Mercury inline 6 150hp rough idle

[sourbsted]

Hi all,
My very old 73 model blue band has a rough idle and misses on when i try to run it on fast idle. Its been out of the water now for over 2 years cause the timing belt snapped. I had it running again soon after with an old timing belt it ran ok, But since I fitted the new belt its been running rough. I also fitted a electric fuel pump that activates when i push the choke button. Saves me pumping the damn bulb all the time!
I'm having trouble trying to find someone to work on her cause of the motors age. I also should add it has 135psi across all cylinders cause it has been re-conditioned..

Mercury Inline Tower of Power 150hp - Holeshot test - YouTube

Just a short video on how it did go before..

 

[Texasmark]

Re: Mercury inline 6 150hp rough idle

Certainly timing needs to be checked. Get a manual, or someone on here to tell you what the numbers are. At idle it is a very low number (BTDC) taken off the top plug wire (#1) and at WOT it is high; like on my later model engine 22 BTDC while cranking, plugs out and throttle wide open. Reason I say that is that if you didn't get the distributor and the crank lined up, before you installed your new belt it could be off and it does matter.

On 2 years sitting crud in the carb could be a problem especially if you used no fuel preservative to protect your fuel system. Besides, I just learned that after awhile it's just good maintenance to pop the carbs and check and clean up. Just solved a tremendous head ache for me.

HTH,
Mark

 

[Chris1956]

Re: Mercury inline 6 150hp rough idle

Idle Pickup timing is 4-6* BTDC. max Spark advance is 21*BTDC. When you installed the timing belt, the distributor can be off 1/2 tooth. That can make the difference in idle quality. Also, as Mark says, dirty carbs will screw up the idle every time.....

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Thanks for the replys.. I will pull the carbies off then. I noticed a small dribble of fuel come out of one the carbies when i turned it off. My guess is either crap court up in the needle&seat or the needle is worn. Then I will check the timing..

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I pulled the carbs off, what a mongrel of a job! I managed to get the top right hand nut off that holds the top carb on without removing the dizzy. Obviously I will have to remove the dizzy prior to fitting carbs again.
I had look at one the needle and seats and it was fine, theres no groove on the needle tapered end. Maybe another one has gunk in it. Is there a procedure anywhere on how to clean these carbs? I can't find my manual anywhere. The filters had a fair bit of rubbish in them..

 

[Texasmark]

Re: Mercury inline 6 150hp rough idle

I pulled the carbs off, what a mongrel of a job! I managed to get the top right hand nut off that holds the top carb on without removing the dizzy. Obviously I will have to remove the dizzy prior to fitting carbs again.
I had look at one the needle and seats and it was fine, theres no groove on the needle tapered end. Maybe another one has gunk in it. Is there a procedure anywhere on how to clean these carbs? I can't find my manual anywhere. The filters had a fair bit of rubbish in them..

Gunk brand has a can and a immersion can in a kit. I never used the brand as it left residue that I didn't like. I preferred Berryman's Chem Tool carb/choke/injector cleaner which comes in liquid and aerosol. Berryman's has some real strong solvents and it will attack paint so if you use it beware. Soaking is the best method for the older Tillotson carbs (opinion) which have passages that aren't as easy to access as the newer VME-XX carbs (opinion).

Soak like at least 24 hours and brush as you can; dismantle what will prior to soaking, clean with soft (brass) brush where you can if needed and blow out with compressed air. The Berryman's leaves little if any residue. For spot cleaning, then you could finish up the process with some aerosol and compressed air. Any you get on your fingers will take the oil out of your skin and an immediate application of hand lotion helps, or wear gloves.

HTH,
Mark

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I went to my local auto store and got some carbie cleaner. They didn't have it in any other form only have it in aerosol cans. I removed the idle tube and mixture screws off two of the carbies one I couldnt remove cause the brass plug is stripped. Both idle tubes appear clean. I'll spray the carbs down soon and then give it a hit with compressed air. All the needle and seats are good, I also checked clearances according to what manual says and all is good.

The idle mixture screws were set at 1&1/4 turns so I hope that's ok. Most of the brass plugs are stripped.
I think I might look into timing next.. the carbies appear to spotless inside not like the last time I pulled them down..
Thanks mark

 

[Texasmark]

Re: Mercury inline 6 150hp rough idle

I went to my local auto store and got some carbie cleaner. They didn't have it in any other form only have it in aerosol cans. I removed the idle tube and mixture screws off two of the carbies one I couldnt remove cause the brass plug is stripped. Both idle tubes appear clean. I'll spray the carbs down soon and then give it a hit with compressed air. All the needle and seats are good, I also checked clearances according to what manual says and all is good.

The idle mixture screws were set at 1&1/4 turns so I hope that's ok. Most of the brass plugs are stripped.
I think I might look into timing next.. the carbies appear to spotless inside not like the last time I pulled them down..
Thanks mark

So what about the one that is stripped? That's 1/3 of your hp.

Mark

 

[Chris1956]

Re: Mercury inline 6 150hp rough idle

You can blow out the idle restrictor tubes on the sidebowl carbs, if you can get the top plug out, to expose their end. No need to remove them.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

You can blow out the idle restrictor tubes on the sidebowl carbs, if you can get the top plug out, to expose their end. No need to remove them.

I'll do that. I got one of the machinists at work to remove the stubborn brass plug. I just have to replace the carb bolts too, my old machanic butchered the old nuts with a screw driver. Hopefully its all good then!

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Well sprayed the jets out with carbie cleaner then gave the jets a blast with compressed air then put it all back together. It started easy ran rough then seemed to go smooth for very short time then went back to how it was. I checked the timing. On a very slow idle it stayed on 6 degrees, that's on the right hand side of the 0 degrees mark. All the leads at the plugs have spark too.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I think its ok now, I turned the idle up and then used the timing light again and set the idle to where it would stay on 4 degrees. It seems to run smooth now.
I don't weather I should get it looked at by pro or just test it out in the water. I've still got to Register the trailer yet anyway..

 

[Texasmark]

Re: Mercury inline 6 150hp rough idle

I think its ok now, I turned the idle up and then used the timing light again and set the idle to where it would stay on 4 degrees. It seems to run smooth now.
I don't weather I should get it looked at by pro or just test it out in the water. I've still got to Register the trailer yet anyway..

Sounds like your efforts were rewarded. Great!

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

Just remember that idle fuel mixture MUST be perfected while ON the water and IN Forward gear. This is necessary to provide the correct exhaust back-pressure and prop load on the motor.

Ensure that all carbs are fully closed and the linkage between then is adjust so that all open exactly the same time. At idle position all carbs are fully closed, all air passes thru the hole drilled into the carb butterfly, now slowly adjust each carb idle screw to achieve the 'Best Idle Speed'. Take your time, make small adjustments and give the motor a half minute to burn off any excess fuel before making another change.

Once at Best Idle Speed the carbs need even more idle fuel to provide the additional fuel necessary for crisp acceleration. Open each idle mixture screw not quite another 1/8 turn. Test acceleration, holeshot, ANY cough, miss, hiccupp, or bog, is proof that even more idle fuel is needed. Make small changes, like just the width of the screwdriver slot and retest acceleration.

Repeat to perfection.

Done. Adjust idle speed still in Forward gear using the idle timing screw on the timing/throttle levers.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Firstly thanks everyone on all the helpful advice.Well after my last post I was planning on hitting water to see how it runs, And then reply with good news.
I tryed to start it today and it won't fire at all. I even put raw fuel into the bores and still no fire. I had a quick read in the work shop manual and it says a faulty trigger starts with erratic idle and then complete engine failure. I havent tested for spark yet I run out of time. I have no idea how the system works. It's never done anything like this before, its always been a pain to start till I put a electronic fuel pump on It. Any ideas anyone?

 

[Faztbullet]

Re: Mercury inline 6 150hp rough idle

Go to CDI website and download troubleshooting manual and also disconnect the mercury tilt switch..

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

It's working again. I squirted fuel into the carbie throats and it started first kick. Ive always had problems starting it on a cold start, I know the bulb needs to be pumped well but most of the time its not enough.
Water test soon..

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

The in-line 6's are well known for their 'thirst' on a cold start.

Firm primer then STAY on the choke til she fires.

Always keep battery cables clean and tight, a slow cranking speed just makes them that much harder to start.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I finally got time to take it out today. It didn't go well, when I tryed to open it up it Boggs down and the revs won't go up at all. It's like it trys to get up on to a plane and it dies, and it stalls if I try to go back to idle.
I tryed to muck around with idle mixtures and it made no difference.
I have a mariner 15 beside the I6 and it was doing the same. I have both motors feeding off the same fuel tank. They are open too, no taps or cut off valves. I disconnected the fuel line on the I6 and the mariner 15 come good. But when I tryed to disconnect the mariner 15 fuel line and run the I6 It run the same. Idles good just doesnt plane.
I tryed to pump the bulb incase it was staving for fuel but made no Differance. I also should add I put a electronic fuel pump in the I6. It connects before the carbies and only works when chokes activated.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I pulled the electronic fuel pump off to make shore it allowed the old pumps to pump fuel while the electric pump is turned off, its good. It's allows fuel to pass one way but not the other way. Next I will test to make shore there is no restrictions in the fuel lines.
There is spark on all cylinders. It was going strong before I pulled it down.
I had a bloke fly past me with an old boat like mine except he had a old Johnson v4 behind his. The way he looked at me.. ggrr..