Boyer Ignition cb750

[philward]

Have been provisionally fitting the Boyer Ignition/mini coils to the CR Rep and when I fit the magnetic rotor, I've only got half a nut on the centre M6 advancer shaft. Surely that's not right. The instructions say if the rotor fouls the cover, to file the rotor so the advance and retard unit dogs fit in the rotor.
Has anybody else experienced this? I could just either cut the dogs off or time it up (few months off that/start up) and then file slots in the rotor to fit the dogs when the rotors in the right place.
Thought I'd ask first as if this is normal, why doesn't Boyer tell you to make the mod - seems strange

[JamesH]

Phil - post a pic so we know what issue you're experiencing. The last time I fitted one I had to chuck the Boyer rotor in the lathe to open up the ID of it so it would fit over the shaft of the honda plate. Pull the plate off and see if you can assemble by hand and make share the tabs on the shaft are seating in the bottom of the rotor hole (make sense?).

[philward]

Pictures are not that good - sorry

[gp_st3]

I fitted the same kit about a year ago to my K4 engine and had the same problem - in the end I did away with the washer and that meant all except the last turn of the thread was covered.  Having checked that the cover to rotor clearance was about 2mm, I gave the nut a decent hand torque with some loctite and told myself at the time that I would go back and notch out the rotor to accommodate the dogs and increase the clearance 'later' but as with many such things, not got round to that yet!

It's actually a rather poor design IMO but the rotor is such a tight fit on the shaft (and has so little mass) that it'll never move.

The other thing I never did understand is why the instructions say to "time to the Full Advance Timing marks ... with the engine running at a steady 4500 RPM" when according to everything else I have read, full advance should be there by 3000 RPM (and the Honda Shop manual says 'above 2,500 RPM)

The thing is, if you set the Boyer to give full advance by 3000 RPM then at higher revs, the advance goes too far so it has to be done according to the instructions and to be fair, the performance is excellent so will remain a puzzle.

G.

[philward]

Welcome G (noticed its your first post) - I agree about the design - all a bit 'home made ish'. I bought it based on the performance and longevity of design (had one on my Z1 in the mid 70's). I've got some half nuts so I'll fit one of those and loctite and peen the end of the M6 advancer shaft for safety. Poor design that you can't just fit it from the box though. I've modded wiring/connections and mounted minicoils as per picture

[gp_st3]

Thanks for the first post welcome Phil, finally ’broken my duck’!

A bit more about the Boyer - in addition to not following the Honda recommendation for the full advance point by some margin, @1100 RPM tick-over the ignition fires about 2 to 3 degrees ahead of the ‘F’ static timing point, which is also a surprise.

Could be that Boyer’s engineers have optimised/improved on Honda’s probably conservative spec (itself constrained by the relatively crude mechanical advance) or perhaps the basic module and timing profile is sold by Boyer for a number of motorcycle models including the CB750 and is therefore a compromise to suit a range of specifications...

It would be good to hear what you think when you have road tested because although happy with the performance, I have only ridden one CB750 so have no basis for comparison!

[philward]

Will do but I'm a few months off fire up on the CR Rep. Additionally, I am running a 836 kit, race exhaust and ram air foam pods so I think I will have some set up issues that I wont be able to isolate from any Boyer related issues. There's plenty of members on here though who are running the system on 750's so perhaps they can give you some feedback?

[gtmdriver]

Could be that Boyer’s engineers have optimised/improved on Honda’s probably conservative spec (itself constrained by the relatively crude mechanical advance) or perhaps the basic module and timing profile is sold by Boyer for a number of motorcycle models including the CB750 and is therefore a compromise to suit a range of specifications...

Basically yes.

The Boyer advance curve is controlled electronically and has been optimised compared to the OEM mechanical system and, as far as I know, they list the same control unit for all the Honda fours of that period.

[Seabeowner]

When we were comparing 300 (750) and 323 (500/550) bob weight advancers some time ago we noticed the difference. The "F" mark is more advanced on the 750.
But according to legend the 750 "F" is 10deg and the advance 25deg and the 500 "F" is 5deg but advance is also 25deg. Both are supposed to top out at 2500rpm.
I think 333 (350) advancers are same as 323, not sure what was on 400s.
So luckily for Boyer the advance is the same for all.
Also rumour has it that the advance of some later 750 was different.