Jota 120 cutting out at speed

C

charlie

New member
Location
France
Hi,

After Keith and Ricardo's work on it over the years, I thought this might be 'Jota 2025 Year of Reliability'. Er, I made it to September.

The symptoms:

Last run on the motorway steady at 140kmph, a stutter, followed by a couple more. Fuel was plentiful but switched to reserve anyway. Slowed to around 90-100kmph then it went ape-shit, big stutters, and became a pretty dangerous rodeo-ride. At 50kmph was able to pull into a service area. Idled and revved perfectly – so decided to take it slow for 15km home, which it did without drama.

First feeling was fuel starvation of course, although I did switch the taps, so maybe that doesn't point to the tank. The violent nature of it made me think afterwards, could be electrics, given the start/stop effect.

Anyway in next couple of weeks after reading much here (and within my mechanical limits!) I plan to:

– Drain fuel, take off taps, clean filters and tank. Bung taps into a borrowed ultrasonic
– Detatch petrol cap (ultrasonic clean perhaps?) in case it was causing an airlock
– Drop float bowls, remove what jets I can, ultrasonic clean (I know I probably should do whole carbs, but beyond my skills, and I believe the carbs have been set up clean-and-well by Keith, even if that was a while back)
– Change plugs (fitted this March, but had been laying around for years). Possibly cut HT leads and re-fix
– Check coil connections (although new Jap units fitted by Keith, doubt they're ropey)
– Check ignition switch connections
– The DMC cable went on me once, but that caused starting and misfiring problems. Don't know if there's a check for that

Additionally:

– Could this be the clutch 'letting go and catching again' at speed?? I say that because I've been tying back the lever for a year or more due to it sticking. I'm hoping one day Red will have a new supply of kevlar clutch plates, and Ricardo can fit them

– Also concerned that Keith wanted to fit a special piece he makes to do with a gearbox shaft if I remember right, he tests by pushing it. (Sorry to be vague.) He said I should do it in a year, two years ago. Could that be a factor?

Sorry for the length of this brain dump. I'm wondering if it's a decent/correct list, and out of interest whether you would guess fuel or electrics based on the symptoms.

Need to do whatever I can within my abilities before testing at speed again, since French breakdown cover is shit. They'll insist on taking it take it to the nearest Honda or Kawa garage. And the Honda garage once asked me where to plug their laptop in :)

Cheers,
Charlie
 
If all this doesn't help: on the German forum, we had similar symptomes coming from a battery that - at certain revs - seem to shorten internally, which caused the voltage to drop below the level that the ignition did want to work on. Just another thing to check if it isn't fuel related...

Check for water in the fuel btw.. With modern fuel, water is "sucked" into the gas and builds up at the bottom of the tank, as gas is lighter than water...
 
You mention DMC ignition.
I had very similar symptoms with my RGS on it's most recent trip to Breganze, very much like flicking the kill switch on and off. It was worse at certain rev ranges and bloody frightening on the autostrada!
After checking and testing so many things, I finally traced the fault to an unseen crack in the live feed to the DMC box - known as the sub-loom, with the plug on the end that fits on the DMC box.
A new sub-loom from Uwe Witt and the problem was solved 😀
 
Good point on the cable, especially if it's a DMC with the mulit-pin-connector.

What my brother once had was a fuseholder that was not tight enough. At certain revs, the fuse started "dancing" and caused the ignition to cut out. He did not find the problem until the fuse jumped out of it's seat. Basically, that was how he got a 1000 SFC switched for his 120 Jota. After removing the seat Unit behind a mout station in italy and opening the fuse-box, he found the fuse falling out. When he put it back in, the two contacts had way to much distance. A bit of bending, fuse in and - the bike started and ran faultlessly ever since!
 
Can only echo a14rgs. Had similar issues with a DMC II. Vibration means the misfiring is very intermittent in nature and a pig to identify. The wiring looks fine at the crimp but the sheath hides the broken copper strands.
 
Before doing a load of different procedures, it's far more important to find the cause of the problem.
The symptons you describe don't sound like fuel starvation.
I, routinely, turn my taps off a mile away from home, to arrive home with a fuel starved engine.
Fuel starvation will result in backfires, loss of power but nothing like you describe.
Ignition, particularly, a loose connection, will.
 
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The Sock said:
Before doing a load of different procedures, it's far more important to find the cause of the problem.
The symptons you describe don't sound like fuel starvation.
I, routinely, turn my taps off a mile away from home, to arrive home with a fuel starved engine.
Fuel starvation will result in backfires, loss of power but nothing like you describe.
Ignition, particularly, a loose connection, will.
Click to expand...
I am interested to know why...
 
LDC420 said:
I am interested to know why...
Click to expand...
It just became a habit, I guess, but it leaves less fuel left to stand in the lines/carbs and it allows me to check that the fuel taps actually do what they're supposed to.
I had one, years ago, that was still letting fuel through when turned "off". I tend to keep a full tank and I don't relish it emptying into the engine while parked.
 
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Thanks. I had exactly that problem, a leaking tap, but so gradual that I had the smell but no pools of fuel. Luckily, at the Willersley event, Graham Rose sold me some new taps and Clem worked out that I was also a washer short in one tap. We live and learn.
All the best.
 
The Sock said:
It just became a habit, I guess, but it leave less fuel left to stand in the lines/carbs and it allows me to check that the fuel taps actually do what they're supposed to.
I had one, years ago, that was still letting fuel through when turned "off". I tend to keep a full tank and I don't relish it emptying into the engine while parked.
Click to expand...
A procedure passed onto me by a14rgs to avoid fuel sitting in the float bowls if the bike is parked up for a while before your next run, going stale and gummy as modern fuel is prone to do and the next thing you know, you're stripping carbs! As an adopted habit it has worked well all this year and the bike has started on the button every time with fresh fuel delivered to the carbs just at the moment I'm ready to set off. It does seem to help to avoid the problem I had with my Daytona 900 which did not benefit from this simple procedure and now has carbs awaiting a strip down and clean!
 
I had a similar issue with the DMC unit on my RGS. What I found was that the thin wires behind the ignition pick up plate going to the sensor had been vibrating against the engine case causing the wire sheath to wear away and allow the bare wire to short out against the case. The bike would pop and fart and eventually cut out. Left for a while the engine would start start and run for a while before repeating the symptoms.
Having traced the fault I apllied liquid insulation to the wire affected and also applied a coating to the engine case just incase. Thr engine's never missed a beat since then.
The wires on the rear of the pickup plate are not fixed to the plate and therefore free to move around at will and as in my case rub against the inner engine case, by slowing down speed the vibration is not so severe allowing the wire to move away from the case and minimising the shorting out. Moisture inside the area makes the condition worse.
The only way to check is to remove the pickup plate and check the wiring behind it.
 
The Sock said:
Before doing a load of different procedures, it's far more important to find the cause of the problem.
The symptons you describe don't sound like fuel starvation.
I, routinely, turn my taps off a mile away from home, to arrive home with a fuel starved engine.
Fuel starvation will result in backfires, loss of power but nothing like you describe.
Ignition, particularly, a loose connection, will.
Click to expand...

I tried using that practice on my IT250 and ended up going through the back wall of the garage 🤣🤣🤣
 
The fuel starvation sytems that you describe Hamish are what happens when the fuel taps are "off" or you run out (completely) of fuel. when the tank capacity is near (but not arrived at) reserve, at a wide throttle opening, say 100MPH, fuel starvation can occur, since the consumption is greater than the supply, you just get a momentary dead engine, on backing off the fuel supply can catch up and all is well again, this can also happen if there are partial blockages any where in the fuel supply system, but under these condition backfires occur only rarely.
CLEM
 
Hi Charlie,
my 3c once was dead and it appeared, that just the multipin connector to the DMC didn't had sufficient contact. Cleaning and putting it back together with terminal grease did the trick. Might be worth a look ...
Jo
 
Thanks for all the great input, I will check water in fuel (tank gets drained after winter every year), battery, loose ignition, loose fuse.

But the DMC issues mentioned really sing out, especially yours, a14rgs: "very much like flicking the kill switch on and off. It was worse at certain rev ranges and bloody frightening on the autostrada!" Exactly that experience.

Will check DMC cabling as best I can. At the plug end, the wiring looks sound, but maybe need to detach the unit (bolted through mudguard) to see better.

"The only way to check is to remove the pickup plate and check the wiring behind it."

So 'baseplate with photocell' according the old translated DMC fitting instructions I have. What's involved in taking that off, do I risk screwing up its settings?
 

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So when you say Jota we speak about a 120° or 180° Jota with ignition pickups/Photocell on the LEFT side of the engine, please? In that case, also check if there is oil, water or dirt behind the cover, as sometimes if oil sprays onto the photo-cell, it can keep it from working, too. Wouldn't explain though the intermitted failure... Check especially the red wire on the connector of the DMC, that is the main feed if I am not mistaken and that is the one causing trouble sometimes.

Also check the cables on the coils, sometimes they become lose. Next thing to check is the ignition key switch and it's cabeling.
 
...more free advice paid for... you went to reserve tap and seems quickly the "fault" worsened, clue one. Some other symptoms point to electrical, many the learned friends have covered, notably DMC known issues. Then of course you may have more than one fault looking like just one fault, that is where the boys stop and the men take over... benefit of that comment has two levels, insult to boys, their gained experience is yet to come, and poor men like me dealing with faults that beguile.... easy things first, highway testing is not safe, you or others, hope that helps... or makes it worse...that is also a useful testing procedure, making it worse means your in the area of the problem.

Stationary test of the ignition system and battery volts would be a process high on list, is there a continuos spark excitation for the DMC without motor running? Not the manual tap the reluctors type? j
 
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