Prop choice

[Ianfs]

I found that the spark on most of the cylinders did seem fairly week but there was no spark at all on cylinder No5.

So you may have found your answer.
And as I said in my first post.............

But also consider that your engine may not be performing, or the hull is dirty!!

I gave the engine a full service just before she went In so we'll see..

Did you change any leads or distributor cap?

1/ Carb rebuild
2/ Spark Plug
3/ Leads
4/ Distributor Cap
5/ Bad Earth
6/ Thunderbolt Ignition connectors

Ed will know more than I, but if it were me I would be eliminating the electrical items in the above. Check each one in turn to verify they work and work backwards, don't assume anything, it should be fairly easy to DIY. Not sure how you check a Distributor cap though, apart from inspecting it. I have heard of some with tiny cracks which are difficult to see. However if the sparks are weak with one missing it might be the Ignition Control i.e. the Thunderbolt Ignition Module usually found attached to an Exhaust Elbow, as I said, check the connectors.

I also found these pictures I took when I was putting everything back together....This is the Ignition module. Interestingly enough there are six plugs, mine is a V6, yours may have 8, I would put 5p on one being corroded.

Thunderbolt female plugs.JPG (214.77 KiB) Viewed 13093 times

And this is the plug.......

Thunderbolt ignition plug.JPG (213.54 KiB) Viewed 13093 times

My questions to Ed would be
1/ Should the spark to the plug via the distributor be weaker than if connected directly at the coil?
2/ If no5 is not working at all and the lead and plug are good, does that point automatically to the Dist. Cap?

[shibbs]

Thanks Ian, I didn't change the leads, i inspected them and they 'seemed' to be brand new in excellent condition, but as Martin pointed out, i will check lead No 5 is working first.. Likewise with the Distributor cap, i did take it off at the weekend and give the connections a clean anyway though.
I will go and check the ignition connectors today and see where its at, photos to follow..
Does the fact that a strong spark is coming out of the coil go against it pointing towards the igniton connectors?
I really need to do some reading on the Thunderbolt ignition, as yet, i have no idea what it does or how it works.

[Ianfs]

Interesting, some modules are mounted on the distributor and some on the Exhaust Elbow. In the diagram I found in my pdf manual it shows the Thunderbolt Ignition Module as an Ignition Amplifier

Ignition.jpg (138 KiB) Viewed 13091 times

[Ianfs]

This will help with the explanation............

http://www.boatfix.com/merc/bullet/83/83_24.pdf

However, what I don't get without studying it fully is that you have a weak spark but one cylinder is completely out. I would guess that if it was the Ignition Module, you may not get any sparks. So pointing towards the Distributor, lead or plug. I'm all out of any expertise now, just pure guessing.

If you Google Thunderbolt Ignition there is a lot of info out there.

As said before this is Ed's territory, I'm able to help only because of some limited experience and I'm on days off and hiding from the rain!!

[shibbs]

Used my lunchtime wisely (but failed to stay out of the rain and wind ) and found the following;
HT leads good. All connectors ok and clean.
Thunderbolt module contacts clean and in good condition..

But, found this..

Clicked the crack back together and tried the Sparks again and cyl No 5, full strong spark all round.
I think that may be the problem, a poor loose connection.
I now need to try to either repair the crack or replace, then do a sea trial and go from there.
Need to wait for this disgusting weather to pass though.

[Ianfs]

Funny thing, mines cracked too, in fact the plastic catch is broken, held together with a cable tie. However I don't think the crack has anything to do with it, its more what you said a bad connection and pulling it apart may have cleared it.

Wow, I think I must have bumbled my way through that one to find the problem without a grown up!!

YES!!!!!!

Lets hope it is a bad connection and not a replacement module.

PS Actually it was you who found it so I apologise for my arrogance!

[Ianfs]

Is it all working now?

[shibbs]

Not had a chance to get back down yet, going to try to fix the housing with some araldite to ensure a better secure connection (maybe even a cable tie or 2 also ), then go down on Friday and do a sea trial, everything crossed!
Will update again when I have an answer either way..

We may even then be able to go back to the original question of prop choice.

[Ianfs]

I am thinking that you will notice an amazing difference, something back to what would seem to be normal!

[mark101]

Fingers crossed shibbs. I hope you have good luck!


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