Poor spark or not?

[jac]

I have a tohatsu 2 stroke that is reluctant to start.

New fuel, carb cleaned and when I squirt carb cleaner through jets It goes through. Fuel runs out of carb when drain open (like a river!) Water in the bucket is also oily suggesting fuel is getting the whole way through. Does look to be a lot of fuel though - too much going in maybe ??

New spark plug, correctly gapped - correct type for the engine.

When I remove and test I get a blue spark in the correct place. However, the spark does look a little weedy but I'm not sure if I'm imagining things and don't really have anything comparable to compare it with.

So two questions.

Am I correct that spark plugs produce different sized blue sparks and if so, likely cause/ fix.

Any other suggestions before resort to the chequebook.

 

[2Tizwoz]

As you have a spark the other question is have you any fuel?

Is the plug getting wet with petrol?

 

[jac]

As you have a spark the other question is have you any fuel?

Is the plug getting wet with petrol?

Damp yes. Not sopping.

Is a smell of petrol In the exhaust after a few pulls.

 

[VicS]

Damp yes. Not sopping.

Is a smell of petrol In the exhaust after a few pulls.

Blue spark sounds OK but you really need to test it with a spark tester to be sure that it is strong enough to jump best part of a centimetre. Just looking at it jumping a spark plug gaps not good enough.

You can buy spark testers or you can improvise :- http://www.ybw.com/forums/showthread.php?123723-High-tech-Spark-Tester


You have proved that you have a fuel supply to the carb. Have you left it for a while with the tap open to make sure its not flooding. (You may have to remove any air intake box from the carb to check)

T

 

[nigelmercier]

When I used to work on my car engine (35 years ago) the most useful device I had was a Gunson Colortune, effectively a glass spark plug for watching the spark and the burn. I'm pleased to see you can still get them: http://amzn.to/1sY8ghr

 

[jwilson]

I have a tohatsu 2 stroke that is reluctant to start.

New fuel, carb cleaned and when I squirt carb cleaner through jets It goes through. Fuel runs out of carb when drain open (like a river!) Water in the bucket is also oily suggesting fuel is getting the whole way through. Does look to be a lot of fuel though - too much going in maybe ??

New spark plug, correctly gapped - correct type for the engine.

When I remove and test I get a blue spark in the correct place. However, the spark does look a little weedy but I'm not sure if I'm imagining things and don't really have anything comparable to compare it with.

So two questions.

Am I correct that spark plugs produce different sized blue sparks and if so, likely cause/ fix.

Any other suggestions before resort to the chequebook.

On both my 2/S Tohatsu 3.5s the sparks always do look weedy, but they start, usually 2nd pull. You can very very occasionally get a plug that gives a spark on test outside cylinder, but not under compression, but it should not occur with a new plug.

Test for flooding as follows: remove plug and turn off fuel tap. Drain carb. At full throttle setting pull starter vigorously 4 or 5 times to blow through any petrol mix in crankcase and transfer ports. Heat plug tip in gas flame to dry and put back in.

Now open fuel tap one-two seconds, shut again and and try starting. Repeat half a dozen times if it does not start. Sooner or later you will have the float chamber at the right fuel level. If it starts and runs a few seconds it's not the plug that is the problem.

You are quite sure the fuel is petrol? Sounds silly, doesn't it.

My boat came back from charter last year with a complaint that the dinghy outboard would not go, did the usual clean carb/check spark/new plug routine yet nothing. Tipped out fuel in tank and refilled with fuel from red can clearly marked "50:1 2/S". Still nothing. Repeated carb off etc. etc. Twice. Still no start.

Eventually discovered that the charterers had used lots of dinghy fuel, and then topped up the red outboard fuel can with spare diesel from the black can marked "DIESEL".

 

[jac]

On both my 2/S Tohatsu 3.5s the sparks always do look weedy, but they start, usually 2nd pull. You can very very occasionally get a plug that gives a spark on test outside cylinder, but not under compression, but it should not occur with a new plug.

Test for flooding as follows: remove plug and turn off fuel tap. Drain carb. At full throttle setting pull starter vigorously 4 or 5 times to blow through any petrol mix in crankcase and transfer ports. Heat plug tip in gas flame to dry and put back in.

Now open fuel tap one-two seconds, shut again and and try starting. Repeat half a dozen times if it does not start. Sooner or later you will have the float chamber at the right fuel level. If it starts and runs a few seconds it's not the plug that is the problem.

You are quite sure the fuel is petrol? Sounds silly, doesn't it.

My boat came back from charter last year with a complaint that the dinghy outboard would not go, did the usual clean carb/check spark/new plug routine yet nothing. Tipped out fuel in tank and refilled with fuel from red can clearly marked "50:1 2/S". Still nothing. Repeated carb off etc. etc. Twice. Still no start.

Eventually discovered that the charterers had used lots of dinghy fuel, and then topped up the red outboard fuel can with spare diesel from the black can marked "DIESEL".

Will try this now, although as at home with no gas will have to rely on the baking sun to dry the spark plug!

Fuel is definitely petrol. Filled itself from the same nozzle that I used to fill up the car (petrol) which has been running fine! Garage shifts a fair amount of petrol so comfortable that is ok.

 

[Daydream believer]

hold the plug over the hole so it grounds on the head with the spark part over the hole.
Connect it up & get someone to hold it with a pair of insulated pliers
Give the cord a pull & as the escaping gas is ejected from the bore the plug should spark & set light to the gas
A small explosion occurs & it dries out the bore so it does not get the plug overly wet
Open the plug gap a tad more to make it work .Hot it up with a blow lamp & put it back a bit smartish
Go through the start procedure again & see what happens
Done it lots of times & it often works- especially with seagulls-- But can go wrong

By the way make sure it is not a Stuart Turner & there is not a lot of fuel floating in the bilges as you are likely to get a fire on board. Most common event tends to happen 20 miles off shore. It's Ok but the crew tend to panic when they see the flames - Mine jumped in the dinghy-- Whimps

it is also works with lawn mowers but it is possible to burn a hole in the wife's lawn- She got the hump but at least i got her b..dy mower going

 

[jac]

Think I'm admitting defeat on this one. Refused to start using jwilsons technique. May give it another go tomorrow after work but is getting to the point where it might need someone who knows what they are doing!! I suspect either the spark is not man enough or it is flooding.

As I've had the carb apart I may try and play with adjusting the float setting - the manual that someone pointed out on lakeys site stated 3mm so will have a go there but running out of ideas/ patience/ time.

 

[Lakesailor]

If you are certain fuel is getting in there. And there is a spark of sorts. The other problems may be a bit more fundamental.

a) reed valve broken of stuck (it's in the bottom of the crankcase on this motor)

b) seal on a main bearing leaking air in.

Both are major strip down jobs. Not difficult, but if you are not too mechanically minded may be a bit daunting.

 

[rotrax]

I suspect the Tohatsu has a capacitor discharge ignition system like many simple two stroke motorcycles.

Test the spark by removing the plug cap and holding the end of the lead near the head or block, leaving a gap of 8mm or so and then pull-or get someone to pull-it over.

If this is done in a dark spot or at night a spark should easily jump the gap and be clearly seen.

It is also worth cleaning the earth connection of the external ignition coil-this can cause a weak spark if dirty or corroded.

Good Luck.

 

[SAMYL]

Try a different spark plug.

Just because you have a new plug does not mean it is working. It may look as if is sparking but it may not be under load.

 

[jac]

Just to finish this story off.

After more attempts I finally bit the bullet and took it to an outboard specialist. He has diagnosed a lack of compression caused by a damaged head gasket. Not sure what caused the damage - outboard is about 12 years old but very lightly used. Won't be fixed this weekend which does rather limit our options this next week but at least it will be fixed and wasn't down to me being a muppet.