A few more questions for 1976 R75/6

[Lifebeat]

Hello all!

I've working on the bike, and things are falling into place, but there are a few things that still boggle me... I need some help.

Biggest issue for me at the moment is this noise that "I think" is coming from the left side. It only happens when I ride, as soon as I got around 10 mph, and the frequency doesn't really change with speed (at least I don't think so, considering the noise and the helmet). The best I could describe this noise is : cricket... A continuous cricket sound, not really metallic or anything, just crickety sounding... I tried spinning the front wheel on the centerstand, I tried runing through the gears with the engine on, and the bike still on center stand. Checked my bearings front and rear when I changed my tires. All seems fine on all these points. Also checked all my fluid levels from engine to final drive. IT'S DRIVING ME CRAZY!!!! I feel like there is something unsafe, but I can't put my finger on it.

Secondly, after lapping my valves on the low pressure left cylinder, and getting it back to normal, I now notice that the right cylinder (that I haven't touched yet, but had 125 psi) is running noticeably hotter than the left one. Strange thing is that the right cylinder has the nicest plug... During my points adjustment, I think I saw that the spark on this right side was a bit week (I'll be getting new coils) but could this generate a hot cylinder?

Third, the carbs. I know I'll have to get into them sooner than later, but I noticed something strange. While I had the bike leaning on its right side, to change the shifter lever seal, the LEFT carburator started leaking out fuel like crazy. It looked like it came from the lever linkage or something... I tried the opposite stance just to validate the RIGHT CARB, and no, there weren't any leaks... This isn't normal right?

Lastly (I think) is the oil and neutral light. The neutral light just stopped working last week... I'll test the circuit to make sure, but is this the type of switch you keep on hand? Moving on to the oil pressure light. Since I got the bike, the oil light never worked... I shorted the pressure switch to the body, and nothing happened. This points to faulty wiring or just the bulb in the cluster right? As a broken wire would failsafe to a open light right? The question is then : do I really have to open the cluster??? Really dad?? really? I don't know why , but I can't see this going well...

Thanks again for all your support... You have no idea how much I don't feel alone knowing you guys are here...

Luc

[melville]

Give the front brake a wee squeeze and see if the noise changes. The pads will lightly touch the disc for a while after you've used the brake. On my own, I'll get a steady cricket sound if I'm on the brakes a lot, say in town or in the mountains. But a few miles of open road and the sound reduces as the caliper piston gets knocked back just that tiniest bit.

[Ken in Oklahoma]

. . .
Secondly, after lapping my valves on the low pressure left cylinder, and getting it back to normal, I now notice that the right cylinder (that I haven't touched yet, but had 125 psi) is running noticeably hotter than the left one. Strange thing is that the right cylinder has the nicest plug... During my points adjustment, I think I saw that the spark on this right side was a bit week (I'll be getting new coils) but could this generate a hot cylinder?

Third, the carbs. I know I'll have to get into them sooner than later, but I noticed something strange. While I had the bike leaning on its right side, to change the shifter lever seal, the LEFT carburator started leaking out fuel like crazy. It looked like it came from the lever linkage or something... I tried the opposite stance just to validate the RIGHT CARB, and no, there weren't any leaks... This isn't normal right?

Lastly (I think) is the oil and neutral light. The neutral light just stopped working last week... I'll test the circuit to make sure, but is this the type of switch you keep on hand? Moving on to the oil pressure light. Since I got the bike, the oil light never worked... I shorted the pressure switch to the body, and nothing happened. This points to faulty wiring or just the bulb in the cluster right? As a broken wire would failsafe to a open light right? The question is then : do I really have to open the cluster??? Really dad?? really? I don't know why , but I can't see this going well...

Re: Secondly
I can't imagine any way that a weak spark could "generate a hot cylinder". There are other things that can generate a hot cylinder and I believe they all will boil down to a lean fuel/air mixture, whether a vacuum leak or carb problems.

Re: Third
I don't know what's normal, since I've never "laid" the bike over on purpose. And any time the bike has been "accidently" laid over, I would have expected a fuel leak. I'm thinking you have a non problem here.

Re: Lastly
I wouldn't be very concerned about opening up the instrument cluster. Things do look a little delicate in there I know. You would want to be very judicious about tightening screws since that old plastic is fragile. And of course you don't want to deal with the tach and speedo mechanisms proper unless you really need to.

What you do want to pay a lot of attention to is the flexible printed circuit and it's connections with the bulbs and the pins which mate with the wiring harness plug. I have spent a bit of time "wrestling" with those connections in the cluster of my R75/6. Corrosion where the wires on the bulbs mate with the flexible printed circuit can be a problem. You probably want to brighten up the copper etch since cupric oxide doesn't conduct electricity nearly as well as copper. But the most vexing problem's I have had involve the pins where they make contact with the etch. They may look OK, but unseen oxidation can screw up the electrical contact, or worse yet be the source of intermittent problems.

It's a bit tricky, but I have peeled the outer coating of the etch where the pin meets and "fixed" the connection with a fine strand of wire wrapped and soldered around the base of the pin and then soldered the other end of said wire to the etch. I don't remember how I re-covered the area that I laid bare. Likely I used RTV silicone rubber from a tube.

The best remedy, if you suspect a faulty flexible printed circuit board, would be to replace it with a new one. But that is spendy. When I did the repair I was in a "poverty rider" mode--or cheap if you prefer.



Ken

[Major Softie]

Re: Secondly
I can't imagine any way that a weak spark could "generate a hot cylinder". There are other things that can generate a hot cylinder and I believe they all will boil down to a lean fuel/air mixture, whether a vacuum leak or carb problems.
Ken

Timing differential will also cause one cylinder to run hotter than the other.

[khittner1]

On the one hot cylinder, I'd be first concerned about a tight or sticking exhaust valve that's not keeping combustion adequately contained.

[Duane Ausherman]

How about rocker arm play? Did you double check the valve adjustment? Did you spin the pushrod to make sure it is straight? Could it be pre-ignition-pinking. Since you had the head off to lap the valves, you could have installed the head gasket backwards and the pushrod is hitting it.

If you hear it on the left side, is your front wheel on the left side? I highly doubt it is related to the front wheel, or rear.

we are not there to hear it, so our best guesses can be way off base.

[Lifebeat]

The hot cylinder is the one I didn't take appart, and the one that presented the best compression when I purchased it. But considering all this, I will be taking it appart pretty soon I think...

So for the noise then... What do you suggest I do? Is it plausible/safe to ride with a buddy that tries to listen leaning down while I ride? Because I've tried to lean over when riding, and theres only so far I can go down... And indeed, the sound doesn't seem to come from the front or rear wheel...

[melville]

The hot cylinder is the one I didn't take appart, and the one that presented the best compression when I purchased it. But considering all this, I will be taking it appart pretty soon I think...

So for the noise then... What do you suggest I do? Is it plausible/safe to ride with a buddy that tries to listen leaning down while I ride? Because I've tried to lean over when riding, and theres only so far I can go down... And indeed, the sound doesn't seem to come from the front or rear wheel...

Turn your sound on and give this a listen (click pic for vid):



Are you getting something like the little wheeze that you hear when the motor is shut off? That's the crankcase breather--if the bike has new rings, or has been sitting a while, it will make that noise more prominently until the ring seal improves. Particularly if the bike still has the original style breather, sometimes called a "turkey gobbler." Bike in vid has been updated to the later style reed valve breather, and so sounds a bit like a lazy saxophone.

But I still like the front brake explanation also--the front disc and caliper are on the left side.

[Jean]

The right-side HOT cylinder might be caused by late spark timing. This "could" be the result of a faulty plug cap or a faulty HT wire! A break in the inner parts of the cap or the wire, or the connector at the coil can make a late spark.
Likewise, a very lean fuel condition is also a possibility. You mentioned that you hadn't been into the carbs so things probably are not OK there.
Do not take the engine down until you are SURE these things are OK.

There is an overflow tube in the carbs. When you leaned the bike over to the right, gas probably came out of it. You need to get a BING manual or at least a drawing of the insides if the carbs. Why the other carb doesn't leak when you lean the bike the other way may mean the tube is stopped-up with crud. A tiny copper wire can be used to clear it.

Discs with holes all 'round DO make a ticking noise against the brake pads. You get used to it.
Do you have a "holey" disc?

Neutral light and oil light. Since BOTH of these are not working and they are "HOT" all the time (they work by completing the ground connection) that suggests burned-out bulbs or bad sockets or both. The charge indicator and the oil pressure lights are on the same hot circuit and share a fuse. Do these lights work? BTW, Hot wire in this case is a green w/black tracer wire. Working on the neutral switch is a PITA but it CAN be done with the tranny IN the bike!!
You have to agile tho.

[Lifebeat]

Well, Melville, I don't think we are talking about the same sound here, but it does give me the idea of trying to record it!

Quick question : I'm getting a timing light in order to do a proper timing of the bike... and in the procedure, I'll get to the carb syncing. I've stumbled upon one or two sites that mention that the spark plug grounding method is really bad for your coils, especially if you have CDI ignition... Now, I'm not planning to convert to CDI, but I am looking at the Bosch Blues, and new leads and socket just to eliminate factors... BUT if the spark grounding method could hurt my new coils, I'd rather know about it and avoid it... What is your take on this?

Alsom to eliminate the doubts on my Bing carbs could an overhaul with a basic Bing refurbish kit be enough? Also, any links to a Bing manual?

Thanks again community!

Luc