Motoscrubs.com

I'm a new member and have spent some time on the bevelhead digest. I met Jim via email and we were talking about his relays. I have a new to me, 1972 250 Mototrans (allegedly 3k miles), that I'm fixing up a bit to be my daily transportation when I relocate to the Dominican Republic, which I'm planning on doing around September 1. There are no street lights, and on a moonless and foggy night, if your light doesn't work...it can be difficult to stay out of the ditch (usually filled with cactus) and on the road, no matter how slowly you crawl in 1st gear! So I'm converting to 12 volts using the MZB Powerdynamo http://www.powerdynamo.biz/eng/systems/ ... 54main.htm that puts out 100 watts. Phillips makes an H4 lamp that is a 67/60: http://www.ebay.com/itm/Philips-9003-H4 ... ff&vxp=mtr

I can run a dedicated circuit with a separate fuse to a relay in the headlight bucket (I'm an electrician, my spade connectors are mostly Thomas and Betts nuclear power plant control panel spec) and I don't mind putting in an LED tail light bulb to save a few watts. It seems like I should have adequate power to run the high beam, even though most of the time it will be on low beam. Phillips claims you get an extra 50 feet of beam. I do know that down in Luperon DR, there are a LOT of black cows wandering the roads at night. A friend jokes, they let the white cows out during the day and the black cows out at night! Fact is, there are black cows out during the day as well...and horses grazing at the side of the road at dawn. Slightly OT, I'm doing something similar with a 750 GT (150-180 watt 916 Corsa alternator) and my Norton. I have enough output with those, I'm not worried.

I suppose I should spill the rest of the story, Malcolme sold me some larger valves and sent me some jam nut rockers, I'm going to put in a Megacycle "stock" cam which I think is similar to a green and white. My head guy is going to raise the floor of both ports and leave the material around the intake valve guide. He's been doing this a long time and knows the right stuff to do and NOT do. I'm sending a 30mm Amal out for a resleeve and am going to get a #2 and a #2 1/2 cutaway slides. I'll be using the stock air cleaner and a Conti replica stainless exhaust. Any commentary on the slide cut away issue? I haven't pulled the head yet and will try to "cc" it so I know what the CR is. I'd rather not go to 10:1 as I want easy starting and longevity. I'm hoping it's 9:1, but suspect it is less. Guidance and/or comments appreciated.
Stevan Thomas

As you've mentioned using an Amal carburettor on your 250, you know I had a really nice running '69 Mk3 250 with these settings:

Amal Concentric
Model R930/300
MJ 250
NJ 106
PJ 40
CA 3
JN 2 ring
CP Centre
No air cleaner

Jordan

I am going to defer to Bob and others, but I will start the discussion by stating that your power budget is, as you know, 100 watts.

Besides the headlight, I would imagine the next two highest loads are the ignition system and the brake light bulb.

If you are going to use an incandescent bulb for a brake light, I would imagine you will have a 15 watt brake light. Add another 5 watts for the running light and your power budget is now down to 80 watts remaining. Using an LED taillight would help you save on some of that power.

Do you have any specs for the power consumption of the ignition system? You need to deduct that power from the 80 watts you have left.

If you are running a battery so as to have stored power for starting the motorcycle, you will need to budget a little power to be siphoned off to recharge the battery while you are riding.

If you are going to illuminate the instruments there will be a little wattage deduction to run those bulbs.

The horn I would not worry about - its duty cycle is (hopefully) small, being on for 5 seconds and off for hours (but maybe it's on more than off in the DR?) For low usage the horn's instantaneous need for power can be sourced by the battery and you are recharging the battery with a small trickle of power when you are riding so no need to deduct the battery power from the power budget.

So if I am thinking clearly you deduct the ignition power from the 80 watts and see where you are. Subtract as best as you can estimate for the other loads and that should tell you the maximum wattage you can afford to spend on the headlight.

See what other advice you get and you should be able to move forward with your headlight purchase.

Jim

This thread could go in many different directions, lol...

Sounds like a nice performance motor setup and I assume you'll be spinning it up some to take advantage there, (though with the driving conditions there maybe not) which is what your 'power budget' will mostly depend on. That and electrical load of course...
I have no experience with your particular alternator but from doing some testing on others, things are largely rpm dependent, that 100w may only be achieved at 6 or 8 k rpm and at lower rpm could be substantially less.
The 'break-even point' where you neither lose nor gain charge varies quite a bit between alternators and load and can be anything from 1k to 5k rpm, depending on a multitude of factors. The headlight wattage is by far the largest load to the point where it's really the single big concern in this case and the easiest variable to control/alter (though not as significant, the already mentioned led tail/brake lights are a no-brainer).

The largest practical sized battery would certainly help and a higher amp hour battery as opposed to a similar sized higher cranking amp one would give some advantage as cranking amps are obviously a non issue with a kick start. So keep in mind when choosing one that battery capacity can be a trade off between amp hours and current capacity. For example the Yuasa ytx series AGM's are more amp/hrs, less cranking amps relative to their ytz series counterparts which are the reverse.
The lightweight/high efficiently LifePo4 batteries tend to be lower amp/hr, high cranking amps but some, like the Shoai's, are a bit better relative to amp/hrs and they all still have the size/weight advantage over lead acid.
My extra-high compression 996 is all about cranking amps, lol, which is one reason I'm so 'critical' on battery selection...

It would seem that the most obvious way to proceed would be to try various amounts of load at various rpm and measure the voltage to find where you need to be to maintain adequate charging voltage, then guestimate your average usage (time at a given average rpm and amount of use with/without the headlight). Then whether the fully charged battery capacity alone will get you through the worst case amount of low rpm night time use and judge the allowable headlight wattage from there.

Bill

By: nortonmarg...
" Phillips makes an H4 lamp that is a 67/60: "

____ Sylvania makes a similar HL.bulb especially for motorcycles, (link: http://www.ebay.com/itm/350445436655?ss ... 1438.l2649 ), that's 65/45-watts. _ With that bulb you can run a lower-power light when you need to run at a lower average-RPM.
Since Duke-models which run with the stock 6-pole alternator well handle a 45-watt headlight (plus all stock loads), your new charging-system's supposed increased power-output ought to continuously-allow even lower average-RPM riding (while running with that same full power-load).


" I can run a dedicated circuit with a separate fuse to a relay in the headlight bucket "

____ That's a good-idea (and simple to do) for the high-beam circuit.


" It seems like I should have adequate power to run the high beam, even though most of the time it will be on low beam. "

____ Your break-even point ought to be adequate enough with your particular combo of power-output & headlight-load.


" Malcolme sold me some larger valves "

____ Lager valves will not help engine-power while matched-together with the STOCK (small sized) valve-seats.


" I'm going to put in a Megacycle "stock" cam which I think is similar to a green and white. "

____ It would be interesting to look-over the specs of that particular cam !
__ But what are you thinking, are you going top-speed racing too ? _ Cuz the Green&White cam isn't of much use except at constant high-RPM ! _ Compared to your stock (Monza-type) cam,, while mid-range RPMs will be roughly more or less equal in power-production, your new low-end power-output will greatly suffer, (and far-more so than the relatively-slight notable gain you'll get only at top-RPMs). _ In other words,, your OVERALL power-production (available from your entire rev.range), would be reduced, (averagely overall). _ That's because such extra-wild cams have been designed to accept great low-end power-losses in exchange for relatively slight increases in max.power-production (at the highest RPMs where RACING is expected to be done, [in which more power is of-course desired] ).
So unless most of your riding-time is spent racing (at high-RPMs !), it would be of better use to you to employ a milder cam (than any cam such as the much over-rated G&W.cam).


" I'd rather not go to 10:1 as I want easy starting and longevity. I'm hoping it's 9:1, but suspect it is less. ? "

____ I believe the stock-piston's CR is 9.5:1,, however, the type of cam you're considering needs to be matched-up with a high-CR piston, otherwise you'd end-up with LESS power (than stock) THROUGHOUT your entire rev.range (with a low-CR.piston). _ In other-words,, while such a very wild race-type cam will allow for better-breathing/cylinder-filling at top-RPMs,
when matched-up with a low-CR.piston (9:1 & lower), the expected power-gain is then likely more than canceled-out (in comparison to a stock/mild-cam & high-CR.piston).


Dukaddy-DUKEs,
DCT-Bob