Topic: dohc ignition on sohc?

[Mantree]

dose anyone know if the electronic pulse generator from a dohc 750 on a sohc engine?  I am slowly fuel injecting my 750 and one of the steps in this is that i want to swap the points for a pulse generator to trigger batch injection and ignition off of.  for time being I will use gm hei ignition units using factory advance.

[HondaMan]

I'd strongly suggest you take a real close look at your power budget: the CB750 SOHC can only generate 200 watts of electrical power, at that at minimum 5500 RPM. This is one of the major reasons why you do not see many of them fuel-injected. Most EFI systems, if they use more than 1 injector (in a common manifold) use about 3 watts per injector per 1000 RPM. With 4 injectors this works out to 12 watts per 1000 RPM, or about 9600 watts at redline. The bike can't feed that much power, let alone keep the lights on, or run the electronics that run the injector(s).

The ones that have been successful that I have seen used Kawasaki LTD (900 cc engine) injectors because they were oversized, letting the pulse be shorter to use less power. It would not idle well below about 1200 RPM (if at all) and was hard to start until the owner made a special long-pulse bypass circuit for starting. The controller he used was hand-built, as even the Megasquirt used too much power (I once tried to design one using Megasquirt, but the fuel pump pressures needed were high enough that the fuel pump alone used 1/3 of the bike's power capacity.)

Also keep in mind: all pulse-driven electronic ignitions use 150% more power (some even more than that) than using points. My Transistor Ignition uses 0.1 amp extra power, which is the least-possible power-cost alternative for electronic ignition, and was designed expressly for these bikes (for that reason).

[Mantree]

i have already switched most of the bulbs to led (just need to swap the headlight)  and i plan to swap in a cb750a generator to produce the power needed, I have already swapped for a slid state reg/rec unit.  i will be using gsxr600 throttle bodes and i am looking for a sportster fuel pump 

[HondaMan]

To get the extra 45 watts of the 750A alternator, you only need to change out the field coil. The alternator is the same unit (windings). The field coil is lower resistance to generate a stronger magnetic flux field, which means that it loses more power at engine speeds below 2000 RPM than the standard version. The 750A was geared low and has a solenoid to bump up the idle when it is stopped in gear to help prevent the idle from dropping below 1000 (1100 is better). The output goes to full charge at about 3000+ RPM with the "A" field coil installed.

There is a 750 with the GSXR600 throttle bodies in LA that is running. He mentioned here in the forums (some years ago) that he only used it for hiway trips as the power dropped too low for Saturday-night in-town riding, causing it to stall out after about 20 minutes of city-only riding.

[Mantree]

I figure if my steps to up and save power aren't enough then i will pull the parts off and install them on my xvz1300 instead and can reinstall my original carbs but i would like to still go to electronic ignition with all the lights switched over to led including dash lights i will only be pulling 57.24w with everything lit including high beam that is just under 5 amp.  that is compared to stock load of 221.28w if using a single bulb tail light (mine had a dual bulb bring it to 248.16w)  now when i had all incandescent light on the bike i had to put on low beams at lights or risk having it stall if sitting for long.

edit
this is all calculated off of max power draw listed for the bulbs.

[HondaMan]

I figure if my steps to up and save power aren't enough then i will pull the parts off and install them on my xvz1300 instead and can reinstall my original carbs but i would like to still go to electronic ignition with all the lights switched over to led including dash lights i will only be pulling 57.24w with everything lit including high beam that is just under 5 amp.  that is compared to stock load of 221.28w if using a single bulb tail light (mine had a dual bulb bring it to 248.16w)  now when i had all incandescent light on the bike i had to put on low beams at lights or risk having it stall if sitting for long.

edit
this is all calculated off of max power draw listed for the bulbs.

You're thinking along the right lines. Here's some tips:
The points-and-coils (aka Kettering) ignition (OEM) is 2.8 amps continuous, about 34 watts.
The headlight + taillight (you already know how to add this one up).
The alternator field coil (stock version) draws 1.6 amps continuous (19 watts): the 750A version draws 2.1 amps (25 watts).

So, with the lights off, the bike runs around 55-ish watts with the lights off. You can estimate the other power loads from how long you might sit at a light, etc., and you will have to add the EFI load as a (constant base load + RPM).

[Mantree]

ok so 57.24w going to lighting and 1.14‬w to ecu (95ma) coil about 34w and field coil at 19w what i have read is that the small injection pumps run around 3a putting them around 36w so using your calculation of 12w per 1k that puts me right around ‭‭159.38‬   putting me so close to what the stock unit puts out so with the 750a coil i should be fine.  the bike doesn't like to idle below 1k with the high lift cam and open pipes (starts to lope real bad and will stumble if you open it fast from low idle).

[scottly]

  I am slowly fuel injecting my 750 and one of the steps in this is that i want to swap the points for a pulse generator to trigger batch injection and ignition off of.  for time being I will use gm hei ignition units using factory advance.

You can use the points as a trigger for the EFI...

[Tracksnblades1]

I'd strongly suggest you take a real close look at your power budget: the CB750 SOHC can only generate 200 watts of electrical power, at that at minimum 5500 RPM. This is one of the major reasons why you do not see many of them fuel-injected. Most EFI systems, if they use more than 1 injector (in a common manifold) use about 3 watts per injector per 1000 RPM. With 4 injectors this works out to 12 watts per 1000 RPM, or about 9600 watts at redline. The bike can't feed that much power, let alone keep the lights on, or run the electronics that run the injector(s).

The ones that have been successful that I have seen used Kawasaki LTD (900 cc engine) injectors because they were oversized, letting the pulse be shorter to use less power. It would not idle well below about 1200 RPM (if at all) and was hard to start until the owner made a special long-pulse bypass circuit for starting. The controller he used was hand-built, as even the Megasquirt used too much power (I once tried to design one using Megasquirt, but the fuel pump pressures needed were high enough that the fuel pump alone used 1/3 of the bike's power capacity.)

Also keep in mind: all pulse-driven electronic ignitions use 150% more power (some even more than that) than using points. My Transistor Ignition uses 0.1 amp extra power, which is the least-possible power-cost alternative for electronic ignition, and was designed expressly for these bikes (for that reason).

I'm having a little trouble with the 9600 watts at redline. What redline? 80k?

That's a huge alternator. I have a spare  Leece Neville 320amp alternator, weighs 35#s, but it's output is only 4325 watts at 13.5 vdc.

My old Lincoln SA200 welder (pipe line special)  only specs at 8000 watts...

That's going to require a healthy injector wiring harness....

I'm thinking maybe the fuzzy math type all taxpayers are subjected to.
 Not that of Zadeh, Luk and Tar..

[HondaMan]

I'd strongly suggest you take a real close look at your power budget: the CB750 SOHC can only generate 200 watts of electrical power, at that at minimum 5500 RPM. This is one of the major reasons why you do not see many of them fuel-injected. Most EFI systems, if they use more than 1 injector (in a common manifold) use about 3 watts per injector per 1000 RPM. With 4 injectors this works out to 12 watts per 1000 RPM, or about 9600 watts at redline. The bike can't feed that much power, let alone keep the lights on, or run the electronics that run the injector(s).

The ones that have been successful that I have seen used Kawasaki LTD (900 cc engine) injectors because they were oversized, letting the pulse be shorter to use less power. It would not idle well below about 1200 RPM (if at all) and was hard to start until the owner made a special long-pulse bypass circuit for starting. The controller he used was hand-built, as even the Megasquirt used too much power (I once tried to design one using Megasquirt, but the fuel pump pressures needed were high enough that the fuel pump alone used 1/3 of the bike's power capacity.)

Also keep in mind: all pulse-driven electronic ignitions use 150% more power (some even more than that) than using points. My Transistor Ignition uses 0.1 amp extra power, which is the least-possible power-cost alternative for electronic ignition, and was designed expressly for these bikes (for that reason).

I'm having a little trouble with the 9600 watts at redline. What redline? 80k?

That's a huge alternator. I have a spare  Leece Neville 320amp alternator, weighs 35#s, but it's output is only 4325 watts at 13.5 vdc.

My old Lincoln SA200 welder (pipe line special)  only specs at 8000 watts...

That's going to require a healthy injector wiring harness....

I'm thinking maybe the fuzzy math type all taxpayers are subjected to.
 Not that of Zadeh, Luk and Tar..

YEAH!
There's a fast-typed typo! Thanks for catching that: it should be 96 watts (12 x 8  for 8000 RPM redline)! Even so, it's a bit much for these 200-watt alternators.

I fixed a lot of the old oilfield trucks using those Leece-Neville alternators: some had me install their 300+ amp units so they could weld out in the field with sticks and battery cables, when a truck broke something out in the boonies.

[Mantree]

I took a look ant the bike that I am using the injectors from only puts out 300w and that also goes to running alot of extra stuff

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[Tracksnblades1]

I took a look ant the bike that I am using the injectors from only puts out 300w and that also goes to running alot of extra stuff

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My son's 2014 Honda CB1100 has a 336 watt output alternator. It factory fuel injection is spot on every time, everywhere. When ever I ride it, cold, hot, or mild, spot on and perfect. It's control unit provides a limiter for RPMs and MPH in 5&6 gear 😩. Wasn't  for sure if you considered Honda's Cb1100 for your injection source.

[Mantree]

To be perfectly honest my decision came down to how close the spacing was and the fact that I could still run independent pods.

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[Mantree]

  I am slowly fuel injecting my 750 and one of the steps in this is that i want to swap the points for a pulse generator to trigger batch injection and ignition off of.  for time being I will use gm hei ignition units using factory advance.

You can use the points as a trigger for the EFI...

Partialy I was just going for the lower maintenance since I was already putting the ignition control under the microsquirt

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[scottly]

A few years ago, I looked at swapping the pick-up's and advancer from a sohc 650 onto a 750. The advancer would bolt onto the 750 crank using the longer 650 stud, but was longer and the stock points cover wouldn't clear. The 650 plate was smaller in diameter than the 750. Perhaps the parts from a dohc 750 would work; some things like the engine mounting points carried over from the sohc to the dohc...

[Mantree]

A few years ago, I looked at swapping the pick-up's and advancer from a sohc 650 onto a 750. The advancer would bolt onto the 750 crank using the longer 650 stud, but was longer and the stock points cover wouldn't clear. The 650 plate was smaller in diameter than the 750. Perhaps the parts from a dohc 750 would work; some things like the engine mounting points carried over from the sohc to the dohc...

Thanks I now know it is worth picking up a unit from a 750 in the junk yard.  I have a finned cover that has extra room inside.

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