Running really rough below 3,000 rpm

[quixotic]

Above that, it runs as smooth as hot butter.  And Idle seems OK.  I'm going to start checking stuff, but was wondering what to check first.  Carb balance?  Valve clearance?  timing?  points gap?  

Thanks in advance.

[Barry]

Valve clearances and ignition timing always before carb balance.

There is a very similar thread already on the go here:  

http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1368969101

[quixotic]

Hmm.  Maybe it is just the "torque pulsing" that Barry mentioned in the other thread.  It's certainly not as smooth as my old slash 5, though.  A bit disappointing.  

On a positive note though, I had terrible brake squeal yesterday, and found that the R65 had the easiest access to brake pads of any vehicle I've ever owned.  Scratched 'em up a bit; put some brake grease on the backs of the pads, and now everything's quiet again.  

[Justin B.]

A 60/5 is about the smoothest Boxer there was (that I've owned) but was very underpowered.  But, you do need to give it a good tuneup, as Barry suggests, before passing judgement.

[quixotic]

I looked at the plugs yesterday, and one was significantly sootier than the other.  Is that a possible sign of carb imbalance?  

[Bob_Roller]

A black sooty deposit on the spark plug, is the result of poor  incomplete combustion .

It could be from a carb problem, or an ignition problem .

I see in your signature line, that the bike is a '79 model year .

There seems to be an issue with the contact breaker points type ignition system, the forward ignition coil mount, has the main grounding or earthing point  for the bikes electrical system .

Not too uncommon to hear of this bracket cracking and causing electrical issues, may not be the cause in this case, but it's a quick check type item .

Other than that, you need to go through the carbs and possibly the ignition system to find the fault .

It just may be a case of cleaning the carb internal parts / passageways .

[quixotic]

So I torqued the heads (and they needed it; the four long bolts on one of the cylinders were probably only at about 10 foot/pounds), adjusted the valves, installed a Boyer electronic ignition, cleaned all the connectors to the coils and grounds and used a bit of dielectric grease.  Then I set the timing with a strobe light.  

Then I started it up.  It seemed to start more easily than before.  The idle and everything below about 3,000 rpm is now VERY smooth.  But from 3,000 up to about 5,000, it's quite rough.  

(I'm not sure about 5,000 and above.  I'll take it out on to the highway tomorrow.)

But the weird thing is that the tach tends to bounce all around above 3,000 also.  Below 3,000, it does what it's supposed to do.  Is there possibly a connection there?  Or would it more likely just be a coincidence?  

I still plan on balancing the carbs some time soon, but I'm wondering if that's even an issue (since the bike runs so smooth below 3,000 rpm).  

[Barry]

The bouncing tach needle above 3000 rpm suggests an ignition problem.

[Luca]

It would probably be worth it to make sure that you have a strong spark on both cylinders using an external, grounded plug.

You can have different carb problems at different RPM's.

Idle circuits will mess with idle and low to lower mid range, while the slides and needles will mess with things at higher RPM's.

Carbs are always the last thing to adjust.  With properly torqued heads and adjusted valves, and proper timing, you should now do a carb balance.  If you carbs were adjusted to run ok on an improperly tuned engine, they will not serve well on a properly tuned one.

Also, make sure that your chokes are fully returning on both carbs.

[quixotic]

It would probably be worth it to make sure that you have a strong spark on both cylinders using an external, grounded plug.

I assume this means taking both plugs out, inserting them back in their wires, making sure they're grounded to the fins, and then turning the engine over?  

I just took the beast out for a spin on the highway.  I think the tach generally works, but when I accelerate, it momentarily (ie, for a second or two), goes down.  And it has a tendency to bounce around a bit (not rock steady, like the speedo).  In general, I'm not even sure I trust it enough to do the timing at 3,000 rpm (though at 1,000 rpm, it seems quite steady and reliable).  

I think I heard a bit of pinging (sounded like rocks in a can), so I'm going to double check the timing.  This time, I'm going to put white-out on the flywheel indents (like I should've done in the first place).  

[quixotic]

WOW!  The W6 plugs that the previous owner put in the bike showed a slight imbalance in soot levels.  But when I put in brand new W5 plugs and did a quick highway run, I got the following.  I suspect that a carb balancing is in order.  

BTW, I checked the choke cables and the right and left activate at about the same lever position, and when shut off, the lever down on the carb is definitely shut off.  

[Luca]

assume this means taking both plugs out, inserting them back in their wires, making sure they're grounded to the fins, and then turning the engine over?

That's the ticket.

Well, it could be an electrical/timing problem causing the unsteady revs, though with 20,000km I doubt your timing chain is worn so I'd look to ignition...  but your problem used to be below 3kRPM and now it's above it, and you haven't done anything to the ignition system except set the timing and clean things up.  I'd go to carbs if the sparks look good and you've set the timing again with white-out on the flywheel (syncing is free too).

Poorly balanced carbs can lead to unsteady revs.  I'm willing to bet your problem lies in the main (needle) jet or the needle itself, given the rev range.  If the cables were off I'd expect the engine to stumble once off-idle...  but again, syncing is free, so why not see if it helps.

Could be a bad diaphragm, or it could be that one needle/jet is more worn than the other (the one with the sooty plug would be more worn and letting more fuel past)  They should always be replaced as a set.  If those parts are bad, you can't really sync the carbs perfectly, though you could probably still improve the smoothness of the engine

As you sync the carbs, you might find that the tach smooths out.  If you have a digital timing light with a tachometer feature try using that while syncing.

I think the tach generally works, but when I accelerate, it momentarily (ie, for a second or two), goes down.

Does the engine bog down too, or just the gauge?

I think I heard a bit of pinging (sounded like rocks in a can), so I'm going to double check the timing.

What grade gasoline are you using?

[quixotic]

Does the engine bog down too, or just the gauge?



What grade gasoline are you using?  

It's just the gauge that flops back down.  If it was the engine, I'd probably get thrown over the handlebars    I re-set the timing last night, and indeed, with the white-out, I saw that I had previously set it a bit on the advanced side.

I only use premium, and of that, I only use the high-test at Shell.  

I'll sync some time in the next day or two, but today, I'll also order the carb rebuild kit from bmw2valve.com.  I see that they don't seem to sell needles and jets, so I'll have to try Anderwerks in Calgary.  

[quixotic]

One thing I noticed when watching this video (at about the 8:35 minute mark):

http://www.youtube.com/watch?v=HShbaC9ORSo

was that the F mark on the flywheel was rock steady under the strobe lamp.  

But when I did the timing on my bike, the strobe seemed to catch the S mark at two slightly different spots.  I assume that this isn't normal, but I also would have assumed that the Boyer ignition would have taken care of that.  Or is that a symptom of something else entirely?  Can a carb malfunction affect the timing in this way?  

[Barry]

But when I did the timing on my bike, the strobe seemed to catch the S mark at two slightly different spots.I assume that this isn't normal, but I also would have assumed that the Boyer ignition would have taken care of that.Or is that a symptom of something else entirely?Can a carb malfunction affect the timing in this way?  

The carb can have no impact on ignition timing.

Is it possible the boyer ignition plate is not centered in the bean can. Does the boyer have 2 magnetic sensors and are they exactly equal distances from the cam.