warmup.....motor speed change....why?

Hewho,
Do you notice this more at certain times of the month, maybe around the full moon or something :lol:
Mike

In regards to wet sumping/crank drag: spinning a crank through oil takes power to acomplish.
Example: BOTT class racing, a Guzzi racer discovered that the bike made 5 HP more on a dyno when it was run a half quart low on oil. (they are a wet sump design)
At idle, the Norton isn't making much power, (most engines don't), so any friction reduction would show up as an increase in RPM's. Also, there isn't much space between crank and case bottom, (the reason for dry sump engine designs-clearance under it), so it doesn't take much oil in there to cause oil/crank contact. ANY contact will result in what you see when you are using a blender to mix drinks or such.
Another example: When we got our belt/cam 900 Ducati's broken in with regular oil and then switched to Mobil 1 (synthetic) at about 7k miles, the idle went up at least 400/500rpm. (less friction)

I seem to recall this idle speed problem back when all we had were points ignition. I usually ascribed it to weak springs on the advance weights. But, replacing them didn't always fix the problem. Wet sumping may have been the real/main cause. I await Hewho's electrical check with anticipation!

Well....it's Saturday and I asked my son to help me check this thing out to the best of our ability. We did the following.

Hooked up a voltmeter between the poles of the battery.
Timing light.
RPM meter.
Oli tank cap on, but loose.

Observations: Oil tank level, after one week, just at the end of the dipstick, Last week it was about half way between the H and L. Maybe 1/2 to 3/4 quart had sumped in a week. Battery volts at 12.3.

Started the bike, started first kick, but had to use choke, two times it had to be started to get it to run at an idle.

Following noted, as accurately as we were able to do...but naturally not resulting in data that you could call, "proven".

After 27-35 seconds, breather had stopped pumping oil and the PCV valve had balanced the air flow in the breather to almost none.

The timing sat at 15 BTDC.
The volts were at 11.8 VDC.
Rpms were under 1000.

By 3.5 minutes, the volts had gradually increased to 13 volts, the rpms gradually increased to 1500. Timing jumped about between 15 and 20 BTDC. The oil pumping up into the tank had a few bubbles in it and settled into a steady flow. Oil level already had risen to the normal level.

At 5.3 minutes, the volts went to 13.5, the timing stayed steady at 20 BTDC and the motor sped up to 1700 and smoothed right out. Oil level and pumping still steady and normal.


Observations, the sump was very quickly cleared by the breather and Oil level quickly reached a normal level and the pump quickly got into an even cycle. The rpms gradually picked up as the motor warmed up and the voltage started lower than I would have thought, but gradually increased with motor speed...until...the voltage reached about 13.5, and the motor smoothed out and increased speed within a period of about 10 seconds. This was a noticable speed increase, less vibration and a happier motor, all of a sudden. There had been a couple of false starts on this, where the motor picked up speed and almost smoothed out, and I thought...here it comes, but when this finally happened, it was unmistakable. A smooth idle and a fast but happy motor.

My reading on all this....? I am as aware as any of you, that my readings and figures on this are to be taken with a grain of salt...but I am pretty sure the oil level was not a factor. The oil system had settled into a normalcy long before this smoothing out of the motor.

The timing and volts gradually increased as the motor warmed up and increased speed , and reached about 18 to 20 BTDC, but the motor was not smooth.
The smoothening out of the motor, and corrsponding increase in the motor speed came, when the voltmeter read 13.5.

I think the boyer was not happy until it got enough volts, and the voltage it wanted, was only reached when the motor sped got up to a point where the alternator could produce those volts. The timing jumped about until the volts reached 13.5.

In conclusion: I can't really say what caused all this, and for that matter, can't even "prove" my results, but it could be caused by volts, or maybe not, and the fact of carb warmup...not even a thing I could measure, but I'm convinced the oil level had nothing to do with it. My gut feeling goes with the volts not being high enough. Incidently, last year, when I replaced the original tail light bulb with the led kit, I was convinced that the bike suddenly picked up a good bit of power..it ran stronger and didn't falter at a stop sign when you put the brakes any more. I attributed it then to the increased voltage the motor now had to run with, which was obvious, because the headlight no longer almost went out when I put on the brakes, as it had since new.

I want somone to run some simular tests and see if they come to a conclusion...be it the same as mine, or be it totally different..... :wink:

Hmm, well somewhere around 13.5 volts the battery will become fully charged and will then draw very little current. I had a different answer, but after looking at the electrical diagram for the bike, I think the only way to isolate the electrical would be to use a variable power supply, to supply a steady voltage that won't change. Most people don't have one so the only other way to try it would to use jumper cables from a running vehicle and that way you would have full voltage from the start. Then see if the rpm's change after the time period. (this would have to be done carefully and one should have some electrical/electronics experience, which you seem to)

Another thought on this is if you have ever helped someone jumpstart a cage that has a dead battery, as soon as his engine starts and you disconnect the jumper cables, your engine will increase in rpms due to the alternator no longer using so much HP to generate the extra current. Same thing happens with an air conditioner, albiet that's a fluid pump, but it still takes HP to run it. And when it starts or stops, it always causes a sudden rpm change just as you describe.

Batt Voltage

Hewho, just a reminder that a 12v batt should be 12.6v minimum when fully charged. Seems you are starting with a weak batt. You might want to check for a constant draw at the batt with ign off.

Killing the headlite when activating the brake light would indicate a dead batt. Replacing the brake light with an LED is just covering up the real problem, which seems to be a lack of current/voltage in the system. Is the charging system still original? If you still have the blue can, the bike will still start with a dead batt. (although it helps to disconect the batt, if memory serves) Voltage of 11.8 is essentially dead for a 12v lead acid batt. If it was electric start, it probably would not crank over.

I don't recall the output specs for the charging system, and can't find my manuals. But, I would check out the system, since what you have described of it's history indicates poor output. (don't forget to check/clean all grounds in the harness)

Hewho
1700 RPM seems way too high for the idle speed anyway. Is that what you normally set it to? And if so,-why?

So Hewho, if i read you right your bike idles at 1700 rpm :?:
Mike

I observed my Boyer-fitted 850 at the weekend, letting it idle with the oil cap off and detected no symptoms. Revs didn't vary by more than 100 r.p.m. over 10 minutes. I have never wanted to achieve lower than a smooth 800 - 900 r.p.m.

I don't think that I would call 1700 r.p.m. a tickover anymore. Can you select gear and ride it at that sort of level or does it fall back again?

I have a set of the extended tick-over screws and find them useful for raising the tickover a touch on winter mornings (at the same time as ruining my gloves by hugging the cylinder barrels).

Inefficient batteries do cause all sorts of odd symptoms, especially with Boyers in my experience. Have you measured voltage at the coils as well ? A couple of oxidised connectors en-route will make things even worse there.

Will try once again. to address all issues in one shot.... :wink:

Yes...1700 is a bit fast for an idle, will have to try and get it down...just HATE messing with the carbs...like a neverending game. I'm the last one to be claiming I'm good at it. Will check through the electrics, Battery is near new and if you noticed, the battery reading at start, was about 12.3 or 5...not really a weak battery. The battery voltage went to below 12 after startup and didn't rise above 12 until the bike had been running a while...maybe due to low motor speed. Alternator is the original, not known for high output, if what I hear is true.....agree that the idea of starting with a power supply and a good steady 13.5 volts right from the get go, might improve the running during the whole warm up period, but have no such power supply at hand. Won't bother with a jump from another battery or vehicle at the moment. As to the head light thing, that USED to happen, but not since I replaced the battery, and then built in the led tail light. If having the head light take a dive is not the way the bike was built, then this bike has had a problem for over thirty years....that was parr for the course with this machine and I never would have known differently as I don't have several machines to ride and judge by. But , you might be right...blue can? Never tried to see if the bike starts without a battery, but I know it won't start if the battery is too low...Boyer just doesn't like a dead battery....unlike a points system, which will start the bike, even if the battery is almost dead.

Having a bike that doesn't vary the idle speed over more than 100 rpms, at warmup? Strange stuff to a guy whose machine picks up about a thousand over the warmup period....
Will clean up the loom, re-do the carbs and see if the situation changes. Thanks y'all ... :wink:

hewhoistoolazytologin said:

Having a bike that doesn't vary the idle speed over more than 100 rpms, at warmup? Strange stuff to a guy whose machine picks up about a thousand over the warmup period....
... :wink:

Click to expand...

I can't really explain it but that's how it was. It was a warmish afternoon. I don't have chokes so I suppose I controlled it with the throttle for the first minute or so until it settled down. The carbs were sleeved last year by Martin Bratby. Quite possibly they're better than new (he sizes the slides individually to the reamed bodies)

I had a lot of trouble with "dry" connections a little while back after fitting a new ("genuine") loom. It had tinned wires in crimp connectors and I was intermittently getting less than 12v at headlight and coils (but not always at the same time.) It rather horrified me just how much can get lost on the way. By-pass wires to the coils and the headlamp provided an interesting control.