outboard backfire/fireing help please

I'm afraid I'm out on this one. It seemed like a classic case of a lean sneeze caused by a dirty carb. The fact that unscrewing the mixture adjust makes some difference still points in that direction or at least to a fuel/carburation problem.

Couple of things. Firstly to Dukes4money, a motor from the mid nineties will be electronic ignition without much doubt.
Secondly to alan17, Outboards don't usually have air filters, just an intake silencer. They tend not to be used on dusty roads very much! *See below*

Couple of other things worried me into asking if you are running this engine out of the water. No problem if you are running on muffs but if you are running it dry you'll have wrecked the water pump impeller by now!

iBoats is the next place for advice I reckon although the Yamaha board is not as well supported as the Johnson/Evinrude one or the Mercury/Mariner one. Someone there might be able to put a finger on the trouble.

** It has an air filter /forums/images/graemlins/blush.gif then definitely try with it in place.
 
yes, the air filter is not like one on car or bike,more of a cover with a maze inside.
do you think it might be an idea to submerge the carb body in caustic soda mix to get to the places that i cant really see, on the whole they look spotless but you never know.
i caustic soda ok on carb bodies?
 
[ QUOTE ]
caustic soda ok on carb bodies

[/ QUOTE ] NO! It'll dissolve the aluminium and just leave all the brass and steel bits.
 
Plugs - when you say black do you mean tainted black, sooty black etc... all makes a difference, high res pic, could help point us in the right direction, as if it's a fuel/air issue the plugs shouldn't look normal. If they do, then it's more likely a cracked exhaust manifold or something else all together....
Piccies please!

Oh! Stuck float valve?

Still piccies please...
 
difficult to see from the pics (better than no pics) and I'm sure Vic will have something to say, but INHO if they're pretty fresh plugs i'd say it/they might be running a tad hot, i.e lean, I think Vic could be on to something - i hope so as this will probably be a cheaper solution than some of the other things suggested. Especially if you wiped off any loose deposits before taking the pics...

could be lean, or could be hot from fouled worn impellor not pumping enough water...?

That's what i'd be inclined to think but hopefully i will have second opinion before the shops are open anyways...
 
i have not checked the impellor,come to think of it i dont know how to or even where its situated.are they hard to do yourself?
sorry i had to edit this.
that sounded like it was not weeing but it has got a strong flow. what i meant was, i have not checked it and dont even know when it was last done?
 
The lower crank seal would be biggish job. Get a mechanic to do it and it will be expensive because of the time. Do it yourself and it won't be. A seal and a few gaskets won't cost an arm and a leg, but I wouldn't want to do the job unless I was sure that the seal really was at fault.

I wouldn't necessarily expect to see oil.

You need a manual.
 
Bin thinking about this one.

Going better with only one plug lead on...

1. I've seen similar on car engines when the head gasket has gone between two cylinders

The effect on a 2 stroke would be to get it to "pop" back through the inlet manifold and exhaust. Putting the choke on would stop the engine - the mixture would be too rich. It would tick over but opening the throttle wouldmake it much worse.

2. The CDI unit is generating sparks randomly for whichever cylinder is not firing. Before you all shriek that it is the coil that produces the spark I would point out that it is the CDI and the coil just transforms it to a high voltage for the plug.

Actually, the thought process is:-

For some reason you are getting some combustion in the cylinder which has its ports open.

For this to happen you need fuel and a source of ignition.

If the head gasket is leaking between the cylinders then you'll have both present in the non-firing cylinder. It may not fire every time, but only occasionally.

If the CDI is firing random sparks out to the coil on the non-firing cylinder then because of the incomplete scavenging of the unburnt fuel you can get ignition in the cylinder whose ports are open. Hence back fires etc.

Shoot me down in flames!

If the crank seals were shot then one would expect application of the choke to "improve" matters.
Coils only malfunction by giving weak or no sparks. They cannot effect the timing of the spark.
'
Triggers work or they don't. They cannot affect the timing of the spark randomly. Unless they are floating about loose......

CDI units take the signal from the trigger and fire a big pulse to the coil on that signal (or when the circuitry in the CDI says it should) If the CDI catches cold, then it usually doesn't work at all, but it can seem to work but do some strange things. Like produce its pulse to the coil at the incorrect time.


Personally, I think that the one-eyed git (GB) or one of his merry band at Zanugnulabour is at the bottom of it. /forums/images/graemlins/grin.gif

Please do tell when you sort it?
Orrabest
 
wow. some very different thoughts here. which is great i`m keeping them all in mind as i go along.i`m going to get some kind of cleaner today for the carbs in case my cleaning by hand has not been good enough and maybe a manual to put my mind at rest that i have put the new diaphrams and gaskets on the right way although my troubles started before i did them.i`m not 100% happy with the kit i was given and the exploded diagram they gave me with it.anyway i`m going to strip them down and start again time permiting!
the head gasket could be quite a cheap job to do myself and put my mind at rest about that,i`ll find out about one of those today.
 
Good luck with it.

You must let us know the result. There have been so many suggestions that one person at least will be able to have a smug look on his face and say "I told you so!".
 
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ignore this i`ll try again

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