mercury blackmax 150 power/wot problems

[cam1399]

I have a 1984 mercury blackmax 150. Prop is 23 stainless. It is very slow to plane and will not reach WOT. It will only hit 4400rpm but very slow to get there all trimmed out. I have replaced stator and switchboxes and does run smoother. Before it wouldnt hit 3500rpm. I have cleaned carbs twice with new needle and seats. Bowls are set perfect. Compression is even on all cylinders with 2 different gauges with one being 115 and other 120. Spark seems good. I have pulled coil wires at night and good spark jumps from the wire. New wires and plugs. I pulled plug wires while it was idling and I do not see much if any drop with a few of the cylinders. They are getting fire when I pull them. Plugs are getting wet so I would assume reeds are good? I have synced the carbs best of my knowledge. But I cannot get it to idle unless I screw in the idle stop to start opening the throttle plates. It will not idle adjusting the pickup adjustment. It seems too low. But pickup timing does move when setting timing with light. What am I missing????

 

[Dukedog]

if moving tha idle timin' screw doesn't change tha idle rpm then ya may have a trigger problem.... thats tha only thing that (supposed to) control tha idle speed/rpm................

 

[racerone]

What boat ?-----You may need to go to less pitch on the propeller.-----Or have actual power output of motor tested .

 

[cam1399]

When I am timing it with a timing light it does advance/retard the timing. But when setting idle when it is running, I couldn't get it to idle up.

I bought a 19p prop to try but haven't had it back on water after that and carb rebuild

 

[cam1399]

17.5 winner fish ski

 

[Dukedog]

is this a new ta you rig?.. did it always act this way?.. if tha gear case has been changed there is a chance that its not tha 2 ta 1 its supposed ta be also.. that would also effect tha rpm and hole shot.... it should be a little slow out of tha hole but still should rpm better than that on a winner............

 

[cam1399]

Yeah new to me. It is loads better than it was. With the new stator. I put a 16 amp stator on it and noticed overcharging. I think it had a 9 amp on it. This wouldn't affect rpm would it?

Gonna verify timing and carb sync again and will test on water. I have the seloc manual for the link and sync and timing procedures. Are these correct in this book? I believe it said timing should be 11 adc idle and 18bdc for full advance

 

[Chris1956]

Seloc often makes large errors in their service info. Idle pickup timing should be 0-9*ATDC and max spark advance s/b 21*BTDC. Hopefully the timing procedure is correct.

 

[racerone]

And the timing on these motors normally does not go out of adjustment.----Be very careful if you decide to adjust stuff.----Then again if it was tampered with by a previous owner ???

 

[Dukedog]

don't worry 'bout idle timin' by tha book number.. after ya get it runnin' put it in tha water... on or off tha trailer makes no difference except for what "speed" ya want at idle.. put it in gear and adjust tha idle timin' screw to rpm/speed that makes you and tha motor happy... idle timin' book numbers really mean nothin'..... max is another story.. like chris says 21* max at crankin' is a good number...............

but if what you said 'bout tha idle timin' screw changed "nothing" (up or down rpm) when its runnin' then ya still have a problem......

 

[jimmbo]

While the the Idle Timing is what determines the Idle Speed, there is a Specific Screw on the Throttle Linkage that is used for that purpose. Messing with the other screws will likely Eff things up. Throttle Cable Length will also need Adjusting after the Correct Screw is adjusted.

 

[Dukedog]

That "specific screw" is tha idle timin' screw.............. 10/32 right above tha bolt that holds tha throttle and timing arm on........... cables are tha last thing ta adjust... you adjust tha cables ta fit what tha link n sync ends up as....... idle timin' can be done anytime.

 

[jimmbo]

Well, the OP had stated he had adjusted a "screw' to open the Carbs to get it to idle... A complete link and sync is gonna be needed.

 

[Dukedog]

thats why i went through tha idle timin' procedure..... so yes if he moved any of tha "other" screws he will need ta go back ta square one...........

 

[racerone]

Often folks start adjusting things instead of trouble shooting and looking for the real issue with the motor.

 

[Dukedog]

Often folks start adjusting things instead of trouble shooting and looking for the real issue with the motor.

fact................

 

[cam1399]

I was gonna go back and do a link and sync again. Just clarifying the correct way. After I got everything back together it would idle too low to stay running. That's when I adjusted the idle screw and didn't bring my idle up. Then I run the idle stop in to bring it up to just run it for a few. I'm gonna verify my tdc again and do it all over again.

 

[cam1399]

I've been trying to troubleshoot from what I posed at the top. I have ran out of ideas. That is what led to here for some help on it.

 

[Dukedog]

if you send me an email address i'll send ya an oem manual in pdf.. its for some of tha later model motors but you can us tha 135/150/XR6 (all carb motors) for link n sync, timing.. jus don't use tha timing numbers in that manual.. tha tdc, link n sync procedures are tha same....

 

[cam1399]

if you send me an email address i'll send ya an oem manual in pdf.. its for some of tha later model motors but you can us tha 135/150/XR6 for link n sync, timing.. jus don't use tha timing numbers in that manual.. tha tdc, link n sync procedures are tha same....

That would be great. I appreciate it