210 Watt alternator 1981 Series2 Jota.

[Ian D]

On the recent trip to Curdievale my bike developed a miss at low rpm about 2/3 of the way over, which I initially put down to shitty fuel.
Travelling through the small towns mostly 60K limit on a trailing throttle at low rpm around 2 thou and a bit, once out of the town limits I would roll on the throttle and the bike would hesitate like a cylinder had dropped out until it got going around 3.5thou plus.
On the way home I eventually turned off the lights and the problem solved. Not really, there is something not right which I need to find.

Check Battery and it is 12.7'volts and has been consistent all week.
Battery is charging 14.5 @ 3thou. no change at higher rpm.
Test OMH's from alternator , 1-2,1-3, 2-3, all reading 0.7- 0.8
Test AC from alternator engine running, at idle, all in the 19.ish v range.
Test R/R with engine running at battery 0.031v AC [Ripple Test?]

The wires from the Alternator are yellow, white/blue to the R/R and green/red, which go up towards the front.
The bike still has the factory reg/rec and alternator. Almost 90,000k's.

All this testing is good but what does it mean ?
Any help understanding this appreciated.

 

[piranha-bro2]

Could it be a voltage drop to the coil/s? Turning off the lights might offer just enough extra juice to resolve the misfire. You'd be surprised how much you lose in volts in the passage from the battery/alternator to the coils. You lose a bit at every multipin or other low-insulation connector.

Battery and charge system unlikely culprits IMHO.

 

[Paul Marx]

Loose connection?
Paul

 

[Rob]

As Clem would no doubt say - check the earth connection on the frame under the seat. I'm not familiar with the S2 layout but RGS models have a tightly routed green earth wire with a round tag under the electrics plate top fixing bolt. Wire strands can break and make for a poor connection.

You can rule charging/voltage issues in or out by connecting the battery direct to the ignition downstream of the kill switch. But if you're still running standard Bosch ignition I'd also try swopping for known good BTZ boxes.

 

[Jota Rob]

It's a simple test with a multimeter.
I've had these break down before.
Be aware there are resistor and non resistor caps.
A good way is a comparative test with all 3.

 

[78jotadave]

Check the ignition switch, which was the source of a similar issue I experienced.

 

[1200ts]

A 1981 S2 you say? So we are talking about a Ducati?

 

[iis_iis]

Replace the oem RR immediately, rewire the 3 phase from alternator coil permanently into the fit for purpose RR ( plenty on that in previous forums ) Unlikely though if you have the dreaded red motoplat ignition coils, then replace those as of yesterday, again plenty of advise on suitable coils that are reliable on the forum here. Easy things first, Jota Rob has a good tip, the NGK spark plug covers are consumables.

Generally a hesitation/stumble is rarely ignition save for BTZ if still fitted, lose those as well. Reads like a transition idle/cruise to needle transition, bigger job, would clean the carbies as per advice here previous forum topics, HTH j

 

[iis_iis]

A 1981 S2 you say? So we are talking about a Ducati?

Think he means series 2 Bruce, not sure about the 210Amp however, j

 

[Ian D]

Just corrected the subject line on my first post. My apologies.

Bit more info.
The coils fitted are the off white / cream colour. don't the name of them.
New mikuni's fitted from Red, about 2,000k's travelled.
Ignition is a Sachse, the one with the black box.
According to the info of the day the '81 series2 Jota's had an upgraded 210 watt alternator. not Amp my error.
With the dellorto's fitted, I would get a similar thing happening when I filled up with Shell after the second tank.
It would clear after a tank or two of another brand of fuel.

The only reason I started to doubt the fuel, which had a couple of top ups with Shell was at the last stop I filled with BP.
Nothing changed until I turned the lights of, after 100 or so K's. Which with the dells would be enough to sort itself out.

I will check everything that had been suggested so far and get back.
Thankyou all.

 

[iis_iis]

Nippon Denso ignition coils, oem in the day and back to the early 1970's, very reliable though well old now. HT leads would need replacing at the least ( how to is on JLO website ). New plugs, new spark plug covers, though NGK are discontinued 115 degree and 90 degree. All easy to replace first, somewhat dangerous on the open road doing diagnostics, perhaps sachse has a self test mode?

Ok on the fuel related discoveries, read that this problem was the same with old and new carbies, all the same any unwanted products et al in the tank can be quick in effect on carby operation, ie water for one. HTH j.

 

[Dellortoman]

Simple things first. Try a new set of spark plugs. Dodgy plugs can cause all manner of strange symptoms.

Sachse ignitions are generally pretty reliable, but I suppose anything can fail. Failure of electronic components can also cause strange symptoms.

I second John's opinion. Get rid of the original RR and replace with a decent 3 phase unit. Come to think of it, I'm not sure the original is actually an RR. It might just be an R (rectifier only) as on earlier 3C and 3CLs, although I'm not sure about the S2 models and haven't consulted a factory wiring diagram. Not that it really matters - same advice applies.
Plenty of RRs available on eBay etc. I suggest you avoid the new "Shindengen" units from China that sell for dirt cheap prices. I can't say for sure that they're rubbish, but for the price (typically below $50) you can't expect a quality product. You'd be better off buying a genuine used Shindengen RR for similar money.

I was going to make a joke about your 210 Amp alternator being able to power your house, but you fixed the thread title before I had the chance.

BTW, 19V AC from the alternator sounds a bit low. I'd expect something around 30V AC or more.

 

[Andy]

Do these models have the detour of one alternator phase up to the headlight switch?

 

[iis_iis]

Possibly Andy they dont though i suspect its possible, political type bet each way and with somebody elses money reply...grin j

 

[Ian D]

Do these models have the detour of one alternator phase up to the headlight switch? Mine does Andy.

BTW, 19V AC from the alternator sounds a bit low. I'd expect something around 30V AC or more.
Yes Cam I was wondering about that, I will check that again after a road test.
John not sure if the sachse has a self test mode, I'll check my notes and get back to you about that.

Todays effort,
New plugs when I left for Curdievale, check, clean and gap. Didn't change them.
Plug caps resistance 5, 4.9 & 4.6 omh.
Nipped a couple of mm of the end of the plug leads. running out of length on the middle one.
Earth under the seat cleaned and retighten.
Found a dodgy connection under the tank, frayed and broken strands. yellow wire, to black wire, to coil. Trim and crimp new fitting.

Started from cold pretty much as soon as I touched the button and settled into steady idle very quickly.
Just need a road test now and see if I can replicate the same symptoms.

Many thanks so far for getting me headed in the right direction.

 

[iis_iis]

Much depends on the type of meter doing the AC measurement. Being an alternator, real grunt does not come until around 3Krpm, maybe lower rpm if well setup. On a CRO it will be 80Vac peak at best.
The 14,5V at the battery says 3 phases are present and actual AC peak voltage normal, looking over the NSW fence to SA... hard to see the meter from here.... j

 

[Ian D]

Finally got out for a road test, that one simple connection was the cause of the problem I hope

Yes John the sachse does have a test mode same as most other electronic ignitions I have, ground plugs etc and gives a continues spark.

Many thanks for all the suggestions. Cheers