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CR750 Set Up

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philward:
As you are probably aware (from previous posts) I’ve got the CR up and running on the road and am trying to fine tune the bike – just need some opinions from the more technically astute members.
To recap, this is the set up
836 standard compression kit, moonpie 4 – 4 race exhaust with KO rear baffles fitted, Ramair foam pod filters, Boyer Micro system inc coils (new rubber head to carb rubbers by the way)
Set up so far. Started with standard carb settings and Boyer set up statically - as didn’t want to set up with strobe at 4500 as per Boyer instructions on initial tight engine. It run as per the following Youtube - https://www.youtube.com/watch?v=YmL8YYWeUMo (rev counter reading double by the ways – Smiths still trying to match odd Boyer signal to rev counter)
As can be heard, sounds ok (but if you run to the end of the video, it cuts out as I blip the throttle at the end) but when on road, short of fuel further up revs and when kickstarting, kicks back and spits back through carbs occasionally when kicking. Starts on 2nd/3rd kick).
After a few gentle miles, changed main jets to 135 and changed needle to second to bottom clip notch (2nd richest). Tried to time to full advance as per Boyer instructions (used a spare standard rev counter) but strobe shows tickover timing ok but doesn’t get near full advance (see Boyer response below). Tried air screw at 1 turn and 1 ¾ (either side of standard?)
Boyer Tech Dept Response:- ‘Thank you for your enquiry, when strobing try reversing the clamp on the strobe gun, also don't use a strobe that has a timing adjustment on it. We think the strobe is flashing on the coil energising and not switch off, this is why it runs ok but shows not to be on full advance’ – Haven’t tried this yet.
Result:- Now revs clearly through mid range (obviously not revved further up scale yet) – cured fuelling issue. On half hour run at mid revs range, plugs around about grey/sand colour. Still kicks back and spits back through carbs occasionally when kicking. Ticks over fine though.
So, what’s your view on the kick back/spitting back issue?
Thanks in advance

SteveD CB500K0:

--- Quote from: philward on September 23, 2018, 06:44:45 PM --- moonpie 4 – 4 race exhaust

--- End quote ---

We have a member on here called lordmoonpie (Simon Tappin). I wonder if its the same guy? He hasn't been onlne for a couple of years...

philward:
I bought the exhausts and a few other bits off Simon Tappin (Moonpie) Steve. I've spoke to him previously but his experience is with the race CR carbs

K2-K6:
I thought the Boyer system fires all of the plugs, all of the time.  Confirmed,  I think, by your tacho receiving twice the signals normally associated with a four cylinder engine.

If so,  as an example when no1 is at tdc and firing,  then one of the centre cylinders is at bdc on intake stroke,  but also firing. At normal dynamics when tickover speed is reached it won't be seen as an effect,  but at low revolutions it could be that which is spitting back from a single cylinder.

Just a thought,  also on that basis you've effectively got the pulse rate of a V8 for each rev so if you have a tach with that option to configure,  it could read correctly when set that way.

philward:
I've also been in touch with Boyer (and copied Smiths in) - here's their reply (which I think supports your view K2 - K6)

'The tacho should be calibrated for two pulses per rev and capable of working with a current pulse ignition system, with this the current pulse is varied by the micro processor depending on rpm. The peek voltage spike is around 200 volts on the primary of the ignition coil.
The tacho needs to trigger on this and ignore everything after it.
If you get stuck we do a tacho recalibration service, as long as we can get at the electronics.
For cost and inquiries contact us at sales@boyerbransden.com'

Smiths have been aware of the Boyer firing sequence but have had a go at the tacho twice (great service really) - Smiths have been given the above and are sending another re-programmed tacho this week to try - Fingers crossed!

Whats your thoughts on the kick back/spit back? (Timing retarded?)

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