Mercury V6 150hp outboard - need help getting it running

**DanH** · 12-16-2022, 10:01 PM

First time posting; Can anyone help me with a 1986 Mercury 150hp V6 2.0L 2-stroke (s/n A942807)?

The issue: the motor starts and idles, but bogs and dies when put in gear/attempt to accelerate.

Any help is greatly appreciated!

I'm using the Seloc manual (18-01408) for testing and tuning procedures.
I have fresh gas/oil pre-mix in the tank. No water.
Carbs are rebuilt. New fuel lines.
ignition is 100% new (stator, trigger, cd boxes, coils, plugs, rectifier), correct wiring verified per Seloc manual.
Fuel pump is rebuilt (makes ~2.5 psi while cranking the starter)
oil injection has been removed
idle stabilizer box has been removed
reeds are original

My specific questions are:
I still need to do a compression test - what psi should I expect with the engine cold? Is 80-90 psi good enough?
I don't see any way to index the stator to the block; is there a method? If it starts and idles, can I assume it's right?
Concerning the bleed lines; the check valve in the air box was damaged/blocked. I assume it should flow air towards the engine, correct? The replacement part I got (p/n 21-426585) does not fit the existing hole in the air box...so I'm not 100% sure it's the right one.

Again, thanks in advance for any help!!

Thanks!!
Dan

**rgsauger** · 12-16-2022, 11:45 PM

Welcome to the forum, DanH! Glad to have you aboard.

#1, do the compression test. Always nice to have the motor warmed up a little bit. Pull all spark plugs out and ground the bodies when you spin it over. Good healthy battery and the throttle should be wide-open. In a perfect world, you will see 110 to 120. Anything under 100 is getting pretty tired. Has the motor been sitting for a long time? If so, you can spray each cylinder with a lot of sea foam and let it sit for an hour or two and then warm it up again. That can do wonder to clean the carbon out of rings.

next, have you checked the timing?

The good news is that it starts and idles. We will get it figured out.

**Baker343** · 12-18-2022, 12:13 PM

I agree compression and timing check. Make sure the timing arm to the trigger is moving freely and not bidding.
Is this your running engine that you changed parts on or new to you

**pcrussell50** · 12-18-2022, 10:01 PM

Your motor identifies as a 1986 XR2. I have one too, and the cylinders on mine measure out at 118-120 psi, (except for the top two, which measure out at 105 and 90). Even still, I managed to tune the motor so it runs pretty well. I've used it that way for several years in fact.*

1) Are you certain of the origins of the,

"ignition is 100% new (stator, trigger, cd boxes, coils, plugs, rectifier)"

There is a lot of cheap crap out there that is marketed in a slick way, such as $50 Amazon switch boxes that use the term "CDI" even though they are not actual CDI branded (the real stuff costs five times as much). The cheapos can be risky to use. People here who know way more than I, have even reported that engine destruction could result from cheap switch boxes that do not behave properly.

2) Did you do the carbs yourself? Once I learned how to do it myself I don't even want to pay someone to do it, even if they know ten times more about outboards than I do. It's just one of those deeply personal things like I imagine packing your own parachute would be (I don't skydive, just using a metaphor). When I do carbs, I take the kind of time that would be very expensive at a shop. Otherwise, if you have deep trust in your mechanic then that is next best.

This leads up to...

3) What kind of testing did your mechanic do, that he did not catch a failure to rev?

4) "Link and sync": make sure the carb butterflies open fully at WOT, and make sure the timing arm advances to full, when you move to WOT, and that it retards to where it should when you close the throttle. I have a motor where the trigger is stiff and hesitates going to full when I go to WOT, (it's a Yamaha two stroke not a Merc, but the concept is the same). It eventually catches up at WOT, but it will continue to be maddening until I get it sorted.

5) I bet reeds are not your problem, but if you bought it used... Nothing wrong with stock reeds as long as they are healthy, but if it were mine and bought it used, I would have the intake off to inspect the reeds because I sleep better at night knowing I've looked. And as long as I'm doing that, I get CCMS reeds anyway. I've never had a stock reed fail. But I like the peace of mind of fiber reeds.

**Everything I have said here takes second place to the legends if they differ from me

*I finally bought another motor from the same generation as my 150XR2 , that is 120 even on all six. And I'm putting my money where my mouth is: I've done the carbs thoroughly, checked and replaced the reeds with CCMS fiber reeds (even though the stock steel reeds looked good), and like you, all the ignition components looks brand new... But unless I can verify their origin, it's all gong on ebay and I'm going to pay through the nose for stuff I trust.

-Peter

**rgsauger** · 12-18-2022, 10:15 PM

What he ^^^ said X2

**OnPad** · 12-18-2022, 11:35 PM

I thought that was normal for a carb merc, at least it idles.
Just kidding around! Kinda!

Stator and trigger wires come straight out the back of
engine.

Can't say about your check valve in bleed hose? Don't have that vintage, or service manual. My later service manual doesn't show a check valve.

You can take your airbox off, and check for misadjusted floats at problem rpm. They could not be closing and flooding your engine,or you might be fuel starved. Anyway it should be evident if you watch your fuel flow.

X4 on setting the timing after electronic replacement.

Everyone gave good advice above.

**DanH** · 12-19-2022, 09:53 PM

Thank you!! I appreciate all of your responses.

The compression test was telling....and unfortunate. It reads 75-85 psi all around while warm. I consider this motor a fun learning experience/DIY project and I'm not too concerned (mentally or financially). I will be contacting a good rebuild shop for a power head rebuild. I'm determined to make it "scream and fly"!

Happy Holidays!
Dan

**Baker343** · 12-19-2022, 10:19 PM

Originally Posted by DanH

Thank you!! I appreciate all of your responses.

The compression test was telling....and unfortunate. It reads 75-85 psi all around while warm. I consider this motor a fun learning experience/DIY project and I'm not too concerned (mentally or financially). I will be contacting a good rebuild shop for a power head rebuild. I'm determined to make it "scream and fly"!

Happy Holidays!
Dan

In my opinion that compression will still run, not great but will not stall. Make sure you have no other issues.
You never confirmed this engine is new to you

**David - WI** · 12-19-2022, 11:06 PM

Originally Posted by Baker343

In my opinion that compression will still run, not great but will not stall. Make sure you have no other issues.
You never confirmed this engine is new to you

I agree.
Also, do you have a "good" compression gauge... where the Schrader valve is in the end of the hose that screws into the spark plug hole? Otherwise it will read low.

**rgsauger** · 12-20-2022, 12:22 AM

Has it ever run well or new to you? Has it been sitting? If so, then sea foam may get some of your compression back for you.

**rock** · 12-20-2022, 08:09 AM

When I see comp numbers that low and consistent, I immediately suspect gauge.

Rock

**David - WI** · 12-20-2022, 10:27 AM

Originally Posted by rock

When I see comp numbers that low and consistent, I immediately suspect gauge.

Rock

That's what I was thinking.

**Jim Speros** · 12-20-2022, 04:47 PM

Link and sync is so very important. All the new parts and work amounts to nothing without linkage set up properly. Low compression as stated by others will still run. If in fact it is really that low. Was compression gauge a screw in type or press to seal basic type?

**Glastron1987** · 12-20-2022, 10:42 PM

Yeah I don't believe that gauge either. From what I've seen usually a cylinder or two are bad, not all evenly low.

**DanH** · 12-21-2022, 01:13 AM

Update - I will obtain a different compression gauge and test again.

History on this motor: This motor ran for a few years after we bought it (cheap/used). It quit while running. Cause (or maybe the result): cylinder #2 piston was fried. With nothing to lose, I disassembled it to determine if it was rebuildable. I cleaned the block and ran a ball hone thru each cylinder. The results were decent enough for me to reassemble it with new pistons, rings, gaskets, bearings and seals. It was cleaned, lubed, torqued and sealed per the book. (I did look for a machine shop before doing all this. I called about a dozen...and nobody in my area would agree to work on it.)

Please note: I am fully aware of the risks involved in DIY work. My expectations of the results are aligned with that. I have no regrets doing this work myself. This motor is a fun and educational project and I can easily afford to play around with it.

In the meantime, I tested for spark again. Using a 1/4" gap tester, I got spark on all but #6.
Swapped #6 and #4 plug wires; no change.
Swapped #6 and #4 coils: no change.
Checked all coil grounds; all good.
DVA voltages (while cranking) on each coil are as follows:
1 = 141
2 = 116
3 = 139
4 = 138
5 = 139
6 = 3

I swapped CD boxes; no change.
Performed OHM and DVA tests on the new CDI Electronics trigger and stator.
Battery voltage was at 12.6 or higher during these tests.
Kill wires were disconnected during these tests.
Stator:
blue = 2050 (range 2000-2500) DVA = 209 (good >180)
blue/wh = 2104 (range 2000-2500) DVA = 210 (good >180)
red = 48 (range 27-55) DVA = 24 (good >20)
red/wh = 48 (range 27-55) DVA = 25 (good >20)

Trigger
BLK/Brown-YEL/Wht = 935 (range 800-1400) DVA = 4.0 (good >4)
BLK/Wht-YEL/Purple = 890 (range 800-1400) DVA = 3.3 (good >4) - I plan to retest this one. And maybe ask CDI about it.
BLK/Purple-YEL/Brown = 898 (range 800-1400) DVA = 4.0 (range >4)
BLK/Brown-GND = open (2.5M)
BLK/White-GND = open (2.5M)
BLK/Purple-GND = open (2.5M)
YEL/Brown-GND = open (2.5M)
YEL/White-GND = open (2.5M)
YEL/Purple-GND = open (2.5M)

Thanks,
Dan