1988 MERC BLACKMAX SLUGGISH FOR 10 MIN

Joined
May 2, 2006
Messages
9
I just purchased a 1988 crestliner with a 150hp black max. I am used to inboards and not too familiar with outboards. The motor starts good but it seems for the first 10 minutes of operation that a jet or something is stuck. <br /><br />At first it planes alright with a speed of about 34 mph. After 5-10 minutes of slowing down and the wot it will cut loose and speed up to 43-45 mph with an rpm from 5000-5200. manual rpm states 5500 rpm. I do live and boat at an elevation of 4500 and the boat has been local from new.<br /><br />I have pulled the jets in the carb, the jets are 074 which seems right. I have run two tanks of sea foam through it but have not run the concentrate. The problem is the same if not worse. I havn't ran a compression check yet but will tomarrow. All the spark plugs look good and the same. I havn't ran the boat for 5 minutes and then checked them before it starts running better though.<br /><br />The carbs have never been rebuilt but will be this next winter unless everything else fails. I have looked through the service reciepts also and havn't seen any replacement of the impeller. I am ordering a repair manually but if there are any other things I should do let me know. My biggest problem is to get it running right.<br /><br />In case you are wondering why the boats name is "NOT FUBAR", is because our last boat was named fubar when my dad baught it and I spent most of my time working on it.<br /><br />Thanks for any help you can give me, awesome site!
 

KCLOST

Commander
Joined
Jun 22, 2002
Messages
2,095
Re: 1988 MERC BLACKMAX SLUGGISH FOR 10 MIN

Check for spark at idle just after start-up...<br />Use a spark gap tester or timing light...<br /><br />Let us know.
 
Joined
May 2, 2006
Messages
9
Re: 1988 MERC BLACKMAX SLUGGISH FOR 10 MIN

I did the decarb on it and it is no longer sluggish at the beginning. the rpm at wot is still only 5000.<br /><br />How much rpm will I loose at 4500 feet alt?<br /><br />manufacture states 5200-5500 rpm.<br /><br />Water temp about 50 degrees, will this affecdt the rpm very much.<br /><br />prop is a stiletto 1419 high performance with a cup?
 

studlymandingo

Commander
Joined
Mar 22, 2006
Messages
2,716
Re: 1988 MERC BLACKMAX SLUGGISH FOR 10 MIN

You may want to post on the props forum, but generally if you can't get the rpms up, you are over-propped. What is the size of your boat? A 19P prop will generally not be oversized for a pretty good sized boat on a 150. You need to state the size of the boat and a good approximation of the weight.
 

andy6374

Lieutenant Commander
Joined
Aug 4, 2005
Messages
1,617
Re: 1988 MERC BLACKMAX SLUGGISH FOR 10 MIN

Two things...<br /><br />Overpropped or no spark on one cylinder.
 
Joined
May 2, 2006
Messages
9
Re: 1988 MERC BLACKMAX SLUGGISH FOR 10 MIN

18'3" and I am guessing it is around 1500lbs. I have pulled the spark plugs several times and I can't see any difference in them but I will change them anyway, thanks
 
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