Info FZR250 purchase

@Linkin - encyclopaedic -



watch out @GreyImport it looks to be that someone may be preparing to challenge your position as the indisputable font of knowledge of all things on this website.

 

I have a more than a sneaking suspicion that on my death bed I will utter near unintelligible mutterings about FZR250 carbs - perhaps I should have an explanatory note tattooed somewhere on myself as to what it all means lest they think me insane

 

FWIW - A rabbit hole that I haven't been down for quite some time is EFI for the FZR250 using Speeduino (or RusEFI) because both can do:
Sequential spark; Sequential AND staged injection (lower flow, low RPM injectors and higher flow, high RPM injectors) AND can run throttle bodies with dual butterflies (this is actually very useful) because there's two candidates for throttle bodies.

Both potential candidates below would need to be cut and re-spaced closer, which actually only involves the butterfly shafts and their spacing.

GSR400 - 30mm throat diameter (the important part because less is more and too big is not a good thing)
https://www.msextra.com/forums/viewtopic.php?t=6602

The GSR400 spacing between cylinders is close ~10mm too wide @75mm; On the FZR250 Yamaha have actually angled the two inner cylinder intake ports ~4mm inwards when measured at the head manifold, intake port mating surface ~65mm - cylinder spacing is 61.3mm, and the inner intake manifold boots are angled also.

That's probably to accommodate the Mikuni carbs width (NUCKING FUTZ IMO if it's actually why )

GSR400 throttle bodies would have to be cut and re-spaced, from the msextra link above, they look to be 75mm between cylinders

and

Kawasaki EX300 2013-2016 throttle bodies (2 pairs) 30mm - they would need to be cut, trimmed and re-racked for spacing and the two pairs would need to be joined.

I think I actually do have the cylinder spacing measurement for the EX300 detailed somewhere ~70mm or slightly less from memory; it's less than the GSR400 AND they're tapered and they're much more abundant for much better prices.

I likely found the EX300 cylinder spacing on the Kawasaki Ninja 300 forums - there's some guys on there that do not have what seems to be most motorcyclists' aversion to measurement instruments (current company excluded obviously as I wouldn't want to hurt your feelings ).

I've found a few threads there, where I was looking for clues and found whole suites of accurate measurements that blew my mind.

Potentially if I can GTFO where I'm living now (which I hate) into a place with a shed I'll pick all of this back up.

I've got STM32 boards and suites of sensors, only lacking a suitable crank position sensor IIRC, which is easily solved.

I was targeting a YZF600 first as I've already got suitable throttle bodies, but everything hardware wise is near identical for the FZR250.

I'd probably check back in on RusEFI as there's complete ECU hardware cross compatibility between RusEFI and Speeduino.

 

I looked into the sequential and staged injectors fairly comprehensively - I've opted for twin sets of different flow rate injectors because to use just large ones would have them operating at ridiculously small pulse widths (low duty cycle) at idle, or if ones suitable for a good idle and low RPM running were selected, they wouldn't cope at high RPM because they don't have the flow capacity in an ever shrinking time window.

It's not so much high RPM that's the problem, it's the necessary RPM range, it's a 10X range, at least from 1600RPM idle to ~16000RPM peak power -> redline, which isn't much worth it really.

Also sequential injection is important, well potentially very beneficial, as opposed to batch injection which fires all injectors at once irrespective of where each cylinder is in it's combustion cycle.