Strange misfire
Hi,
First of all my bikes a 2000s. A couple of weeks ago I was out and about when having pulled away from a junction I revved it up to the red line and it cut on to one pot. Due to missing allen keys I couldn't do much with it so ended up limping home on one. As I was limping along I noticed that when I closed the throttle it was popping and banging burning fuel in the exhaust. When home I checked which pipe was hot and determined that the rear cylinder was the dead one. Next morning I checked the plug cap was on, pulled the plug (a couple of thousand mile old iridium number) and checked all the connections a round the coil. Nothing was wrong. So I fired her up and went for a 30 mile test ride. She was fine I tried high revs chugging along at low revs all was well. Fast forward to yesterday I went for another blat. I noticed that after a couple runs up to the red line she was reluctant to rev past 7500. Fine up to there no matter what throttle I used but not revving past 7500/8000. My tacho is an after market one that uses pulses from the rear coil (easier to get to) I noticed that it started fluctuating when misfiring, several hundred revs either way, so not reflecting the engine speed. I'm now wondering is the tacho fluctuation caused by a lack of voltage to the low tension side of the coil or would a lack of spark cause there to be no signal from the coil? If the former is it likely that one signal from the ignition box could break down under load/ when hot? If the later can I change the HT lead on this type of coil or are they moulded in? Any other idea about what might cause this sort of thing? Thanks for your help. |
Re: Strange misfire
Why are you redlining it?
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Re: Strange misfire
You're right to be focussing on the rear cylinder as all symptoms point that way. Don't change that HT lead yet. Have a look on you tube for how to test the whole coil first. You'll need a multimeter. Maplin do a decent enough one.
Riding around on one cylinder could damage the bottom end so stay close to home when doing test runs. |
Re: Strange misfire
My first response would be why not? Or because I can. The engine is designed to be safe to redline and probably a bit beyond. However in this case redline isn't actually where I went, I went to shift light set at 9500. I don't normally bother with the red line or full throttle for that matter but occasionally it is nice to go a bit nuts. Having found this problem the only way to see if it fixed or not is to replicate the failure mode. If it is a load/heat problem I assume it will continue to deteriorate until it becomes a problem in my normal riding mode and as such I'd like it fixed before it does.
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Re: Strange misfire
Dave, sorry I didn't see your post when I started mine. I have a multi meter and will test the coil. I suspect it will be fine cold as the issue is only at high revs when hot. I don't do high revs on a cold engine.
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Re: Strange misfire
Also check the resistance of the plug cap.Standard it should be 5K ohms but are usually a bit higher around 9k ohms but anything above that get a new one.
These are the red version plug caps, http://www.ebay.co.uk/itm/Spark-Plug...wAAOSw7NNT6WRf and these are the black, http://www.ebay.co.uk/itm/1x-NGK-Res...EAAOSweW5VX6ll You can make a rubber skirt/seal to emulate the originals from some old inner tube. |
Re: Strange misfire
The only bike I've had a plug fail was on a 02 curvy, it would sporadically fire then miss for a few revs. In your situation I'd try a new set of plugs first (non iridium) and then suspect the coil. Not sure about the significance of the rev counter variance.
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Re: Strange misfire
Id agree that substitution of first the rear plug,then the cap/lead and coil for known good items is the way to find the culprit.Can you borrow any of those bits from anyone?
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Re: Strange misfire
Right well I've tested the coil primary and secondary and loo to be Ok at 4.7 ohms on the primary and 28Kohms on the secondary. I'll have a play about with the plugs and caps and bits during the week.
As an aside whilst searching for R1ffR4ffs plug cap numbers (thanks for posting the link) I came across an old post about restricted SVs. My bike gets up near a ton easily but then runs out of puff. I'm not really bothered about this as with no fairing hanging at those speeds is not fun. I also put it down to an old bike and a fat pilot. However reading that thread made me think "33hp struggles to break a ton" Humm I wonder. So assuming the restriction is in the ignition module does any body know the part number for a normal module? My part number is J54 20F0 BB7708 OB29. |
Re: Strange misfire
Restriction was carb washers on the Curvys, not the ignition module.
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Re: Strange misfire
Thanks, looks like it just an old bike and a fat pilot then. back to fault finding.
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Re: Strange misfire
Quote:
In your situation I'd check the coil is getting power and if it is and all connections are good I'd look for a replacement good one. |
Re: Strange misfire
Well I think I've cracked it. Checked the plug cap and it had 12K ohm resistance so that got replaced. Whilst I had the plug cap off I thought I'd check the HT lead as well. It tested at 1 ohm which seamed a bit much for 6" of wire. I checked my 1m length of HT lead and it tested at 0.1 ohm so I did the HT lead whilst I was at it. Quick test ride and it looks to be sorted. It even felt crisper from idle but I don't know how much of that was in my head. Thanks for the suggestions everybody.
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Re: Strange misfire
Looks like you got it fixed.More often than not ignition faults aren't the failure of just one component but a cumulative affect of parts wearing over time.
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Re: Strange misfire
Quote:
***Aftermarket*** restriction was via carb washers, the Suzuki restriction was by a set of different CV throttle slides that had a great big hole in them and so restricted how far they would open. I bought a set of carbs that had them fitted without realising. Fitted the carbs to my 700cc SV and it made 35hp on the dyno! :confused: Stuck the old ones back on and up to 80hp! |
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