Why's my fuel pump wanna act like that

[Beau-Kat]

I've been searching for what's wrong with my Millenium.

 

It's idling a little lumpity lump crappy. Idle slows down sometimes. It has only died out once while idling. Seems to run well down the road.

 

Today, I did the following:

Replaced the plugs (had 17k miles on them). #2 and #4 looked fine. #1 and #3 were a little darker, but not bad at all.

Replaced the fuel filter (but the old filter still flowed fuel very well).

Drained all carbs (very slight bit of water in #3 bowl). With the bowl drains open, I ran the pump to push new fuel through them and out the drain hose.

Drained the tank and inspected fuel (looked fine).

Checked the main and reserve petcock screens (both were clear).

Tested the fuel pump (clicking along and shooting fuel, albeit, I don't know how well it should shoot fuel).

 

This is what I find happening:

 

Every time I turn on the key, the pump will run for about 6 seconds. I turn the ignition to "on", but don't try to start the engine. The pump runs for 6 seconds. I turn off the key for a second or so and turn it back to "on", the pump again runs for 6 seconds. It does this no matter how many times I cycle through this procedure, although never trying to start the bike.

 

I have never before noticed the pump running every time I turn on the ignition. Usually, when the bike has been sitting for a few days, of course the pump will pump up several clicks when I turn on the ignition. But normally, if the bike has been ridden recently, the pump would only click a time or two and it was all it needed.

 

I don't believe that I have a stuck float as I don't distinguish any gas in the oil.

 

I haven't had the carbs off yet. Probably gonna go there next. Has 54k on the bike now.

 

But I'm still wondering if the pump is working properly.

[Steel Horse Cowboy]

Most electric fuel pumps have a check valve to keep the fuel from back flowing when key is off. If valve is bad or has debris in it, when you turn the key off, it releases or loses the pressure it would normally hold. Then has to build it up once the key is turned back on. You could remove the hoses from the fuel pump and use an air nozzle with very low air pressure (15-20 psi) to blow into the inlet side to try and clear any debris. (Disclaimer)-Be careful that you are not standing in front of or looking into the outlet of the pump when applying air pressure. If pump continues to do the same after this, the check valve is probably bad, this could effect your idling.

 

C.R.

Edited December 4, 2010 by Steel Horse Cowboy
mistake

[Beau-Kat]

Thanks Cowboy.

 

Good point!

 

Didn't think of a check valve being in there.

 

I guess that maybe something buggered up in the pump when I was working on the bike's fuel system yesterday. The bike was running crappy to start with, that's why I was working on it. But I didn't notice the fuel pump running oddly until after I put everything back together. I'm going to go out and look things over again today.

 

If my pump is bad, I'm gonna get one of the Mr. Gasket ones to replace it. I see where others on here have done that swap instead of buying a new Yamaha one.

 

The Mr. Gasket 42S is $46 at Advance Auto Parts and that store's only a mile from me. The inlet and outlet are on opposite ends, so some piping work would be in order.

 

There's enough brains on this forum that most anything can be figured out sooner or later.

 

Rusty

[V7Goose]

Your pump is behaving exactly as if the gas is not on. Your tests proved it could push gas through a carb, so the only two possibilities that come to mind right now would be either the fuel was not turned back on when you got all done and did that last test, or the pressure switch in the pump is not working to shut it off.

 

If you had a stuck float, it is extremely unlikely that any fuel would be getting into the oil anyway. That would require an intake valve to be open and the gas to flow by the piston rings in the cylinder - something that happens very slowly. In addition, that gas would have to be squirting through the tiny holes in the jets, which could not possibly handle the full pump volume. If a float is stuck, the gas would be pumped out one of the overflow hoses that open in front of the air filters.

 

I personally do not know anything about a check valve in the pump, but even if there is one, I doubt if it could cause that problem. First, when the carbs are full, the bowls are cut off from the input line by the float valve, so they are staying full no matter what. Second, there is a very short hose between the pump and the carbs, and everything behind the pump is up hill to the fuel in the tank, so there will be a fair amount of head pressure on there. It would be impossible for any appreciable amount of fuel to flow back through the pump since liquid is not compressible and the three lbs rating of that pump could not possibly push against the head pressure on the fuel line. If there is a problaem with a valve inside the pump, it would not be that fuel is flowing backwards after it is shut off, just that the pump cannot build up the three lbs pressure needed to shut it off.

 

I suggest you repeat the open drain test on just one carb to prove that fuel is indeed flowing now. Put the hose back on the carb drain and open the valve while holding the end of the hose ABOVE the carb level and turn on the key. Depending on how long the hose is, you may have to cycle the key more than once to fill the hose and refill the carb, but if the gas begins spurting from the hose, put your thumb on the hose to see if the pump shuts off. If it does not, I'd suspect a bad pressure valve.

 

One last point - listen to the speed of the clicks - are they slowing down prior to stopping? If so, then it indicates a build-up of pressure/reduced flow, which is normal. If it is still clicking at full speed, then either there is no gas to the pump, the internals of the pump are bad, or it is just pumping it straight through to somewhere.

Goose

[Beau-Kat]

Hey Goose.

 

Thanks for taking the time to prepare such a great information-filled response!

 

I went back to the bike the next morning and turned on the key. The pump clicked once. Something I would have expected. I could not replicate the 6 second pulses of the pump every time the key was turned on like the night before.

 

Anyway, I started the bike and lightly finger pinched the inlet line (because it is a softer line that the outlet line and is easier to feel the pulse) about an inch from the pump. I could feel its pulse. Seemed to be working fine.

 

I mixed some Yamaha carb/valve stuff, some MM oil, and a little gas and put a hose directly into that and let the pump suck it into the carbs and run the engine for a couple of minutes on it. I'm letting that sit in the carbs for a few days right now. Then I'll drain the bowls again and run fresh fuel through them and go for a ride.

 

I did pick up a Mr. Gasket #42S pump as a "just in case".

 

Thanks again for your assistance.

 

Rusty

[Seaking]

Hey Goose.

I did pick up a Mr. Gasket #42S pump as a "just in case".

Rusty

 

Hi Rusty.. can this pump be a straight up replacement part or only good for an "emergency replacement to get you home until a proper pump shows up"?

 

I found where they are available here in Canada at a good price.. Might be worth the while to pack a spare just in case as well.. ya never know..

[V7Goose]

Hi Rusty.. can this pump be a straight up replacement part or only good for an "emergency replacement to get you home until a proper pump shows up"?

 

I found where they are available here in Canada at a good price.. Might be worth the while to pack a spare just in case as well.. ya never know..

Any of the solid-state fuel pumps with a low enough pressure can work as a permanent replacement just fine. You just need to check the specs on both pumps to be sure that the pressure is OK. Just going from memory here, but I think that most of those pumps have about 7 lbs pressure and out bike only uses 3 lbs.

 

Check the tech library - I believe that Ponch did a great write-up on this replacement.

Goose

[Beau-Kat]

This one is rated at:

 

2-3.5 psi.

 

28 gallons/hour.

 

105 liters/hour.

 

Small enough to fit where we need to put it to replace our stock pumps.

 

However, it isn't a direct swap. Inlet and outlet are on opposite ends of pump.

 

I would think that it should work as well as our $175.00 pumps. I'll probably mock up the connections on the pump and have it in the saddlebag and ready in case mine fails.

[Seaking]

Thanks for the info Goose and Beau-Kat.. I'll look into it as a winter project... I hope my new one replaced as warranty the other year will last a long time.. but ya never know

 

Cheers