'04 150hp XR6 Problem

[fireant21]

Bought a used boat with this motor on it back during the summer. First time I took it out no problems throughout the day. I had my mechanic put in an inline fuel filter and an hourmeter and changed out the plugs. Engine has maybe 60 hours on it. Compression test prior to purchase was all around 110.

The problem only occurs later in the day. I can choke the motor and crank it easily for a carbed motor first thing in the morning. Run around to three or four spots, and then it happens. Usually after 11:00 or so. No matter if I put the engine in gear or are simply idling in place, the motor dies out in 8-10 seconds (it cranks easily just prior to this occurring).

I have to then work and work with choke and throttle to get the engine running again. At this point, it is running rough, vibrating the boat. As I told my fishing partner, I think there are two raccons chasing each other underneath the cowling. I will place the motor in gear and it will rough idle up to plane with a moment or two of hesitation and once on the top end will run like a champ.

I suspect maybe varnish or other problems with the low end jets. The previous owner had filled up once back 4-5 months ago, but swears he used stabilizer when filling up. I have since went through 1 1/2 tanks myself. The primer bulb is firm prior to starting each time. I am just at a loss as to what is causing this.

Thanks for your help.

 

[CharlieB]

Re: '04 150hp XR6 Problem

Describe your start sequence IN DETAIL

Suspect that you are flooding it and making it very difficult to start, once started it takes a bit to clear it out.

Choke/enrichener button is only to be TOUCHED or BUMPED, not held in for more than a heartbeat at a time.

Fast idle, about 1500 - 2000 a minute, till the pistons/engine builds a little heat and rpm raises and smoothes.

Return to idle, drop into gear and slowly advance throttle until up 1500 - 2000 until engine is up to operating temp.

Then WFO

 

[fireant21]

Re: '04 150hp XR6 Problem

not a flooding issue when it starts acting up. I turn the key without pressing in choke and fires right up. As I described, it doesn't matter if you put it in gear or simply idle in place, I have about 8-10 seconds before the motor cuts out. I try and crank it back up without choke and its a no go. I then push choke in once and throttle up to try and get the motor started. Usually this is a 10-15 second process at this point. Motor is vibrating badly, and struggles to idle at the low end. I place it in gear, all the while the motor is still vibrating terribly. Push the throttle forward and it hesitates a moment or two at 2000 rpm, then it smooths out an planes out the boat.

Once I set the boat down after running, it will crank right back up with no problems, but if you let it sit more than 40-45 minutes the problem starts up again.

One item that is a little off, the RPM guage jumps when the bendix doesn't engage consistently when cranking during this process. This may be normal, but its my first Mercury motor after dealing almost exclusively with Yamaha engines for a number of years. I thought the stator may be bad, but it runs well on the top end and only exhibits problems later in the day. Also the ground wire to the battery was not tight when I first ran it and this happened. Tightened that up and checked ground leads to the coils and all looked good.

Thanks for the reply.

 

[fireant21]

Re: '04 150hp XR6 Problem

any ideas?

 

[j_martin]

Re: '04 150hp XR6 Problem

I'll hazard a guess.

It's missing on one or 2 cylinders, or maybe a whole bank. The question is why.

Check compression. Should be even, somewhere around 120 lbs.

Check the plugs when it's acting up. You might need to trolling motor to a shallow spot to work on it. If it's flooding in a cylinder, it'll show up on the plugs.

Things that can cause a miss. basically everything. The trick is to discern if it's mechanical, (compression or reeds) electrical or fuel, and then dog it from there. There's a sequence of tests for the ignition system that someone will post if you need it.

hope it helps
John

 

[CharlieB]

Re: '04 150hp XR6 Problem

Before restarting squeeze the primer bulb after it has sat to see if the carbs are low on fuel.

Possible that the heat soak is evaporating fuel and they are low.

Is the engine level during the time off and during the restart?

Try leveling the engine PRIOR to turning it off AND idle it down to cool a bit before turning it off. Just to see if it makes any difference.

 

[fireant21]

Re: '04 150hp XR6 Problem

Thanks for the replies.

Tried squeezing primer bulb the next trip out after the problems began on the previous trip. Made sure the bulb was firm each time before starting. Also motor is trimmed all the way in. I was trolling around this last time looking for submerged stumps on each spot prior to shutting down.

It is just so odd that it only occurs later in the day, and no problems on top end.

The plugs were just changed 4 hours ago.

Compression was fine and consistent across the board. I reviewed my mechanics check from when I purchased the boat and it was all around 115, not 110 as previously mentioned.

 

[j_martin]

Re: '04 150hp XR6 Problem

Depending on how much your boat leans back at rest, and the angle of the transom, you might want to trim the motor out a bit before you start it.

It's got carbs, so it wants to be level. Also, if you bury the exhaust reliefs in the lake, it'll balk at start.

hope it helps
John