Author Topic: Rev Limiter w/ OEM points (Read 7240 times)

Bubba0374 · « **on:** February 16, 2009, 07:29:45 PM »

I know this might sound odd to some of you but I am planning a build for a 75 cb750 and I would like to forgo the electronic Ignition as it is far from a "period" upgrade and I feel it changes the spirit of these old bikes. The only thing I was worried about is I heard once you lighten and balance the crank these bikes rev up so fast you can easily destroy the engine. Are there any other ways around this? What did racers back in the day do?

bwaller · « **Reply #1 on:** February 16, 2009, 07:51:09 PM »

Up shift

fuzzybutt · « **Reply #2 on:** February 16, 2009, 08:56:35 PM »

they installed a dyna ignition and rev limiter

the dyna s has been around for a long, LONG time.

Soos · « **Reply #3 on:** February 17, 2009, 06:16:29 AM »

or go with dyna2000. rev limiter built in.

Why hasn't hondaman made a rev limiter to go with his system...

hrmm.

l8r

Duke McDukiedook · « **Reply #4 on:** February 17, 2009, 07:18:40 AM »

Quote from: Soos on February 17, 2009, 06:16:29 AM

or go with dyna2000. rev limiter built in.

Why hasn't hondaman made a rev limiter to go with his system...

Did you ask him about this? Extra parts sometimes = more things that can go bad/wrong.

moham · « **Reply #5 on:** February 17, 2009, 08:07:32 AM »

I can't comment on the technical aspect of your question, but you're right that it does seem odd to try to recreate the feel of a "period" when racers, etc were trying to develop technologies that are readily available now, unless your goal is to represent a "snapshot" of the state of things in a given period. It seems to me that when faced with the same question you have (how to limit revs for instance), their answer was: develop an electronic device to do so...

754 · « **Reply #6 on:** February 17, 2009, 08:18:29 AM »

There is nothing wrong with building a period correct bike. That being said, would it be more correct with points & limiter, or full electronics?? I am thinking points &limiter..

I would probably buy a limiter for points (non-stock) if it were available .

I have another question, is there anything out there for a magneto to limit RPMs?

moham · « **Reply #7 on:** February 17, 2009, 10:09:02 AM »

Quote from: 754 on February 17, 2009, 08:18:29 AM

There is nothing wrong with building a period correct bike.

I totally agree. A complete stock restoration would be a good example of that concept. And granted, this is a bit of a semantic argument. There just seems to me to be a gray area when considering what modifications would be "period correct". The idea of guys modifying their rides for performance seems to rest, in part, on an embrace of "advanced" technology, blurring the time lines of any "period" you might want to capture. Just my thoughts, no value judgment implied. I am interested in just about any project that somebody can come up with...

Bubba0374 · « **Reply #8 on:** February 17, 2009, 05:20:09 PM »

ok to clarify I am interested in building a higher performance 750 motor but i would like to stay as close to how it would have been done at that time. for example trading out the oem carb on your classic car for a holley 4 bbl. while this is not the stock carb its what someone would have done at the time for a performance upgrade.

754 · « **Reply #9 on:** February 17, 2009, 05:33:24 PM »

There are certain things that can acceptably be over looked.

And safety and insurance are right up there.

Things like better tires if original is not avaliable.

A rev limiter does not increase your performance it is more insurance. To me its not cheating like hiding a nitrous setup, or going big bore and lying about it..

Myself I never ran a limiter but have thought of it.

Jonesy · « **Reply #10 on:** February 17, 2009, 05:35:50 PM »

On many points-fired machines, the spring on the points was designed so that the points would "float" at a certain RPM (hence the articles about doubling up the springs to increase the revs). I don't know if the CB750 was designed this way or not...

Bubba0374 · « **Reply #11 on:** February 17, 2009, 05:45:39 PM »

point float was going to be my next question, I dont think mechanical points can even keep up around 17,000 RPMs so does that mean the old rc racers were electric? I believe the rc 166 red lines around 17,000

754 · « **Reply #12 on:** February 17, 2009, 05:57:43 PM »

They used Maxi-Dwells...

Wondering now if the 5 cyl 125 had 5 sets of points??

cb650 · « **Reply #13 on:** February 17, 2009, 06:01:38 PM »

Accel used to make one. Bought it but then realised it wouldnt work on the 650 cdi. Kept it just cause.

Bubba0374 · « **Reply #14 on:** February 17, 2009, 06:25:13 PM »

ok only had a sec to read up on the maxi-dwells but this exactly the type of mod i was looking for, i realize it does not limit revs in anyway but it is a period upgrade that can handle the high rpms.(anyone looking to get rid of a set

) Also some of you guys with lightened cranks how easy would you say it is to go past that point of no return

Steve F · « **Reply #15 on:** February 17, 2009, 06:48:45 PM »

Quote from: Bubba0374 on February 17, 2009, 06:25:13 PM

ok only had a sec to read up on the maxi-dwells but this exactly the type of mod i was looking for, i realize it does not limit revs in anyway but it is a period upgrade that can handle the high rpms.(anyone looking to get rid of a set ) Also some of you guys with lightened cranks how easy would you say it is to go past that point of no return

It's easy to do with a stock crank! Just miss an up-shift at redline and see how fast your tappet adjuster screws will come loose! (Don't ask me how I know).

Bubba0374 · « **Reply #16 on:** February 17, 2009, 07:42:27 PM »

wow thanks for all the input guys you have definitely given me a lot to think about, I really like the concept of the maxi-dwell although I am seriously considering the insurance of limiter. no one happens to know around what time dynatek began making ignitions for the sohc do they?

seaweb11 · « **Reply #17 on:** February 17, 2009, 07:46:57 PM »

There is some info here on rev limiters...........http://forums.sohc4.net/index.php?topic=17831.330

I've been lazy and it hasn't been wired up just yet, but I believe the issue is "missing a shift"
..................ziiiiinnnnngggggg and it can all go bad very fast with a peppy lightened alt/ motor.

hope this helps

fuzzybutt · « **Reply #18 on:** February 17, 2009, 10:07:27 PM »

ok but the dyna s was available when these bikes were still being built. jus' sayin is all

crazypj · « **Reply #19 on:** February 17, 2009, 10:43:11 PM »

One 500 and 550 the stock points 'float' around 10,750~11,000 rpm.
decent electronic ign allows around 13,500 rpm.
If you have correct points, (not generic aftermarket) they wont allow ignition at excessive rpm.
You will still have a problem with inertia though, if it builds rpm faster than you can control you probably shouldn't lighten crank (probably not a good idea for street driven 750 anyway)
PJ

754 · « **Reply #20 on:** February 18, 2009, 07:44:05 AM »

I have never had a tappet nut come lose and hit 11,00 frequently, and missed a few shifts.

Maxi-Dwell works well up to 11K or better, they are better points.

You know, in the early 70,s there simply were no rev limiters, and everyone still rode as hard as they could.

I was running mine on the street without tach or speedo, and would shift around 11k.One day I was racing against a Monster and we were fairly even, so I just revved it a bit higher to see if it would help, but I think I hurt it

Beside the Monster I could not really hear it like I usually can), think I will have to run a tach again..

Maybe we should make some new Maxi,s

Bubba0374 · « **Reply #21 on:** February 18, 2009, 10:14:38 AM »

I would definitely be interested in some, or if anyone knows where to find and original unit would be even better. Also out of curiosity did they make these for other size bikes like the cb500/550/650 ?

TwoTired · « **Reply #22 on:** February 18, 2009, 11:12:51 AM »

Quote from: 754 on February 18, 2009, 07:44:05 AM

Maxi-Dwell works well up to 11K or better, they are better points.

Can you describe the properties that make the points better?

I've seen this statement "they are better" in the advertising for the Maxi- dwell. But, no real evidence to support it.

I'd like to know just what makes them better. What brand points do they use?

Cheers,

Bubba0374 · « **Reply #23 on:** February 18, 2009, 02:27:26 PM »

Quote from: crazypj on February 17, 2009, 10:43:11 PM

If you have correct points, (not generic aftermarket) they wont allow ignition at excessive rpm.
You will still have a problem with inertia though, if it builds rpm faster than you can control you probably shouldn't lighten crank (probably not a good idea for street driven 750 anyway)
PJ

If this is true doesn't that make it the same exact concept as electric ignition w/ a rev limiter??? meaning you could still easily over spin your engine same as with points or elec w/ limiter

NitroHunter · « **Reply #24 on:** February 18, 2009, 04:51:38 PM »

About the lightweight crank rumors...
I once dragraced a stock F-2 with no dyno at all, just a sleeve over the oil hole, total loss ignition. It doesn't wind up all that fast, even in 1st gear. They just don't breath well enough. That's with about 8 less pounds of rotating weight on the crank.

I've also run a Falicone lightweight Supercrank with aluminum rods in a big bore hot rod motor, again no dyno. Now THAT wound up quickly, but unless a shift was missed at hideous RPM it could still be caught without limiter.
I wouldn't advise it tho...

Several companies make RPM limiters for mags, it depends on which type. I have one for the Mallory Sprint mag on my turbo.

When you get those rc 166 points figured out, I've got a tach for you...

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Author Topic: Rev Limiter w/ OEM points (Read 7240 times)

fuzzybutt

fuzzybutt