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Ignition coils for Lucas Rita ?

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GuzzTim View Drop Down
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    Posted: 21 Nov 2018 at 14:19
As part of my LM4/1000S rebuild, I've fitted a Lucas Rita igntion and one of these 12v dual output coils - small enough to tuck away under the tank


I get a nice fat spark,  the bike starts on the button first time and ticks over OK, but doesn't run right at mid-higher revs (and it won't go past ~6,000 at all). The carbs are clean and balanced, so I don't think the problem is there. I'm told the 1 ohm primary resistance of these types of coil is too low for a Lucas Rita - it's designed to use either stock coils (wired in parallel) or 2x 6v coils, either way it's expecting 3-4ohm resistance.

So.... Has anyone out these used a twin output coil coil with a Rita igntion? which coil did you use and/or can you use 1 ohm coil with a ~2.5ohm ballast resistor? Or is there anything else I should check?

Thanks for any help, Tim
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Mike H View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2018 at 16:41
Yes 1 Ohm is way too low - you are risking f***ing up the output transistor, then it's scrap.

Blimey 6,000 pm, don't think I got my LM much past 5,000. Either with the points ignition or a Rita.

Rita amplifier does have a rev limiter, of sorts, but more like around 10,000 rpm, if memory serves. So don't think it's that.

I would stop what you're doing and go look for two bog standard 6V coils. 1.5 Ohms each.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote sardineone Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2018 at 17:10
"Blimey 6,000 pm, don't think I got my LM much past 5,000. Either with the points ignition or a Rita."
Mine with stock coils and points has never had any trouble reaching the red-line of 7,700 except when one of the stock coils went bad and turned my 1000 into a 500 single. Big smile  The LM4 comes stock with a 'rev limiter' as well, called the pushrods! Ouch
 
Ok back to subject, I'm currently running low resistance Dana HV coils with a automotive ballast resistor with points.  I got fancy and wired a relay to remove the ballast resistor when starting just like 50's & 60's American cars did with the ignition switch.  Maybe a call or e-mail to Lucas Rita, but I'd suspect 1 ohm too low as well.  BTW just an observation if you can go higher voltage coils & .040" plug gaps, they help low rpms on my Lemans more than higher revs!  Go figure.
 
Good luck!
George

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2018 at 18:33
I had a Dyna twin output coil on Rita with no problems. But you do need to end up with a primary of around 3 ohms or more. You end up with 3 times the current flowing though 1 ohm which as Mike says, won't do the o/p transistor any good.

BUT the Rita does have a restricted advance so always set it up with a strobe at 5k rpm. You may find the tickover a bit lumpy as it will be a tad more advanced at that point. This could be why you can't get higher revs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 2018 at 20:49
Could be. Altho was same with points IIRC, and I once tried tweaking the distributor body a bit either way then trying the bike, all that happened was I found out not to get it too advanced or it just vibrates horribly. I was sure there was something wrong with that engine but exsmokingbiker, who's got it now, has had it all apart and can't find anything wrong.


Originally posted by sardineone sardineone wrote:

Maybe a call or e-mail to Lucas Rita,


Not a chance, went out of business long time ago. LOL

Rita ws actually made by Mistral Engineering, southeast London somewhere, did have the address once, actually went there once with a mate who was buying a system, but they've been gone a while too now, the boss guy retired a few years back IIRC.





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gfiver Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 2018 at 21:25
Rex's Speed Shop can supply new circuit boards for the Rita box. Very easy to fit if you need one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzzTim Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2018 at 10:21
Thanks, guys - this is very helpful. I think I'll try the ballast resistor first, as it's only a few £ - I'll let you know how I get on

Cheers, Tim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2018 at 10:51
Originally posted by Mike H Mike H wrote:

Could be. Altho was same with points IIRC, and I once tried tweaking the distributor body a bit either way then trying the bike, all that happened was I found out not to get it too advanced or it just vibrates horribly. I was sure there was something wrong with that engine but exsmokingbiker, who's got it now, has had it all apart and can't find anything wrong.


Originally posted by sardineone sardineone wrote:

Maybe a call or e-mail to Lucas Rita,


Not a chance, went out of business long time ago. LOL

Rita ws actually made by Mistral Engineering, southeast London somewhere, did have the address once, actually went there once with a mate who was buying a system, but they've been gone a while too now, the boss guy retired a few years back IIRC.






Leyton, I think. Do you remember MCS? (The Motorcycle Shop) there. They sent me to the factory (hut) with a flea in my ear after I asked to buy the bits to convert a T150 back to points.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2018 at 11:26
Bit of information here if it's any help.

Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Normski Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2018 at 18:32
The coil you are using sounds like it is made for CDI ignition and as others say it is not suitable for Rita, even if you get it to run right for a while the coil will fail prematurely. One characteristic of Rita is that if the wires from the pick up are transposed the timing will be fixed i.e. no advance. Have you strobed to see what's happening?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 24 Nov 2018 at 00:02
+1 on the CDI application - it's not intended to have large amounts of current flowing through it. Just short pulses.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote GuzzTim Quote  Post ReplyReply Direct Link To This Post Posted: 24 Nov 2018 at 14:01
The plot thickens, but I'm not getting any nearer to solving the problem...

I've measured the resistance accross the coil - it's 4ohms, so should be OK

Normski - the connector between the pickup and the amp can't be reversed, and the wiring colours (Yellow->White/Purple, Black->White/Orange) correspond to those on Rita wiring diagrams posted online, so I think the pickup is wired correctly.

I can't get my strobe (it's a cheap Powerspark strobe, bought from an ebay shop) to flash, so I can't check the timing myself. I had the bike shop check it when it went in for its MOT, and they said it was fine, but they may have only checked it at idle. 

When I try and rev the bike, it feels like it could be the timing not advancing. One cyclinder (left side) feels like it's misfiring at higher revs, and runs noticibly cooler, and the plug is quite sooty (the RH plug is a perfect colour)

I guess I need to get a strobe working and check the advance...

Thanks again for all your help, Tim
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 24 Nov 2018 at 16:17
I know I've said this recently on another thread but do check the correct seating of the "choke" piston on the sooty cylinder. It's quite commonly overlooked. You can chase "ignition problems" only to find that the problem was the "choke" Guess how I know this. It's as well to eliminate this possibility right at the start.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 24 Nov 2018 at 19:24
How did you set up the ignition timing?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 24 Nov 2018 at 20:28
Originally posted by GuzzTim GuzzTim wrote:

The plot thickens, but I'm not getting any nearer to solving the problem...

I've measured the resistance accross the coil - it's 4ohms, so should be OK

That could only mean 3 Ohms of dirt / oxide. Measuring very low resistance with a multimeter is notoriously difficult. A friend who was a maintenance technician says they would file their multimeter probes to sharp points, to penetrate down to actual metal and get a better contact.


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When I try and rev the bike, it feels like it could be the timing not advancing. One cyclinder (left side) feels like it's misfiring at higher revs, and runs noticibly cooler, and the plug is quite sooty (the RH plug is a perfect colour)


It's a wasted spark system so if it works perfectly for the right, it must also or the left. Either spark plug, HT lead or plug cap is duff, or carb is too rich and letting too much petrol though.


Ballpark static timing in absence of a strobe - take cover off the dizzy. Turn engine to TDC on the compression stroke for the right cylinder. One of the lobes on the Rita rotor should point toward the pickup.

The other, left hand, lobe, points toward a screw that holds a small cable clip for the two wires coming out of the pickup. Release the dizzy bolts and turn the body so that the LH lobe aligns exactly with the centre of the screw. What I used to do then was tweak it 'by feel', i.e. ride the bike and see how it goes, then tweak the dizzy body forwards / backwards as necessary a gnat's whisker at a time until it feels right.

Or something else is wrong.

HTH










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