Yamaha 70 HP top cylinder not firing

[pmreb]

I have a 2006 70 hp 2-stroke yamaha outboard motor. When I throttle up the top cyclinder does not fire. If I put on the emergency fuel switch ,red button, the top cylinder will fire after some working with the RPM?s to get to plain. When I come back to an idol the motor runs rough with the fuel switch in the emergency poistion but will go back up to plain. If I idol for 10 minutes or so, the same issue arises. Once I get the top cylinder firing I can switch the emergency fuel switch to normal and it will run fine. If I go back to idol it does the same thing and will not fire on top cylinder and have to inact the emergency switch again.

 

[99yam40]

Re: Yamaha 70 HP top cylinder not firing

pull and clean the carbs and make sure fuel pump and prime start diaphragms and passages are in good clean shape along with the rest of the fuel system

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

Where could I get a carburator kit. I am aauming I will need this. Also I currently have an in-line fuel filter that is not a factory type. It does not mount to motor but rather an in-line itself supprort. I noticed that this is not full and only runs about half way full at tops. When I am at full throttle it has a tendancey to be just barely showing. Any issues with this? Also what is the best product for eliminating ethanol seperation? Thanks for your help.

 

[jeffersondodson561]

Re: Yamaha 70 HP top cylinder not firing

What's the story with this engine? How long has this sat? Was fuel treated with stabilizer? Verified spark? Compression?

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

Checked compression against other cylinders and it was in line. Can't remeber the numbers. Verified spark timing, could not tell you if the fuel to air mixture is right but the setting is the same on all cylinders. This motor has been started at least twice a month since it has been down in November. This problem existed prior to my use this season. It is not a new problem. Get this. Pulled off plug wire with throttle wide open to see if this was the dead cylinder for about 10-15 seconds and put wire back on and it sputters a bit then fires up like there is nothing wrong.

 

[jeffersondodson561]

Re: Yamaha 70 HP top cylinder not firing

I would run the motor at just off idle say about 950-1000 rpms, take some carb spray (have to take the airbox off) and spray short burts in each carb if:
RPM increases=fuel mixture is to lean (probable carb rebuild)
No RPM change=improper combustion (spark plug, trigger, etc.)
RPM drop=this is what you want to hear (means carb fuel metering is correct)

After you have determined you have correct fuel mixture, timed spark is controled by the variable resistance CDI. Check linkages and pickup timing,

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

Thanks Jeff I will try this. I cannot remember if the RPM drops or not last time I tried to clean carburator with cleaner. If RPM drops then I look to the CDI. What am I looking for and does this mean I need to reset timing? If no change I would look at the trigger I guess, be cause I changed the spark plugs already.

 

[jeffersondodson561]

Re: Yamaha 70 HP top cylinder not firing

I was using trigger as etc.(ignition). If you have verified spark on every cylinder then all components of igntion delivery are good, this does not mean timed ignition is correct, but like the post suggest this is a variable resistor CDI (wiper arm). So you need to verify that igntion is advancing properly, after you have. Yamaha makes excellent CDI equipment if you suspect a CDI is bad keep looking, it should be the last thing you change and if you do replace it, immediately buy a lottery ticket.

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

Thanks for all your help. One more question. I have always had a hard time starting this engine. I takes a few seconds to fire. What would I look for as far as the choke working or would it be something else? It was always like this even when I bought the engine new.

 

[jeffersondodson561]

Re: Yamaha 70 HP top cylinder not firing

What year did you buy it?

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

2007

 

[jeffersondodson561]

Re: Yamaha 70 HP top cylinder not firing

Chances are they did not stabilize the fuel when it sat on the lot, being an '06 it was produced at the end of '05 so it could very well have sat for a year and then the techs could run some ringfee or something of that sort though the fuel system to get it running good enough. I am just speculating but I know BPS was really bad about this.

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

Wondering if anyone could help me out with some information on how to set up my carbuators after I rebuild these. Not sure on the jets and idle settings or advanced spark and choke. The choke has never worked properly since I bought the engine. Takes quite a while to fire off. Maybe 8-10 seconds. You know kinda a run down on what I need to do to make sure it will be functioning properly. This is a 2006 yamaha 70 hp. Thanks

 

[99yam40]

Re: Yamaha 70 HP top cylinder not firing

There is no choke on that motor from what you have stated it is a Prime Start system, which works automatically when cold, enriching the fuel mix and advancing the timing.

If you follow the owners manual starting procedures it should start up usually on the second or 3rd 2-3 second turn of the key if it is working properly. If you lift the fast idle lever while trying to start it will over ride some of the prime start and cause some problems maybe.

A Yamaha service manual for your motor is a recommendation we all give to all who work on their own motors. It will give all the steps and specs you will need

 

[pmreb]

Re: Yamaha 70 HP top cylinder not firing

Thanks again 99yam. This makes sense. I tried the lift of the lever and does not do anything. Will get the manual for my specs.