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Old 07-10-2021, 12:17 PM   #31
PPuxley
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No I have not done anything , to the pickups ,, i think I may buy one or 2 just for ,,er peace of mind or desperation ha ha ,,I am borrowing a strobe from a mate to see if its out of synch ???? I also have a colortune ,, but they can be awkward to understand what one is seeing
The colourtune for simply seeing the spark fail on the rear cylinder is very straightforward, it just goes blank. It was flashing at idle then when the revs are raised.....Nothing. Quite clearly showing no spark.

If you are getting new pick ups, you can get them from Electrex World £36 each Type P08. 460 ohms.
Or with a bit of modification Brads suggestion Yamaha CY-7, 200 ohms

But you might as well wait till Ive tried!
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Old 07-10-2021, 12:44 PM   #32
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Despite what you have been told by an expert, pickups and also crankshaft position sensors do fail intermittently. This is usually brought on by rising heat. After the engine has cooled down the sensor/pickup will function again.
Yours is not a heating problem, but rather affected by increasing revs. In my mind I don't see why a weak pickup would fail to see the trigger as it sped up.

I know that it interrupts a field, but not what is producing the field. If it is the sensor then replacing it should restore the field, but if it is the trigger, then that should be suspected.. Unless of course the trigger is common to both pickups?

A high resistance connection somewhere in line between the pickup and igniter might cause this problem, especially if the current decreases with revolutions.
Or maybe just the subtle increase in vibration could jiggle a connection out of contact?

I'm sure that the pulse from the pickup is quite a low current? So wouldn't put up with much interference?
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Old 07-10-2021, 01:28 PM   #33
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Unless of course the trigger is common to both pickups?
It is common , isnt it, its the raised lump on the flywheel that passes both coils. That leaves the pick up.

As Sherlock said
When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
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Old 07-10-2021, 02:06 PM   #34
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Originally Posted by PPuxley View Post
As Sherlock said
When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
I've never agreed with Sherlock on that one to be honest.
The way I see it, once you've eliminated the impossible, whatever remains is nothing more than "the possible" ..... of which there may be many variants.
But then again, why would you believe Sherlock ? After all, his very existence defied "the truth".


I know that isn't of much (if any) help in solving your problem though.
I remain intrigued and wish you luck.

An afterthought ......
Could it be that both your cylinders, and Jerry's, have developed vertigo in their old age ?
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Old 07-10-2021, 04:02 PM   #35
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Could it be that both your cylinders, and Jerry's, have developed vertigo in their old age ?
No cant be that...one of the tests I did was to start the bike rotated 90 degrees, but the fault remained on the back cylinder!!!
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Old 07-10-2021, 04:35 PM   #36
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vertigo !!!!???? ha ha im ust more confued than ever ,, but Patrick and me can try and co-op on this ,, It was made by Italians so we should be able to sort it out ,,'' in vino veritas[''
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Old 08-10-2021, 11:53 AM   #37
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I wont break open the champagne yet, but I think I may have solved the issue! I need to balance tune and road test yet.

This morning I installed a new pick up coil for the vertical cylinder.

On start up with the colourtune in place on the vertical I was immediately able to see it was receiving a spark and firing throughout the rev range. I then set up the strobe and again I was now able to see the strobe working at all engine speeds, I was also now able to confirm that the dynamic timing was spot on at both idle and revs.

So it would appear that it was indeed my vertical pick up coil that was causing the issue. Inspite of inspecting the old coil carefully I could see no fault on it , let alone a fault that might only develop at speed.

In summary, for a fault on firing of a single cylinder, it is relatively easy to swop coils, HT leads, plugs, LT wiring to see if the fault changes cylinder. A fault in the carb or pick up does involve a bit more dismantling and rework effort. The fault can be made all the more opaque by apparently seeing the correct resistance in what turned out to be a faulty pick up coil.

I would also now recommend using a Colourtune, (not necessarily as a quantative analysis tool for tuning), but theres nothing like being able to physically see into the firing (or in my case, non firing ) chamber. Although the non working strobe at revs was indicating the same thing the colourtune let you physically see the spark stop working as the revs were raised.

So it may be axiomatic that you find the fault in the last place you look........but its always a shame when its the last place you COULD look rather than the first!
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Old 08-10-2021, 12:45 PM   #38
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Eureka!
It was screaming pickup to me, but it doesn't help when people tell you that pickups either work or don't work.
So what we have learned here is that not only can a pickup failure manifest when it gets above a certain temperature, but also when engine revolutions exceed a very low threshold.
This proves that they can work just a little bit, but not enough!

I'm delighted you've cracked it and without mauling the carbs too.
You only ever find what you're looking for in the last place you look unless you insist on continuing to look after you've found it..
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Old 08-10-2021, 12:54 PM   #39
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Excellent news ! Waiting intently on the report of your shakedown run and pics of the final job. Smashin’.
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Old 08-10-2021, 01:01 PM   #40
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Quote:
Originally Posted by Mr Gazza View Post
Eureka!
It was screaming pickup to me, but it doesn't help when people tell you that pickups either work or don't work.
So what we have learned here is that not only can a pickup failure manifest when it gets above a certain temperature, but also when engine revolutions exceed a very low threshold.
This proves that they can work just a little bit, but not enough!

I'm delighted you've cracked it and without mauling the carbs too.
You only ever find what you're looking for in the last place you look unless you insist on continuing to look after you've found it..
I very nearly commented on the pickup issue as from my experience that wasn't entirely true. Coils can behave differently or oddly if there is internal corrosion and can break down under certain conditions, as you have found. Same for HT coils or coil sticks as I found. So that was unhelpful comments from Electrex. Glad you got it sorted in time for a few weeks of fun.
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Old 08-10-2021, 02:39 PM   #41
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Eureka!
So what we have learned here is that not only can a pickup failure manifest when it gets above a certain temperature, but also when engine revolutions exceed a very low threshold.
And possible the other way round. We will know when Jerry has a go at swopping his out, because his fails at low revs and then comes in as the revs are raised.

Just taken it for a spin up the lane , less than a mile round trip.
Well, thats better! When I said it was running a bit flat before, it certainly was, I was riding a 450 single dragging another dead 450 around!! Just a tad crisper now

Weather looking a bit grim here so thats it for today. Thank you for all your input.

But here are the requested piccies of the finished article (which have actually been posted already on the build blog)

Album

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Old 08-10-2021, 02:51 PM   #42
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Yay!


(Itís obvious now youíve found it)
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Old 08-10-2021, 02:59 PM   #43
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Of course I knew exactly what it was all along and was only doing it for all of your entertainment.
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Old 08-10-2021, 04:44 PM   #44
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So glad you found the issue, even if it did lead you a merry dance!
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