mercury 1150 questions

[Captain Nino]

My merc is only getting 4000 rpms at full throttle- in gear. I removed the engine to rebuild the transom and I disconnected the controll cables. When I put the engine back on I just guessed at the control cable adjustment. Is this the problem? How do I correctly fix this?

When I rev the engine with the Idle arm there is a slight lag. (A well tuned car revs RIGHT as you touch the gas. My boat does not do this- at least with the idle arm.) Is this normal? Is it a problem?

When I throw my boat in gear and open up the throttle- once again- there is a lag. Worse yet; the boat begins to speed up slowly (I hit top rpms about 4-6 seconds after I gun it) Then suddenly Bam! the engine kicks in with its power. After three seconds or so of somewhat lagish exceleration Bam! I'm goin! Actualy though, it plains better before the engine kicks in. then it comes off it's plain a little, but it's still powerful enough to keep it cruisin. I don't understand what is going on. Can this be fixed?

The engine is a 1975 merc 1150 long shaft, electric start . The boat is a 1975 16 foot tri hull Imperial. The engine is very reliable. I only bought it in June but it's never let me down yet....It's just....well....a little odd. Thanx for your help.

 

[daveswaves]

Re: mercury 1150 questions

My merc is only getting 4000 rpms at full throttle- in gear. I removed the engine to rebuild the transom and I disconnected the controll cables. When I put the engine back on I just guessed at the control cable adjustment. Is this the problem? How do I correctly fix this?

You may have too high a pitch prop, the engine should rev at 5200 at wot. I doubt that it is the cable adjustment, but you can look in the carb throat and see if the butterfly is fully open when your throttle lever is fully forward. Engine not running of course.

When I rev the engine with the Idle arm there is a slight lag. (A well tuned car revs RIGHT as you touch the gas. My boat does not do this- at least with the idle arm.) Is this normal? Is it a problem?

Normal,not a problem, the idle arm only advances the timing a bit to increase the idle speed, the carbs open with the main throttle.

When I throw my boat in gear and open up the throttle- once again- there is a lag. Worse yet; the boat begins to speed up slowly (I hit top rpms about 4-6 seconds after I gun it) Then suddenly Bam! the engine kicks in with its power. After three seconds or so of somewhat lagish exceleration Bam! I'm goin! Actualy though, it plains better before the engine kicks in. then it comes off it's plain a little, but it's still powerful enough to keep it cruisin. I don't understand what is going on. Can this be fixed?

Sounds like your engine is either too high or too low on the transom a picture would help.

The engine is a 1975 merc 1150 long shaft, electric start . The boat is a 1975 16 foot tri hull Imperial. The engine is very reliable. I only bought it in June but it's never let me down yet....It's just....well....a little odd. Thanx for your help.

see my notes in your post

 

[Captain Nino]

Re: mercury 1150 questions

The prop is 13X21. The previous owner had about a half inch shim on top of the transom before I rebuilt it. I took it off thinking that it wouldnt matter. I dunno....

 

[daveswaves]

Re: mercury 1150 questions

The prop is 13X21. The previous owner had about a half inch shim on top of the transom before I rebuilt it. I took it off thinking that it wouldnt matter. I dunno....

In my opinion the 21P is too steep for that engine, the engine height looks about right, the extra 1/2 inch would help to unload the prop and get the revs up a little higher. I would see if I could borrow a 17P from a friendly marina and see how that works in comparison to the 21 P. The prop on the engine in my avatar is a 17P, 5200 RPM 45 MPH. Same engine as you have.

 

[flatcat77]

Re: mercury 1150 questions

that half inch shim was bringing it up to cavitation level thus letting you push that bigger prop. after you took out the shim the anti cav plate on your motor is probably lower in the water and there is no way you can pull that much water. i'll go with daves suggestion. to much prop and you wont pull the rpm's. to little prop and you'll top out and not really go anywhere.