NC29 MISFIRE - Problem solved

[greggo]

You can get the head off the NC29 with the engine in the frame. I've done it quite a few times.

[mrdidlydingo]

Ok Not plugs leads or coils, all replaced tested or tested or swapped for known working items with no effect !

That buggers my electrical theory assuming that the CDI etc is all in good working order, which I can only presume as the bike runs fine above 4-5 K (Brave assumption I know)

So based on the above and some time spent pondering with some friends the only tangable theory we can now come up with is the diapragm in one of the carbs is leaking, the theory goes that if one of the carb diapragms leaks there is no vacuum at low revs so when the throttle is shut off the slide drops but when reapplied it takes 3K revs or so for the vacuum to overcome the leak and the slide to rise hence the low range misfire.

So prior to me attacking the carbs later tonight does anyone have any comments ?

(I soooo didn't want to mess around in the carbs )

[lloydiecbr]

check your air box to much air not good not enough not good . i had this on my 600 to much air being forced into air box ie ram air its worth a look

[mrdidlydingo]

Hi, Finally got the NC29 firing as she should today after working my way through the entire ignition system and back again thing were not improving and when finally after all had been changed and checked out I found a fault in the wiring loom leading to the LHS coil, 5 mins with a soldering iron and all is well again in the CBR world at Dingos house.

It was pretty much found more by luck than deduction and it was breaking intermittantly so it could possibly never been spotted I had a multimeter in my hand and just attacked the loom as a last resort prior to stripping the carbs !

Right, a big thanks to all who assisted me you don't know how much the suggestions were appreciated

A few bits of data which I have learnt during my time solving this hopefully some will be of use to those who search for NC29 misfire !

LHS coil feeds cylinders 1 & 4
Cylinder 1 from top lead
Cylinder 4 from lower lead
RHS coil feeds cylinders 2 & 3
Cylinder 3 from top lead
Cylinder 2 from lower lead

No 1 Primary coil wire black & white
No 2 Primary coil wire black & white
No 3 Primary coil wire blue & yellow
No 4 Primary coil wire yellow & blue
(second colour is the stripe)

Plug Gap 0.8 to 0.9 mm & makes a big difference if not correct

Fuel pump is not constant 12v but a pulsed feed from the coil wires

Hope this of some use to someone someday !

[CMSMJ1]

Good to hear it mate! You going to come play out tomorrow then?

Meet us at J28 M1 at 0915 in the layby going south on the A38 lol

no, really good that it works - hows the rest of your bikes coming along?

[mrdidlydingo]

The rest . . . . . . . Its just a case of 1 down 2 to go !

If the bloody postie would get her act together I would be testing the V4 by now on the Bakewell TT

The ZXR goes for MOT at the end of the week, it'll be a miracle if it all comes together right though !

Re meeting you guys - no chance my missus and her sister have been out on the bikes from the crack of dawn, bloody typical all work no play !!