77 Merc 4.5 parts questions

[groovy.dude]

I have been having trouble getting my motor started. It takes a lot of pulling for me to get it running(6-20+ pulls). Last season I went through the carb & replaced the cracked gas lines, reset the float bowl & replaced the impeller.

Once I get it running it runs fine, but at really low idle it will also die on me. A friend suggested that I inspect what I am calling the points, thinking that maybe I am not getting a strong spark. I am not sure if this is the problem or not but I looked at the points and they were in really rough shape. Now I am looking to replace the points but am not exactly sure what I am looking for. i have found some parts places on the internet that have pictures(www.dougrussell.com), but the picture is grainey so I am not exactly sure. I think they are calling the entire assembly a high speed coil. I was hoping that I could just replace the little connector points, but can't seem to find them on the parts list. Does anybody have any insight for me.

Thanks

 

[emckelvy]

Re: 77 Merc 4.5 parts questions

Those points act as a very high voltage switching device for the electronic ign. My manual says it's not uncommon for the points to have a burnt look to them.

I'd expect that if you cleaned up the contact surfaces on a whetstone then polised with crocus cloth, it'd be more than adequate to trigger the ign.

You can check for good spark by sticking a conventional spark plug in the spark plug boot. Make the gap on this plug very wide and lay the plug against a convenient place on the block.

Spin the flywheel as fast as you can by hand and you should get a strong, purplish spark across the wider-gapped plug. If the spark is more orange-ish in color it's weak.

BTW more common to see problems with the little insulating block that connects the points to the ign system wiring than with the points themselves. Also, the ign coils tend to develop cracks which cause spark to arc to ground. You'll see obvious cracks in the outside of the coil and in extreme cases, burn marks. You'd need to unmount the coil to inspect the back side for cracks.

On the Doug Russel parts diagram, what you're looking for is called a "maker assembly", Ref. #23 on the diag. As you can see the "points" are a bit $$pendy at almost $40 retail.

The insulating block that goes bad and causes sparking issues is Ref #33, "insulator, cable to contact housing". At less than $3, a lot cheaper!

I would seriously consider cleaning/gapping the points and replacing the insulator block as the extent of your maintenance under the flywheel. Gap the points at .020".

I don't see any gain in replacing the points as this type of ign system, which "makes" instead of "breaks" to fire, is not as sensitive to contact surface quality.

Your running problem could be as simple as the idle mixture adjustment. These small motors can be quite sensitive to idle mix and if too lean will be very cranky and extremely hard to start.

You should adjust for best, stable idle with the motor warmed up and running in gear in the water. Try to run it on the rich side of the adjustment range (go CCW for rich, CW for lean).

Check your choke to make sure it's closing completely.

And most Mercs need to have the primer bulb pumped up hard before initial startup, to ensure the carb is completely full of fuel.

Anyway, there's a few things to try, let us know what happens...........ed

 

[groovy.dude]

Re: 77 Merc 4.5 parts questions

Wow, you sound very knowledgable. I will try your suggestions. I tried sanding down the points with some light emery paper, but their surfaces were really pitted, and not just burn looking. If I tried sanding them down until the surfaces were smooth I don't think there would be anything left, which is why I am thinking replacement. But there is obviously a spark so i will check the color of it.

Also you bring up an interesting point that, when I cleaned the carb I fully closed the the idle mixture screw & then 1 turn out(I think!, I followed the manual to spec but have a poor memory). But it says you are supposed to make these adjustments while the motor is running. Is it safe top pull the top off the motor once I get it started, or is there a way to get it started without the top cover on?

thanks again

 

[emckelvy]

Re: 77 Merc 4.5 parts questions

I wouldn't worry about a few pits, just clean them up to something generally smooth, degrease, reinstall and gap.

And that "one turn out" setting referenced in your book is only a baseline, you do have to make a final running adjustment to get it tweaked-in. The range of adjustment where the motor'll run well is pretty narrow, so you might be a bit off. I'd try 1-1/4 to 1-1/2 turns out as an initial adjustment.

It is possible to remove the cover while the motor's idling, however the flywheel is very close to the cover's innards and you're likely to get some rubbing !

I've had some motors that ran well enough that once warmed up, you could just spin the flywheel with your hands, and it'd start right up.

If you're very careful you can try wrapping a starter rope around the recoil starter 'teeth' in the flywheel, however be aware they really weren't meant for this and I've had the rope get caught before at the end of the pull. :%

Just a cautionary, usually it'll work fine. Just don't have a real big knot in the starter rope.

Some of the small motors with the recoil in the top had a hole drilled thru the cover, where you could stick a screwdriver thru to the idle mix needle. Unfortunately yours ain't one of them! I imagine it'd be quite simple to drill a hole for this purpose, just be sure to get it in the right place!

G'luck...........ed