Yam 40 ss 2000 weak spark

brokenyam40 · 08 June 2009, 19:06

Hi

I bought a yam 40 from a wonderful seller on ebay, turns out I paid over the odds for a dog.

The engine ran twice, and after that fails to start, there is a spark but have been told by a mechanic that the spark is weak, all 3 sparks are weak, he changed ht leads and plug with no change.

Without charging me he said it was likely the cdi unit, any bright ideas, already out of pocket and cannot afford the £300 for a new cdi.

Thanks

spartacus · 08 June 2009, 19:26

Not sure what else you can do. The Yamaha 40 CDi ignition unit isn't cheap, even second-hand. If the mechanic is fairly sure that's the cause of the fault - then what choice do you have.

brokenyam40 · 09 June 2009, 08:28

Just wanted to post a bit more info:

When the engine arrived in autumn it came without the 10pin ignition loom so i could not start it up, but was told it was running fine and was oiled so okay for winter. It looked stunning under the hood and was a very tidy model)

In the spring I got the 10pin ignition and after some trouble (the fuel cut off was turned off) got it started and running out of the water.

It seemed that at low revs and tickover it sounded very rough, but at high revs ran lovely.

After 2 uses it stalled and would not start again, tried a new battery, changed fuel, checked sparks and checked fuel, all were present but still no firing.

Took it to the mechanic who said the thing about the weak spark.

spartacus · 09 June 2009, 16:17

Would also be worth checking HT leads.

PeterR · 09 June 2009, 16:52

Sorry to sound stupid you said 40 ss is that 2 stroke or 4 stroke and what did you pay.You havent mentioned the seller only interested as i also got sticked up down that way.Bodmin .I also may know or be able to help as far as a part is conserned but need more info .regards Peter

Jizm · 09 June 2009, 18:30

know anyone with the same motor so you can swap parts and diagnose that way?

Poly · 09 June 2009, 19:35

Quote:

Originally Posted by brokenyam40

... changed ht leads ...

Quote:

Originally Posted by spartacus

Would also be worth checking HT leads.

Jizm · 09 June 2009, 20:14

gotta be worth new plugs aswell....

fast fred · 10 June 2009, 02:14

cdi's don't die like that for the most part, they will miss, and or just drop dead. check all grounds, there are ways to test it, or the other way which is NEW PARTS TILL IT STARTS which is just guesswork. get a service manual, be the best coins ever spent.

outboardtech · 11 June 2009, 19:34

i agree with fast fred 100% . has the technician put a proper spark gap tester onto the HT LEADS . I have had loads of Yamaha engines with a weak spark or WE think its a weak spark but its actually normal . the spark gap tester will tell you the answer here , if its a continous jump against the ground on the tester then i can be 100% that its OK . If you had a weak spark the engine will still want to fire and want too run . QUICK TEST HERE . Get the engine running and push the choke in / if the engine picks up @ idle and sounds better we have a fuel problem here . chow baz

Jizm · 11 June 2009, 19:41

Quote:

Originally Posted by outboardtech

i agree with fast fred 100% . has the technician put a proper spark gap tester onto the HT LEADS . I have had loads of Yamaha engines with a weak spark or WE think its a weak spark but its actually normal . the spark gap tester will tell you the answer here , if its a continous jump against the ground on the tester then i can be 100% that its OK . If you had a weak spark the engine will still want to fire and want too run . QUICK TEST HERE . Get the engine running and push the choke in / if the engine picks up @ idle and sounds better we have a fuel problem here . chow baz

What does a spark gap tester look like, out of interest?

brokenyam40 · 12 June 2009, 09:03

Its seems from the replies that perhaps I had taken bad advice on the weak spark, so I have dropped it into a local dealer and just told them it won't start, giving them a limit of 2 hours time to try and diagnose (I don't have the money to just find and fix, but at least if they can accurately identify I have an idea where to go)

Thanks for all the responses

fast fred · 12 June 2009, 10:14

Quote:

What does a spark gap tester look like, out of interest?

thare are a bunch, but has a main ground, a set gap or adjustable, you put all plug wires on it and set the spec gap ( OMC 3cyl spec gap is 1/2" or 13mm) ground it, hit the starter button, they should through a lightin bolt across to the ground, if they do you are all set.