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PostPosted: 25 Sep 2016, 11:59 

Joined: 13 Nov 2014, 08:01
Posts: 734
Thanks, I am used to inboard engines with centrifugal advance, wasn't thinking of fixed linkages.

Always learning . . .


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PostPosted: 25 Sep 2016, 18:57 
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Joined: 15 Mar 2014, 16:57
Posts: 1915
Location: CT
CedarRiverScooter wrote:
Why does the motor have to be under load to check timing? Isn't it just RPM related? As long as you don't over rev it, why not just do it in neutral?


BECAUSE PAPPY SAID SO THAT'S WHY!!!



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For Sale - Custom Hand Tied Jigs, Bladed Jigs,Custom Rods

2002 Alumacraft 1436LT w/ 1984 Mariner Tiller Converted to Remote & 55# Minn Kota Terrova 12v (removable)

1985 Bass Tracker III - Restoration w/ 1988 Mercury 60hp
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PostPosted: 25 Sep 2016, 19:39 

Joined: 05 Oct 2014, 13:19
Posts: 184
Here is one reason maybe..

My '76 15hp has an upper needle bearing and needs running clearance. And has points. When static checking the timing the magnet in the wheel forces the crank towards the head. When running the load changes 180 degrees on the crank. The points are not exactly 90 degrees from this movement. I have found the timing when not running is different then when running. Had to set the points differently from each other for the timing to be correct when running.

Got a couple of atom point eliminators and all is good now.



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PostPosted: 26 Sep 2016, 08:51 
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Joined: 15 May 2010, 00:38
Posts: 2621
Location: Central Florida
Sinkingfast wrote:
Here is one reason maybe..

My '76 15hp has an upper needle bearing and needs running clearance. And has points. When static checking the timing the magnet in the wheel forces the crank towards the head. When running the load changes 180 degrees on the crank. The points are not exactly 90 degrees from this movement. I have found the timing when not running is different then when running. Had to set the points differently from each other for the timing to be correct when running.

Got a couple of atom point eliminators and all is good now.


On the 1974-1976 9.9-15hp engines the outer plastic ring that locates the mag plate assembly is probably the culprit on the points gap/timing issue. You are sort of on the right track though. The magnets in the flywheel, when running, pull against the coil laminates and will change the gap in the points when the mag plate is loose. There was a bulletin to change out the original plastic ring for a newer Delrin ring. Stabilizes the plate nicely.


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PostPosted: 26 Sep 2016, 21:16 
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Joined: 15 Mar 2014, 16:57
Posts: 1915
Location: CT
Getting that motor positioned relative to the surface of the water was very tricky. 1" too far in and there is too much load & I can only reach 5300 RPM. Pull the truck forward 3" and I don't have enough load & I spike all the way up to 6000 (target operating range 5000-5500). Spent more time adjusting the vehicle on the launch than anything.

Realized my issue with the timing light last time was my mistake - I forgot to ground the motor to the battery that was powering the timing light (pull start).

So after getting that squared away I was having doubts that I adjusted the timing on my 25hp on my boat correctly, same back & forth with the truck on the launch to get the prop load correct. Finally settled and adjusted it to 5800 RPM @ WOT with a target operating range of 5500-6000...I hope that's ok. I haven't gotten out with the new tach to see where I'm at on my boat with the 25hp and a 13P cupped prop - I'm hoping with the little tuning adjustment it should run that much better. I should raise the motor a smidge to get the cav plate to the waters edge while running so it isn't dragging.

One thing I noticed on my motor is the idle adjustment is kinda meaningless as there isn't enough rebound pressure in the timing advance to get the motor to idle under 850RPM. The trigger is advanced 2 degrees from where it should be at idle - perhaps I need a spring to draw it back? I don't see one on the other 20hp I was playing with tonight, but that motor the timing adjustment retarded enough at low speed that the fast idle marks on the flywheel required a little throttle to get them to line up from idle - my 25hp i couldn't find any adjustment that would let it slow down to 700 RPM without me pushing back on it with my thumb.

There is no pressure driving the idle adjustment screw against the stopping point you adjust it off of...ease up on the screw to lower the RPM and all it does is float out in front of the push plate. I even pulled the dashpot off the backside of the throttle cam to alleviate any pressure at all and I still couldn't slow it down. Not that it doesn't hold idle, but its rough as the timing is already advanced to where it should be running 1200rpm but the throttle is closed.

Perhaps my spring needs to be replaced (P/N 17 in the below linked diagram)

http://www.boats.net/parts/search/Merc2 ... parts.html



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I have a marriage license and a fishing license, but I only carry one in my wallet.


For Sale - Custom Hand Tied Jigs, Bladed Jigs,Custom Rods

2002 Alumacraft 1436LT w/ 1984 Mariner Tiller Converted to Remote & 55# Minn Kota Terrova 12v (removable)

1985 Bass Tracker III - Restoration w/ 1988 Mercury 60hp
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PostPosted: 26 Sep 2016, 21:34 

Joined: 05 Oct 2014, 13:19
Posts: 184
Pappy wrote:
Sinkingfast wrote:
Here is one reason maybe..

My '76 15hp has an upper needle bearing and needs running clearance. And has points. When static checking the timing the magnet in the wheel forces the crank towards the head. When running the load changes 180 degrees on the crank. The points are not exactly 90 degrees from this movement. I have found the timing when not running is different then when running. Had to set the points differently from each other for the timing to be correct when running.

Got a couple of atom point eliminators and all is good now.


On the 1974-1976 9.9-15hp engines the outer plastic ring that locates the mag plate assembly is probably the culprit on the points gap/timing issue. You are sort of on the right track though. The magnets in the flywheel, when running, pull against the coil laminates and will change the gap in the points when the mag plate is loose. There was a bulletin to change out the original plastic ring for a newer Delrin ring. Stabilizes the plate nicely.


Yea, I've got the brown ring and I dimpled the pivot boss on the motor to tighten that area up. Thing is the upper crank race area measures no wear and I have tried 2 used and one new needle bearing and all have the exact same clearance at .0045in. So I looked up clearances for needle bearings and that falls where it should.

I did install a spring on the mag plate to hold things from rattling around. That helped more than anything except for the Atoms. I was thinking about adding the charge coil to maybe balance out things but...haven't yet.

I guess timing error running or not, loaded or not is probably motor dependent.



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PostPosted: 27 Sep 2016, 00:23 
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Joined: 15 May 2010, 00:38
Posts: 2621
Location: Central Florida
There were other issues with that vintage of 9.9-15 as well. Some ran well and a lot did not. The engines following 1976 were fantastic in comparison.


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PostPosted: 27 Sep 2016, 08:29 

Joined: 24 Dec 2011, 22:06
Posts: 974
Location: 72032
Use a test prop.


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