Merc Black Max 150 Carb Jetting.

[Haoleman]

I recently picked up an Answer craft 18 center console with a cobbled together Merc Black Max 150. The model number on the block freeze plug is 6043178. The carbs on the motor are WH 21-1, 2 and 3. The jets are all .076 for the mains and .050 for the idle jets. I have just rebuilt all the carbs and they are in great condition. The engine is very rich at idle. Looking for suggestions based on sound information to get it tweaked. Compression is 125 on all cylinders.. Thanks!

 

[Faztbullet]

The jetting is correct so the 2 likely issues are : floats are heavy and allowing carbs to flood or idle timing way low..

 

[Dukedog]

The jetting is correct so the 2 likely issues are : floats are heavy and allowing carbs to flood or idle timing way low..

This..... but will add bleed lines and fittings. You also might make sure motor is at least trimmed level or a touch positive when idling....

 

[Haoleman]

Thanks! I also found I had bad fuel so i hooked up a separate tank with new non ethanol fuel. We took it out yesterday and it seemed to idle just ok. We have to idle for about 1/2 mile and when we got out to the bay we added throttle and it died. restart and tried again . It took off and ran under 3/4 throttle for about 15 seconds and then bogged down and died. We did this two more times and went right back into port. we consumed 2 gallons of fuel for this short trip of less than 20 minutes and only 2 minutes above idle. One more thing. the plugs in the motor were NGK BU8H and not thinking these might not be the proper plugs, I replaced them with new ones of the same type. We checked them when we returned and they were all wet with fuel/oil mix. I know with so much idling it is hard to get any accuracy on this. Are these plugs good for this motor or should I be using something else. Might the plugs be part of my problem? Thanks in advance. I am getting frustrated with this motor. I just found out that the air jets are not what the book spec says. The book calls for .092 air jets and the jets in the carbs are .096. How would this affect the operation?

 

[jerryjerry05]

Any letters on the freeze plug?
Approx year?
The plugs are probably right.
Your gonna get fuel/ oil on the plugs.

Do a spark test.
Check the fuel pump diaphragm.
You have the primer on your motor?
Possible the diaphragm in the primer is bad.
After you start it cut off the fuel going to the primer.
Take it for a ride.
If the primer is bad it will flood the motor and waste a bunch of fuel.
Make it run heavy(bogg) and stall.

If you take the carbs off check the reeds for damage.

 

[Dukedog]

Plugs are right. If you are satisfied carbs, fuel pump are right ya need ta start checkin electrical stuff. Switch boxes, trigger and stator. Timing, link n sync. Lotsa things will show these symptoms.............

 

[Haoleman]

Ok, took carbs apart again and cleaned them. My fuel tank has salt water in it! I tasted the crystals in the carb! I have a new six gal tank with fresh fuel im testing with for now. Primer is good and working. I noticed that for the V 150, it lists the main jets as 080. Mine are 076. Also air vent jets are 096 and according to the book they should be 092. What will that do to performance?

 

[Haoleman]

Im going to look at fuel pump diaphram. Check for spark and timing next.. Also the freeze plug has only the listed numbers on itand a big M whici i assume is for Mariner.

 

[Dukedog]

WH21's all six mains .076, all six idle .050. vent 1, 2, 4, 6 .092. 3, 5 none......Vents are really a non-issue

Freeze plug listed numbers? What are they? Where did you find WH21 number?

 

[Dukedog]

Ok, took carbs apart again and cleaned them.

Did you replace ALL GASKITS inside and out including tha little round gaskets at needle seat and jets? No mater how easy they come apart and how good they still look they stand a real good chance of not doin' they're job right tha second n third time around..........