air into fuel line, Backwards facing primer bulb (not likely), Fuel Tank Vent clogged, Fuel Pump clogged or diaphragm broken - not pumping enough gas - need to pressure test, bad spark plugs, bad wiring, bad distributer, bad stator - frayed wiring under the flywheel, bad CDI or switch box, bad stabilizer module, bad coil, Sticking float(s), clogged carbs - requiring rebuild/cleaning - Check main jets & imulsion tube - reset/check float levels, out of sync carbs, out of timing, crank case vent hose clogged, compression may be bad.