NC29 MISFIRE - Problem solved

[mrdidlydingo]

Prior to ripping the bike to bits wondered if anyone had any suggestions to the cause of this problem.

Bikes a bit of a cow to start when it does you get 3 cylinders the fourth chimes in after a few seconds or a couple of throttle blips.

When riding the bikes fine above about 5K, but a bit chocked below, when you've been shifting and gear down or go on overrun it goes back onto three again until it clears a few seconds later and off you go again !

Bear in mind I haven't looked, it could be as simple as a failing plug, but I found it odd how it was only on overrun, last year I seem to remember the 3 cylinder at start problem but it just went away (yes I know should have sorted it then!) it seem/feels to my left foot like its pulling too much fuel through on the overrun ?

[paasker]

Maybe a foul HT lead or foul sprk plug.
Could be gunk in one of the carbs...

Kind regards
Martin

[greggo]

One of the float bowls may not be filling properly?

[Waza4]

Strip down clean and balance carbs & HT lead as Passker said.


If it still persists check the valve clearances.

[mrdidlydingo]

Thanks folks, you seem to have the same thoughts as me so I'll go throw a spanner grenade at the bike this afternoon and see if it can be solved !

[mrdidlydingo]

just an update as I finally got round to looking at the bike, easy option first I checked the plugs all very clean nice colour etc, then I noticed that according to the honda? (coil 1, 2, 3, 4, ) labels on the leads two and three were the wrong way around there are left and right coils from riders position from memory left hand lower lead does cylinder 1 upper cylinder 3 right hand upper is cylinder 2 lower is 4

this doesn't tally with markings can anyone check ?

anyhow the replaced plugs mis got worse, going for leads next then coils !

its popping and banging like a good un!

I'm convinced now its electrical not carbs so help please on what the culprit may be it was 3 & 4 that were not firing last night which come from different coils ?

p

[leopard_pagan]

after you do get the HT leads right way round... if they are wrong. (pass)
get 4 nail varnish colours (borrow em). put a dub of one colour on HT lead and same colour on the coil outlet for that HT lead.. and so on.
makes life easy for when you come to dismantle them again for sparky change.

also.. when you do change the plugs,, only do one at a time. this also stops the wrong HT lead being put on the wrong plug. i always start with the outer left as its a bugger, the rest are easy.

[mrdidlydingo]

Coils tested okay on primary and secondary circuits, replacement HT leads on way !

Still defeated by this misfire, is there any way to test ignition systems etc other than that which listed in the Haynes, or is it a case of swap out each time.

The firing order was correct the leads labelled wrongly this much I know, cylinder 3 is the one backfiring 4 doesnt seem to be firing properly, could a head gasket failure cause these types of problem, really stumped here guys any help would be welcomed !

[Baronnoir71]

Check the dip stick, If it's creamy like a cappachino, then you most likley have a failing head gasket, hope this helps

Cheers, Joe

[mrdidlydingo]

Its not looking like the head gasket but the only real way to tell is to chemically test it or whip the head off both of which involve removing the motor - there is no visible emulsification of the oil in the sump so that is a good sign !