Yammy 700 ran wild, why??

[Nate]

A Long thread, but I really want to know what happened.

I had my 95 Wave Venture out all day Sunday banging in the waves. It was pretty rough, but we were having a great time. Half way through the day it starting running funny. It idled fine, but when you started on the throttle it wanted to stall out like it was too rich. As long as you eased it up to higher rev's it ran okay for the rest of the day. Just figured there was too much mositure or something.

There was lots of moisture in the hull so I let it air out. The next day I tried to fire it up on the trailer to see if the problem was still there. It was so I changed the plugs and fired it up again.

It started with the same too rich thing for a second than the thing went WILD!! WOT but I wasn't touching anything. I tired the stop button, then the kill switch, then the gas selector to OFF, and then pulled the full line at the filter. It ran WOT without coolant for about a minute (felt like an eternity) and then died down. An hour later I turned it over and it wasn't ceased.

What the heck happened!!!! That could have been deadly at the marnia. I haven't had the time or heart to try and get it going yet. Can these Yamaha motors take that kind of a beating....

 

[Jeff Walkowiak]

Re: Yammy 700 ran wild, why??

intake vacuum leak, if it does it again turn off the ignition and open the throttle wide open to make it shut off. but you need to locate where the vacuum leak is.

 

[Nate]

Re: Yammy 700 ran wild, why??

Thanks Jeff!

I thought if I turned off the ignition the plugs would stop firing, I guess it's not the case. If I'm not touching the throttle, where is all the fuel coming from??

I found a good website on vacuum leaks. This issue just started Sunday, it was running great until then. I guess hoses are the first check, but with all the banging around it may be gasket related.

http://www.aa1car.com/library/vacleak.htm

 

[Jeff Walkowiak]

Re: Yammy 700 ran wild, why??

it has no spark and it runs like a diesel engine, carbon on top of the piston gets glowing hot and ignites the fuel, as long as it gets a lean fuel supply with no load on the engine it will run wide open, once you open the throttle plates the mixture isn't lean and it extinguishes the glowing carbon shutting down the dieseling effect.

 

[Nate]

Re: Yammy 700 ran wild, why??

thanks!!

 

[boatmonkey82]

Re: Yammy 700 ran wild, why??

single carb or twin carb , i think its a single so its much better to diag it , crank it up and with it at idle spray a bit of carb cleaner around the base of the carb and around the intake and maybe around the rear of the engine where the drive shaft goes into the motor but be carefull there is no ignition sources and it can ' run away ' with you again . to prevent this take the covers off of the carb and be prepared to cover the carb with your hand to shut the air off to the engine if it runs away with you again . but when you spray the carb cleaner on a vacume leak the engine rpm will either drop and speed up . and when it does that then you have hit pay dirt and fix the leak. and yes yamahas can hold quite a bit of abuse

 

[Nate]

Re: Yammy 700 ran wild, why??

Jeff, you were right on the money with in vacuum leak. When I hit the throttle it wanted to stall so I pulled the choke last time and it rev'd right up, proving the too lean thing.

Checked all the hoses and everything looks good so I snugged up the nuts holding the carb body to the block. I took it out for a ride yesterday and ran pretty good. Still a little hesitation from idle, but no stalling.

Can I over tighten these nuts, my service manual doesn't have a torque for them. I can only get a 4" 12 mm wrench on the nut so I doubt I'm over doing it, but I want to go a little tighter.

 

[JUSTINTIME]

Re: Yammy 700 ran wild, why??

better find that leak or your going to blow the motor
carb cleaner works great

 

[Jeff Walkowiak]

Re: Yammy 700 ran wild, why??

I would suggest pulling the carbs and carefully replacing the base gaskets under the carbs, I always use a slight amount of non hardening permatex on both sides of the gasket to be safe.