High rev fueling problem and eventually starvation at idle...

[ozscott]

Hi all - took Nine Mile out to the Bay yesterday. What a great day. At the ramp the '93 115 V4 Yammy started straight away and idled nicely. Took her to the pontoon and mored up idling and waiting for my better alf to part the truck. After about 4 mins on normal idle 700rpm the motor sounded like I had turned the petrol tap off...just slowly died. I found the primer bulb empty and re-primed using the bulb (with enough fuel being primed up as though it hadnt been started for weeks...). So I wondered whether the primer check valve was stuffed (its only 6 months old but they can fail that early). After that she idled and ran like a dream up to Harry's and back to Peel for a swim at Horseshoe bay and idled around there after the swim and then back on the to the plane for a later arvo trip back - nice. Halfway accross the paddock and I wanted to outrun a cruisecraft 6m and a 15m cruiser before their washes contributed to the pressure waves and nor easter waves that were causing the usual washing machine near cleveland pt...so I had her at 5,300rpm and 58kph and had been there for a minute when she started hicupping at those revs....back off slightly and then back to 5000rpm and sat at that with no problems. It sounded dictinctly like fuel startvation at 5300 rpm.

So Im thinking that perhaps the 16 year old diaphragm in the fuel pump might be suffering from age and a pin hole or two. Perhaps the primer bulb might be suspect also...any ideas?

Cheers

[Mr__Bean]

Some other possibilities:

Mud wasp nest in the fuel breather.

Air leak in the fuel pipe

Dirty fuel filter

- Darren

[Chimo]

Hi OS

I not sure its the diaphram. At least not one of the springs. As you may remember I had both my 115's fuel pump diaphrams play up within ten hrs running. In both cases the motor would idle fine and only cut out if the revswere raised much above fast idle and from memory it too a few minutes for the affected motor to die.

A drop of 300 rpm to fix the issue sounds like something else but I wont guess from this far away.

Can you change fuel lines etc and try one thing at a time and do a bit of isolating?

Cheers
Chimo

[ozscott]

Thanks fellas - I will check all the usual suspects again. I thought that it was the diaphragm because I did the fuel lines recently...so I thought until you blokes mentioned it and I looked back and in fact it was more than a year ago!!! Time does fly...same for the fuel filter.

Cheers again