tested boat in water for first time. Need help.

[sti1471]

I just got done replacing my head gasket on my 1984 Mercruiser 3.0L engine. Today was the first time I have put my boat in the water since I bought it to test for leaks and see how the engine ran after fixing it up. On the trailer hooked up to the water muffs, I set the dwell to 32, set the idle at 700 RPM, and set the timing to 6* BTDC. I had a noisy rocker (must have missed adjusting that one when doing valve adjustment). I readjusted the valves again following the mercruiser #3 manual. I started the engine on the trailer, adjusted the idle mixture screw and it was running very smooth, engine was not shaking (like before the gasket repair), idle was at 700 RPM, and it was running great.

Took it to the lake today backed the trailer in the water. Left the boat hooked up to the trailer during my tests in case of a leak or engine issues. I started the boat, and the engine was shaking at idle. I revved the engine to 2000 RPM slowly, and the engine seemed to run smooth at 2000 RPM, but during the slow climb from 700 to 2000 RPM the engine was kind of shaking (slight sputtering). When I brought the engine back to neutral, the engine was idling around 500 RPM then died. I turned the idle screw to raise the idle and started the boat again. The engine again shook a bit. I put the boat into forward gear and the prop turned. I gave it some throttle and the boat responded and pushed against the trailer hard, and the boat felt great then, but when returning to idle it was shaking still.

What might be the problem? I am wondering if maybe the valves to be adjusted again now that it is under load and I have them too tight, or loose? The first time I adjusted the valves after the rebuild, the engine was shaking at idle. I then realized I adjusted them too tight, and readjusted them again to manual specs. then the engine ran great. So the idle on the water this morning kind of feels like it did when the valves were not adjusted right. While the engine was running, there was NO clatter on the valves that I could hear so if they are loose they are not too loose.

during the rebuild I did the following.
replaced condenser
set dwell to 32
set timing to 700 RPM
Disassembled the carb, cleaned from top to bottom, and set float levels to spec.
cleaned carb screens in accelerator well
adjusted choke spring and made sure choke was closing / opening.
added new 91 octane fuel to the gas tank
changed the engine oil
replaced the fuel pump filter.
inspected the dist cap for cracks, arcs and the cap looked brand new.
removed the wires all around the engine cleaning the contacts and replacing corroded connectors with new.
tightened engine belt.
new spark plugs
cleaned flame arrestor
Compression on the engine is;
1- 120
2- 124
3- 130
4- 132


Anything anyone can thing of that might need adjusting that would affect engine/idle between trailer and under load?

thanks everyone.

 

[slag]

Re: test engine in water for first time. Need advise.

Re: test engine in water for first time. Need advise.

My 1989 3.0 liter engine shakes at idle, but once over 1100 rpm or so, smooths out. I think its just a characteristic of the 4 cyl 3.0 liter engine.

 

[sti1471]

Re: test engine in water for first time. Need advise.

Re: test engine in water for first time. Need advise.

The part that has me thinking there is an issue is that it runs so good on the trailer. And on the water, what used to be 700 RPM idle setting setting is now making the engine die at idle. I did not think the carb would have such a different setting between trailer and lake.

I am wondering if the adjustment of the Valves was good enough for the trailer, but once under load it is showing me that they need to be adjusted better or something. I thought the engine might shake, but I did not expect it to shake that much at idle.

 

[Volphin]

Re: test engine in water for first time. Need advise.

Re: test engine in water for first time. Need advise.

Bring up your idle speed to spec in the water and slightly advance the timing. Richen her up a bit on the carb idle screws (out) until she smooths out. Are you sure the choke is opening up all the way and that you don't have a vacuum leak?

 

[sti1471]

Re: test engine in water for first time. Need advise.

Re: test engine in water for first time. Need advise.

Bring up your idle speed to spec in the water and slightly advance the timing. Richen her up a bit on the carb idle screws (out) until she smooths out. Are you sure the choke is opening up all the way and that you don't have a vacuum leak?

I am never sure on a vacuum leak, but I did put new head gasket, exhaust manifold gasket, and carb gaskets on. I would think that if I had a vacuum leak, it would be present on the trailer, but maybe putting a load on brings out the leak.

Yeah the choke plate closes and opens all the way as it gets warm. I think maybe I will give your trick a try and see if moving the timing will make her happy. Is there a timing that I should shoot for? Maybe going from 6* BTDC to 8* BTDC?

Maybe moving the dwell to 30 might help? I think my plate on the engine says Dwell 28-36.

 

[Jim_25]

Re: tested boat in water for first time. Need help.

I have a 1989 3.0 and it does not shake ideal set at 650 while in gear and dwell is 32 timed at 4*BTDC just my 2 cents

 

[sti1471]

Re: tested boat in water for first time. Need help.

your engine is timed to 4* BTDC? I have not heard of many people going below the 6*, I have heard some moving it to 8 or 10* but never lower, this might be worth a try.

however let me clarify, when the engine is shaking, it is while the engine is in neutral idle at 700 RPM, not in forward gear idle. I have not tested the forward gear idle since I left it hooked to the trailer during my tests.

What I think I might try is putting it back in the water on the trailer, start the engine and check the choke again. raise the idle to 700 and check the timing in case it has adjusted for some reason when it has back pressure. Then see if moving the timing to 4 or 8 helps smooth it out. If it does not then I will put it in gear and see how it idles under load.

also I noticed that sometimes when I shift out of gear, the engine cutoff switch will move up to let it out of gear, but then it does not return to center thus killing the engine. If I walk back and push on it a tiny bit, it will spring back to center. Do the springs on these wear out, or is crud build up more likely. However maybe I am not shifting from forward to neutral fast enough.