Mercury inline 6 150hp rough idle

[mr 88]

Re: Mercury inline 6 150hp rough idle

Link n Sync if done properly will fix your acceleration problem as it sounds like your timing is off in relation to your fuel delivery.

 

[CVX20SPRINT]

Re: Mercury inline 6 150hp rough idle

Link n Sync if done properly will fix your acceleration problem as it sounds like your timing is off in relation to your fuel delivery.

There are no accelerator pumps on these carbs,so the idle jets need to be opened up pretty far to get over the transition from low speed to high speed jet when you are trying to get on plane.
I got the identical motor and after I made sure the basics were good a Link & Sync did mine a world of good.Just make sure that when you do the Link & Sync you don't skip anything.Do everything step by step and you will be surprised at the result.

P.S. When I picked mine up(at an OMC Dealer)they figured the reeds were shot and the motor was not worth fixing.I had never had the hood off of one of these motors never mind fixed one and after doing a bit of reading I was able to do the Link & Sync with pretty good results.Other than being a pig to start cold and a fuel hog it has worked well for the last 3 years.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Well I printed a copy of the link&sync I had a good read of it and looked at the motor and from what I can see is the butterflys are not completely closed on idle.
I know this new timing belt I fitted is a lot firmer than the old one. I could rock the top dizzy cogg back and forth with the old timing belt.
I really don't want to adjust anything until I'm shore on what to do..
The weather and work are against me at the moment, so keen to sort this engine out, its frustrating.

 

[mr 88]

Re: Mercury inline 6 150hp rough idle

They liked to be over primed when cold. Squeeze the bulb until it is hard then give it a few more pumps to " force "more fuel into the carbs.This helps the fuel hit the reeds and get to the spark plugs quicker.

 

[quicktach]

Re: Mercury inline 6 150hp rough idle

Sometimes the "de-carbonizer" or "mechanic in a can" that you can get at your friendly Merc dealer or a local auto parts store can perform wonders on getting a motor running smoothly ...makes one heck of a cloud behind your engine though ...not environmentally the best thing....but it does get rid of piston and chamber top crud!

 

[Lone Duck]

Re: Mercury inline 6 150hp rough idle

They liked to be over primed when cold. Squeeze the bulb until it is hard then give it a few more pumps to " force "more fuel into the carbs.This helps the fuel hit the reeds and get to the spark plugs quicker.

On mine I pump the bulb up very hard. Then I turn over engine full idle throttle and full choke ,if it does not fire I pump bulb hard again then turn it over. Starts right away. Works every time. I have got so I do not even try to start first time, I just turn it over then pump the bulb agin and start it. This is just for cold start.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I might buy a bulb first I think. I had a machanic tune it a while back, I really don't want to change anything till I can rule out fuel delivery problems. I have to pump the bulb at least 30 times before it goes hard, its terrible! Is that normal? I got some of that de- carbonising stuff in a spray I will give it a go then..
Thanks everyone for the advice

 

[Maxz695]

Re: Mercury inline 6 150hp rough idle

If the bulb is not getting hard in about 8 to 10 pumps I would first check the tank vent and be sure it is clear allowing free flow and not back suction from the tank. Happened to me.

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

How old is that primer bulb? The check valves must be junk.

Get a real Merc bulb, they have check valves on both inlet and outlet. Most of the aftermarket bulbs have only one check valve and also do not flow as well.

How old are the rest of the fuel hoses? If hardened, replace them with alcohol resistant rated hose.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

Yeah the bulb is very old, I got it with a mariner 15hp I just bought. I bought a new one a short time ago but its gone very hard, like the sun has wrecked it.

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

15 hp?

That 15 may only use a 1/4 fuel hose, I sincerely hope you are not using anything smaller than 3/8 hose all the way from the tank to the motor to feed that stacked 6 or you may fry the motor running it lean. Small hose cannot flow near enough fuel to make any serious HP

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

It's the same size pipe work that I have always used mate..I went to the boat shop and bought a new bulb and fuel line. It pumps up a lot better now, both motors start a lot easier.
I put the boat in the water again the 15hp runs like a charm but the old I6 dies in the arse when trying to accelerate. I can rule out fuel delivery as a problem now.
I noticed when its not in the water **and I try to give it a quick hit on the throttle it misses, breaksdown. ( I know free reving is no good for the motor, I don't rev it hard) link& sync is my next job on the list. Wish I filmed it when I done the water test..

 

[Maxz695]

Re: Mercury inline 6 150hp rough idle

does this engine have a distributor. It sounds to me like either the float level is too low or the timing is off maybe due to a stretched belt

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

............................I went to the boat shop and bought a new bulb and fuel line. It pumps up a lot better now, both motors start a lot easier.
I put the boat in the water again the 15hp runs like a charm but the old I6 dies in the arse when trying to accelerate. I can rule out fuel delivery as a problem now.
.................................................

If the ONE primer bulb feeds BOTH engines, then you still have a fuel delivery problem. Y'ing the fuel hose AFTER the primer is a definate NO NO, once the motor is running the fuel pump sucking will pull air into the fuel system from the carb of the 15 HP, that air leak will not allow the fuel system to keep all carbs totally full, the upper carb will run low then you start having these problems.

T the fuel hose BEFORE the primer bulb and use TWO primers, one for each motor.

To prove this air leak, temporarily install a clear hose between the fuel pump and carbs, run the motor and watch for any air bubbles passing thru. It may take a couple of minutes as priming the bulb will fill all carbs on both motors, but it won't be too long before the fuel level in the 15 gets down 'just' enough for the float to open the needle off the seat, then the bigger motor's fuel pump will start sucking air back thru that open needle/seat, drain that section of hose, then the air starts getting thru the bigger pump and then the upper carb starts getting low on fuel and it starts running wrong.

Just remember to remove that clear hose once finished testing and making repairs as the clear hose is NOT recommended nor approved for fuel use.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

When I tested the motor last time in the water I disconnected the motor I wasn't using. It made the 15hp mariner go better but when I tryed to do the same on the I6 no luck. I even tryed to pump the bulb just before I tryed to get on to a plane.
I found somethings that don't sound good..
I followed the basic link& sync procedure and..
- the throttle butterfly is open on idle (i read its not meant to be)
- with all plugs out except #1 and timing light connected.
- started turning the motor over. I Advanced the throttle till I reached TDC. Then the butterflys started to open ( so the butterflys are suppose to start to open at BTDC 4 degrees?) I wanted to adjust the throttle actuator plate but I don't have the spanner..

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

...................
- the throttle butterfly is open on idle (i read its not meant to be)
...........................................
.......................................... I Advanced the throttle till I reached TDC. Then the butterflys started to open ( so the butterflys are suppose to start to open at BTDC 4 degrees?) I wanted to adjust the throttle actuator plate but I don't have the spanner..

I may be slightly confused by what you have said.

At idle all carbs should be FULLY closed and the carb linkage should NOT be touching. There should be a small gap between the carb linkage and the timing such that the throttle control arm advances timing, raising engine speed and creating power, BEFORE the carbs start to open.

Linkage between the carbs must be adjusted very carefully as having even one carb open even just slightly will cause that pair of cyls to try to accelerate the motor and the other 4 cyls will 'lagging' and not contributing to a smooth running motor.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

When the motor is in idle position the carbs are slightly open and when it reaches BTDC 2 degrees the carbs start to open more. So the carbs not being completely closed in the idle position is no good then? Unless maybe I have idle set to high, but then the carbs shouldn't be opening on BTDC 2 degrees.. I haven't got a tacho either which can makes more confusing..

 

[CharlieB]

Re: Mercury inline 6 150hp rough idle

If the throttle cable is set too tight that will hold the carbs open aand the timing advanced.

Disconnect the throttle cable and see if the linkage will push back farther, let the carbs close and leave a small gap between the carb linkage and timing. If so then readjust throttle cable.

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I'll look at that, thanks.. I wa

 

[sourbsted]

Re: Mercury inline 6 150hp rough idle

I'll look at that, thanks.. I wanna try that clear fuel like test to..