Dominator missfire

I have just spent the last 3 months rebuilding one
complete NX650 out of a box of two so I had no guide as to how things were
assembled.
Now its done and on the road and all is well apart from it will not
rev above about 2000 under load and about 4000 with no load without very
erratic running. it starts perfect and runs perfect at idle and up to about
2000RPM.
Above that it runs a little like a 2 stroke when its 4 stroking. and there
is a little black smoke which led me to strip and check the carb but
after checking all jets,float height,and choke return, the piston
diaphragm, and blowing the complete thing out its still the same. I have
changed with a spare the coil and the CDI unit and it has a
new plug but still its was still the same. Have tried it with the air
filter removed as well. The only thing I haven't changed that I can think of
is the
pulse generator and this looks like a lot of work so I am asking here
first although it checks on the resistance according to the manual
One thing I am not sure of is the two pipes that go the
carb,Are they both vent pipes, One on the bottom and one on the side. Oh
and I have replaced the rubber carb mounting tube as there was a small
crack.
Any ideas??

Thanks in advance
Ken in England

 

ken Booth wrote

Which is a classic any number of things, 90% likely to be fuel/air
related.

If you do suspect the HT side of things and given the symptoms you have
every right, then one of the easiest checks to do is to run the bike at
night and have a look underneath for a pretty plasma display. If there
is one then you have issues. Better still if you can take it for a ride
in the rain first.

 

Sounds like an ignition timing issue to me - possibly related to
advance/retard, but I'm not familiar with the bike so wouldn't hazard
any more of a guess than that.

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Black smoke means it's running really rich, so I doubt it's the
ignition system. Have you got the needle properly seated?

 

Is it *definitely* related to RPM rather than throttle position? I.e.
will it pull fine in a high gear with full throttle up to 2000rpm? If
so, I'd suspect the advance/retard. If it is more throttle position
related, it'll be jetting.

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Excellent point.
Just a stupid question but does it make any difference whether the
headlight is on or not ?

By pulse generator I am not sure if you mean the ignition 'sender' unit
that triggers the CDI or perhaps some kind of charging coil in the
alternator that supplies juice to the CDI unit.

If the latter, then have known similar symptoms on a Morini, but far
more pronounced when the lights were also drawing current from the
system. Definitely revs and not throttle position in this case.I suspect
this somehow affecting the flux in the lighting coils and thereby
reducing the output from the ignition coil (LT windings not HT). The
*load* factor could also be due perhaps to spark breakdown.

Probably totally different on your bike though. Howvere, on any CDI
system bike I would try and find what kind of voltage to expect from the
relevant windings as well as resistance.

Anyway, you need to find as much diagnostic info as you can before
spending too much on replacing stuff that may not be the problem (unless
you can do a substitution test at no cost),

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Thanks for the replies
Yes by the sender I do mean the pick up inside the engine that times the
spark.. And yes the needle is seated I have completely rebuilt the carb
quoting the book and its all spot on. I was thinking the misfire may be
related to the fact that if its missing several firing strokes as it
misfires there will be a build up of unburnt fuel in the exhaust and the
black smoke is only a small amount. It misfire is when under any load above
2000RPM I have to say I would have suspected a plug but I have head two new
NGK new plugs in.

Thanks Ken.

 

Your welcome, but if I were you I would post your reply *below* the
quoted text next time or you might mildly annoy other UKRMers.

<BAD FORM I know that's not quite the usual tone>

Sorry but I am unfamiliar with the bike so will shut up before I confuse
you.
Best to ask Honda experts and even better Dominatror gurus.

However apart from RTFM I would add that if it is a totally CDI system
with a dedicated set of windings in the alternator for the ignition (the
acid test being that with true CDI no battery is needed to produce a
spark) then you need to check the output from those windings.

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Meaning the choir boys won't be properly seated again for a while.

--
Krusty.

http://www.muddystuff.co.uk
http://www.muddystuff.us
Off-road classifieds

'02 MV Senna '03 Tiger (FOYRNB) '96 Tiger '79 Fantic 250