Author Topic: Power Loss  (Read 2582 times)

Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Power Loss
« on: July 01, 2007, 09:27:14 PM »
Original problem 2 weeks ago: After riding for 10-11 miles (always about the same distance), the bike acted like it was running out of fuel.  Lost power but continued to run.  I replaced the fuel petcock (brand new one from Yamaha) and the fuel filter.  Ran great on the next ride, no problems.

Two weeks later (today), I took her out for another ride.  Went about two miles, and the problem re-appeared.  Pulled over to the side of the road, and kept the engine going but it still sounded like it was fuel starved.  I tried the "prime" and "reserve" positions, and could see gas moving through the clear plastic filter but still very little power.  I headed back home, and got about a mile before it died completely.  I sat for about 4-5 minutes, trying to restart the bike a few times with no luck.  Finally, it fired up, and ran great all the way home (another mile).  Temp gauge never got past the middle of the dial.

Does this sound like the fuel pump, stale gasoline, or something electrical?  I'm stumped.  And yes, the tank was almost full.  Thanks.

inanecathode

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 3005
  • Vive la V!
Re: Power Loss
« Reply #1 on: July 01, 2007, 09:43:23 PM »
Carbs could be dirty.
//////////////////////////////////////////////////////////////////////////////////////////
If you can't tell your friend to kiss your ass then they aren't a true friend.
//////////////////////////////////////////////////////////////////////////////////////////

Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Re: Power Loss
« Reply #2 on: July 01, 2007, 10:07:49 PM »
I cleaned the carbs when I replaced the petcock, so I think they're okay.  It's such an intermittent problem, I would think dirty carbs would be more consistent.   Power is great when it's running right.

QBS

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 3282
Re: Power Loss
« Reply #3 on: July 01, 2007, 10:28:10 PM »
Is your fuel cap venting?  Next time it acts up,  run it until it quits.  Then, with your helmet off, remove the cap and listen for a vacuum release.  Or, in your garage, pull the fuel line off the petcock, put a long drain line on in its place, put the petcock on "Prime", drain the tank into a catch can.

If your cap vent is plugged, after a short time the fuel flow will stop.  If it stops, remove the cap, listen for a vacuum release, and look for reestablished fuel flow.  If you get a vacuum release and reestablished fuel flow it's the cap vent.

If your cap vent isn't plugged,  consider buying a fuel pump rebuild kit and installing it.  The parts are cheap and job is easy to do.

Additional note:  If the problem is a non venting cap, the problem will be much worse with a full tank than with an almost empty one.
« Last Edit: July 01, 2007, 11:16:31 PM by QBS »

Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Re: Power Loss
« Reply #4 on: July 01, 2007, 11:01:20 PM »
Thanks, I'll start with the fuel cap.  It's pretty ratty looking, and looks like someone has tried used some type of gasket material to repair it in the past.  That may be the problem.

YellowJacket!

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 5434
  • Don't blame the economy...blame the management!
    • My Vision Blog
Re: Power Loss
« Reply #5 on: July 01, 2007, 11:21:46 PM »
you may also want to check for any kinks in the fuel line. As the bike heats up, the rubber gets softer and the kinks form much easier.
My first choice is the fuel cap though.

David


Living the dream - I am now a Physician Assistant!!   :-)

MotorPlow

  • Visionary Expert
  • *****
  • Posts: 1268
  • Am I less of a Caveman for owning a Vision?
    • My Yamaha Vision Page
Re: Power Loss
« Reply #6 on: July 12, 2007, 10:43:27 AM »
Sounds like your Rev Limiter. Cut the Rev Limiter wire at the Igniter box. I just had to do this myslef...

http://motorplow.blogspot.com/2007/07/pissed-off-gremlins.html

h2olawyer

  • Visionary Grand Master
  • *****
  • Posts: 6259
  • 1982 Yamaha XZ550RJ+ Vision
    • Robert M. Grover
Re: Power Loss
« Reply #7 on: July 12, 2007, 01:50:26 PM »
If it is the rev limiter, I recommend taking the back off the gauges, unscrewing the terminal & wrapping it in electrical tape or heat shrink tubing.  Replace the screw in its proper place.  That way, you aren't cutting into the wiring harness.

H2O
If you have an accident on a motorcycle, it's always your fault. Tough call, but it has to be that way. You're in the right, and dead -on a bike. The principle is not to have any accident. If you're involved in an an accident, it's because you did not anticipate. Then, by default, you failed.

Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Re: Power Loss
« Reply #8 on: July 14, 2007, 04:19:13 PM »
I took another test ride, and when it began to lose power, I loosened and finally took off the fuel cap, but it still continued to lose power until it died and stayed dead for about ten minutes. (@#$#%)  So, I nursed her back home and followed the fuel pump diagnostic steps in the Haynes manual.  The fuel pump was pumping but, as my urologist says, the stream was weak and dribbly.  So, I decided to pull the fuel pump and take it apart per the manual.  But something didn't look right.  After studying the photos in the manual, and digging out an extra set of carbs I had boxed up, I think I finally figured out the problem.  The question now isn't, why was she running poorly?  My question now is, how did she run at all?  I'll take a test ride later today and see if it's fixed.  In the meantime, look at the attached photo and see if you spot the problem.  And whether or not this was the problem, I'll still disable the rev limiter tonight.

Night Vision

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 4503
Re: Power Loss
« Reply #9 on: July 14, 2007, 05:02:04 PM »
..... In the meantime, look at the attached photo and see if you spot the problem....

2 e z....

pmup leuf thgir eht ton s'taht < start here for answer  ;)
if it ain't worth doing it the hard way....
it ain't worth doing it at all - Man Law
 ;D


if it ain't broke..... take it apart and find out why


don't give up.... don't ever give up - Jimmy Valvano

supervision

  • Visionary Expert
  • *****
  • Posts: 1305
Re: Power Loss
« Reply #10 on: July 14, 2007, 08:31:06 PM »
  Hi, Dave, If it was starving for fuel, it should act like you could run around at slow speed for ever, but as soon as you try and go fast, would shut down entirerly.  sounds to me like it dropping one cly. and the easy thing to do is the rev limiter, many people have had that cause running just like your saying.  See what wire it is on the TCI plug , and cut it.  You will know right away if it makes a difference, and if it doesn't , you'll still be ahead with-out it.

" border="0

kiwibum

  • ROV Full Member
  • ***
  • Posts: 262
Re: Power Loss
« Reply #11 on: July 14, 2007, 10:05:54 PM »
um... so what's the problem with the pump? ZX400's don't have them so don't know what to be looking for. I now do have a 550 waiting for me to pick it up, was going to take the pump out as I don't really see the need for it if the 400 runs happily with out one.

Brian Moffet

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 2648
Re: Power Loss
« Reply #12 on: July 14, 2007, 11:02:33 PM »
Here's a photo of the 1983 fuel pump. (with attachment bracket)


Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Re: Power Loss
« Reply #13 on: July 15, 2007, 11:31:12 AM »
Sometime in the past, the body of the pump must have been disassembled and put back together upside down so the fuel was trying to flow through backwards.  I'm not sure how this would work but it must have flowed some fuel.  I guess the float bowls were getting enough fuel to either idle or go under partial power but not enough to accelerate.  The backward flow probably couldn't keep this up for more than a couple of miles, so it eventually died.  After sitting for about 10 minutes, enough fuel probably flowed by gravity into the float bowls, giving me enough gas to get back home.  Anyhow, I reassembled the pump the right way and it runs great now.  But I'm still going to do the rev limiter today.  Thanks for all the suggestions.

PS:  Anyone know the technical details of how this fuel pump works?  Just curious.

Brian Moffet

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 2648
Re: Power Loss
« Reply #14 on: July 15, 2007, 12:28:33 PM »
Sure.  The bottom connection goes to the vacuum source.  Most people think that the vacuum is a regular pull, but it's not.  It pulses.  That pulsing is used to move a diaphragm in and out inside the fuel pump.  The other side of the diaphragm is connected to a chamber, with appropriate one-way valves so that when the vacuum pulse happens, it pulls fuel into the chamber from the fuel tank.  When the pulse stops, the diaphragm relaxes, pressurizing the fuel which goes to the carbs. 

It's a rather simple, and yet elegant method that doesn't require electricity.  And, the pulses happen faster as the engine increases in RPM, thus providing more fuel.

Brian

Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Re: Power Loss
« Reply #15 on: July 15, 2007, 01:43:28 PM »
Thanks, that is a pretty simple method, and certainly seems to work well when you don't try to do it in reverse.

Night Vision

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 4503
Re: Power Loss
« Reply #16 on: July 15, 2007, 02:01:04 PM »
It's still the wrong fuel pump (for an 82)  ::)
if it ain't worth doing it the hard way....
it ain't worth doing it at all - Man Law
 ;D


if it ain't broke..... take it apart and find out why


don't give up.... don't ever give up - Jimmy Valvano

Cougar Dave

  • ROV Junior Member
  • *
  • Posts: 22
  • Riders of Vision .net
Re: Power Loss
« Reply #17 on: July 15, 2007, 08:24:07 PM »
I have two sets of carbs, both off '82s and both with the same fuel pumps.  I guess over the years, parts may have gotten swapped from other bikes.

Night Vision

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 4503
Re: Power Loss
« Reply #18 on: July 15, 2007, 09:24:01 PM »
oops, I guess mine with the "middle part" upside down would look like that  :-[
if it ain't worth doing it the hard way....
it ain't worth doing it at all - Man Law
 ;D


if it ain't broke..... take it apart and find out why


don't give up.... don't ever give up - Jimmy Valvano

inanecathode

  • Contributing Member
  • Visionary Grand Master
  • ****
  • Posts: 3005
  • Vive la V!
Re: Power Loss
« Reply #19 on: July 16, 2007, 12:33:49 AM »
its like the bottom end of an old pumper carb, like the ones they put on snowmobiles
//////////////////////////////////////////////////////////////////////////////////////////
If you can't tell your friend to kiss your ass then they aren't a true friend.
//////////////////////////////////////////////////////////////////////////////////////////