Chasing the powerloss ghost...

[clouseau]

OK guys, I'm back from stripping and resealing my tank thinking I had a fuel delivery issue.  
Guess what?  Same.  Loss of power between 3000-5000 rpm under load. When not riding, it's fine.
Fuel delivery from the tank and tank cap can be ruled out.
It's definitely firing on both cylinders.
Did a valve job about 100 miles ago.
Replaced all air delivery hoses from air box.
Rebuilt carbs with factory BMW/Bing parts.

I am going to attach the Twinmax and take it for a ride and see what she reads when the loss of power kicks in. My hope is that the needle leans towards one if the carbs. It holds steadily at 0 all thru the power band when on the center stand. Just because I rebuilt the carbs doesn't mean it was done correctly... (even though I've done it twice already)

[clouseau]

Twinmax holds steady at 0 at powerloss.
Hmmm.

[Justin B.]

I guess maybe for grins hook up a timing light and observe your timing marks as you rev the engine.  The "idle" mark should disappear and another (Z?) should crawl into the window by 3500 RPM.  If your timing mark is not moving your advance mechanism may be frozen and with no advance there would be a sharp drop-off in power...

[Barry]

It sounds like a hell of a big flat spot for this to be the cause but how about Monte's theory on diaphragms. Have you tried raising the needles a notch.

If you changed the main jets try putting the old ones back in. Some of the jets around are not genuine Bings and may not be accurately sized. People will tell you that Main jets only affect 3/4 throttle upwards. This is very misleading I once fitted 105 mains from a later R45 instaed of the earlier 123's. The result was astonishing the bike would not exceed 3000 RPM on a gentle hill.

[clouseau]

Justin.  I did replace the o-ring on my "bean can" but I put a level on it and drew a line and was pretty sure I got it back on correctly.  However, I advanced it a bit, no change, then retarded it a bit with no change. Same power loss. I've never played with timing before so I don't know how much slight adjustments should affect the timing.

Barry, I used genuine Bing parts.  Mostly directly from Bing, the others from BMW. I will check the needle position but I put them on 3 which measure approx. 1.5 inches of exposure.

[Barry]

Yeah I know you did all the right things buying genuine parts but I thought you might be clutching at straws by now. Who can say if even genuine parts are exactly the same as the originals after all these years.

The reason I mentioned jets was because I read about a guy who got so frustrated when new jets didn't perform as he expected that he set up a rig to measure actual flow rates through jets of various sizes.  He found that in some cases jets just didn't flow like the labelled sizes. How about a 195 jet that behaved like it was a 165!  Thats a huge error.

[clouseau]

I think you may be on to something Barry.  
Ideally, I would just like to swap carbs with a shop and take for a spin.  If the power loss is gone, then I know where the problem lies.

[clouseau]

What do you guys make of this?  Assuming the replaced new Bing parts are slightly different in size that would create this condition?
http://bmwmotorcycletech.info/R80,%201980+,%20Airboxmods.htm

[Barry]

As far as I can tell from Snowbums web page everything he is talking about is for early R80's.  The R65 only gets reffered to as the unequal length snorkel type of airbox.

Going back over all your posts the problem started with rebuilding the carbs so the problem must be fuel related.  (You have had the Bean can off but are sure you got it back in the same position. I still think you should check the timing with a strobe some time).

If you can borrow a known good set of carbs it's got to be worth a try otherwise it's back to checking your own carbs carefully.  Assuming it is mixture related you need to detrmine if during the power loss you have an excessivley weak mixture which is most likely or a rich mixture.  Can't remember if you have tried applying the choke/enricher during the power loss. If it helps that would confirm a weak mixture which might respond to raising the needles. Clutching straws again are you sure the needle jets are in right way up.

 

  

[clouseau]

I'm not sure of anything anymore, Barry.
The powerloss/flat spot seems equal to both carbs since the Twinmax holds steady.  

I did Snowbum's fuel delivery test last night. I got a little more than a cup of fuel from each carb (almost an exact amount BTW from each) at 1 minute. I had a cup under each carb rather than doing 1 at a time.

I did replace the crank case valve gasket a long with the hose that leads to the airbox.

Looking back, I now realize how completely stupid/impatient I was. I should have done one thing at a time, then moved to the next.

I am going to play with the needle position and check the timing.

[clouseau]

OK. I removed the top of the airbox and left the K&N exposed and poof! Power band loss is gone!  So am I running to rich? Are me needle positions off?  The the air box lid with snorkels are totally fine.

[Bob_Roller]

When was the last time the K&N filter was washed really good ?

[Barry]

That's a very suprising effect but yes from what I understand of the way the snorkels work it would indicate you are running rich.  So I would either try the mods  indicated  in snowbums article or lower the needles.

[nhmaf]

When you cleaned and adjusted the carbs, did you reset the mixture screws (underneath, toward the 'front' of the carb that goes toward the head)?   I would think that you'd see some sooty plugs with all this if running too rich at such common RPM levels.

[clouseau]

**UPDATE**
I started thinking about what Barry mentioned about jet sizes and raised the needles to #4 (shortest exposure) and the midrange is back!  
The receipt from Bing says 2,66 for the jets and the one from realoem says 2,64.
http://www.realoem.com/bmw/showparts.do?model=0365&mospid=47853&btnr=13_0464&hg=13&fg=05
I'm calling Bing tomorrow to raise a little hell and curse myself for tossing the jets I replaced (man, I'm a bad mechanic). I have a BMW guy I can take the bike to and swap out jets as well.