Outboard with no spark

PBrook

PBrook

Active Member
Joined
4 Jul 2008
Messages
64
Location
Poole, Dorset, UK
h20-ciaobella.blogspot.com
Hi, I'm sat here scratching my head. I recently bought a second hand Tohastu 6HP 4Stroke (MFS6A2S) as my old 2 stroke had given up the ghost while I was out for a weeks sailing a couple of months ago. It looked fantastic, has been regularly services but took ages to get going. I assumed this was stale fuel so changed that, it was still a struggle to get going but once running was great. The starting got worse and eventually wouldn't go at all. It's now back home for the winter I have time to look at it.
I have changed the plug and now I'm on terra firma I can confirm that there is intermitantly, either a weak spark or no spark at all.
Having looked at the price of coils and CD units and picked my self up again I have decided that I need to test the components to see which is causing me all the grief.
Can anyone help me with how to test the ignition components on these engines? I have a reasonably good multimeter, lots of enthusiasm but absolutely no idea what to do :D
 
Have you tried a brand new plug. That's your first stop. Dirty plugs are not easy to clean.
It's not easy to see the spark and it's strength can be a variable thing depending on the plug gap and your pull.
To measure the spark on my Johnson I made a air gap measuring device. This disregards the plug altogether.
Yes they are nails. The black tape helps you see the spark and I used a jump lead to connect the earth contact to the motor.
You need to check the air gap for your motor.

Sparktester.jpg
 
I have given up messing with outbds, just pay and get it fixed at the dealers.....nothing worse than breaking down.
 
Thanks for the super speedy reply.. I bought a few brand new plugs, and have tried two of them as I know how tempremental they can be (Japanese motor bikes seem to eat them).
I love the tool that you made.. Im just going out to the garage to make one.
I will check this, however I think there is a problem further down in the system... I'll report back when I've done it :)
 
PBrook said:
Hi, I'm sat here scratching my head. I recently bought a second hand Tohastu 6HP 4Stroke (MFS6A2S) as my old 2 stroke had given up the ghost while I was out for a weeks sailing a couple of months ago. It looked fantastic, has been regularly services but took ages to get going. I assumed this was stale fuel so changed that, it was still a struggle to get going but once running was great. The starting got worse and eventually wouldn't go at all. It's now back home for the winter I have time to look at it.
I have changed the plug and now I'm on terra firma I can confirm that there is intermitantly, either a weak spark or no spark at all.
Having looked at the price of coils and CD units and picked my self up again I have decided that I need to test the components to see which is causing me all the grief.
Can anyone help me with how to test the ignition components on these engines? I have a reasonably good multimeter, lots of enthusiasm but absolutely no idea what to do :D
Click to expand...
You need some special equipment
You'll need a peak reading meter or a DVA adapter to use with your meter.

Somewhere on the CDI Electronics website IIRC there is a guide to testing ignition systems.

Somewhere on the iboats forums there is a design for a DVA adapter .

Got to go out so cannot spend much time looking and sadly I dont have any links noted
 
Ah Bugger. I just came back to the thread to suggest the kill cord switch. They are a bit fiddly on these motors and sometimes the "wedge" doesn't do the job properly.
 
Here is the circuit for a DVA adapter

176293d1307240579-johnson-50hp-has-mechanics-stumped-dvacircuit.jpg


Expected readings should be in the troubleshooting link I gave above.


Good luck!

SWMBO now expected to arrive at Liverpool Street 31 minutes late!

Started off in total chaos this morning with trains running half an hour late ( or cancelled)
 
Thanks Guys, I have disconnected the kill switch, that was my first thought. I have just knocked up the air gap tool as per Lake sailor. No spark at all :(
My meter records max / min readings.. will this do the same job as the DVA or do I still need to make the wee circuit? Thanks for that by the way.

I had seen the CDI site and have saved it to my favs but didn't understand what a DVA was. I guess I can get on and check that now.. well maybe in the morning.
 
My meter records max / min readings
Click to expand...

It probably means that it records the max and min readings of a fluctuating input.

What you need to be able to do is measure the peak voltage of pulses. This is what the DVA adapter will enable you to do
 
In my youth a friend of mine checked the spark on his Norton Commando by getting his little sister to hold an HT lead. It only worked once and wasn't very quantitative.

:eek:
 
Dipper said:
In my youth a friend of mine checked the spark on his Norton Commando by getting his little sister to hold an HT lead. It only worked once and wasn't very quantitative.

:eek:
Click to expand...

I didn't realise all your acquaintances were nasty.
 
Remembered I have an oscilloscope :)

While routing round the loft this morning looking for electronics bits I found my old Oscilloscope... Plumbed it all up and the bad news is that I only have about 1V in the low tension side of the coil (Black / Yellow wire), CDI electronics say should be at least 150V. Other readings are ok, does this definately mean I need a new CD unit?

Exert from CDi Electronics,
4, 5 and 6 HP
NO SPARK:
1. Disconnect the Black and Brown stop wires and retest. If you now have spark, the stop circuit has a fault.
2. Test the stator (exciter) and trigger (pulsar) stator coils while connected as follows:
Red Lead Black Lead Resistance DVA Connected
Eng Gnd Black/Yellow 150 V Minimum
Black/Red Eng Gnd 150 V Minimum
Red/White Eng Gnd 3.5 V Minimum
If the above readings are OK and there is no spark, the ignition coil is likely defective.
 
does this definately mean I need a new CD unit?
Click to expand...


Has what you have done eliminated the possibility of a short in the primary winding of the ignition coil?

Have you established that the stator coil is OK ?

I think you are pretty much breaking new ground for these forums.
If I were you I would post on the Honda/Tohatsu/ Nissan board of the iBoats forums http://forums.iboats.com/forum.php

and possibly also the Nissan/Tohatsu board of the MarineEngine forums http://www.marineengine.com/boat-forum/forum.php

If you do the above keep us informed
 
Before you go too mad, the problem in my Tohatsu was the "deadmans switch" which was well ..dead, hence no spark. As this switch essentially earths the output, hence no spark. Disconnect the switch and try again
 
Has the problem been sorted? Same engine, same symptoms here. Unfortunately there are no local outboard dealers here. Spent serious money on the bloody engine already without ever having been able to run it. :(
 
You must log in or register to reply here.

Other threads that may be of interest

N
Integral Battery Electric Outboards… with MORE POWER!
Replies
11
Views
742
ontheplane
O
W
Charging problem
Replies
8
Views
410
lustyd
lustyd

Share this page

Top