Ignition coils for Lucas Rita ? |
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GuzzTim
Falcone Joined: 08 Aug 2018 Location: Cambridge Status: Offline Points: 49 |
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Posted: 21 Nov 2018 at 14:19 |
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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
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
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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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"Chicken nuggets don't dance on a Tuesday."
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sardineone
Senior Member Joined: 30 Oct 2018 Location: Indiana, USA Status: Offline Points: 443 |
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"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. The LM4 comes stock with a 'rev limiter' as well, called the pushrods! 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!
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George
One owner 86' Lemans 1000 (member of the family) / BMW R1200ST (current work horse) You are what you have ridden! |
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17641 |
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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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Brian.
Better 5 minutes late in this world than years early in the next. |
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Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
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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.
Not a chance, went out of business long time ago. 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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"Chicken nuggets don't dance on a Tuesday."
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Gfiver
Senior Member Joined: 26 May 2017 Location: Somerset Status: Offline Points: 121 |
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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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GuzzTim
Falcone Joined: 08 Aug 2018 Location: Cambridge Status: Offline Points: 49 |
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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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Jerry atric
Senior Member Joined: 24 Nov 2014 Location: Wiltshire Status: Offline Points: 3367 |
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Brian UK
Moderator Group Joined: 13 May 2014 Location: Surrey Status: Offline Points: 17641 |
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Brian.
Better 5 minutes late in this world than years early in the next. |
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Normski
Senior Member Joined: 28 Jan 2015 Location: Devon Status: Offline Points: 110 |
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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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Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
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+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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"Chicken nuggets don't dance on a Tuesday."
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GuzzTim
Falcone Joined: 08 Aug 2018 Location: Cambridge Status: Offline Points: 49 |
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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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Dave P.
Senior Member Joined: 12 Jan 2015 Location: Northants Status: Offline Points: 5573 |
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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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TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.
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Brian UK
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How did you set up the ignition timing? |
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Brian.
Better 5 minutes late in this world than years early in the next. |
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Mike H
Senior Member Joined: 21 May 2014 Location: East Anglia Status: Offline Points: 8733 |
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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.
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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"Chicken nuggets don't dance on a Tuesday."
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