Newbie question- No spark on ducati L twin

[Paul_H]

Matt, yes I agree that the piston of the vertical cylinder does reach TDC 90 degrees after the horizontal cylinder TDC compression but the valves will be in the overlap position and therefore the cylinder will not be on compression. Do the same test as you did before starting with the horizontal cylinder at TDC on compression and then rotate the engine 90 degrees. Use your screwdriver an check that the vertical cylinder piston is now at TDC. Pull the throttle body off the vertical cylinder, look down the port with a torch and I think you will find that the inlet valve is lifted about 6 mm off its seat. Can I suggest that you have a look at a recent post by Grippo to the 'V Twin Ignition Woes' thread as he gives a very good explanation of how a missing tooth single crank wheel works with dual spark mode for an odd fire engine. I know that you are using a cam wheel but the basic principles are the same so that logic can be applied to your setup as well.

[alan_3301]

honda33cr, have you verified that the vr wires in the harness are in the correct position?
I have a microsquirt on my ducati, and after getting it running and discovering that output #2 was dead, I realized pins 32 and 33 were swapped, effectively reversing the vr1 polarity, and running 2 + wires to the vr2 sensor.
Check that out.

Also I initially had -330 trigger offset, but dwell was cut back after 2000rpms and it wouldn't rev up. I had to remove and install the flywheel 180deg to get -150deg offset. This helped a lot, but it may still be too much negative offset.

Another thing. An easy way to make sure you are firing on the compression stroke is to remove your belt covers, and check the belt timing marks with the timing light instead of the flywheel. With the non-wasted spark, it will only fire when the marks line up. Just make sure you are checking off of the cylinder that the belt marks are timed with.

Good luck.

Edit:

Sorry, I got my pins wrong. As written in a previous post:

For the miss problem I would first make sure you were not one of the few lucky ones who got the harness error where the shield and the center conductor are reversed - the center conductor (VR+) goes to ampseal pin 32, and the shield (VR-) goes to pin 33.

[alan_3301]

Nevermind my first post, I obviously didn't read all the posts.
I didn't realize you had the single cam sensor.

and as far as my engine goes..

at 0 degrees the horizontal is at TDC on the power stroke. Vertical is 90* before TDC on exhaust
360 degrees the horizontal is at TDC overlap, and Vertical is 90* before TDC on compression.
and so on.

If there was an offset for output #2 on the trigger wheel mode, I would set it at 225* or -135*

[honda33cr]

Ok, by now I am completely confused as to what settings do what in Megatune. Could somebody breifly explain what the following settings do any how the interact with each other:

trigger offset, skip teeth, advance for output 2.

If you could please explain them with an oddfire engine in mind it would be greatly appreciated. I have read so many different things that I have confused myself.

Thank you for your time,
Matt

[SQLGUY]

Trigger offset is at what point, relative to mechanical TDC, you get your tach pulse from the pickup. A trigger offset of 0 would mean that the VR pickup gets its tach pulse directly at TDC; -90 would mean that the pulse occurs 90 degrees after TDC; -270 would mean the pulse occurs 90 degrees before TDC.

This value should never be positive, so, instead of +60 one would use -300. If you have a choice, you want your tach pulse to occur somwhat after TDC (say -60 or -90 trigger offset), because dwell cannot start until the tach pulse is received, so having an offset of -60 gives you 300 degrees in which to "fit" dwell and advance in a wasted spark setup.

Trigger offset applies to both ignition channels in dual spark setups.

When cranking, if crank trigger is set to trigger rise, spark will fire at the tach pulse, so a trigger offset of -60 would mean a trigger rise cranking spark 60 ATDC - probably a bit too late. If you use calculated for the cranking trigger, than the spark advance table will be used to calculate spark, and the trigger offset will be taken into account. In that case you probably don't want much advance in the high kPa, low RPM, corner of the table.

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Skip teeth, as I understand it, is what tooth past the missing tooth is to be considered the tach pulse. By changing skip teeth you can effectively change the mechanical part of your trigger offset as if you had moved the pickup(s) or rotated the trigger wheel relative to the crank.

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The advanced offset is an additional offset to add to the second ignition channel in dual spark mode. For my setup I have dual VR pickups, and they are 180 degrees apart. My coils also fire 180 degrees apart, so I have 0 additional offset in my advance settings. If I were to use a single pickup, then I would need to set 180 degrees of advanced offset to get the coils to fire at the right times. Since your cylinders are 90 degrees apart, you're going to have some multiple of 90 for your advanced offset (unless you have two VR pickups that are already mechanically placed to trigger at the right point relative to the cam or crank - in which case you just need to get the base trigger offset set right and leave advanced at 0).

Hope this helps,
Paul

[honda33cr]

Skip teeth, as I understand it, is what tooth past the missing tooth is to be considered the tach pulse. By changing skip teeth you can effectively change the mechanical part of your trigger offset as if you had moved the pickup(s) or rotated the trigger wheel relative to the crank.

I thought that delay teeth was the setting that does what you are describing. From the mega Manual:

Delay Teeth (Delay_Teeth): Number of teeth to delay after 1st tooth after the missing teeth before 1st tach synch declared. You get synch as soon as you detect "first real tooth after the missing tooth". If that tooth is at TDC when it is detected, then there is 0 delay. If TDC doesn't occur until the next tooth is detected, then there is a delay of one tooth, and so forth.

I am confused as to what the skipped teeth actually means. The manual says:

Skip Teeth (No_Skip_Teeth): Number of teeth (between tach pulses) to be skipped. You must create the same number of 'tach' signals as you want ignition events. On a four cylinder four stroke engine, this is two per revolution. Suppose it has a 60-2 wheel. What you need to have happen is for MegaSquirt-II to 'skip' a certain number of teeth so the only the right number of teeth are counted as 'tach signals' per revolution. Since we have determined the number of tach signals we want is 2, we need to skip 60/2 = 30 teeth

I am interperating this as I need two Tach pulses and I have a 48 tooth wheel so it should be 24 teeth. Now I read somewhere that this setting influenes when the output 2 fires. It said something like

Because you are skipping 24 teeth this means that another tach event is happening approximately 360 crankshaft degrees later and this will trigger output #2 which will be wired to the coil for the front cylinder. But because compression on the front cylinder occurs 270 degrees after compression on the rear cylinder, you have already gone 90 degrees past where you need to be. So you need to shift the trigger back by 90 degrees by applying -90 degrees in the advance offset for #2 output.

If this is the case then the offset for output 2 is relative to the skip teeth and not output one. -90 degrees from when output 1 fires is much different then -90 degrees from 24 skipped teeth.

I really appreciate all the help and any further clarification would be appreciated.

[grippo]

You are correct about the delay teeth The skip teeth defines how often you want a plug to fire. For example, with a cam wheel and 2 cylinders, you want each cylinder to fire once per 720 crank deg, so there will be a firing every 180 deg, so you want skip_teeth = 24 for a 48 tooth CAM mounted wheel. Now because every engine on this forum is completely different, this alone may not be enough, because you have to determine where TDC is when the VR tach signal comes in. So that is where trigger offset comes in. Then you have to look and see if there is enough time to dwell + spark before the next tach signal FOR THAT cylinder comes in, assuming you have 2 coils, which you do. If there isn't enough time, then you have to either move your VR sensor or use the delay teeth. The latter does the same thing without having to modify hardware. Tooth 1 is by convention the 1st tooth after the missing one, and a delay of 0 teeth means the tach event starts on tooth 1. If delay is, say 2, then you wait for 2 teeth to go by and start the tach event on tooth 3.

[honda33cr]

Thank you for clearing that up.

The physical set up on the bike is that the vertical cylinder is at tdc and then 90 degrees later the horizontal cylinder is at tdc ( both compression stroke). 450 degrees after the vertical cylinder is at tdc the vr sensor is in the gap of two missing teeth: 15 degrees before the first tooth comes in. I am a little confused as to how to set this up but I am thinking that the horizontal cylinder should be cylinder one with a -90 degree offset for output 2. I am thinking that it should be 24 delay teeth and -15 degree trigger offset. Please make any suggestions that may help. I am open to any good ideas.

Does the offset for output 2 measure from output 1 or from the skipped teeth? So if I put in -90 then is it 90 degrees before output one or is it 90 degrees before 24 skipped teeth? Thank you for your replies, it is finally starting to make some sense.

Grippo Wrote"For example, with a cam wheel and 2 cylinders, you want each cylinder to fire once per 720 crank deg, so there will be a firing every 180 deg, so you want skip_teeth = 24 for a 48 tooth CAM mounted wheel"

Maybe I am understanding this wrong but shouldn't there be a firing every 360 degrees? (720 /2)

Thank you

[SQLGUY]

Unless you're doing wasted spark, you're only firing each cylinder once every 720 crank degrees = once every 360 cam degrees.

What I would do is this:

1. Get a timing light. You can get a cheap one for $40 or so. It's worth it for the guesswork and aggravation it'll save you.
2. Set up the delay teeth so that the #1 tach signal is somewhere between 30 and 90 degrees ATDC - this should equate to a trigger offset of -30 to -90.
3. Set cranking trigger to calculated
4. Set the cranking corner (high kPa, low RPM) of the spark table to 0's.
5. Remove the plugs and turn off fuel.
6. Adjust rising edge / falling edge, trigger offset, and delay teeth until the timing light shows TDC firing on #1.
6a. I would imagine that your cam wheel has timing marks on it, but if not, you can add them with a Sharpie.
7. I think, from what Grippo said, that you'll need to configure skip teeth as half the number of teeth on your cam wheel.
7a. Since your #2 cylinder isn't 180 degrees from the #1 cylinder, but only 90, you'll probably need -90 for the advanced offset.
8. Play around with the advanced offset until your #2 cylinder is also firing at TDC during cranking.
9. Recheck that #1 is still firing at TDC. If it isn't, try switching rising edge for falling edge or vice versa and repeat 6-9.

My setup wasn't quite the same, as I am using wasted spark, dual tachs on the crank, and even firing, but I still think this sequence should get you at least most of the way there. Let us know what you find.

Cheers,
Paul

[alan_3301]

I only remember seeing advanced offset #2 for dual spark mode... It is my understanding that the OP is using trigger wheel mode. I never saw the advanced offset setting under that mode..