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Discussion Starter · #1 ·
It's been months now since I last had my triumph working correctly and I'm absolutely lost to what it might causing it. The symptoms appears to be that one cylinder isn't consistently firing and the bike isn't possible to ride.

At first I thought it was 8 stroking and changed all the jets in the carb (even though the jets had only been replaced last summer anyway). I've decoked the engine, fitted new piston rings, lapped the valves and set valve clearance to within spec.

Finally, I've replaced all electrical components in the bike except for the wiring harness and bypassed the switches to eliminate a dodgy ignition switch. Except the bike is still misfiring, the problem is frustrating to say the least and my patience is close to breaking point i.e. thinking of scrapping/selling the bugger if I can't get it running again this week.

I'll load a video up and place the link here, if it helps with troubleshooting!
 

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My guess is that there is a passageway in one carb that is stubbornly clogged.

Need to remove them, soak carb bodies in hot Berryman's Chem-Dip for an hour, flush, and re-assemble. If you have access to a sonic jewelry cleaning rig, soak them in boiling hot water in the sonic rig for a while, too.
 

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Discussion Starter · #6 · (Edited)
Taken all day to upload two videos. I'm not sure if the sound is very good but it was having trouble firing on both cylinders. The right hand cylinder fires fine but the left hand cylinder is struggling.

https://www.youtube.com/watch?v=3II3pWx2qzU
https://www.youtube.com/watch?v=vgxtC2AlLtw


I'm running a MKIV boyer ignition unit, boyer power box, 12v gel battery of 11amp/hrs, 6v lucas coils...all of them are brand new and fitted with the last few weeks as I've been trying to remedy the problem. No luck so far though!

Also checked timing with a strobe and it seems to be spot on 38 degrees from TDC at 4000+rpm

It has a single carburetor and I've placed the carb in a sonic bath (twice) as well as a weak acid bath (once), replaced the jets, needle and float (although they had only just been replaced last summer anyway.)

I'm absolutely scratching my head with this problem as there doesn't seem to be any obvious cause.

I've just done a compression test too. The right hand cylinder has a 180psi when cold and the left hand cylinder has 165psi when cold. I'm not sure whether would make any difference to the running of the bike.

There is no kill switch in the bike and I've bypassed the ignition switch with a cheap switch that i bought at the electrical shop.
 

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Both cylinders will spark at the same time
That's how EI works.

Swap the plug leads (if they are long enough) so that the existing set up fires the opposite cylinder.

The first video is set to "private"
 

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Not mentioned replacing plug leads ? Daves swap test may show that up.
 

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Having a longer set of plug leads is really handy as (if using EI) you can swap a known working cylinder's ignition to fire the malfunctioning one. That eliminates duff electrics, or confirms
 

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Discussion Starter · #11 ·
I've crossed the plug leads over and the symptoms don't travel. Right hand cylinder still firing ok but the left hand cylinder is struggling/no ignition.

Sometimes the bike might fire on both cylinders for a short spurt (2-3 seconds) whilst riding. Otherwise it's just the right hand cylinder doing all the work. I've replaced the high tension cables and caps and checked continuity with a multimeter, so I'm confident that they are in good working order.

I've checked valve clearance and they are ok...although the left hand cylinders inlet valve clearance isn't as generous as the right hand inlet valve clearance. Furthermore, I noticed when doing the compression test on the cylinders that the left-hand cylinder required more kicks before the needle on the compression gauge reached it's max value than the right hand cylinder. i.e. (I got 165 psi on the left hand cylinder after 10 kicks where as I got 180 psi on the right hand cylinder after just 4-5 kicks.)...Could this indicate a mechanical problem with the valves on the left-hand cylinder...the cylinder head was fitted with new valve sleeves and valves 18 months ago, + there wasn't much wiggle on them when I decoked the engine a few weeks ago. I'm not ruling anything out however but worth giving as much info as possible.

As it's a single carburetor, I would have assumed that a carb problem would have effected both cylinders?

Also both videos should be viewable now :)
 

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Did I overlook something or have you tried replacing the spark plugs?
 

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Discussion Starter · #13 ·
Good point Tjoko but I'm afraid I already have and it had no effect..

I was speaking to one of old timers in the mc garage about it he suggested that there may be a gasket leak somewhere...When I removed the cylinder head a week ago..I did notice black deposits in the center of the copper gasket, indicating that has been a leak. Any confirmation that this could be causing the issue of no ignition in one cylinder despite correctly timed and strong spark, as well as a well working carburetor?
 

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There shouldn't be that much difference in the compressions between the cylinders.
Try the low one again with a squirt of oil down the plug hole and see if it improves a lot.
If it does it's the rings, if not it's probably a leaky valve.
 

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Discussion Starter · #16 ·
I'm not too sure whether it is a stock intake manifold or not. It's been working fine with that intake manifold for months previously though and upon inspection, it appears to be all intact.

I put new plugs in but the problem is still persistent. If I give it full throttle, both cylinders seem to fire and the bike runs fine, between idle and 1/2 it tends to just be the right hand cylinder firing with the left hand cylinder combusting now and then or not at all...
 

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A few things to try.
Loosen the tank filler cap.
Do a fuel flow check.
Remove both plugs and tape them to earth together.
Chech both plugs fire together with nice blue sparks.
Note the colour of the plugs.
 

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Discussion Starter · #18 · (Edited)
Went through the tips you recommended caulky...and everything seems in order.

I've gone through 6 pairs of spark plugs in the last few weeks. The second they go into the engine they turn black. I took the triumph out for a ride just now. Absolutely bloody horrible to ride. Full throttle, it'd ride fine but anything less and it was on one cylinder...After 5 minutes of riding the whole thing starting cocking up on me. Hiccuping behaviour. On...off...on...off. I've already bypassed the ignition switch and have no kill switch, So I'm sure it's not that.
 

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Your engine is running too rich.
It looks like the pilot jet is blocked or the the air screw (horizontal) screw is screwed in too far.
You need to buy a .016" guitar string and file the end to de-burr it.
Remove the pilot screw and using a torch (flashlight) insert the guitar string into the jet hole.
Then spray carb cleaner into the jet.
Refit the pilot screw fully, then unscrew it 1 1/2 turns. (or a little more)

Your needle could also be in the wrong notch.
Maybe lower it by using a higher notch.

It`s possible to clean sooty plugs with fine emery paper.
 

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Your bike seems to be running too rich, and the way to fix that is to increase air in the fuel mixture by the methods that Caulky has described.

Another less common cause for spark plug fouling is the wrong spark plug wires. Wires that are meant for a car do not fit in motorcycle coils properly, resulting in a poor electrical connection and inconsistent firing. It may run better at full throttle, but at lower speeds the spark is intermittent, and may be worse on one cylinder than the other. The result is rapidly blackening spark plugs.

Motorcycle-specific plug wires fit snugly in the coils and provide a good connection and consistent flow of electricity to the plugs, resulting in consistent firing.
 
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