Outboard with no spark

[CAPTAIN FANTASTIC]

I have a Tohatsu 6hp 4 stroke for a few years without any problems at all, however, my one year old Mercury 3.5 hp, which is a Tohatsu with a Mercury label, went wrong after few months and was cutting out when hot, the problem was the cdi ignition which was eventually replaced by the dealers and now its fine. So the ignition packages do go wrong and can perform unpredictably.

 

[2nd_apprentice]

It seems the CD unit costs ~100 quid, not keen on spending that really!

Also read something about an "exciter" which could and in fact did go wrong on an identical engine

It turned out to be the exciter coil. The resistance was about half of what it should have been. Although it had a spark it wasn't man enough. The new exciter was a doddle to fit and the engine has been fantastic all this season.

 

[2nd_apprentice]

That's odd, having done a google image search I remember seeing this exciter coil on board. I think my engine has been fitted with an optional alternator which might explain why the exciter coil was replaced. I really need somebody to have a proper look.

 

[CAPTAIN FANTASTIC]

In my case the engine was still under guarantee, however, when I initially checked the spark plug for a healthy spark, I was surprised how weak the spark was, which leads me to believe that the problem perhaps was the exciter coil, which I presume is part of the cdi package. I presume you will be changing the exciter coil at the first instance.

 

[davidpbo]

My Tohatsu 3.5 was showing what was in IMHO a weak spark, however as it suddenly decided to run fine and even sweetly I haven't tried to break it again.
Actually might be electrical if it comes and goes I will have a look at the spark again now it is running oK.

Original post here: http://www.ybw.com/forums/showthrea...oke-problems&p=4340644&highlight=#post4340644

 

[Stemar]

I don't know if they're the same, but my Toh 3.5 gave me grief a year ago and the problem turned out to be the the terminal of wire that earths the coil to the engine body. A quick clean of the ring terminal and surrounding bits and all was well.

Good luck!

 

[John the kiwi]

My expereince FWIW
I have a 15 year old honda 15 hp that came with the boat and was a pig to start. I cleaned the carbie and checked all wiring and found that by jiggling the (low tension)wiring near the CDI i could make it either start if not started, or stop if it was running. (Funny thing is, once it was running it always kept running, unless one fiddled with the low tension wires!)
Got it! must be a wire break, but could i isolate it? could i heck. So i bought a new wiring loom anyway (Boats.net in america - half the price of local honda agent. delivered to your letterbox)
The wiring loom arrived, i fitted it with great hope - and still had the same problem!
Eventually bit the projectile and bought a new CDI unit. Now this is a lump of plastic, mastic and epoxy and silicon and whatever all fused together in a block with no moving parts and the pins are fixed into it like teeth, so how can this be the problem?
New CDI arrived and i fitted it and motor has started either first or second pull ever since.
At least I have a spare wiring loom now!

Cheers

 

[AndCur]

Hi i would check the exciter coil, this can be done with a multi meter. I have a Mariner 6hp which is the same engine as yours and have had to replace this coil before as engine would not start when warm.