Mercury Black Max XR2 150HP won’t rev out

Hi, wondering if any one can help me out with my motor issue.
I have a Mercury Back Max XR-2 150hp. Serial No 0A166611.
When I purchased it the gent said the it ran fine one season then wouldn’t run properly the next. I thought, great I like a project.
I took it to my local boat mechanic who told me that the timing was advanced to make it idle at 2000rpm.
Got it fixed to as best that they could at the time. Told me best place would be to start with the fuel system. So I ordered new carb kits, needle and sets and fuel pump kit. I have checked the reed valves for any chips or any issues. They all look good.
Carbs were cleaned and then run through an ultra sonic cleaner.
Set the timing back to factory (11 ATDC and 22 BTDC at cranking) and found i could only start it with some throttle.
Did some reading. Found that the base timing usually ends up around 6 degrees ATDC. So I have set it at that currently. Seems better at starting but still needs to be a little more tweaked. Idling at around 800 rpm in gear. I will need to drop that back a little to get it to the desired 600-750rpm requirement.
Took it to the dam over the new year break. Did some hull shots. Seemed to stumble then take off. Maxing out at 52km/h (32m/h) at around 4000rpm max. Prop is a 19P Laser II.
Removed the carb covers so I could watch the throttle on progression. It seemed to stutter while constantly throttled on until the carbs opened up and would power off.
The stator has been replaced at some stage. Has a date of April 2001.
Trigger was also replaced dated March 2006.


Thanks Brad


https://www.dropbox.com/sh/xnaxbu0j02hwnwp/AACQFC-UZX51H3x2ZvVT_hexa?dl=0


Hopefully this works. I have some pictures and videos to the motor running


Thank you in advance for any help.

Did your mechanic do a compression check on the ole girl?

XS POWER said:

Did your mechanic do a compression check on the ole girl?

Click to expand...

yes they did. I did ask them if it was ok and they seemed happy. I did do one before I purchased. From memory it was around 120ish psi. I would have to do it again to confirm.

The manual on 3-4 cylinder engines says that 120 is a pass/expect problems point. So you are good to go there. You are correct in your wanting to lower the idle timing to get the specified idle RPMs in F gear, to help in smooth shifting with minimum gear wear.

I didn't see a new fuel filter in your list of replaced items. Suggest you do so and in doing so, cut the old one open. If full of crud. expect that to be your smoking gun. If full of black tiny specs, replace you internal, black fuel lines. If tan chips, and/or pieces, circular in shape, replace the fuel line and bulb from the fuel tank.

There are other potential issues, but what I mentioned caught me on a couple of occasions since I had my head down looking at particular items and didn't back off and view the big picture.

Do a compression test today.---Post value for each cylinder.-------Run with timing light one cylinder at a time observe spark on the light as you go to full throttle.

I had time to watch the first video. Sounds like it's hit/ miss on a cylinder or two. I suggest examine spark plugs closely. You may find the problem cylinder/cylinders. Stupid question....new spark plugs? Really sounds bad to me, 4000 rpm? Not compression problem, seems spark problem. Just my opinion watching your nice video. More users here should post videos, it puts us in the driver's seat. Thanks, good post.

Agreed. You might have to install some conventional plugs (assuming you're using gapless) to read the cylinders. I've used Autolite 303s for that purpose. And you'll need to run it for at least 10 minutes on plane to get a good reading.

Jeff

Get rid of the idles stabilizer, set max timing to 23° at cranking speed, reinstall front induction plate an cover as running like in video will lean out carbs

..."reinstall front induction plate an cover as running like in video will lean out carbs"

Are you sure of this?

Seriously.

Jeff

100%...messes with venturi signal and can/will cause lean running on top end. You can run without it but need to jet up. This is why when you take em off people say they run better as A/F mixture is leaner and 2 strokes love running on the lean side as this is where more HP is produced. When jetting our race motors we actually went down 1 or 2 sizes on high speed and picked up RPM. But these was short runs only and factory motors are jetted to the conservative side for everyday usage.

Hey Pappy, you seen that Merc "tower" on YouTube with the 6 megaphones? Holy crap, eh?
Agreed, you can force in air directly with that opening to the front....especially traveling 35 mph, eh? Gonna "tweak" the mixture for sure.

Thanks. I've run without the hood many times and had "weird" problems. Maybe this is why.

Jeff

Wish I still had all my old pics that burnt up...I had a Twister2 for several years till it broke a crank. Never could find a replacement and sold it. The whole lake knew when I was coming!!!!