Do I need a new fuel pump?

[john day]

I'm trying to chase down a problem with an intermittent miss and not sure if the fuel pump is to blame. I have a 1989 120 Johnson with the vro disconnected and I premix. At mid throttle and wot the motor is missing. I read some posts that recommended testing the pump by removing the outlet hose and turning the motor over, lanyard disconnected. The gas pretty much dribbles out. I read I should have strong spurts of gas instead. Is this a sign of a defective pump? John

 

[boobie]

Re: Do I need a new fuel pump?

When you say intermittent miss, does the mtr just fade away or start to jerk ?? Did you try pumping the primer bulb ??

 

[john day]

Re: Do I need a new fuel pump?

Boobie, the miss comes at several times.

Idles pretty good, then at 2200 motor breaks up (jerks).

Motor begins to clear at about 3200 this is when all cylinders start to fire and the motor accelerates to 4000 rpm or so and planes off.

The motor will run pretty smooth at 4000-4200 and up but will miss on and off. This is more of a vibration we feel coming and going. If I play with the throttle just a little like tapping just slightly the motor seems to catch and smooth out. Also, at this rpm, if we start hitting some rough water the motor may lose rpm.

At WOT the motor will only go to 5200 rpm which has taken all summer to get to. This is about 3/4 throttle, after this there is no more acceleration and feels like the motor is being held back. Instead of that smooth sewing machine sound these motors can have it just sounds off. There are also times when the motor will only turn up to 4800 rpm. This can happen with other people on board or alone with a 1/4 tank of gas.

Pumping the bulb does nothing and hitting the choke will cause it to bog down. Since my post I have put a clear hose just before the fuel pump with a loop and the hose seems to fill and almost empty at idle with occasion large air bubbles going into the pump. At the 2200-3200 range the clear hose is full of fuel, no bubbles, then when up and running the tube seems to be filled with a lot of bubbles.

John

 

[boobie]

Re: Do I need a new fuel pump?

Sounds like an ignition miss. Put a timing light on each wire when in acts up, turn it around and look for black spots in the light. That is the cyl that is misfiring. It could be anything from a coil,pack,stator or timer base. Let us know what you find.

 

[john day]

Re: Do I need a new fuel pump?

I'll do the timing light test. Are all timing lights compatible with the motor? John

 

[Bob_VT]

Re: Do I need a new fuel pump?

I'll do the timing light test. Are all timing lights compatible with the motor? John

Yes. Any automotive timing light will work.

 

[john day]

Re: Do I need a new fuel pump?

Thanks Bob.