Bmw r75/5 microsquirt project for a newbie

[LAV1000]

Hi fefenin,

Nice to see you back
About the big injectors that was me
Try to find some throttle body's which match your bike performance.
Use the inside diameter off the inlet manifold as a guide, you don't need much bigger.

Or adapt the original throttle bodys to some small car efi injectors.
Use PK/cillinder as a guide.
For instance injectors used in fiat are much cheaper then BMW or Ducati.
Do you live in Europe ?
Magneti marrelli pico injectors are used on a lot european cars, fiat,renault,peugeot,citroen,alfa, vw.

And sell those ducati parts, to gain some money for your Beemer.

[R100RT]

I believe you were using the throttle bodies off another BMW boxer engine, right? What bike did they come off (the size may not be that far off)
Getting a cam signal may push you towards many more modifications that are perhaps not really necessary. I may have influenced you in that "Sequential" direction, but for general purposes you should be fine with a regular ignition system, waste spark etc. I re-machined a stock BMW "bean can" to contain a single tooth and a sensor. I'd stay with a crank tone wheel/ sensor and wasted spark. Send me all your engine specs, injector sizes and I'll run an MSQ on wasted spark for you (in my spare time).

[LAV1000]

I think he is/was using ducati 748 throttle body's.

[fefenin]

Thank you for all your advice . I will have a look for injectors body from an other boxer as the r850r that is closer in diameter and CC .
And I was using Ducati 748 bodies that were modified so I am not sure I can make money from them.

For the cam sensor I found an elegant solution by replacing the trigger point plat by a custom made plate holding a hall sensor. When the sensor is in place is it really more work in software?

Ok now rebuild time will take place and seeking for new injectors...

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[fefenin]

R100RT : my bike is a r75/5 from 1973 rated at 50 horses power.
749 cc or very close
Crank wheel is 24 teeth counting the one missing (24-1)
Hall effect sensor for that.

Injectors few info I have say iw724 give 310cc at 5 bars
I use them at 3.5 bar
The were mounted on a superbike at more than hundred HP and reving way higher

With the new alternator battery is very healthy on the 13,8 side.

Cam sensor will be mounted maybe . Could do later. Only with a magnet on the shaft glued and heat shredded.

Do you need more infos ?


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[fefenin]

LAV1000: yes i live in France
I don't really get how to choose my injectors then . Those one are too big so they have are time to open a little right?
But the dead seam critical also so I don't know how to choose really



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[R100RT]

I stand corrected on those

Here's my opinion - the throttle bodies might be okay having 44mm restrictors which may be slightly further reduced by your inlet tubes which perhaps are the small ones (the tube that threads into the intake port). The green injectors (show as p/n-IW724 Magneti Marelli) may have a reasonable fuel output for your 750cc engine, when the pressure is reduced as you mentioned. 5 bar = 72.5psi, while 3.5 bar = 50.7psi. You could even bump down to 3 bar for 43.5psi which is pretty standard over here. That would drop your flow cc rating well down into a good zone for reasonable PW. If you can't locate the Dead Time specs on line you might choose a reasonable starting number (like 0.8ms) to get running and then use the alternate squirt method to view your afr changes. That part is quite easy to dial in regardless.
If you have a plan to add a Hall sensor to a stripped out cam mounted "Points Plate" then the sequential ignition settings are "Not" hard to use.

One thing once the engine is together and requires breaking in (and the airheads require some good loading and hard running to get that right) - you might want to consider running the original points ignition and carbs until some miles are on her and then resume doing the MS conversion. There is no point harming a fresh engine if there are some issues to deal with.
Just some thoughts.
Lorne

[fefenin]

Ok got it ... Really not cool it is heavy mods to put back carbs and ignition...but I'll see what I can do

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[R100RT]

Well, you don't have to put the carbs and points back in - its just a way to go. If you proceed carefully on wiring and msp preparation, you may just turn the key and drive it away for the break in procedures.

[LAV1000]

@fefenin,

I would use something like 140-160 cc/min on a 3 bar system.
A lot of systems run on 3 bar, so there is more choice on pressure regulators.

I first used something bigger whit lower pressure 2.5 bar.
But this setup was to close to deadtime of injectors on idle.

I now use 3x IWP023 on 3 cillinder 1000cc aircooled engine at 3 bar, rev max is set at 9000 RPM.
Also using modified throttle body's of a kawasaki GPZ 1000 think it is 30-32 mm.

[fefenin]

Found a sv650 body would that do? Plan to remove the secondary motor driven butterfly.

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[LAV1000]

How well do they fit to the inlet manifolds ?
Any idea on injector flow ?

Secondary valve out seems to be a good plan.

[fefenin]

They fit very closely maybe 1 mm bigger at diameter I didn't check the flow yet but will have a look ASAP.

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[fefenin]

This info is had to find but the suggested flow rate you told me about seams very very low...

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[LAV1000]

They fit very closely maybe 1 mm bigger at diameter I didn't check the flow yet but will have a look ASAP.

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Seems to be a nice fit, far better than those 748 units.
What is the resistance (Ohm) of those injectors ?

[fefenin]

I have seen 12 ohm somewhere but have to check again time is flying...

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[fefenin]

Have really hard time to find any data exept that it is from Suzuki sv650 and it is named 15710-17G00

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[LAV1000]

The proper way to calculate dead time is on this "U" tube video, but a bit more involved and dangerous if you're using gasoline.
https://www.youtube.com/watch?v=lJgi8l-2XG4

Lorne

Use this for flowrate and deadtime, R100RT posted this earlier.

If you don't have a graduated cilinder you can also measrure the weight (gr/sec) of fuel and convert this to cc/sec.
Kitchen scale will work, don't work in the gram region but stay above the 10 gram whit measured fuel.
Oh, and don't tell the missus about the kitchen scale

12 Ohm is also a good value, so it is no weird low spec injector.

[fefenin]

Thanks à lot . I'll have to wire everything back , then...

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[LAV1000]

Did make a mistake upon the units has to be gr/min and cc/min.