Hi, looking for a little help here from those more knowledgeable. My Thunderbird 900 runs fine until it doesn't. This seems to be an intermittent fault that can happen at any time. Basically the bike runs great, then can suddenly cut out, sometimes it will start again while I'm riding. The tacho will shoot down to 0 revs. It then may start normally straight away, or may take a few minutes before it can be started. Sometimes it runs with no problems at all. The carbs have been re-built professionally recently, as the garage thought it was a fuelling problem. They replaced an ignition coil at the same time. At the MOT today (different garage), the thought was it must be electrical. Fortunately (kind of) the problem happened at the garage and the chap could see the symptoms. Could this be the crank position sensor? I've checked it as per the Haynes manual that gives the resistance as 530 ohms +/- 10%. Mine measured consistently at 592 so out of spec yes, but is this out by enough to cause problems? Should I replace this or are there other potential problems I should be looking at first? Any help would be very much appreciated.
Did you measure it hot or cold? If the insulation is breaking down then this could affect the readings given. I'd measure it again at different engine temperatures.
Hi, I have a 2002 1200 trophy whose engine and ignition is a very close cousin to your 900 thunderbird. I had problems where the engine would run very rough and wanted to cut out, but not all the time. I did the carb cleaning, new air filter, new plugs etc, no significant change. Checked the coils (2 of them on mine), one had infinite resistance on the HT side, so I swapped it out, no change. The other measured fine. HT lead no 2 was reading lower on Kohms so swapped that out, no change. CPS was 570ish cold, 700odd ohms hot, so I swapped that out, no change. So swapped out the good coil. Hey presto main problem went away. It still had a slight issue which turned out to be a faulty new No 2 HT lead. I wish I'd just bitten the bullet and swapped out both coils at the start (but they were a bit more expensive on mine £89 each). Our bikes are getting on and the coils are in a very poor position, heat wise. Your coils are cheap to replace, sprint manufacturing do a pvl copy for £25 each and you only need another 2. It may not fix your problem but it's an easy swap and they have a bad reputation for failing over time. I'm also glad I replaced the cps (even though it wasn't at fault) as it's removed that worry from my mind and the bike runs like new now. BTW, if the cps reads open fault when the bike fails then it's likely to be the cause, but a raised resistance as seen by mine isn't necessarily the fault.
Thanks Wattie That'll probably be my route (eventually), change out the 2 remaining old HT coils along with a new pick up coil. That'll eliminate any problems there and highlight if there's anything else. I agree about the position of the coils being bad, I've looked into the stick coils but not sure if I want to go down that route (yet). Yes, these bikes are getting old, I bought this a year ago, knowing I would want to personalise it somewhat. I'm actually enjoying the learning curve that these little problems present. That probably makes me weird. Thanks again for the advice, now off to run the bike and recheck the resistance when it's hot..........
OK, so I measured the resistance on the sensor when cold at 554 ohms. Ran the bike to warm (not hot enough for the fan to kick in) the reading was then 621 ohms. I'm assuming that the Haynes ideal reading of 530 ohms is the cold reading? and the +/- 10% is to allow for changes in temperature? If so, then I assume the sensor is faulty. Sorry for all the questions.
@Payney No not weird in any way. That is what this forum is good at and people here are only to happy to led a helping hand. I do hope you get sorted soon as they are great bikes and need to be pampered.
I've just checked my notes. My cps was reading 576ohm cold, 686ohm warm (i.e. after idle for a bit), hot 704ohm (after riding and bike starting to run faulty). As I said before, I swapped out the cps but it turned out not to be the fault. I didn't write down the new cps readings but as I recall it was just below the quoted specs and didn't change after coming back from a ride. This is from memory only, though.
Thanks Wattie, that's very useful. I'm going to order a new CPS and 2 new coils. If the CPS fixes the problem 2 spare coils are worth keeping as, like you say, they are prone to failure. It's good to know that the stated specs are for hot and cold values, this was what was confusing me.
I was asked to work on a friends ZZR 600 after he'd tried numerous times to resolve an issue. I ended up condemning one of the two coils and he wasn't willing to buy a brand new one due to the cost. A secondhand one could potentially have been twenty plus years old, and I warned him of the dilemma that could cause. However, it not only resolved the problem but he stated it was running the best it ever had. He later declared the fault may have been there from when he bought it, and was over the moon with it's new running smoothness and power. Coils can be tricky to resolve especially if its heat related and sometimes substitution is the only real way to test them, but not great if you don't have access to spares. My mates 675R had an intermittent issue, full power, smooth running, then stall and reluctant to start. Eventually fire it back up and all 100% again All very frustrating, especially on one day out I recall! I told him he could, if he wanted, take them off my 675 and run with them for a few weeks as I was using the 765. Issue resolved. Three coil packs bought and mine refitted. Good luck
Thanks Eldon. Hopefully one or another or a combination of the new parts will solve the problem. All parts are on order. Thanks for everyone's input on this. I'll let you know how it goes.
Thanks Eldon. Hopefully one or another or a combination of the new parts will solve the problem. All parts are on order. Thanks for everyone's input on this. I'll let you know how it goes.
The CPS is now changed. Took it for a run yesterday, only 20 miles or so, but enough to warm everything up. The stuttering revs have disappeared and I thought the problem was fixed but a mile from home and the middle cylinder stopped firing. This is the one with the new coil. I think this may have been a combination problem from the start, hopefully one part is remedied, now got to cure the next. If it helps anybody, on my return home the resistance on the new CPS was around 620 ohms, I forgot to measure it cold but will do so today.
