Mercury inline 6 150hp rough idle

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I'll do that, I had it planeing a couple of weeks ago with the engine covers on. But yeah a exhaust leak could contribute to it struggling to plane. Motors needs fresh air.I did remove the engine from the mid section, I used new gaskets but all that back pressure from being in water could cause it to leak. Good point!

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

An exhaust leak will cause a significant power lose and suck a lot of fuel, just about fouling spark plugs and possibly leaving a rainbow sheen of unburned fuel in the water.

After dealing with the exhaust, recheck your WOT Timing adjustments, Clams really knows the stacked 6's, follow his advise closely. After setting WOT timing, idle speed is set with the carbs fully closed and adjusted by timing ATDC.

The throttle pickup air gap should be enough that timing advances to around 4 degrees BTDC which begins to speed up the motor and make a little power just as the carbs then begin to open.

Hopefully you already have made SURE the fuel system is CLEAN, including the fuel inlet screens at each of the carbs, the fuel pump rebuilt, maybe substituted a clear section of hose between the fuel pump and carbs just to test and see if any air bubbles are passing thru, which would clearly show any air sucking into the system, is so, find that air leak and tighten the clamp, replace the hose or leaky fitting so it can properly flow fuel, not air, to the carbs.

Lastly, do a web search of your boat hull, find the manufacturers specs for weight, boat, motor, and trailer. Take yours somewhere and weigh it, see how it compares. Wet soggy foam floatation in the hull can add a serious amount of weight and make it difficult, sometimes impossible to get up on plane if too heavy.

Find your leaks and seal them, I've known owners to flood the boat with a couple of inches of water while on the trailer so they could find a pinhole or hidden crack in the hull before they could seal lit up.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Charlie, I attempted clams link& sync on Saturday. I posted a reply on how I went. If you can have a look to see what you think. I couldn't get below ATDC 5 degrees on idle or with starter motor going.
The hull has no foam thank god but, it could well have some serious leaks..

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

After setting WOT Timing (spark plugs out, wires grounded, cranking on the starter)

Reinstall the plugs and start the motor, warm up then start setting idle timing which sets idle speed. You won't get idle speed much under 1000 when on the hose without the exhaust back pressure that you would have with the boat in the water. Final idle timing/speed must be set while on the water. THEN if you check idle timing you should find it near that 4 or 5 degrees ATDC. The number is not critical, idle speed is critical so the engagement dogs of Forward and Reverse gears do not clash so hard as to round off their nice square edges when shifting.

As throttle control moves it advances timing, to zero/TDC, then more toward 4 or 5 BTDC as the carb linkage pickup contacts, then more timing as the carbs are opening until you get to max timing about half the carb opening you hit the timing limit, from there to WOT it just the carbs opening against the timing limit spring.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

So that's why I can't get below TDC, cause the motor has no backpressure. I would get ATDC 5 degrees then if I started to drop the rpm anymore it would stumble and drop off to the 464 marker. So the link sync is done in the water then or test tank..

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

I hope Fazt is reading this.

I haven't seen an idle stabilizer module on a distributor ignition, but............ the way you describe the sudden advance to the 464 when the idle gets too low sure sounds like an advance module advancing timing to increase idle speed. I would really like to see if there is a second ignition box, small black, a little smaller than a pack of Camels, wired into the main ignition.

IF, and this is highly unlikely that it is, but IF it does have an idle stabilizer separate from the ignition it is currently working,

HOWEVER, it is recommended that it be removed as WHEN an idle stabilizer module goes bad, and they do, they advance timing, if the motor is already at max timing, like at a large throttle setting, the extreme advance will almost INSTANTLY grenade the motor.

This occurs on the switchbox ignitions, I have yet to see an idle stabilizer module on a distributor motor, but I ain't seen everything on this planet either.

Fazt??????? Need another opinion here!!!!!!

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I will take pic later.. there's a big box then there's a small box near it.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

It RETARDS to 464 marker when I try to drop the idle very low. Won't hover below TDC at all, just stays around 5-6 degrees ATDC then when I try to drop the idle any more it shoots straight to the 464 marker..

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I took a pic of the electrical system I have.

Here's a pic of the flywheel.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

So when you look at this flywheel decal BTDC 5 degrees is the right hand side of the Zero.. correct? I thought the right hand side of the zero was ATDC 5 degrees. I think I need the factory manual, do they sell them on eBay, on CD, PDF..
Thanks for your patience everyone.. especially Charlie

 

[Maxz695]

Re: Mercury inline 6 150hp rough idle

The fly wheel spins in the picture from left to right making the left side before TDC is it comes in rotation before the 0 mark and fires before it makes it to the red dot. And to the right of the scale the red dot would come after it passes the red dot TDC [/ATTACH] View attachment 178908 View attachment 178909

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

The flywheel turns clockwise.

On the far left the white paint marking between 21 and 23 degrees BTDC for max WOT advance.

The numbers to the right of the Zero are ATDC, idle timing should be on the right side once perfected. The actual number isn't near as critical as the actual idle speed in the water. Without exhaust back-pressure idle speed will increase so you will have to make your final adjustment once launched.

The wiring diagram is correct for your ignition. It does not claim to have an idle stabilizer.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Thanks, I want to get the link& sync sorted. I don't know if the timing light has a fault, when i have the engine idling the light flickers a bit. Like you can see the 5 degree then nothing then it lights up again.
When I had the carbs pulled down, I noticed one out of the three floats was different. It was slightly different then the rest, a bit smaller. They must have problems in the past.

I broke the top starter motor bracket, the "u" shaped one that clamps the starter down. My nearest outboard shop has a genuine brand new one for $47. I wont break that again. Dow..

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

A good weld3er with a TIG can repair most any aluminum bracket, just have to weight the cost vs the new part to decide.

Custom parts and NLA parts, no contest, got to be fixed, just file the edges and a coat of paint, often fit, functions, and looks fine.

I still suspect your major problem is fuel supply and delivery.

Just for giggles, pull the fuel hose off the top carb, point it into a suitable container and crank the motor to watch the fuel stream. You should get a nice fat pulsed stream the diameter of the hose I.D. and at least an inch and a half out horizontally before it begins to arc down. A weakk stream and the upper carb/cyls can run low onfuel within a few seconds, severely limiting power, leaning out the upper cyl making them run extremely hot, possibly damaging the pistons if left WOT in attempt to get up on plane.

Pretty much the same scenario if a main jet is restricted/dirty. Those cyls will be running lean.

The entire fuel system, from the dipp tube picking up the fuel in the tank thru the carbs must be spotlessly clelan and flowing properly because the motor demands full fuel to make full power.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

My mariner 15 was dieing under acceleration. I tryed pumping the bulb, that didn't work. I worked out if the bulb isn't rock hard prior to starting then it may not work well under load. I wonder if its the case with I6. I'll test the pump, and I might install a facet ele fuel pump.

If I let the I6 idle for bit then open up full throttle then it would have a better chance of planeing rather than half throttle than punching to get onto a plane. Just surges.. sounds like fuel.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I work in a non- ferrious foundry. I could get the part made using the old part as a pattern. It's just a lengthy process getting it made. The old part is diecast,can't weld it. Not at work anyway..

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

If it is fuel delivery problem the pump must work better at high rpm. It has two small pumps rather than other I6 that only one..

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

This is my pumps to carbs setup..

When cranked the motor over there was very little fuel coming out. Shocking :0 like a slight dribble. Not much more than a fast dripping tap!
But when hooked up the facet electric pump it was a constant flow, certainly enough to feed the engine.
I stripped down one of these pumps, the diagram looked good, not stretched of brittle.
Could this be the end of I6 drama!! LOL

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I put kits through both fuel pumps, then I started cranking the motor over unfortunetly I got the same result. BUT when I connected the electric fuel pump it did get good fuel flow but also got a lot of air bubbles. (using clear pipe) So there must be air getting sucked from somewhere.
Just got to find out where,shouldn't be to hard.

 

[Maxz695]

Re: Mercury inline 6 150hp rough idle

It may be the quick disconnect seal i would bypass it from tank line to bulb then the first fuel pump and retest or it could be you need to recut the line ends as they may not be sealed. I prefer clamps as opposed to zip ties as they don,t always clamp securely. I,t is possible that the pick up tube in the tank has an issue. Try a poratable fuel can with premix to test. It easier than trynig to remove the pickup if it isn,t the issue.