YAMAHA 40BE Not running smooth/Ignition?

[npn75@hotmail.com]

I have a rather old 40BE Yamaha outboard engine (early eighties?).<br /><br />The engine is not running smooth at higher speeds.<br />We checked compression => Ok<br /><br />We found on the ignition system 2 diodes (for each piston 1). Actually one diode is connected in the inverse position of the other. I think this is very strange. Could someone inform me in this matter?<br /><br />Is this problem familiar to you?<br /><br />Were could I find electrical schemes or a repair manual.<br /><br />Thanks for the help and see you on the water!<br /><br />Fred

 

[rogerwa]

Re: YAMAHA 40BE Not running smooth/Ignition?

It may be easier to rule out fuel delivery first. What are the symptoms exhibited when not running smoothly. I assume this idles fine.<br /><br />Does it hunt, miss, surge, etc..

 

[npn75@hotmail.com]

Re: YAMAHA 40BE Not running smooth/Ignition?

More in detail when my engine iqs not running smoothly:<br /><br />At low rpm it is running smooth.<br /><br />When highering the rpm, some slight hesitation of the engine can be heared.<br /><br />When opening gas to max, engine speeds up to about 80% of the power, engine running rather good at this speed but only for a 30 seconds. Then engine starts losing power, then regains it, and so on...

 

[Ross J]

Re: YAMAHA 40BE Not running smooth/Ignition?

Sounds like Rogerwa is onto something here, you describe what sounds like a fuel problem. It could be delivery, partially blocked fuel lines - closed air vents - blocked filter - squashed line - old fuel lines (splitting) - or it could be after the fuel meets the motor. then one I would look at the fuel pump - carb - final filter - jets - fuel mix (if 2 stroke) - fuel quality? this sounds strange but I've had problems with quality before!<br />Be sure also that the outboard isn't cavatating on you at top revs. Just some ideas to consider<br />Ross

 

[12Footer]

Re: YAMAHA 40BE Not running smooth/Ignition?

Here is your 3rd opinion, and I agree with Roger and Ross.<br />The ignition part you described is porbably the rectifier block. It basicly turns the AC from the stator into DC. Or it could be a voltage trippler,to take low voltage DC and bump it up for spark (ignition pack).<br />In iether case, it does sound like fuel hunger.Don't hesitate on finding the cause, as running a 2cycle without full,uninerupted fuel supply is death to them. And as Ross mentioned, fuel quality. Sniff te tank (one siff per customer,don't want any brain damage )<br />If it smells like varnish with gas in it, it has gone stale and is unstable. It will cause more grief than you would believe, worst case being,completely trashing the carb and fuel pump to the point of needing rebuilds.<br />Let us know what u find.

 

[rogerwa]

Re: YAMAHA 40BE Not running smooth/Ignition?

Check your bulb when this is happening. Is it sucked flat?( obstructed pickup or bad bulb) If you pump it does the problem disappear. (air leak, bad bulb, fuel pump)<br /><br />You may also have water in the fuel. It may only suck the water at high speed based on the shape of the tank..

 

[evil_hahaha]

Re: YAMAHA 40BE Not running smooth/Ignition?

I have a similar but opposite problem. Our Yamaha 40BE will run very well at high revs but will often misfire and stall at idle. I have a feeling that it is the oil mix. It is meant to be run at 100:1 but I prefer to run it at 50:1 because of its age. I am going to change the mix to 100:1 to see if there are any noticeable differences at low and high revs but I would prefer it ran well on high revs than having it stall at such high power. p