Bonneville America Forums Forums Technical Forums General Tech Replaced coil, still firing on one cylinder

Recently replaced the left coil and the bike ran 300 miles without issue. On the way to work this morning, it dropped the left cylinder. Turned around and limped the bike to the shop. I get switching the coil wires to test them, but how does the cdi play into this? Could it be a defective new coil or the cdi? Feel free to explain the function of a cdi and if that needs to be replaced.

I don't know about explaining the function other that it gives the signals to the coils.
Your description is exactly what I went through a couple of years back and replacing the cdi fixed it.
Switch the coils and the problem stays on the left side, it's very likely the cdi.

The guy working on the bike is going to test the new coil to see if it's defective. If it isn't, a cdi will be ordered.

I happen to have a spare low-mileage OEM igniter for a 2007 America that I may be willing to sell, if you want to go that route.

I realise that this thread is a few months old and the problem has probably been sorted but thought my experience with losing power on one cylinder might be helpful.

About a year ago, my 2005 Speedmaster started cutting out when warm and then died altogether - classic pickup coil problem (tested it and it was a goner). Replaced the pickup coil and it ran fine for maybe a week or two when the right hand cylinder began intermittently cutting out.

The problem didn't migrate to the other side when I switched around coils or cables so I bought a Procom igniter. Bike ran well most of the time but misfired badly when cold.

The misfire got worse until the right cylinder would no longer fire at all and, with winter and other matters that I had to deal with, the bike sat idle for several months.

Fast forward to last weekend, when I found some spare time. Took out the spark plugs and found one was very black (the one that had been in the misfiring cylinder) so gave them both a good clean and put them back in. Bike ran okay but had a misfire on one cylinder at low throttle openings and WOT. Put in a set of new plugs and it runs like new, doesn't even play up when cold, which can be a problem with Procom igniters.

I'm a bit disappointed (and embarrassed) that I missed out on several months of riding because of something as simple as a carboned-up spark plug but the moral of my story is that failures (especially electric ones) upstream can have consequences for components downstream and you should always check to see whether the downstream components (particularly cheap ones) have sustained any damage before deciding it's all too hard.

on one of mine it would be hit and miss.It would work fine most the time but always came back to running on one cyl.Changed out the CDI and haven't looked back.

I can't tell you what's wrong from here, but I had a 2005 Speedmaster with firing problems. I changed out the original CDI with a known good unit, and problem solved.

Two dealers told me the price of a new unit, and I almost keeled over. Thanks to this site, I asked one dealer about a "Goodwill Claim." The dealer said he would try, and Triumph made good on it loooong after the original warranty was over. Price for a new CDI - $0.

Point of interest - two dealers gave me CDI pricing. Neither offered the "goodwill claim" option. Apparently one has to ask for it. I'm thinking maybe, and I'll repeat "maybe" 'cause I don't know -- the dealers get some labor $ out of this method, so perhaps they're not too put out by doing the goodwill claim. I installed the new CDI myself, for I'm allergic to dealer service.

Just my guess - I wouldn't be surprised if the CDIs go bad from heat, as in extensive idling and warm ups that allow engine heat to surround the unit.

Triumph did not want the old CDI, so I took a band saw to it. It was epoxy throughout, so there was no way for me to see where it failed short of a CAT scan.

Triumph Twin Power beats the OEM price in a fair way for an igniter. That said it may be worth it to check the pickup coil that signals the igniter and insure the gap at the stator is correct. Should be .8mm if memory serves. Also, at least one member here diagnosed one as testing good cold but failing when warm ( you might be able to dredge the thread up).

Surprised to see an old post as one of the top threads. To make a long story short, work and cold weather has prevented me from picking up the bike until last week. The mechanic is out in the boonies so it's not convenient as well. Anyway, the second Procom was installed and it ran fine on the way home. If it's warm enough Sunday afternoon, I'll go for a ride to see if all issues are solved. This has been a very frustrating two years.

By the way, he checked the pickup coil and it was fine.