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Discussion Starter · #1 ·
hi guys,

i have a pre unit tr6 that is doing my head in. i've had numerous problems with it, which with the help of this forum i've managed to sort out but i've hit a wall.

the plugs become fouled to point of spark suppression incredibly quickly.

the bike starts easy and runs perfectly pretty much until the engine is warmed up, then it starts to cough when idling and shortly after it'll cut out and will not be restarted with the kicker. sometimes it'll accept a bump start, but not always. even if it does bump start it'll only cut out as soon as i idle again.
i remove the plugs and they are pitch black with soot which cleans off easy with a wire brush. the bike then needs to cool down before it'll start again.

timing is correct, valve clearances are correct, i've tried adjusting the float bowl height, new plugs, new leads etc and i have good fat spark. i'm stumped.

it's a 1956 tr6 with a brand new amal mk1 900 concentric, jetted more or less to the book using amal's conversion advice. i know to the book isn't always right for every bike, but i thought it was a good place to start.

anyway i'm not sure where else to go and i've exhausted the forums as far as i can see, also the manual.

any help is, as ever, hugely appreciated.

apologies if this issue has been covered, i couldn't find anything that helped at this point, feel free to school me...
 

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More info needed
Jet size,air filter,what grade of plug,state of motor etc
 

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you say it's tuned by the book, have you tried leaning out the idle jet and maybe larger cutaway slide, this is the area where most of motor work takes place unless you're on the highway.
what exhaust set up are you running, any smoke, if so what colour.
ps what ever you change remember do one thing at a time.
 

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Sounds as if your magneto is your problem, either condenser or windings on there way out. I would check for spark once it cuts out, just carry a spare plug and fit to ht lead and give it a boot ,should be a nice blue spark if it is yellow or faint then my money,s on the mag.. Dave
 

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Discussion Starter · #6 ·
hi guys, thanks for the replies, i will answer in order!

richbob, specs are main jet 200, throttle slide 3, pilot jet bush, needle jet 106. no air filter, straight through pipes. ngk plugs, can't remember which but i have some champion n4c plugs somewhere i think. motor is used but seems to be in decent order apart from this. was rebuild maybe 5 years ago by previous owner and used often since.

goldy it's magneto ignition.

thunderbird ive tried the idle jet in and out with no joy. it affects the idling, but either way doesn't affect the fouling. isn't it only for idle anyway? straight through pipes, there was lots of smoke coming from exhaust actually, white but since i adjusted the valve clearances there is only small smoke coming from the left cylinder and only when i give it some revs. and yes one thing at a time, i learnt that the hard way, haha!

tribsa once i clean the plugs out it has decent spark again. is it blue though? i can't remember in all honesty. how blue are we talking?

thanks everyone
 

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Yes, as Tri bsa uk already said, it sounds like a magneto issue to me. I've beed confronted with the exact symptoms you are discribing before on several occasions. As he suggested, check your spark after the engine is warmed up, should be a nice fat blue spark. A puny red, or orange spark is not up to snuff...it results in poor burning and will soot up your plugs in short order.


hi guys, thanks for the replies, i will answer in order!

richbob, specs are main jet 200, throttle slide 3, pilot jet bush, needle jet 106. no air filter, straight through pipes. ngk plugs, can't remember which but i have some champion n4c plugs somewhere i think. motor is used but seems to be in decent order apart from this. was rebuild maybe 5 years ago by previous owner and used often since.

goldy it's magneto ignition.

thunderbird ive tried the idle jet in and out with no joy. it affects the idling, but either way doesn't affect the fouling. isn't it only for idle anyway? straight through pipes, there was lots of smoke coming from exhaust actually, white but since i adjusted the valve clearances there is only small smoke coming from the left cylinder and only when i give it some revs. and yes one thing at a time, i learnt that the hard way, haha!

tribsa once i clean the plugs out it has decent spark again. is it blue though? i can't remember in all honesty. how blue are we talking?

thanks everyone
 

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Discussion Starter · #9 ·
Yes, as Tri bsa uk already said, it sounds like a magneto issue to me. I've beed confronted with the exact symptoms you are discribing before on several occasions. As he suggested, check your spark after the engine is warmed up, should be a nice fat blue spark. A puny red, or orange spark is not up to snuff...it results in poor burning and will soot up your plugs in short order.
thanks goldy, i'm going to test tomorrow and check the spark. the spark when cold is sort of blue? i'll be honest i can't really tell but from pictures i've checked out of healthy, spark blue really means blue... encouraging to know i might be nearing the end of the hunt though, it's been driving me insane. this is my first old bike i feel slightly like i've dived right in the deep end with this one, haha!
 

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Sounds like a weak mag to me, incomplete combustion, mind you it isn't often I have found an old Triumph that will run well on the std jetting.
 

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Mag coil on it's way out sir. They always break down when they get warm. Coil/Condenser. May be worth putting some new leads on her too!
 

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Discussion Starter · #12 ·
okie dokie so i ran it yesterday till it cut out as usual, checked the spark and as suspected it's bright orange. mags dead. i've ordered a clever electronic ignition system to replace the points which as far as i can see from all the reading, is a fit and forget type deal. i'll report back once it's in!
 

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so you're switching to EI and coils?.
The Easycap condenser replacement would have been my first stop, used it with great success..
Whatever, if it gets you back on the road.
 

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Discussion Starter · #14 ·
so you're switching to EI and coils?.
The Easycap condenser replacement would have been my first stop, used it with great success..
Whatever, if it gets you back on the road.
yep! brightspark aren't accepting orders and while they're a much cheaper option, i can ride over to sussex motorcycles next week and pick up a thorspark myself. i did tons of reading and tbh i like the sound of it

EDIT, just seen they are still on ebay but with a month delivery! fuck that, i'm going EI. it's a shitty chopper anyway i don't care much for originality in this instance and i'm pretty sure i can hide the coil under my seat and no-one would be any wiser
 

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EI will transform your old Triumph , I have had a boyer setup on my 750 Pre unit Tribsa for last 15 years with no problems ,starts right up 1st/2nd boot , most mags are way out when you put a degree disc them to check points openings.I have just spent 4 hours setting up a magneto for my latest Triumph with a degree disc and buzzer ,this one was 8 degrees out between points openings now have it equal after grinding points cam.
 

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grinding points cam ?
how did you do this (im looking for cam ring for k2fc there hard to find and not cheap)
 

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it sounds very typical of a Magneto slowly losing it's magnetism due to age, they will fire up cold, then as heat gets to the mag body, the magnetism gets too low to efficiently produce a good spark till it dies, totally repairable but will need to be re-magnetized, it can be done by many firms in England or look on youtube for videos on how to do it yourself with home made equipment,
being in England there are many places here for you to get it done, the 'Magneto Guys' in East Sussex are some of the best & will sort it out for you The Magneto Guys - Vintage, Veteran, Classic Magneto and Dynamo Repairs
 
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