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identifying a triumph miss...

1418 Views 9 Replies 9 Participants Last post by  Tiger Dale
How would one determine if a "miss" was electical or fuel? T140V, accell coil, boyer MKIII, misses at or about 3000rmp and up, especially under load... checked my wires, all seem tight and well connected... wonder if my coil is crapping out, or maybe carbs are worn- I've heard amal 930s can go from fine to crap in 50 miles or so. The slides do have some play... The plug wires have popped out of the coil several times from bumps/vibration, but this time seem to be seated well... Sort of at a loss here, so any advice would be really appreciated (like were to start trouble shooting?)
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I had a problem like that - that stumped me for quite a while until by accident, I found that one side of the fuse holder was making intermittent contact...sliding in and out of the plastic holder. I fixed it and no more miss.

Also, in case that isn't it and per John Healy, long time Triumph mechanic and parts distributor, etc. etc. as well as the moderator for the Triumph forum on

"One Rule of Thumb I have found to be handy diagnosing these kinds of problems is:
If it happens at the same THROTTLE OPENING it is usually carburetion.
If it happens at the same RPM it is usually ignition.
It doesn't always work out that way, but I find it a very good way of approaching a given problem."
Hi there,as regards fuel,is the fuel cap venting OK, always a good place to start. Only a though as i had similar prob,also cleaned the pet lock the rubber can breakup over time and cause minor blockage and work your down though the carbs
I'm with whittiger650. Depending on where it happens is likely going to point you in the right direction. But it sounds like a carb issue to me since it happens throughout the throttle from 3k up.
I had exactly the same issue on my '65 Tiger 500. I tore the carbs apart, rejetted and tried every combination. Checked the valves, sat online reading threads and got nowhere. Took the tank off to look everything over and found a coil wire crimp connection slightly loose. Crimped it down and never had an issue again. It never, I repeat never broke up until I hit 3k. Weird but true. The vibration would just get nasty enough to shake the connection. Idle was perfect. Good luck. I would just take a deep breath and go over everything (especially connections) and recrimp or even redo anything remotely sketchy,
good luck.
I have ran several sets of origional 1960,s Amal carbs that work great. The slides in new ones have some play too. They are made the same way i think you should expect the same kind of longevity. Sounds electrical , with the breakup being at the same place consistantly. you didnt say battery or not but with a low voltage in the charging system/battery i think you can get breakup at the higher RPMs without any at the lower r,s...
After having my ass kicked a couple times, I ALWAYS assume the ignition FIRST.
And I've been right about 90% of the time, since.

I like the tip about rpm relating to ignition, and throttle opening to fuel delivery... It is definitely an rpm thing. there is a stumble at about 2200, then it falls apart completely after 3000. timing checks out, going to go through all my connections this week... definitly is worse under load (hard accelleration, cliimbing a hill. passing a car, etc...)
Are your plug wires solid copper core? Also high resistance or dodgy contacts in the ign. switch or kill button can cause a miss with a boyer. Check by running a jumper wire from the battery to the boyer to eliminate the rest of the ign. system and take it for a ride and see. Jack
Boyers need a good battery. No less than 12V loaded. With the bike off turn on the head light for at least 30 seconds. Leave the light on and check the battery. Any less than 12V chuck the battery and get a new one.

That should be your first test then proceed with all the good suggestions.

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