Jota hot starting

M

Mole87

New member
Location
Wellington Shropshire
After riding my Jota for the first time a few weeks ago, I noticed it was missing when I tried to rev over 5k. It also was a pig to start when warm. I have since stripped the carbs, cleaned and replaced gaskets etc
Starts fine off the choke, warms up, ticks over be it a bit lumpy at about 1500 revs. Turn it off. Struggles to start
I thought it may be heat sync but the inlet stubs have nylon bushes and there’s little heat in the carbs
Any ideas?
1980 180 Jota
 
Mole87 said:
No I Havnt touched the plugs
What are the correct plugs?
Click to expand...
You'll have plenty of differing opinions on that. Stick a set of NGK B8ES in. It will at least allow you to see if you have a problem there. In my recent experience, including today, plugs can have a pretty short life now days. A few cold starts can kill them.

Keep away from fuel additives. there's enough muck in petrol as it is.

Paul
 
New set of plugs is a good start
Is the petrol fresh?
You'll know what jets, slides & needles are fitted if you have stripped the carbs - what are they?
Did you check the choke plungers and their rubber seals are in good condition...and enough cable slack for them to seat properly when choke is off?
How did you clean the carbs? Did you check the pilot circuit isn't blocked?
Are float heights correct?
Do slides lift fully to clear the venturis on full throttle?
Are the carbs synced?
 
Plugs fowl easily if the choke stays on for ANY time longer than necessary. All the above tips are spot on the money. Check for all that. here are a few very well known failure points for these old bikes and they all need to be checked for including wiring insulation that decays in the conditions around where they exit the engine affecting the spark and advance of the spark. There isn't much this bunch here hasn't seen on Laverdas over the years. Another is the fuel cap breather being blocked so try riding with the cap open and see what revs you get too.
 
Had similar problems with the 120 Jota, ran like a pig when hot. Suspected the coils and resistors so replaced with new coils and binned the resistors. Finally replaced ignition with an Ignitech unit using the original pick ups. Runs better than when new.
The SFC also had problems with the coils and replaced them too.
Can't expect too much from 40+ year old coils.
 
ETHANOL PROOF FLOAT VALVES

All the above previous posts above are highly relevant, but.............

have you had the bank of carbs, off the bike?
if no, then do that, if gives the oportunity to check them thoroughly, this can only be done to very limited means with them on the bike, the float valves and seats inside all three carbs are very likley to be not ethanol proof and (to me) are showing early signs of decay, if they have black tips, they need replacing and with ones which have red tips. when they are seriously gone, fuel will get into the sump, so (easy check) pull the dip stick and give the oil a good sniff, and even sniff the threaded hole, using a tube, smell petrol??? clear sign of fuel leaking past the old float tips. The oil will need changing if this is the case.
CLEM
 
Rob said:
New set of plugs is a good start
Is the petrol fresh?
You'll know what jets, slides & needles are fitted if you have stripped the carbs - what are they?
Did you check the choke plungers and their rubber seals are in good condition...and enough cable slack for them to seat properly when choke is off?
How did you clean the carbs? Did you check the pilot circuit isn't blocked?
Are float heights correct?
Do slides lift fully to clear the venturis on full throttle?
Are the carbs synced?
Click to expand...
Carbs are all good and set up and synced
Petrol is fresh. I’ll try new plugs first and maybe coils
 
CLEMTOG said:
ETHANOL PROOF FLOAT VALVES

All the above previous posts above are highly relevant, but.............

have you had the bank of carbs, off the bike?
if no, then do that, if gives the oportunity to check them thoroughly, this can only be done to very limited means with them on the bike, the float valves and seats inside all three carbs are very likley to be not ethanol proof and (to me) are showing early signs of decay, if they have black tips, they need replacing and with ones which have red tips. when they are seriously gone, fuel will get into the sump, so (easy check) pull the dip stick and give the oil a good sniff, and even sniff the threaded hole, using a tube, smell petrol??? clear sign of fuel leaking past the old float tips. The oil will need changing if this is the case.
CLEM
Click to expand...
Cheers will check
 
Rob said:
New set of plugs is a good start
Is the petrol fresh?
You'll know what jets, slides & needles are fitted if you have stripped the carbs - what are they?
Did you check the choke plungers and their rubber seals are in good condition...and enough cable slack for them to seat properly when choke is off?
How did you clean the carbs? Did you check the pilot circuit isn't blocked?
Are float heights correct?
Do slides lift fully to clear the venturis on full throttle?
Are the carbs synced?
Click to expand...
Reunited Chris said:
Had similar problems with the 120 Jota, ran like a pig when hot. Suspected the coils and resistors so replaced with new coils and binned the resistors. Finally replaced ignition with an Ignitech unit using the original pick ups. Runs better than when new.
The SFC also had problems with the coils and replaced them too.
Can't expect too much from 40+ year old coils.
Click to expand...
What coils did you fit. I have seen plenty for 1983 years onwards but mine is 1980 180 Jota. Will these fit?
 
Paul Marx said:
You'll have plenty of differing opinions on that. Stick a set of NGK B8ES in. It will at least allow you to see if you have a problem there. In my recent experience, including today, plugs can have a pretty short life now days. A few cold starts can kill them.

Keep away from fuel additives. there's enough muck in petrol as it is.

Paul
Click to expand...
Should I go iridium plugs or stick with copper?
 
The only reason why you should run them is if it's configured to be really hard to get to the plugs like my transverse V6 car which takes half the engine out to reach them so they need to run for 100k before changing them. It won't make it go better, high tech plugs won't fix engines that need work, guess how I learned that. NGK B8ES should work and last if all else is ok.
 
Mole87 said:
What coils did you fit. I have seen plenty for 1983 years onwards but mine is 1980 180 Jota. Will these fit?
Click to expand...
I fitted Dynatek DC3-2 Coils.
Had to modify the coil mounting plate to bolt them on.
On the SFC I made small angle brackets to hold the coils, the mounting bolts for the coils are horizontal.
With the 120 Jota I made up a new plate as the original was cracked. Same shape but out of stainless with mounting lugs welded onto the plate.
Frame is the same as the 1980 under the tank.
 
Vince said:
my transverse V6 car
Click to expand...
What sort of car do you have Vince?

Mole87 said:
Should I go iridium plugs or stick with copper?
Click to expand...
Iridium refers to the centre electrode of the plug. Plugs now come with a range of electrode options including silver, gold and platinum as well as iridium. These metals are chosen for their electrical properties as well as corrosion/erosion resistance. The ones with fancy metals are advertised as such. If nothing is specified then the default material is usually some kind of nickel alloy.

I'm not aware of any copper electrode spark plugs on the market (but I'm happy to be proven wrong). I'd guess that they may have used copper in the early days of IC engines because of its good electrical conductivity. But it's a pretty soft metal, so would probably erode quickly.

As others have said, there's no need for fancy expensive spark plugs in our old Laverdas. Stick with boring old B8ES.
 
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