 Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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Loquacious
Joined: Jan 2007
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2006 America. Carbed, 790.
I haven't ridden this bike in months (long story), but when I did take it out a couple of weeks ago, I was about 30 miles into a ride and it started missing, popping and generally running bad. I noticed one of the vacuum caps was corroded, so I replaced them all. I was able to make it home, but the problem progressively got much worse. It starts and will rev but starts breaking up, missing and backfiring, then dies. It will restart, but same symptoms. HARD!
I checked the usual culprits this weekend - plugs/wires, battery connections and everything seemed okay. Before I take it to the shop next week, what should I expect and are there better-than-stock aftermarket options that I should hold out for?
I should add that the problems started about 10 minutes after a "spirited" run up through the gears, but while I was just cruising along at 50 mph. It's not fuel related.
Advice from the experts please.
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Re: Misfiring? Backfiring?
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Joined: Sep 2015
Posts: 797 Likes: 17
3/4 Throttle
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3/4 Throttle
Joined: Sep 2015
Posts: 797 Likes: 17 |
Check the Air Filter and make sure it is clean and clear.
Pull the plugs and see how each cylinder is running.
Check all the rubber fittings. You can spray them down with carb cleaner and see it the engine smooths out.
Check the filter in the fuel line and then clean the carbs.
If it is not the fuel system then I would go to the Coils, CDI and plug wires. (Go here first if no spark in a cylinder)
That would be my starting point.I am sure others will be along with other suggestions.
Air-Fuel-Spark that is about it.
Last edited by BillyIndiana; 09/18/2019 7:34 AM.
Road Rash Heals. Freckles Grow Back. Ride
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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Loquacious
Joined: Jan 2007
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Thanks Billy,
Air Filter (K&N) - clear
Plugs - normal
Rubber fittings - checked and/or replaced
Fuel - fresh and it doesn't act like a starvation or contamination issue.
It starts, but won't idle. I'll try pulling a plug wire today and see if I can isolate a coil.
Based on the severity of the misfire/backfire, I'm guessing coils, CDI or a timing issue, but I'm clueless and toolless when it comes to tracing electrical issues and don't want to just start throwing parts at it. I have an appointment with the local mechanic Tuesday, but I think he'll want to stick with (probably overpriced) Triumph factory parts. If I can isolate the problem, I'll be able to source/obtain what's best and preferably from Fasteddy or another forum vendor.
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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OP
Loquacious
Joined: Jan 2007
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UPDATE: It started right up, idling and revving just fine. I pulled each plug wire individually and both are firing. After about 5-6 minutes, it gradually started missing, increasing until it would neither idle or rev. without backfiring. 
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Re: Misfiring? Backfiring?
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Joined: Sep 2015
Posts: 797 Likes: 17
3/4 Throttle
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3/4 Throttle
Joined: Sep 2015
Posts: 797 Likes: 17 |
I have my original CDI and Coils and will send them to you for testing if you like. They were in good working order when I removed them.
Just message me your address.
I upgraded to TTP Firestarter and TTP Blue Flame Coils a couple years ago. You can get them through Fast Eddy.
It could also be the plug wires. They have resistors in them.
Both of these failures can happen when things heat up.
Also do not overlook that hidden inline fuel filter. It is in the fuel line by the T to the carbs.
Road Rash Heals. Freckles Grow Back. Ride
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Re: Misfiring? Backfiring?
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Joined: Feb 2008
Posts: 2,668 Likes: 14
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,668 Likes: 14 |
If the bike starts and runs normally when cold & then runs very badly after about 5 to 10 minutes of running, & when cold again will run OK & then repeat the issue, that points to a probable ignition sensor (a/k/a "pick-up coil") failure.
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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OP
Loquacious
Joined: Jan 2007
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Quote:
I have my original CDI and Coils and will send them to you for testing if you like. They were in good working order when I removed them.
Just message me your address.
I upgraded to TTP Firestarter and TTP Blue Flame Coils a couple years ago. You can get them through Fast Eddy.
It could also be the plug wires. They have resistors in them.
Both of these failures can happen when things heat up.
Also do not overlook that hidden inline fuel filter. It is in the fuel line by the T to the carbs.
Very kind offer and I thank you! If I was doing the repair myself, I'd take you up on it. But since I've already scheduled an appointment with the mechanic for Tuesday 0900, I'll see what his equipment diagnoses before I start swapping parts. If it's the same as you think, I'll order the parts from alwaysFASTeddy.
I appreciate the input from you and B02S4. Mechanical things I understand, but this electrickery stuff always boggles my mind. Now I feel better prepared for Tuesday.
Thanks! 
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Re: Misfiring? Backfiring?
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Joined: Feb 2007
Posts: 23,133 Likes: 52
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,133 Likes: 52 |
I agree with the pick up coil theory, they work when cold then when hot start to fail. You can test it by removal, heat, resistance tester. Some oil in a pot on the stove to emerse it in works for heat. (do that with pistons to fit the wrist pins.)
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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Loquacious
Joined: Jan 2007
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I'd forgotten all about the pick-up coil. Now I remember watching this Johnny Cactus video on it. https://www.bing.com/videos/search?q=200...8&FORM=VIREI wish I still had the patience to follow through on this kind of stuff. Unfortunately, I don't have the time, workspace or temperament anymore. I do appreciate the information folks! I'll report back once the mechanic has a look. I just hope that at $78/hour, he comes up with the right diagnosis quickly.
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Re: Misfiring? Backfiring?
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Joined: Aug 2008
Posts: 146
Adjunct
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Adjunct
Joined: Aug 2008
Posts: 146 |
Couldn't a clogged fuel filter act like this? While the bike sits the fuel slowly passes through the compromised filter until the fuel bowls are full and the needle valve closes. When the bike is started it runs perfectly because the carbs are full of gas, then slowly as the engine uses fuel faster than the clogged filter can flow fuel the bike starts acting up.
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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Loquacious
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I guess it's possible, but it just doesn't feel that way. When the bike is cold, I can rev it for several minutes w/o hesitation. Only once the misfiring begins, do I start smelling unburned fuel. The misfiring seems too abrupt to be fuel starvation and the backfiring can literally be felt through the seat.
Hopefully I'll find out when I take it in on Tuesday. I'm making note of all these suggestions to discuss with the mechanic.
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Re: Misfiring? Backfiring?
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Joined: Aug 2008
Posts: 146
Adjunct
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Adjunct
Joined: Aug 2008
Posts: 146 |
I think you're right about fuel not being the problem. If you smell unburnt fuel after the misfiring begins then it seems that fuel is there but maybe no spark to burn it.
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Re: Misfiring? Backfiring?
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Joined: Feb 2007
Posts: 23,133 Likes: 52
Fe Butt
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Fe Butt
Joined: Feb 2007
Posts: 23,133 Likes: 52 |
Besides, clogged filter or plugged vent usually act up faster before temperature would become a factor. First thought through my head was a clogged vent , especially after reading it had been sitting, but after thinking through the description of the issue I suspect the pick up coil too.
I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!
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Re: Misfiring? Backfiring?
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Joined: Feb 2008
Posts: 2,668 Likes: 14
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,668 Likes: 14 |
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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Loquacious
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Not yet. I dropped off the bike Tuesday morning and the mechanic told me he'd been hit with a lot of unexpected bikes coming in since we'd talked. It's a 2 man shop and there are a lot of bike events remaining on the calendar (including Biketoberfest). I have another, so I told him to let mine sit for a few days. I'll swing by next week.
We discussed the pick-up coil, but he always does a full inspection before he calls me. Will post what he says.
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
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Loquacious
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Loquacious
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IT'S ALIVE!  And now for the rest of the story.  Spark Plugs. It seems there was a crack in the electrode inside the insulator and not visible to me or the mechanics on inspection. Not just one plug, but BOTH! Both plugs looked just fine (had been replaced just a couple thousand miles ago). When cold, they fired just fine, but once hot they started failing - intermittently. I have never before had a spark plug failure cause a backfire so severe that I could feel it through the seat pan, but I guess live and learn. Ten years ago, I'd have been ticked off for not finding this myself, but today, I'm just glad that I don't have a $300 parts bill added to the labor. Out the door and riding again for $99.50. Man does it feel good!
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Re: Misfiring? Backfiring?
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Joined: Feb 2008
Posts: 2,668 Likes: 14
Loquacious
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Loquacious
Joined: Feb 2008
Posts: 2,668 Likes: 14 |
Quote:
IT'S ALIVE!
And now for the rest of the story.
Spark Plugs. It seems there was a crack in the electrode inside the insulator and not visible to me or the mechanics on inspection. Not just one plug, but BOTH! Both plugs looked just fine (had been replaced just a couple thousand miles ago). When cold, they fired just fine, but once hot they started failing - intermittently. I have never before had a spark plug failure cause a backfire so severe that I could feel it through the seat pan, but I guess live and learn.
Ten years ago, I'd have been ticked off for not finding this myself, but today, I'm just glad that I don't have a $300 parts bill added to the labor.
Out the door and riding again for $99.50. Man does it feel good!
Well...whoda thunk it. What plugs were they, specifically?
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Re: Misfiring? Backfiring?
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Joined: Jan 2007
Posts: 3,445 Likes: 1
Loquacious
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OP
Loquacious
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Almost positive they were NGK. I bought them from the local Triumph dealer - same # as OEM. What I'm still curious about is how/why it happened (so it doesn't happen again). I was cruising along at a sedate 50 mph, though I did have a spirited 20-80 mph run-up about 10 minutes earlier. Maybe a bad batch of plugs.
It was a mystery to the mechanics too. After the plug change and over a 2 day period, they rode it 35 miles, with 3 separate warm up/cool down cycles and had no misfiring. Another 15 miles on my way home was the same.
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Re: Misfiring? Backfiring?
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Joined: Sep 2015
Posts: 797 Likes: 17
3/4 Throttle
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3/4 Throttle
Joined: Sep 2015
Posts: 797 Likes: 17 |
Glad to hear you are back on the road. Cracked plug that is one I have not heard before. It will be on my list now.
Road Rash Heals. Freckles Grow Back. Ride
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