Stumbling question

[sylok]

Hi,

Needing some help. My TA (XL600VX - the err, 50th anniversary model) has developed an intermitent "stumble" when ridden. It feels as though one cylinder intermitently cuts out and I suspect that it is the rear one since the rev counter doesn't falter during the "stumbles".
I know some earlier models of the TA suffered from similar problems from faulty ECU's, but I thought this was resolved with the introduction of the single black-box.

Please help as this is starting to get a wee bit dangerous....

Could the ECU be at fault?

My local Honda delear are stumpted (though they do agree that the rear cylinder is probably at fault, though they don't not what or why!!)

Any ideas/ comments/ suggestions gratefully received

Ta,

Symon

[IanS]

Once had a dodgy plug lead on a car. Car would die then restart and drive away with no problem.
Put it on a good analyser and you could see the lead breaking down on the graph.
New set of leads and it never happened again.

Maybe stick the bike on a rolling road with all the electronic's so you can monitor what's happening.

Good luck

IanS

[robelst]

Start with the simple things, like draining the carb-bowls (see any waterdrops?) and plug(lead)s. In case you didn't know, the carbs have a drain hose and a little screw to open the drain. You may want to close the fuel tap before you do this

Plugs are actually less likely because having two of them per cylinder should hardly make a difference if one is cutting out, but still worth looking, they may both be faulty. If it mainly happens in the wet they are indeed suspect, as well as the ignotion coil.

Also check earth connection to the frame and battery connections.

I once had a crappy ignition lock, causing cut-outs: fiddle with the key and see if you can make it cut out (apart from turning it all the way to the left of course ).

There's even a chance your bike suffers from carb-icing; my Buell does that severly and even my AT does it a bit sometimes, as in the cold fog we had recently. These are usually short cut-outs (feels like running out of fuel for a fraction of a second) and usually when you open / close the throttle. Interestingly it always happens after 5 or 10 miles, not right from the start
There are fuel additives to prevent icing (I usually get the Harley winter additive for the Buell, works well in Hondas too ).


If that doesn't help ask a real expert (I'll get me coat now )

Good luck!

[Wee Jack]

It could be a carb diaphram - but if you've had it at a dealer this should have been high on the suspect list for them. Unless of course they are total numpties !! Did they actually have the bike in the workshop to check or were they just heads scratching ??

[robelst]

were they just heads scratching ??

Those are the good'uns; it's the ones that get their tools out you want to be really careful with

Carb diaphragm is good suggestion btw. Or a leak on the inlet rubber (usually results in unstable idling as well).

[sylok]

Cheers for the suggestions and ideas.

The bike has been into the local Honda dealers a couple of times now to no avail, hense why I thought I`d ask you guys.

Interestingly enough, the stumbling does seem to appear after riding the bike around 5 or so, miles when you would think it was warmed up.

I`ll have a bash this weekend at trying some ideas (weather permitting)

Symon

[robelst]

Interestingly enough, the stumbling does seem to appear after riding the bike around 5 or so, miles when you would think it was warmed up.

Could be carb-icing then. Is it still doing it now that the temperatures are up again? (if so, it's probably something else altogether ).

[robelst]

I dived into me old archive of German (don't ask) bike mags and found some info in Motorrad about the Alp being sensitive for icing. This is supposed to have been addressed by a Teflon coating on the carb's piston, from early '90's models on
I wonder how that works but if the Jerries say this it's probably true

[Lord Stig]

Syloc,

If the fault is intermittent I would first look at sparks rather than fuel, as you seem to suspect. It's possible that you have either corrosion or a short to the frame on one of your coil LT leads. I had corrosion problems with my AT front coil earth connection because the front cops all the salt. Yen had similar problems if I remember correctly - in fact I think he alerted me to the possibility that this could be the cause of my problems.

I had a short to the frame on my last TA, which was caused by the LT lead to the rear coil rubbing on the frame under the seat - over time the insulation had worn thin and allowed current leakage to the metal of the frame. It was intermitent because the wire wasn't always in contact, but it was normally worse in the wet. Of course, if you are loosing a cylinder due to electrics the cause at least can't be the HT leeds - the engine will run fine with only one plug cap connected. So you can rule them out, as Robelst suggested. It could be a coil itself, of course, or, as I mentioned above, the LT feed to the coil. If the last of the 600s had a single ECU it seems unlikely to be that; breakdown of the circuits could, concievably, cause one cylinder to drop out, but this would seem relatively unlikely.

My first move would be to release the cabling along the nearside (if the LT wire still is situated there on the latter 600 TAs!) and check for rubbing, breaks in the insulation etc. by pulling it out and inspecting. Do the same for the front - it might be just as vulnerable even though the seat isn't on it. Next, unbolt the earth connection to the frame on the front and rear coils, give it a clean up, grease and re-fit. If that doesn't cure it, suspect the coil....

Hope that helps,

Stig