TOPIC: New boat from Australia

G'day from Australia.

Just inherited an old 1960's Swiftcraft 15" runabout with a Mercury 1150, which if the decals are correct is a 76-78 model. The lower cowl cover says 1500 but after measuring the gaps between the port holes in the cylinders, which are quite thick, pretty sure it makes it a 1150. The serial number plate is long gone and stamped number blank, so probably a replacement block.

The hull is in great condition, cable steering is in great shape. Mechanically I've replaced the water pump,gear oil,spark plugs,rebuilt fuel pump,new fuel and breather balance lines,new stator wiring,fuel pump pulse lines,reset carb floats and cleaned fuel Bowls. Link and sync carried out, idle mixture and speed set as per clams' instruction. Motor starts fine with some choke, great power and hole shot. Can't really fault it.

Now for the issue. While connecting a digital timing light, the rpm's were all over the place, some cylinders were more stable than others, though seemed to jump up, double rpm or more. Has anyone heard of a bad trigger multi sparking per cycle? The switchbox signal sourced tach has also stopped working, one of the original mercury two connection ones. Could this be a switchbox failing?

Another.

Another.

Interior.

Damon,
Have you inspected the inside of the distributor cap for debris that might be causing the miss-firing?
Also check the condition of the center carbon & its ability to move freely while you have the cap off.
The rotor does not come off of its shaft as it is bonded to the shaft.
If you have a small black coil, carefully watch it to see if perhaps the miss-firing is caused by the coil arcing to ground periodically due to a crack that may or may not be visible.
Then check for arcing to ground on the outside of the distributor cap near the sparkplug wire boots.
The sparkplug wires and the primary lead going to the coil unscrew from the distributor cap, but the coil wire pulls out of the coil at the coil end.
Have you taken the steps to test the trigger in the distributor?
If you do not have the procedure to test the trigger, just ask & I will find it and post it.
If you want to try a good used switchbox once these inspections have been completed, I have some and would be willing to mail you one.
If interested, please contact me via my listed email addy.
Please put something relative in the 'subject' line of your email.
Doc Frankenmerc - Keeping Mercs Alive Since 1965

Thanks Doc, I'll check the coil and distributor as you pointed out and let you know. The motor has ran brilliantly the last 10 outings since the good once over, I'm just perplex I can't measure a stable rpm with an inductive timing light and the strobe light is also erratic. I read these beasts can multi spark per cycle which puts strain and can weaken the spark? It's not actually miss firing while running and have ordered a new stator driven Faria tach to use.

Could you post how to test the trigger?

Just remember to move the brown tachometer wire from the brown terminal on the starboard side of the switchbox to either of the terminals on the rectifier that have a yellow stator wire already attached. And,...Set the tachometer on the '6p' setting - not the '6c' position.

MERCURY BATTERY-POWERED CDI TEST
FOR DISTRIBUTOR MODELS, Courtesy of Clams Canino & added clarifications by Dr. Frankenmerc

This test is for the 332-2986 switchbox used from 1967-1978 on all the inlines.

This test assumes your coil is good (most all are).

DISCONNECT BATTERY

1. Turn off ignition (temporarily for safety)
2. Disconnect all 3 wires on the distributor side of the switchbox.
3. Remove the HV (High Voltage) lead from the coil to the center cap (remember it unscrews
from cap)
4. Reconnect that HV center lead to the COIL side only. (this will leave the end with the brass threaded end free to put in position as per step #5)
5. Position that HV lead about 3/8" from ground (block, shrouds etc)
and find a way to hold it there. (I gently grip the insulation of this lead about 2" away from the brass threaded end with a small pair of vise-grip pliers. The weight of the pliers can aid in positioning the brass threaded end about 3/8th inch gap from engine ground - the block)
6. Jumper the brown and white terminals on the dist. side of the switchbox together. (leave them attached to their terminals and add a 'jumper wire' that connects these two colors together)

RECONNECT BATTERY

7. Check that you have +12 V at red terminal.
8. Now,...Turn on ignition and verify +12V at white terminal that is on the red terminal side of the switchbox - (starboard side)
9. Touch the black terminal on the distributor side of the switchbox to ground (the metal case of the switchbox should be a good ground source and a metal screw-driver shank can be used to briefly make this terminal to ground contact) - This temporary contact should cause spark between the brass threaded end of the HV lead and engine ground each time you briefly make the black terminal to ground contact.

If you get a nice spark to jump about 3/8" between the brass threaded end of the HV lead and engine ground in the above test, but when everything is re-assembled and you do NOT get spark to jump at the spark plugs while they are resting against engine ground, suspect the trigger is defective as the switchbox and coil have just proven they are okay.

Doc Frankenmerc

All checked out fine. The distributor body above the rotor was very dirty so I cleaned it up, touched up the terminals in the cap and rotor tip which were very gunked up. Removed and cleaned out the coil and short coil lead so now if should earth better. I did find the magnet around the coil is cracked though all intact could this cause issues??

The motor still starts and runs terrific, idles steady and even though my digital inductive timing light rpm readout is all over the place. It reads accurate, then jumps double and almost tripple. When I move the pick up to different leads it works for a bit, then jumps up.

I guess nothing to worry about at his stage as it runs great, charges the battery fine ans seems reliable.

Installed the NOS Faria tach and works a treat! My 19p prop has wot at about 4,700 rpm and the 15 is right on 5,300rpm so I think I'll stick with the 15p.

Just a bump for my last post, any problems using a coil with Broken but intact magnets?

damonharris,

WELCOME ABOARD, Mate! NICE boat, too.

yours, satx

Can you be more specific about the "broken magnets" there are no magnets around the coil. There is a ferro ceramic core and they often crack. If it is cracked you can get a double spark, that may explain your digital tach variations. It would not show up on an analog tach.

Thanks guys. Dave your probably correct, I think it's the ferrite outer shell, maybe it's just some sort of insulation? Hers a pic ( not mine). It was very hard to get a stable reading from the digital timing light.