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Old 06-17-2015, 09:30 PM   #1
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Default Triumph low speed dead cylinder

I have a single carb Triumph 650. New problem started tonight, at idle it only runs on the left cylinder. After you build up a few RPMs it comes back and seems to run down the road just fine until you come to a stop/idle again. In the spring I set the timing and points, it's got two new coils. All the connections seem tight. I took the points cover off and didn't see anything that looked out of the ordinary other than the one cam lobe seemed to be a little far away from the points when they were closed, but that was for the left cylinder which seems to be the one keeping it running.
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Old 06-18-2015, 03:21 AM   #2
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Default Re: Triumph low speed dead cylinder

Sounds like a spark plug. Had a very similar problem on my T140. I had new plugs in, carbs set up right, ran well at high revs, but tick over was down on one side. Got a good spark with the plugs out, but a friend had had the same trouble.

I tested the plug resistance, between the probe (centre) and the thread of both plugs. On the good side, with the meter set at 1000v, and megaohms, there was no continuity. On the suspect side, there was a very high resistance showing, where there should have been no continuity. This meant that on this side, there would have been a spark, but ever so slightly weaker than on the good side. So the spark was breaking down at low revs, then on revving it would get more "oomph" and spark across OK.

The plugs were NGK, and on mentioning it to some mates, it seems there were some dodgy ones out there.
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Old 06-18-2015, 08:34 AM   #3
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Default Re: Triumph low speed dead cylinder

Good to know. I just put a new set of NGK's in it when I tuned it up in the spring. It's only got about 400 miles on it since then. I'll try swapping them side for side and see if anything changes. Odd, I never had a problem with NGK before I always thought they were good.
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Old 06-18-2015, 08:37 AM   #4
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Default Re: Triumph low speed dead cylinder

Just a Note...A Plug is a Plug...It either starts a fire ...or it don't ..that is the only job they have. No Do-Overs.. There is No "Magic Plug"
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Old 06-18-2015, 08:50 AM   #5
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Default Re: Triumph low speed dead cylinder

a fouled plug will do that, and you don't mention what what the plug looks like on that cylinder... though you may have left that out because the plug looks good.
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Old 06-18-2015, 09:29 AM   #6
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Default Re: Triumph low speed dead cylinder

I didn't even pull that plug yet. I just pulled the points cover and made sure the plug wires were tight. I'll pull the plug and post back.
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Old 06-18-2015, 09:46 PM   #7
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Default Re: Triumph low speed dead cylinder

Okay swapped the plug for a new one tonight and same thing. Wire looks good, coil is new. I don't see anything jumping out at me. I'll have to get my multimeter and do some digging next.
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Old 06-19-2015, 02:36 AM   #8
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Default Re: Triumph low speed dead cylinder

tried firing it up in the dark to see if there is any arcing ?

just a thought.
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Old 06-19-2015, 07:30 AM   #9
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Default Re: Triumph low speed dead cylinder

Quote:
Originally Posted by '59 View Post
tried firing it up in the dark to see if there is any arcing ?

just a thought.
There is always some arching at the points...Semi-Normal...Hard part is Identifying Too Much..Indicating bad condenser. Generally a Bad condenser [open] will cause engine to start and idle, but, not accelerate.
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Old 06-19-2015, 09:22 AM   #10
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Default Re: Triumph low speed dead cylinder

pull what you can off and give it all a squirt of wd40/or similar
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Old 06-19-2015, 11:00 AM   #11
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Default Re: Triumph low speed dead cylinder

A plug is not alwAys a plug BUT how they are positioned in the combustion chamber WILL effect their performance .....it may be voltage. Valve depth, ect.ect....I had that similar issue....I just swapped the plugs...simple elimination and troubleshooting..
Dual or single points? dual or single coil? ...

side note....what exit are your from???
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Old 06-19-2015, 11:29 AM   #12
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Default Re: Triumph low speed dead cylinder

Any chance a vac leak at the head would do it? I'm not a trump guy, so I can't see it in my head.

Maybe a head gasket leak on that one hole?

Just spit balling here....
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Old 06-19-2015, 11:50 AM   #13
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Default Re: Triumph low speed dead cylinder

just read.."will not accelerate"... im with JAWS on this...leak...maybe a head gasket....do a leak down and compression test on BOTH cylinders...
My unit at one point would start and rev fine...warmed up, if you got on the gas felt like the stator was grinding on the rotor...like something was dragging...thought maybe the primary chain maybe binding....
Nope head gasket...blowing between each other...
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Old 06-19-2015, 02:35 PM   #14
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Default Re: Triumph low speed dead cylinder

It's definitely not getting spark at the righthand plug. I swapped plugs with another new one and still no spark. I'm running dual points and dual coils. I just cleaned and adjusted the points a month and 300 miles ago and it was running great. As of right now the bike is hard to start because it's only hitting on the one cylinder when it starts. Otherwise seems fine.
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Old 06-19-2015, 02:42 PM   #15
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Default Re: Triumph low speed dead cylinder

Dual points...dual condensers ....swap the condensors....see what happens... I'm not sure if there is a way to "test" them...
If there is no change...poss coil or wire....give the wires from the points to the coils a once over...and your grounds
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Old 06-19-2015, 02:44 PM   #16
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Default Re: Triumph low speed dead cylinder

What's the voltage at each coil? What is the resistance of each coils primary and secondary windings? I would check the circuits to each and from each....
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Old 06-20-2015, 04:44 AM   #17
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Default Re: Triumph low speed dead cylinder

re test in the dark; I was thinking more arcing out along a duff lead, I've also come across some repo plug caps that have no continuity straight out of the box, but no mention of these being changed.

As previous posters, it's a process of elimination.
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Old 07-06-2015, 11:45 AM   #18
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Default Re: Triumph low speed dead cylinder

Well I checked for spark this morning. Nothing on either cylinder. I started at the battery, I have 12.5 volts with the key off, but as soon as I turn the key on it drops to 9.5. I checked at the coils and I have 9.5v at the coils also. I'm thinking I have a bad battery. It's about 4 years old and it's always on a battery tender. That could explain why I had spark at speed but lost a cylinder at idle.
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Old 07-06-2015, 11:59 AM   #19
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Default Re: Triumph low speed dead cylinder

OK, never fails.....from now on any threads having to do do with starting /running issues.....my first question is gonna be "How old is the battery"!!!!
I think I read it somewhere here in the forum..."most of your carburetor problems are usually electrical.."... Best place to start, at the beginning...the battery AND the terminals...
Especially with a issue surfacing "out of the blue"....
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Old 07-06-2015, 01:35 PM   #20
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Default Re: Triumph low speed dead cylinder

Use jumper cables to a buddy's battery that you know is good and se what happens before you buy one. OK so what I'm a cheap ass.

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