1974 Mercury 1150 has new rectifier/stator and now won't idle

bassboy416

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1974 Mercury 1150 was not charging battery. Replaced stator and rectifier. Old rectifier was rectangle with 3 posts. New rectifier does not fit properly it is much smaller and triangular. Marked bolt hole when I took off the flywheel and am pretty confident flywheel is on properly. Timing should not have been changed. Now boat starts and runs but only idles if I advance the throttle. Tach has never worked before and is now working, but it is reading incorrectly. It will occasionally jump from 1000 to 2000 while engine is at a consistent RPM and is not changing. When I read the volts coming from the stator wires my multimeter starts flashing like a strobe light and the most consistent number I see is 18. If I don't advance the throttle the boat will idle too low and will stall out. Could I have messed up some wiring? Do the yellow wires matter which post they go on? Also, boat has always idled PERFECT until now.... NEVER have I had an issue with idle. Ran great last weekend.
 

Chris1956

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A 1974 Merc 1150 will have a battery powered ignition. The stator plays no part in the ignition. Also, unless you removed the timing belt, the timing is unchanged. Normally idle issues are caused by dirty carbs.

The replacement rectifier should also have at least 3 posts. I never saw one that was triangular. The yellow wires will need to be on the AC posts on the rectifier. The case of the rectifier needs to be grounded, and the red wire on the DC post of the rectifier. The tach jumping is likely caused by dirty connections.
 

bassboy416

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This is the new rectifier. The bolt holes in my motor were not the right size to mount this and the bolts were too big to fit through the slots in the rectifier. Had to file out the edge and even now it is only being held in with one bolt on top and nothing on the bottom.
$_57.JPG
 
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bassboy416

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no I did not retime the motor I just put everything back the way it was. Do I need to retime it?
 

Chris1956

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OK, that rectifier is a rectangle, normal looking one. The base of the rectifier must be grounded to the cowling support, or it will blow. If you did not change the position of the timing belt, the timing did not change. Any idea if it was timed correctly before your work?
 

wired247

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Yes. The stator controls the timing. If you change the stator , especially on OLD motors like yours , the timing should be checked and adjusted as needed. Idle timing is going to be set to get the RPM correct at idle but if your idle tiing is off its a good bet your WOT timing is off too which is an engine or performance killer.
 

bassboy416

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timing was correct before my work. I've had it out on the water and it idled perfect and ran perfect at wot. It is a bit of a dog when you go from idle to wot but I believe that to be carb/fuel related. been wakeboarding behind it for over a year... So how do I check timing and adjust if needed? Could it be anything else such as wiring of the new rectifier or the fact that it isn't the bolted in properly? Its my birthday tomorrow and all I want is to get out on the water. any help is much appreciated. I know it runs well i just gotta figure out what has caused this change and how to fix it.
 

Chris1956

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Wired, He should have the two wire stator, on that motor.

BB, Idle pickup timing (just when the carbs are about to open) shoud be 4-6*BTDC. Max spark advance should be 21* BTDC. I would check it if you can.
 

wired247

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Wired, He should have the two wire stator, on that motor.

BB, Idle pickup timing (just when the carbs are about to open) shoud be 4-6*BTDC. Max spark advance should be 21* BTDC. I would check it if you can.



Ha ha . Yep. Almost blocked those things from my memory. Battery powered ignition.
 

bassboy416

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can anybody give me help figuring out how to check the timing on this motor? I talked to a mechanic friend of mine who believes the new stator may have advanced the timing and that its a simple adjustment, but he does not have the ability to do it this weekend.
 

wired247

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Those stators do not advance the timing. Chris1956 is right. Your distributor controls the timing on that motor. After that series motor the stator controls the timing function along with the trigger but yours isnt set up like that. Setting the timing on those distributor motors is a bit of a hassle but its not too bad once you decifer the shop manuals convoluted way of doing it.
 

sam am I

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Question BB, you said you just replaced the stator and rectifier, so.......when running (poorly or not) have you checked that the charging system is in fact now working properly?
 
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bassboy416

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I have tested in the following ways since replacing: 1) tachometer has never worked before and now it is work ing but seems to have a hiccup here and there 2) tested wires coming off of stator (2 yellow ones). Tried ac setting and dc setting and it was flashing like a strobe light on my multimeter jumping all over the place but seemed to be around 18 Vdc. Tested the battery while it was running and I was definitely gaining volts there went from 12.8 before to 13.8 running. The timing has never been off and I didn't change any settings. I thought about raising the idle becuase it would run fine if the idle was higher, but I don't want to run it if the timing is off. Something feels wrong. I'm not certain my old rectifier was bad, so I'm thinking about putting it in just to see if it makes a difference. The new rectifier is not a direct fit and is a replacement for a replacement part. If the stator doesn't have anything to do with timing on this motor, why would anything I did change the idle speed of the boat and why is the tach showing numbers that are higher than the actual rpms of the motor?
 

sam am I

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Hmmmm, can ya snap some quick pic's to post of how the new replacement rec is installed with its associated wiring?
 
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enginepower

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You need a DVA for your meter to read correctly on the stator wires. The voltage is just too high frequency and spiking for meter to capture. Now on the output of rectifier, you should be able to read the dc voltage on that. If the output wire is making your meter go crazy, rectifier is faulty and letting ac voltage get through. This is also what your tach is probably reading off of.
 

bassboy416

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UPDATE: Tonight I pulled the flywheel and inspected the timing marks on the timing belt when at TDC. The marks indicated on the pulley were one tooth off. NOTHING happened that should have allowed this to happen. It ran 7 days ago without any problems besides the battery not charging. Moved the mark so that it lined up which was 1 tooth off and it idled great. Started it up and tach stayed stuck at 2000 without any movement at all. Battery was still indicating charge so I inspected tach wires. All wires (especially red wire) going into the tach were completely shot. Going to deal with this in the morning and test on the water. Timing belt had about 1 inch deflection (1/2 inch on each side). But seriously I don't understand why the timing would have been off if it ran last week great. I'm not feeling real confident in tomorrows outing but I am going to give it a shot. It sure idled better tonight.
 

sam am I

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Cool, glad you found it.......not sure how that goes together but I know certain config's can and have been known to "jump a tooth" if the belt/chain/gears etc are loose/worn........GL
 
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