115 V4 Autolube-Fuel starvation?

[happyjack76]

Hi Guys,
Have just fitted this 1986 motor to my 20 foot cruiser. On my first test run she fires up and runs fine at idle. Using the fast idle lever I can get the revs up fine (but only held it there very briefly).
At low revs she ran fine but when I got to open water and opened her up she cut out without gaining any increase in revs. She started again no problem and this time I opened the throttle very slowly and she eventually picked up speed and got the boat on to the plane. The revs only went up to between 3500 and 4000 though even at WOT. After about a minute the revs dropped right off and I had to throttle back to stop the motor cutting out completely.
My first thoughts went to a problem in the fuel system so I have checked the operation of the primer bulb, had the fuel filter out and pumped fuel straight through. The filter is as clean as when it went in.
The motor hasn't been left with fuel in the carbs so I don't expect them to be gummed up. However I am prepared to give them a strip down if I can find a 'How to' post to talk me through it.
My thoughts now go to the fuel pump. I have found a place which can supply the gaskets and diaphrams to do a strip down. I'm in England so don't know if this site can send parts to here.Am I going in the right direction with regards to the pump? Could it be the spark plugs breaking down? Any thoughts would be very much appreciated.
Thanks, Jack

[robert graham]

First thing I'd do is remove, inspect, clean or replace spark plugs to ensure you're getting good spark. Check, rebuild or replace fuel pump, if it needs it. Best guess is that you have one or more dirty or partially plugged carbs. Drain each carb float chamber for water or debris, run the motor to check for improvement. If you're going to clean/rebuild carbs yourself, best to purchase a manual and carb kits, or you can have it done by a Yamaha Dealer. If a carb is plugged then best to not continue running motor as lean fuel mixture can cause burning of pistons and serious damage. Good idea in any event is to install a fuel/water seperator type canister filter and use a fuel stabilizer like Stabil or Seafoam all the time to help eliminate fuel related problems. Good Luck!

[happyjack76]

Thanks Robert. Have put in new plugs but made no difference. Gonna bring her home tomorrow and will check the float chambers and look at the pump. Do the carbs have to come off to clean the jets?
When I started her today she wouldn't run at idle and I've had to wind in the throttle stop screw quite a way to get her to tick over. Does this tell us anything?

[TownsendsFJR1300]

Thanks Robert. Have put in new plugs but made no difference. Gonna bring her home tomorrow and will check the float chambers and look at the pump. Do the carbs have to come off to clean the jets?
When I started her today she wouldn't run at idle and I've had to wind in the throttle stop screw quite a way to get her to tick over. Does this tell us anything?

Yes, the carbs are gummed up.

You should remove the carbs and take them to a clean workbench. Drain the float bowl looking for any crap coming out (as stated above).

There should be a main jet, larger, poking out the most and an idle jet, much smaller, recessed. The idle jet(s) has pretty small orifices. Pull both jets (don't just look at them in the carb body). You should be able to see clearly thru them easily if clean or once cleaned... Some are small enough I've had to use a wire from a wire brush to clean as a sewing pin was way too large. Carb cleaner and an air compressor are your friend when cleaning the jets. Use caution on the carb body with cleaner as some of the cleaners are very aggressive and will attach plastic/o-rings, etc...

Once you get it running, you need to start using Seafoam (my preference, but some sort of stabilizer, which is a stabilizer/mild cleaner) or it'll gum up again, even if ran dry... Chevron "Tectron" is also a good fuel system cleaner to add to your gas tank as well.

If water intrusion is a problem (built in large tank), I found this product works excelllent: K100 Fuel Treatment : Fuel Additive, Fuel Saver It cleans, stabilizes and helps burn off any accumulater water in the system... Kind of expensive but it does work and very well...