spark plug issues with 78 Jota

D

DaveinTas

New member
Location
Tasmania, Australia
Hi all

I am having a lot of trouble with my 78 jota, running on unleaded petrol, it misses and pings.  I have tried different octane ratings, 91 was a disaster, 95 was better, 98 did not seem much better than 95. 

just a bit of history.  10 years ago the bike had a complete rebuild, new pistons, bearings etc, completely rewired, fully rebuilt carbs, Witt DMC ignition. etc spent way to much money.  the bike has done almost no work since the rebuild, less than 500km.

about a month ago I got the bike out of the shed for the first time in 5 years.  carbs were striped, cleaned and rebuilt, new spark plugs were fitted.  it ran ok for a while but feels very under powered. one cylinder was not working at all, very weak spark on that plug. 

so in a attempt to resolve my problems I am seeking some advice of spark plugs.  currently I have  NGK BR8ES spark plugs.  but they always look black and fouled with the unleaded fuel.  should I be looking at a different kind of plug, a hotter plug or even a more modern iridium style plug that may work better with the unleaded fuel 

cheers  Dave

 
I dont know much about the green smoke but I dont think you can run resistor plug caps and resistor plugs at the same time.Most run B8es not BR8es plugs
 
stick to 98 octane fuel or higher octane if available and do as Vince suggests if the caps have resistors.
Sounds like your middle coil or the connections to the coil have issues, hence the lack of power.

good luck
Gerald
 
G'day Dave

Welcome.

Yeah, Vince is right. If you have resistor plug caps (which most Laverdas do) then you don't want to be using resistor plugs.

If non-resistor plugs (B8ES) don't fix it, you might have a timing issue or a problem with one (or both) of your pickups or coils.

Do you have the original pickups? The insulation on the pickup wires is often less than ideal after nearly 40 years. I have a spare stator plate complete with pickups that you can try if you think yours might be dodgy. It was working when I took it out of my Jota. I have some spare coils and a Witt DMC around somewhere too. So if you need any bits, give me a shout.

I'll send you an email with my phone number. I'm in Bellerive.

Cheers,
Cam
 
You say the carbs were stripped and cleaned, but how far did you go?
Ultrasonic bath clean, or a quick wipe down?
Usually the carbs get gummed up even after a few months, so after several years I would think they were high on the suspect list.
Swap to the correct plugs.
What curve are you running on the Witt box?
What are the valve clearances? Have they settled down since the rebuild?
 
I think Grant is on the money there...unlikely to be just plugs. Annoying though, but double check the ignition as advised I reckon...
 
thanks for the feedback

I have now checked leads and caps, they are resistor caps so I will change plugs for B8ES as suggested and let you know how I get on.

the carbs were cleaned in a ultrasound bath.  they were a new set I got from Wolfgang in Canada and had done very little work, the reason the bike was left for 5 years is because the fuel had dried out and the carbs were all gummed up and I avoided the challenge of pulling them off and cleaning them.

not sure what curve is on the ignition

I have not checked the values since the rebuild so another thing to look at.

the  coils were new as part of the rebuild

cheers

Dave

 
Carbs rebuilt... float heights and jet sizes?  Clean carbs are no guarantee for proper set-up.

Fat spark with fresh plugs?  NGK 8s are on the warm side of things, shouldn't be sooty if carb and ignition are in order.

piet
 
I had an email from Dave. He lives about 15 minutes from me, but I didn't know about him until he posted here.

Occasionally I hear rumours of some bloke who has a Laverda tucked away somewhere. But in Dave's case, not even a hint of a rumour, which is a bit of a surprise in a small place like Tasmania. Makes me wonder how many other Laverda owners are flying under the radar.

Red will probably be here shortly to ask for the engine/frame numbers for his Aussie Laverda registry.

Cam
 
Hi all

I replaced the BR8ES plugs today with B8ES plugs.

the bike runs much better, on three cylinders and with much more power.  but it is still a bit rough above 4000 rpm

I will check the valves and timing next; carbs after that

my bike was originally a cream coloured 3CL that has had engine modifications to Jota standard, high compression piston, 4C cams etc

frame number 12571
Engine 4517
1/78

I bought the bike in 96 from Sydney.  the previous owner had made the modifications and repainted the bike , silver frame and orange.

I rode the bike from Tas to Western Australia in 97, minor issues on that trip.  a lot of starter motor problems. 
In 98 I rode up the east coast heading for the Northern Tas.  I burnt a hole in the centre piston somewhere in the middle of nowhere.  the bike got a train ride back to Melbourne and I spent 36 hours on a bus.
this incident triggered  the major rebuild.  the bike was fully strip and rebuilt from the ground up.  most of the work was done by Vee Two in Western Australia.  I go the bike back in 2004 and it has not been out of the shed much since (kids, house renovation etc)

regards

Dave
 
Sounds like there has been a carb issue for quite a while.
Check float heights are correct.
 
Engine is a '76, frame number should be 4 digits as well, 12571 looks wrong.

Did Brooke Henry do the engine work? Still got a triplex chain primary or has it been swapped to belt drive? Does it still have original ignition pickups and original alternator?
 
Hi Dave, also in southern tassie with 4055. Number not far from yours. Also Jotarised and painted silver and orange. Expect  flack from some forum members re colour.
 
Mine in WA is 4045 green with silver frame from birth, I believe 4046 is in Vic
 
Hey Dave that number you quoted from your frame is the homolagation number not the frame number, the frame number will be LAV1000*----* and if your bike is of the 4000 vintage the  number will be stamped on the LH side plate that the swinging arm spindle goes through.
 
Just checked the numbers,  the fame, engine and Aus compliance plate are 4517.  compliance plate does show 1/78 but that might reflect sale in Australia not manufacture.

the engine work was done by Mike Turner  of V twin in WA.  I had originally discussed with Brook Henry of Vee Two, even sent him the engine from Tas in Nov 98 but he got busy with other things and recommended Mike.  Given the recommendation and that the engine was in WA I ran with Mike.

I am positive he engine still has triplex chain primary

the alternator is a 140W version an am sure it is the original

cheers

Dave

I haven't confirmed the pickups are the originals.
 
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