bigpants Posted October 28, 2017 Posted October 28, 2017 Hi everyone. I just got my 1100 slabby up and running after a lay off of 8 years . I had a few short fun filled journeys but it's now developed a problem. Sometimes when I start it it pops and drops out just above about 2000k and wont run through it. But here's the weird bit (almost) every time when this happens all I have to do is change to a spare cdi and the bikes fine. Next day I get the bad running again and switch back the cdi . Any ideas ? Quote
colinworth79 Posted October 28, 2017 Posted October 28, 2017 sounds a bit strange , I would say possibly when your changing over the cdi you disturbing a connector or wire that's the problem . I would personally check all multi pin plugs and put a drop of electrical grease on them . Check earth points and fit some new plugs . Also worth checking the voltage at the battery when its running with the lights on , I once had a strange running fault on my 750 slingshot and found I had nearly 17v when it was running due to a faulty reg . I take it the carbs are all free from any muck that might have developed from being sat 8 year ? Quote
Crass Posted October 28, 2017 Posted October 28, 2017 Sounds like connections to me or a dodgy wire. When you do the swap you disturb the wiring, which 'fixes' it for a while before it plays up again soon after. Probably something loose or a wire which is internally fractured but makes a connection a bit of the time. Have a thorough check of all the connectors and wiring which will be getting disturbed. Quote
bigpants Posted October 28, 2017 Author Posted October 28, 2017 Yeah the wiring blocks were my first guess so I have gone over and over them and can't find any problems. When it's running badly I can give them all a wiggle and it's never made any difference . Carbs cleaned and new plugs and coils fitted. Quote
colinworth79 Posted October 28, 2017 Posted October 28, 2017 5 hours ago, bigpants said: Yeah the wiring blocks were my first guess so I have gone over and over them and can't find any problems. When it's running badly I can give them all a wiggle and it's never made any difference . Carbs cleaned and new plugs and coils fitted. have you a spare pick up , have been known to play up . Quote
bigpants Posted October 28, 2017 Author Posted October 28, 2017 Yeah I've got a spare engine I could pull from. Can you think of any reason why changing a cdi every day sorts it ? Can they get confused or stuck in some way ? Quote
teltwosheds Posted October 29, 2017 Posted October 29, 2017 Check the resistance of the wires whilst wiggleing them. You got a loose connection or burnt out wire in the loom. Quote
suzook12 Posted October 29, 2017 Posted October 29, 2017 When you swap CDI out, does it run for short time then start doing it again or is it ok for rest of the day? Quote
Gixer1460 Posted October 29, 2017 Posted October 29, 2017 Std coils or aftermarket? Does the misfire occur 2 or 3 days in a row whatever CDI is fitted? Maybe coil breakdown through heat is a possibility - one pair or cylinders or across all 4? Mind you running any engine at 2 million revs is gonna lead to issues LOL! But 2000 is fairly low for electrics to give up - maybe it is gunge in a carb - idle / pilot circuits? Quote
bigpants Posted October 29, 2017 Author Posted October 29, 2017 When I've swapped the cdi 's it's usually been ok for the whole day though couldn't swear it's been 100%. And coils were cheap aftermarket ones off Eblag , I know that's not a good choice but I had a non running bike and couldn't throw too much money at it. And I'm pretty sure it's all 4 cylinders breaking down , also I forgot to mention earlier -when it's bad the Rev counter stops working in a way that suggests it's lost all signal/power. Quote
alfiestorm Posted October 29, 2017 Posted October 29, 2017 It could be that you have two duff cdi untis maybe. or power feeding the cdi is being interrupted or high resistance build up reducing the power feeding the cdi, most likely caused by heat build up such as above the engine area. Or you really do have to tempramental cdi boxes Quote
bigpants Posted October 29, 2017 Author Posted October 29, 2017 Hmm, the high resistance thing sounds plausible . It's an old bike with lots of small electrical repairs so I could see how a build up of small probs could conspire to produce a low voltage supply. Not sure why swapping cdi's would temporarily fix it tho. Quote
micktodd Posted October 29, 2017 Posted October 29, 2017 This may eliminate some possibilities http://www.weeksmotorcycle.com/intermittent-spark.html Quote
bigpants Posted October 29, 2017 Author Posted October 29, 2017 Cheers for that , I'll get the multimeter out tomorrow. Quote
Macduff Posted October 29, 2017 Posted October 29, 2017 (edited) I wonder if the coils are the wrong resistance for the slabby CDI . Probably too low on the primary resistance value which could cause the CDI to overheat. Slabby coils are I recall about 5ohms and slingy coils likely to be around 3ohms. I recently converted my slabby to run coil over plug ones and needed a resistor to be bring the coil resistance up . Edited October 29, 2017 by Macduff Quote
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