Dead spots around 4-5K

[VaSteve]

1980 R65

I have been chasing this problem since I bought the bike.   I have a dead/flat spot around 4-5K.  Basically, it's like hitting a rev limter in the car.  It's worse if the engine is under load.  I will be in 3rd doing about 50-55 (indicated) and try to accelerate.  The motor will bog (either hang at about 4500 or even drop   ) before it hooks up and pulls to redline.   I'd like this fixed because a) it's annoying, b) I'm concerned about safety.  Nothing like going for more power and it's not there.  

I took it to the dealer and here's what has been done so far...
- Valve adjustment
- Carb adjustment

When I rode it home in the freezing cold the issue was still there.  I didn't have time to circle back and mess around at the dealer.
I called the dealer and he suggested to check the timing and run a bottle of fuel system cleaner through it.

I did both.  Timing appeared OK with the strobe light.  Put some fuel cleaner in.

I rode the bike 20 miles the other day and didn't notice the problem.  I rode it today and noticed the same issue.  It's less prevalent once the bike was warmed up, but stiill there.

Any suggestions?

[Bob_Roller]

Have the carbs been opened up to see if the diaphrams are  hardened and cracked?

[Rob Valdez 79 R65]

Or even just some small holes will do it.  I wonder if the 'dealer' bothered to check them during his carb 'adjustment'.

If you are interested in checking these for yourself, we can give you instructions.

[Justin B.]

That's wierd that once you got past that spot it would pick back up or I would agree whoeheartedly with Bob.  Maybe one of the slides is binding or has a burr that causes it to hang at that spot, jumps past it and then hauls a$$.  I think it would be a good move to remove the tops like the others suggest and check everything out...

[Semper Gumby]

I bet when you open it up its running too rich or too lean.  The questions are which and why?  What I'm going to suggest is quite possible dangerous.  If this was going on on my bike, I would put the colortune adaptor on in place of each plug, and go out after dark so I could see the plug riding the bike on a straight stretch of rode and see which it was.  Then I'd go from there.

Other wise I would completely disassemble the carbs, clean and reassemble replacing all the o-rings, gaskets and the diaphrams.  I would verify that the needle number and needle height were the same and correct.  If there are a lot of miles on this bike I would replace needles and the needle jets.  Verify that the float height is set properly.  Check everything on the carbs.  I would even suspect if the enrichener wheels are on the correct side.  Maybe the DPO mixed them up during some maintenance.

Can you get your hands on another set of R65 carbs?  Try 'em.

Also check the rubber intake tubes between the carb and the cylinder head.  If there is ANY sign of age - replace them.

It smells like a carb problem and I know you said you checked the timing but on the 1980 the timing marks are hard to see.  The idle 'S' mark on my 80 is faint and there is a 1/8" hole drilled into the wheel in the same place.  When the throttle is advanced the, Z mark should come into view.   I used a long thin modelers paint brush to paint some whiteout on the marks so I could better see them.

You might also consider replacing the points and the condensor.  They are not likely the problem but at least they are inexpensive.

[VaSteve]

Hmm.  According to the records I got with the bike, the carbs were rebuilt a couple of years ago.   Because I want to put some more miles on the bike, I'm riding it back down there ~50 miles (one way) and let them have a look.  I'll continue to run some cleaner through the system.   I'll report back with the results.  

If it needs rebuilding, I'm sure I can do that.  My goal was to baseline the bike at the shop and I would take over the maintenance.   Other than this issue, the bike runs pretty good.

[donbmw]

I'll have to go along with Bill. You need to go through the carbs. I let mine set up and varnish. I though that I cleaned the good but the bike ran like sh"""""t. It would not idle right and stumble at low rpms then pick and run ok. I change jets and it ran great but when you would adjust the mixture it had little efect. I final went back in to the carbs and did and full rebuild and soak in carb cleaner. After this I was able to go back to the orginal jet and the mixture adjusted like the should.

Don

[Semper Gumby]

Hey VaSteve,

This would be much simpler.  Go out during the day and run the bike in the zone where it bogs (the 4-5000 k place) and while its doing its bogging thing hit the kill switch and clutch at the same time and pull off the road.  Pull the plugs and have a look.  If you don't have the colortune this is the next best way to figure out what is going on.  White insulators - the bike is too lean.  Sooted insulators and the plug is too rich.  It may be just one cylinder.  

Good luck.

Bill

[Justin B.]

You need to start out with new plugs for this "plug reading" method...

[VaSteve]

The service writer at the shop rode it for me yesterday.  He said it just needs a good cleaning.  Ah, a thanksgiving weekend project.  I just hope I can get it back together...

[VaSteve]

Ok, an update.  My brother and I took the carbs off an cleaned them real thoroughly.  I found that one of the O rings on the right side idle circuit is a little boogered up, so I probably need to rebuild them.  What is the trick for getting the floats off?  We were going to remove them to clean them, but couldn't get the pins out.

Anyhow, after reinstalling them I got to take it for a ride today.  There is still a little stumble, but nowhere near as bad.  When the bike is warmed up, it runs great.  Everytime I work on this bike it gets a little better.  I spent a couple of hours cruising the back roads, and could barely force myself to dismount.     Good times!

[donbmw]

Just use a small puch and hammer and tap the pins out, you can also use a automatic center puch.

Don

[Justin B.]

But, they only should be driven out in one direction.  If you look at the pin very carefully you will notice that one end is knurled.  You push/drive from the other (non-knurled) end...

[Rob Valdez 79 R65]

And if you don't know the age of the floats (and they have yellowed), seriously consider installing new ones, so you have a baseline.  Even if you don't keep a logbook, keep your receipts in chronological order, and that will give you a record.

As long as you have the floats off, replace the float needles, they are cheap enough. They have a rubber tip on them that will deteriorate given enough time, and will cause uneven operation.

I think.

[Semper Gumby]

Sounds like time to order a rebuild kit from the Big Agency.  Is this less expensive than ordering from BMW?

http://www.bingcarburetor.com/

The carburetor manual is worth it!