Near total loss of power

[pierre]

Riding home yesterday I was left stranded and DOA.  I would greatly appreciate diagnostic help that you can share.   I'm just going throw everything  I remember out and hope you can point me down the right  path. or any reasonable path.  Sorry if this gets long.  

On my way home yesterday, about 25 mile to go I started experiencing what started as slight irregular dips in horsepower.  Maybe 5-10%.  As I continued along the dips in power got more severe and more regular until I felt like a was pulling a truck with a moped.  I finally called it quits when I knew I would not be able to safely get over the golden gate bridge to get home.  Had to call a tow truck  

More info:  
1.when the power loss started I noticed that the RPMs stayed constant. @ 3200 RPM.  no drop.
2. as things got worse I noticed that I could not make any more that 3200 RPMs in all gears.  Except if in neutral on the side of the road  where I could crack the throttle to well over 5K.
3. Until the very end, the engine didn't ever seem to want to kill, it just didn't have muscle. It was running great for the first 50 miles of the ride.  
4. Eventually the power loss was so severe that the bike did quit on me while making a tight hairpin turn uphill, but there was enough momentum to bump start it and make it through the turn.
5.  When things got real bad the engine sounded awful, kinda like a lawn mower when in gear.  In neutral on the side stand it still runs good.
4. no warning lights ever came on.

Also, note, FWIW, 2 weeks ago I had to replace a leaky fuel line which required me having to take the airbox almost completely off to thread the fuel line to the right carb.  No fuel leaks and the air box looks in tact.
It ran good last weekend (5 miles trip)

I don't know where to start. Fuel? Air? Carbs? or Worse?

thanks so much!  

[montmil]

Confirm fuel flow to both pots. Check any fuel filters. Tank petcock possibly clogged. Pull float bowls and look for debris and/or clogged float seat. Do a plug reading. Confirm valve clearances. Do the simple stuff first. It's usually the simple stuff...

Monte

[Justin B.]

If this condition now is the norm take it down the road until it startss messing up, turn off fuel tap, kill engine, coast to side of road, and check your float bowls to see if they have any gas in 'em.  Sure sounds like you are "running out" of gas!  The symptoms sound a bit more severs than those usually presented with a bad diaphragm but I suppose it's also a possibility...

[Bob_Roller]

Did you have this problem before you replaced the fuel  line ?

Could you have possibly put a kink into the fuel line, or restricted the fuel line at the airbox ?

[nhmaf]

If fuel related it could also be a non-venting fuel tank - as gas leaves the tank it ends up with a partial vacuum inside the tank, and fuel doesn't flow.   If you can get the problem to re-occur near home or in the driveway, try unscrewing the filler cap -  if you hear/see gas gurgle down the fuel line and power comes back, then you've solved it!

I supposed it could also be that you've got one cylinder that is not firing intermittently (coil/ICU/plug/wire related)

[pierre]

Thanks for the directions and suggestions.

I'll check the fuel in the tank for debris.
How do you clean the built in fuel filter that's in the tank?

I'll also drop the carb bowls and see what I find.
Wondering if I should just order a rebuild kit for the carbs and take them down and clean them inside and out?

[Lucky_Lou]

Ive had problems with rust blocking lines if you flick it on reserve does is pick up power if so you definately have a blockage ive fitted a clear fuel filter after the fuel tap and a 15g filter in the tank over the pipes since then no probs was considering lineing the tank with resin but going to wait and see how the filters work out will post a picture of the set up.
Lou

[montmil]

Thanks for the directions and suggestions. I'll check the fuel in the tank for debris. How do you clean the built in fuel filter that's in the tank? I'll also drop the carb bowls and see what I find.
Wondering if I should just order a rebuild kit for the carbs and take them down and clean them inside and out?

Drain the fuel outta the tank and remove the petcock. You'll then have access to the screen filter. If you find some junk in the tank, that'll need to be flushed out.

Reread my previous before spending too much money chasing ghosts...
"Do the simple stuff first. It's usually the simple stuff..."

It's likely a debris problem. Do you have an inline filter in the fuel line below the petcock?

All these suggestions hinge on your problem being one of fuel delivery. Odds are that's what it is.

Monte

[pierre]

No inline fuel filters.

I removed the inline filters a couple of years ago because I was told the ethanol in the gas (california) would create problems with the paper filters.  

I might rethink that decision.  :-/

[bruce_launceston]

Hi Pierre, have a look for the little conical in line fuel filters with the sintered metal filter element.

[R65Guy]

My first thought is that it is running on one cylinder...  put it on the centerstand, start it up and let it idle.  Hold your hands over the end of the exhaust and any problem is readily apparent - one side warm, one side cold?  Bad plug cap, plug wire, coil (was it a damp day?) or badly torn diaphragm?

Good luck
Neal

[Rob Valdez 79 R65]

I'm leaning toward a bad diaphragm on this one.

If the float bowls have gas in them, and you have good fuel flow through the lines, you can probably eliminate fuel starvation.

Do you know if you have the original ignition coil on that bike?  They were prone to cracking, and while the symptoms would typically show in wet weather, one never knows.  


But a diaphragm with a hole or tear will cause the symptoms you are describing.

[pierre]

Not the original coil.

Guess I'll be breaking the carbs down to check the diaphragms.

FWIW - officially outside my comfort zone, but willing to do what needs to be done and learn.  

Thanks for all the help!!!!

[montmil]

...FWIW - officially outside my comfort zone, but willing to do what needs to be done and learn.   Thanks for all the help!!!!

Removing the carb tops actually may be the most challenging aspect of checking the condition of the rubber diaphragms. The two screws securing the tops are often stubborn. If yours come right out, good on ya. I had to drill the heads off two of the four screws on my '81 R65. A previous thread confirmed that a 10-32 screw is a suitable replacement for the OEM screws. This is Just In Case info for you.

You can also remove the carbs from their rubber sleeve mounts and get to the diaphragms by carefully removing the throttle and enrichment (hereafter referred to as choke) cables from the carb body. This will maintain the existing cable adjuster settings. One less hassle to deal with.

When you remove the diaphragm, you will see that it also pulls out the carb slide. The key element is to note the small molded tab on the bottom of the outer edge of the rubber diaphragm... this fits into a notch in the carb body. Should you need to detach the rubber, note the position of the slide and its reinstall relationship to the diaphragm and carb body.

Suggest lots of digital images for replacement and memory assist.

Post up any concerns... operators are standing by.  [smiley=thumbsup.gif]

Monte

[Bengt_Phorqs]

I'm like Rob & Monte on this one, check the diaphragms.  Had the same problem on an '81.  When under load it just wouldn't respond.  Fortunately you've come to the right place.