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Discussion Starter · #1 ·
So I have run out of ideas. My 1971 Triumph Bobber is intermittently not firing on the right side. I have problem shot the following:
  1. Compression is @125 each side
  2. Just did the valves
  3. The Boyer Bransden Micro Power ignition, tested in spec.
  4. Rebuilt / Ultrasonically cleaned Amal carbs
  5. Open shortly exhaust
  6. Jomo 15 cams
  7. Custom manifold to run dual carbs on a Tiger head.
The bike will fire up and idle. It is only running on the left side. The left open exhaust gets hot and you can feel the power coming out of the exhaust. The right side pipe does not get hot and the exhaust is weak. I pull the right side cap off and put in a spark plug and it firing. I remove the left side and the engine stops. This is where it gets weird. I use the right side carb plunger and fill the bowl. I remove the left side cap. The bike roars to life and the right pipe gets hot. You can feel the powerful exhaust. I put the left side cap on and for a brief second you can heard both running, then you put your hand over the right exhaust and its weak again and the right side isn't firing
I thought it was the right carb originally, so I switched it out. I also checked the petcocks.. they work. Its got spark, fuel and compression......
I am stumped... any thoughts would be appreciated.
Thanks!
 

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So I have run out of ideas. My 1971 Triumph Bobber is intermittently not firing on the right side. I have problem shot the following:
  1. Compression is @125 each side
  2. Just did the valves
  3. The Boyer Bransden Micro Power ignition, tested in spec.
  4. Rebuilt / Ultrasonically cleaned Amal carbs
  5. Open shortly exhaust
  6. Jomo 15 cams
  7. Custom manifold to run dual carbs on a Tiger head.
The bike will fire up and idle. It is only running on the left side. The left open exhaust gets hot and you can feel the power coming out of the exhaust. The right side pipe does not get hot and the exhaust is weak. I pull the right side cap off and put in a spark plug and it firing. I remove the left side and the engine stops. This is where it gets weird. I use the right side carb plunger and fill the bowl. I remove the left side cap. The bike roars to life and the right pipe gets hot. You can feel the powerful exhaust. I put the left side cap on and for a brief second you can heard both running, then you put your hand over the right exhaust and its weak again and the right side isn't firing
I thought it was the right carb originally, so I switched it out. I also checked the petcocks.. they work. Its got spark, fuel and compression......
I am stumped... any thoughts would be appreciated.
 

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Discussion Starter · #5 ·
Thanks for the advice so far. I have been doing some reading and thought I would make sure the pilot circuit in the right carb was clean. I pulled of the carb cleaned with a guitar string and carb cleaner. Put it back on, same result. So at least I eliminated that. I will try changing the plugs, but try Champion instead of NGK's as seen on a few posts. Would the coil be faulty and not working under load??? As mentioned I have tested it and it in spec and both terminals are spark? Thanks again.
 

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you have the wasted spark so swap things around to eliminate an ignition problem and narrow down to the plug or carb'.
 

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you say you have swapped carbs and the problem stays on the right side. so it isn't carbs.

you say you have 125 psi both sides. that's not high, but it should be enough. so the valves are not the problem.

you say you have spark both sides, so the ignition is still minimally functioning

you say that you have adequate flow through the petcocks. is that 300 ml per minute? compare both sides.

a guitar string isnt best for the idle passage. buy a 14-cent #78 drill bit and glue it in a small tube, then spin the mung out of the idle passage. you can poke the passage clear and it will still be too small. a #16 guitar string just pushes the mung into the mixing chamber under the venturi floor, where it is free to plug up the idle fuel ports.

even though its sparking, it sounds like ignition.

if it were th ecoil the problem would be both sides.

whats left except the plug wires? replace them and run new plugs. the NGK B8ES is no longer available, but you can use champion N3C, which is the current recommendation.
 

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Discussion Starter · #9 ·
Thank you @dorset I have an update. I reached out to Boyer Bransden, they suggested the pickup plate and pickups. I inspected them and tested resistance and it seemed fine. I remembered I had an extra pickup plate that was the same. I switched it out and changed the spark plugs to Champion N3C as recommended. After a few kicks it fired and was running on both cylinders. It was farting abit, but I have to dial in the timing. Didn't have a timing gun, so picked one up today. I will time it and report back. Thank you for all the support. Cheers
 

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Discussion Starter · #10 ·
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Heres a picture of the dual carb setup on a tiger head... Brought it from a guy of e-Bay years ago...
 

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I suggest you try champion RN9YC ... I use them in almost every bike I own. Never had a fouled plug.
 

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I had either this or a very similar problem that drove me crazy for weeks until i finally took the bike for a test ride in the dark. When i looked down into the frame i could see the wire connected to the ignition key sparking - it ended up being a simple short. I assumed it was carb related, or plug related because it would worsen when i pulled on the throttle - but really it was just that wire was connected to the coils. Maybe check your wiring
 
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