Detecting a faulty fuel pump

[Vassago]

Hello everyone,

I have a 30hp Evinrude with poor starting/idling problems and a hesitation at full throttle. A number of things have been done so far including a carb cleaning and gas line and tank replacement, both of which were necessary.

I'm new to all of this so I'm kind of bumbling through this troubleshooting process. I've been doing a lot of reading on the topic, including great link that Fleet Admiral provided in a recent post entitled "Standard outboard fuel pump troubleshooting". Thanks Admiral!

Unfortunately I don't have all the required tools to do the troubleshooting, like the pressure gauage to test the output PSI of the pump and I'd like to be a little more certain before I go repairing or replacing my fuel pump.

I disconnected the fuel line at the carb and squeezed the bulb and observed a steady flow of fuel. I then tried turning over the engine with the fuel line still disconnected. Instead of the steady stream I got a couple of spurts and spits of fuel, but no stream. Is this normal operation when the engine is turning over? Can all pump/diaphram problems be visibly detected? Is there any other test I can perform on the pump to help determine if it's failing?

Thanks in advance for your help. Apologies for the newbie style of question, but if anyone can help out, it could really save me some bucks.

 

[Joe Reeves]

Re: Detecting a faulty fuel pump

You didn't list the year, however the fuel pump operates off of crankcase pressure which is caused by one piston in its down mode motion. At cranking speed, this would result in a fuel spurting action with every revolution of the engine.

With the engine actually running, that spurting would closer resemble a flowing action due to the speed which the piston is traveling.

A rule of thumb.... If all is well elsewhere, and the engine runs fine when you're pumping the fuel primer bulb but does not when you stop pumping it, suspect the fuel pump.

 

[Vassago]

Re: Detecting a faulty fuel pump

Thanks Joe, that's exactly what's been happening.

I couldn't maintain a full throttle without continuously pumping the primer bulb.

Another symptom is I'd need to re-prime with the bulb after about 15 minutes of stop time (while fishing, of course.

Lately it's manifested as poor starting and an inability to idle as well.

It's a '90 30hp. Electric start.

Thanks again!

 

[Vassago]

Re: Detecting a faulty fuel pump

One other point, I just inspected the pump this morning and the diaphram looks OK. I don't see any tears in the rubber.

Sounds like I should rebuild the pump anyhow.

 

[F_R]

Re: Detecting a faulty fuel pump

Unless the diaphragm has a hole in it, a fuel pump will NOT cause hard starting. Continous need to squeeze the primer to keep it running is a classic symptom of a bad pump though. But it also could be caused by air leaks between the fuel pump and gas tank...including around the little pins that the fuel connector push in on the tank outlet. Fuel pumps are best repaired by replacing the whole pump. In fact, parts are not offered for most of them.