tower of power rpm's

[octaneforce]

i have a 1984 mercury inline 6 115. i finally hooked up a tach for the first time to it, and when i was out today it only got up to about 4200 rpms. this motor sounds great and seems to be revving high enough, but shouldnt this motor get closer to 5k? the previous owner said he had the timing at 18 degrees to prevent pre detonation, could that cause me to lose rpms? the thing runs so good that im actually beginning to think that the tach is off. but if not, feel free to run any other suggestions by me. -thanks

next time im out ill find out how fast im going and what prop i have. that can be used to find out rpms, correct?

 

[Chris1956]

Re: tower of power rpm's

WOT RPM should be 5500-5800. 18* max timing will cause reduction in max RPM. Normally we set them at 21* max advance.

The prop pitch and GPS speed can help to detemine RPM, but that will be based upon guessing what the slip is.

 

[octaneforce]

Re: tower of power rpm's

how do i advance the timing a little? ive never tried doing that on these motors.

 

[Chris1956]

Re: tower of power rpm's

There is a link and synch procedure for your motor in the FAQs. You will need a timing light and a fairly accurate way to measure from top of piston to cylinder head, in order to make sure the timing pointer is accurately set.

 

[octaneforce]

Re: tower of power rpm's

what is the timing set on these motors from the factory?
also, could i just adjust the spark advance screw until it runs better while somebody else is driving the boat?

 

[daveswaves]

Re: tower of power rpm's

what is the timing set on these motors from the factory?
also, could i just adjust the spark advance screw until it runs better while somebody else is driving the boat?

You could, but its a long paddle back. They tend to run absolutely wonderful just before they melt down.
The factory timing is on the faceplate of the engine and is likely 23 degrees. That is too much for todays fuel. The previous owner had the right idea but overdid it. 21 degrees is a better target. You really need to check your prop pitch.

 

[octaneforce]

Re: tower of power rpm's

You could, but its a long paddle back. They tend to run absolutely wonderful just before they melt down.
The factory timing is on the faceplate of the engine and is likely 23 degrees. That is too much for todays fuel. The previous owner had the right idea but overdid it. 21 degrees is a better target. You really need to check your prop pitch.

well if i adjust the max timing just until it gets closer to 5k, that shouldnt cause pre-detonation and blow it up, could it? currently, if i push the throttle forward on the controls while the motor is off, the max timing screw appears to max out at around half throttle. and your right about the prop, i gotta figure out what it is

 

[daveswaves]

Re: tower of power rpm's

well if i adjust the max timing just until it gets closer to 5k, that shouldnt cause pre-detonation and blow it up, could it? currently, if i push the throttle forward on the controls while the motor is off, the max timing screw appears to max out at around half throttle. and your right about the prop, i gotta figure out what it is

If you were being directed by a GPS right now it would be saying.."re calculating" make a U turn.

You are off track. In fact, the timing is all in before the throttle butterfly opens. Take the easy steps first. Check the prop pitch.

 

[octaneforce]

Re: tower of power rpm's

just found the box that my prop came in. it says 13.25 x 17.00

 

[daveswaves]

Re: tower of power rpm's

just found the box that my prop came in. it says 13.25 x 17.00

You certainly should be spinning closer to 5500 with the 17P.

 

[octaneforce]

Re: tower of power rpm's

yeah i agree. i could put the motor in neutral and pin the throttle, and it will only go up to 4200 rpms. i know its unhealthy to do that but i guess i just got too curious today when i was messing with it. either my tach is off, or this motor is not getting up to the correct rpms.

 

[daveswaves]

Re: tower of power rpm's

http://forums.iboats.com/showthread.php?t=168855

Follow this link to find the link and sync procedure. If everything checks out you need to check your timing.

 

[Gomer50]

Re: tower of power rpm's

I dont know about the 1150 inline 6 but on my 78 90hp inline 6 on the front cowl support it say's 21 degree's max advance @ 5000 rpm.I dont know how heavy your boat is etc. but a 17 pitch prop should turn that motor easy up into the 5000+ rpm range.

 

[octaneforce]

Re: tower of power rpm's

http://forums.iboats.com/showthread.php?t=168855

Follow this link to find the link and sync procedure. If everything checks out you need to check your timing.

everything checks out pretty good. the previous owner set the timing before he sold it to me, so he must have followed all the instructions. i guess i am just a little confused as to why i cant just back up the max advance screw a few turns to see if i can get some higher rpms.

 

[Chris1956]

Re: tower of power rpm's

Did you tell us what kind of boat you have and it's weight? Weight, prop pitch and hull design will limit RPMs on boats. Is the motor running on all 6 cylinders? Is the compression even and above 100PSI on all 6 cylinders?

If you simply advance the timing, and you overdue it in error, the motor will blow up. Why is it you seem to be obsessed with doing that?

 

[daveswaves]

Re: tower of power rpm's

everything checks out pretty good. the previous owner set the timing before he sold it to me, so he must have followed all the instructions. i guess i am just a little confused as to why i cant just back up the max advance screw a few turns to see if i can get some higher rpms.

We are trying to help you save your motor. You can do whatever you wish, its your motor. Sorry we cannot help you.

 

[octaneforce]

Re: tower of power rpm's

Did you tell us what kind of boat you have and it's weight? Weight, prop pitch and hull design will limit RPMs on boats. Is the motor running on all 6 cylinders? Is the compression even and above 100PSI on all 6 cylinders?

If you simply advance the timing, and you overdue it in error, the motor will blow up. Why is it you seem to be obsessed with doing that?

the boat is a 1970 17ft formula with a serious deep V hull. it weighs just over 2000 pounds without the motor (its a pretty dense boat). the motor sounds like its firing on all 6 cylinders, and the compression is about 115 on all the cylinders. i guess i seem to be obsessed with fiddling with the timing advance screw just because its so damn tempting! its getting nicer out by the day and i was looking for a quick fix. sorry i sounded so ignorant by suggesting it several times. im sure a few of you guys can sympathize with me. im gonna take this thing out of the water this week and do everything properly. i really appreciate all the help so far.

 

[daveswaves]

Re: tower of power rpm's

With thanks to Wayne, the one on the right is what happens when you melt down.

 

[Nidz]

Re: tower of power rpm's

Post Removed

 

[daveswaves]

Re: tower of power rpm's

Nidz, please start a new topic, thanks.