Witt Rev Limiter or other problem

henrywillms

henrywillms

Hero member
Location
Canada
Had the Witt DMC 2 (optical pickup) on my RGS Corsa for years. Late last year it crapped out, would not fire on #2. After doing all the diagnostics on coils, wiring, caps, grounds etc,  I narrowed it down to the Witt box. Wolfgang sent me a new one and it immediately fired up and ran well. Double checked by reinstalling the old one and problem back. So new one installed. Only had time for a short test ride as winter arrived, I don't recall if I got the engine to red line territory. 

Got the bike out of hibernation a few weeks ago and noticing that as I get  to 7000 rpm territory (reading  the RGS tach) that the ignition  starts to cut out. It feels like a crude rev limiter in that ignition seems to get a break down, it gets intermittent and cuts out relatively quickly and consistently. As soon as I back off a few revs it returns to normal. Other than that the bike runs good.

On the old Witt box that crapped out,  I never experienced the rev limiter that I recall, certainly nothing at 7000rpm.  I see from trolling the archives Piet states the rev limiter is set at 8800 rpm. Is it possible the rev limiter on the replacement box is set too low? Or more likely a new problem like a bad plug (new when I replaced the DMC) cap or coil (they are relatively new), bad ground or other connection has crept up?  Off to Wolfgang's rally in a week and would like to figure this out quickly. Any help appreciated.         
 
What setting is the box on?
For sure try new plugs, plug caps, cut back 1cm of HT lead before fitting the new caps.
Are the earth points ok on the bike?
No damage or oil mist on the optical pick ups ?
 
Might be vibrations at a given rpm are taking their tribute on an already weak connection. Would recommend to check the entire wiring of the box for broken cables or loose connectors, especially on the multiple connector which goes onto the box. Don't know how much of vibes is going trough the handlebar on a RGS, if any, then you might consider looking for the condition of the kill switch, too. Over the years I experienced some cases of erratic behaviour from NGK plug caps, but would not guess all 3 of them failing at the same time.
 
Thanks guys.  I should have included that it feels like all three cylinders cutting out at same time, it does not feel  like just one spark plug is not firing. I will look for a common problem like optical sensor being dirty, or wiring harness connection or ground. In replacing the box maybe I knocked something a bit loose. Curve is on 10, same as before. I hate problems like this where it is is intermittent and only occurs at high revs so hard to diagnose in the shop.   
 
I had to buy a new connector block, including associated wires, for a Witt-equipped bike I was working on.
The main live into the connector block had an intermittent contact. Couldn't see anything, couldn't fix it but a new one solved the problem.
 
Well I guess the good news if I can't figure it out before Wolfgang's rally next week,  I'll just keep the revs below 7k and on the ride there. Once at Wolfgang's I can try a new harness, optical sensor etc. 
 
Likely culprit is wiring termination in the crimp at the DMC connector - an apparently well known weakness caused by overcrimped wires on some batch(es) when the incorrect crimping tool was used.  Also because the wiring is usually tightly turned as it exits the connector block it is susceptible to stress fracture if not well supported.  Pit box visitors at Spa last year and this could have witnessed the evidence for themselves!  :-[ 
 
Could not find the problem by visual inspection and tugging on wires,or  measuring continuity. Didn't want to get into trying to rewire the individual pin connections, if that is even possible, before leaving for Wolfgang's rally tonight. I will confirm that it is not just the rev limiter at the rally (as I said earlier I never felt the rev limiter before changing out the box, but it feels like a crude rev limiter), and if not the box itself I'll get a replacement harness from Wolfgang. Either that or steal one of his bikes. Thanks for the pointers guys. 
 
So the end of the story, hopefully, is that the replacement Witt box was defective. The original Witt was many years old (at least 15), and on a ride it stopped firing on #2. Diagnostics pointed to the Witt. I replaced it with a new one, and problem solved. However after a short few rides I notice the ignition is breaking down at about 7000 RPM in 1st and 2nd gears, total misfire on all cylinders, back off the RPMs and all is well. Looked for connection problems, ground problems etc, nothing. While at Wolfgang's he gives me another box to try and instant fix. Just to confirm I put the previous box back in and problem returns.  In with the new box, and several hundred kms later it is still working well. No idea what was wrong with the other one, Wolfgang is going to send it back to Witt. 
 
You must log in or register to reply here.
Back
Top