Fuel pump problems (postings)

POSTINGS FROM FUEL PUMP PROBLEMS (compliments of Mike Sayers)

Guys,
I went through an e-mail tutorial on fuel pumps directly with Jim Furbur to
save bandwidth on this list, but I thought some other people might be
interested in the transactions as sort of a mini-FAQ. The story had a happy
ending thanks to Jim. Perhaps we'll need to have the Furbur Steering Fix
AND the Furbur Pump Fix.

From: William Delaune
Date: Wednesday, January 21, 1998 4:06 PM
Subject: VMax Fuel Pump Question

Jim,
John suggested that I ask you about this. I've taken my pump apart
on several occasions now, but the little rubber diaphragm seems to jump out
of its retaining place pretty quick. When the fuel pump is working well, the
bike is wonderfully smooth. When it is not, the bike still runs relatively
well, but somewhat rougher.
I'm pretty sure that the fuel tank side of the pump is O.K. and
neither clogged nor kinked. I've cleaned the filter several times and have
been very careful in reseating the hose. I have a feeling that the
diaphragm has been compromised by existing in a folded state for a while.
Are there any sources for these little rubber thingees? Any suggestions as
to keeping it in place? Thanks for your help. I'm getting amazingly quick
at fuel pump removal and tear down!
Bill De l'Aune

At 09:04 PM 1/22/98
Know what you mean Bill, I've been there! About 6 times before I got it
right! The thing is , you've GOT to make sure you have it completely under
BOTH the spring and the disc as well. Also, the blockage usually isn't in
the feed line from the tank but in the INLET into the tank(when you're
riding, fuel is drawn out of the tank creating a vacuum. The vacuum creates
such draw that the pump cannot work against it and the rubbers are pulled
through the small hole.) To find out if this is happening to you, either
drive around a little bit, enough to draw fuel out (at least 10-15 miles)
remove the fuel cap. If you hear air sucking in, your inlet is blocked. Also
you can drive around w/out your fuel cap and see if the problem
persists.( not highly recommended, especially w/a full tank ,haha)

Jim Furbur-Lunatic Fringe Racing-WERA#594
Lehigh Cycle, Macungie, PA.610-366-VMAX(8629)

Date: Friday, January 23, 1998 5:37 AM
Subject: Re: VMax Fuel Pump Question

Jim,
Really appreciate your time and expertise. If you ever need a
complex statistical analysis (my area of expertise) let me know!
My gas tank cap fits very loosely, so I don't think that's the
problem. I wish I could visualize what you are talking about in terms of the
spring and the disk. I take the top part of the pump off (the part with the
hoses) and I see a hole with a rubber disk sticking out. When I remove the
rubber disk, which has one smooth side and one side with a little bump in
the center, I see a silver metal disk with a center hole. This disk is
spring mounted and closes against the ledge of the hole in the plastic base.
I've been taking a tweezers and putting the rubber disk back in under the
ledge with the little bump fitting in the hole in the metal disk.
Everything moves freely and bobs in and out. I'm assuming that the rubber
disk should fit between that metal disk and the plastic. I can feel the
effects of a spring but can't see it. Am I in the ball park?
Thanks,
BILL

At 06:54 PM 1/23/98 +0000, you wrote:
Hey Bill.
Sure wish I had an old pump here I could take apart to refresh. You
should be able to take apart both sides of the pump to get @ both valves
(and the spring side of the one your working on)not only does the rubber
need to go back under the silver disc,the nipple needs to be pushed firmly
into the center and the ring around the outside of it needs curl around the
edge of the disc as well.many time it is easier to work from the back of the
valve. Also, check to make sure BOTH valves are correctly in place. If one
is out (the hidden one it can cause the suction to be greater on the
upstream on causing it to fail.

But back to the original problem the reverse suction (or gravity)
should not be sufficient enough to draw even a weak rubber out of the
hole it only has about 2 ft. of tube to draw up and only about a 1 &
1/2 ft. are vertical. Think of it like trying to drink out of a glass
w/ a 2ft. straw. it wouldn't be very difficult and the gravity of the
liquid wouldn't be very hard to hold up inside the straw.I still think
you have some kind of vacuum drawing back on it causing the failure.
Good luck w/ it. If your still having problem let me know, I think I
may have one around. I'll open it up to go over it.

Jim Furbur

Date: Friday, January 23, 1998 9:49 PM
Subject: Re: VMax Fuel Pump Question

Jim,
Thanks. They key will be getting in from the back. I've only taken
the front apart, and obviously never seated the diaphragm correctly. The
back pressure may have originally come from a massively clogged filter
behind the pump. After my first seating of the rubber, I took apart the
filter and cleaned it. After the second seating of the rubber, I took it
apart again and found some additional crud. My third attempt found it
almost completely clean. I think that the rubber was originally blown by
the back pressure, but keeps coming out because I only had it sandwiched in
between the metal plate and the plastic lip -- a precarious perch compared
to your description of it being wrapped around the plate. I was not even
aware of a second valve. I'll try to take it apart this weekend to
correctly mount the first and check the second. The amazing thing is that
the pump seems to still function relatively well in this highly compromised
condition! Good design.
Thanks again. I'll let you know how the pump repair works out.
Bill De l'Aune

Hey Bill,
Just a little to explain how the pump works. it's actually a simple
design that work well through it's simplicity. What it is, is basically is a
canister with two one way valves and a plunger. As the plunger is actuated,
on each stroke it draws fuel in one valve and pushes it out the other.
That's why there should be a double barrier against flow back, and it will
continue to work until both fail completely and the fuel can flow freely
back into the tank @ which point it can no longer be recovered. Hope this
help when you're checking it out again

Jim Furbur

1/26/98
Jim,
The little nipple from on the diaphragm needed to be tucked into the metal
disk. I'm not sure if the edges of the diaphragm can be tucked around the
metal disk. I checked by vent tube on the gas tank and it was sealed shut!
Everything is put together and works wonderfully. About 3-5 clicks before
start-up then silence. Bike runs smoothly once more. Thanks again.
Thanks,
Bill

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