Combat performance issue - RITA

NickZ

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I have been trying to get to the bottom of a performance issue with my 72 Combat Interstate. Performance seems fairly normal in 1st - 3rd gears but in 4th gear the bike does not accelerate like it should, struggling to get past 4000 rpm. I read the thread on this subject posted by @ILLF8ED starting in 2015. As suggested there, I have eliminated fuel flow and valve timing as causes and have moved my focus to ignition timing. This bike, as did ILLF8ED, has the RITA electronic ignition.

What I am seeing with my unit is that when I set it up as specified in the Mistral Engineering documentation, I get the 20 deg BTDC advance at 2000 rpm as expected, but the advance does not top out at 28 deg at 6000-6500 rpm as the documentation suggests it is supposed to, but has increased up to around 40 deg. At 4500 rpm it is around 36 deg advance.

2 questions:

1- Could the excessive advance at these higher rpms be the cause of degraded high end performance?

2- Are these advance readings "normal" for the Lucas RITA AB11 ignition?
 

NickZ

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Regarding my question #2 above, I found this item from an old @dynodave post showing RITA advance curve compared to Boyer and points/AAU curves:

Combat performance issue  - RITA

dynodave points out that because these measurement were taken using his distributor test setup .....
"To the uninitiated, the way to look at a distributor curve is to be, (1) very aware these are distributor degrees and distributor RPM, and that there is no such
thing as initial advance until you install and set these components on an engine. Only at that point should you talk in terms of initial timing and engine
degrees. The timing would then be 2 times distributor degrees plus initial advance)
."

Looking at just the shapes and comparative height, it looks to me that the RITA provides more advance at higher rpms than the others, but it appears to top out somewhere near 30 deg BTDC. Mine doesn't appear to be doing that.
 
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You more or less always set ignition timing to be correct at full advance/high rpm and let low rpm timing take care of itself.

How can you even think of riding around with timing at 40 degrees when it’s supposed to be 28?
 

L.A.B.

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Looking at just the shapes and comparative height, it looks to me that the RITA provides more advance at higher rpms than the others, but it appears to top out somewhere near 30 deg BTDC.

The Boyer would normally be set to 31 degrees BTDC at 5,000 crankshaft (so 15.5 at 2,500 'distributor') RPM...

http://www.boyerbransden.com/pdf/KIT00053.pdf
"Start engine and time with a stroboscope to 31 B.T.D.C (28 DEG. with standard ignition) with the engine running up to 5000 r.p.m."

...however, "At 4500 rpm it is around 36 deg advance." seems too much advance to be normal for a RITA.
 

NickZ

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You more or less always set ignition timing to be correct at full advance/high rpm and let low rpm timing take care of itself.
That makes sense. I guess I could give that a try. Probably won't even see the timing mark on the scale in the inspection hole at low rpms.

How can you even think of riding around with timing at 40 degrees when it’s supposed to be 28?
I didn't realize it was getting that high till now when I strobed it.
 

NickZ

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The Boyer would normally be set to 31 degrees BTDC at 5,000 crankshaft (so 15.5 at 2,500 'distributor') RPM...
Right. I don't know what version Boyer Dave was testing in 1989.

http://www.boyerbransden.com/pdf/KIT00053.pdf
"Start engine and time with a stroboscope to 31 B.T.D.C (28 DEG. with standard ignition) with the engine running up to 5000 r.p.m."

...however, "At 4500 rpm it is around 36 deg advance." seems too much advance to be normal for a RITA.
That's what I was thinking. Maybe the part of the circuit that is supposed to limit the advance is not function properly on my unit. Otherwise, it seems to be functioning ok. As I said, after setting up the static timing per the instructions, it strobed 20 deg at 2000 rpm as the instructions said it should.
 

ILLF8ED

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I’m using my RITA with rebuilt module using this board from Rex’s.
D12F2973-78BA-4116-A396-A8D26234A74B.jpeg
 
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Fast Eddie

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Right. I don't know what version Boyer Dave was testing in 1989.


That's what I was thinking. Maybe the part of the circuit that is supposed to limit the advance is not function properly on my unit. Otherwise, it seems to be functioning ok. As I said, after setting up the static timing per the instructions, it strobed 20 deg at 2000 rpm as the instructions said it should.
If it’s correct at 2,000 rpm and advancing more than it should at higher rpm, then I’d say you’re correct in assuming the unit to be faulty.
 

cliffa

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I know Mistral could alter the ignition advance characteristics to suite different bikes, (e.g. they also made RITA kites for the Moto Morini 350) so perhaps it’s not the correct unit for a Commando? Has it ever run properly?
 

L.A.B.

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Right. I don't know what version Boyer Dave was testing in 1989.

Would be Boyer MkIII.


Maybe the part of the circuit that is supposed to limit the advance is not function properly on my unit.
I get the 20 deg BTDC advance at 2000 rpm as expected, but the advance does not top out at 28 deg at 6000-6500 rpm as the documentation suggests it is supposed to, but has increased up to around 40 deg. At 4500 rpm it is around 36 deg advance.

If I remember correctly it's the RITA pickup that provides the 'advance' curve, not the (AB11) box as there's no specific 'Norton', 'Triumph', etc. AB11 so perhaps it has a Triumph twin pickup because a Triumph twin would require that much advance.
 
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I believe the Combat motor runs better at 28 degrees fully advanced vs the 31 degrees of the standard motor.
Agree that the data would suggest a Triumph unit.
Given the modest price of the Pazon for instance I'm also in agreement with Ed. For the cost of a couple of hours at workshop rates would pay for it easily.
I haven't tried the Vape unit on a Norton yet, but I haven't heard any negatives about them either.
 
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Did old Lucas company bother making different RITA advance ranges for different bikes?
My only experience was with them on T140Es, where a failed amplifier caused an engine failure due to going fully retarded, and a new amplifier restored the A/R function.
This would suggest 'there can be only one' curve if there's only the AB11 out there.
That said, I don't believe Boyer, Pazon etc offer any bespoke Norton curves either?
 

L.A.B.

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Did old Lucas company bother making different RITA advance ranges for different bikes?

There was a Thread on the BritBike forum some time ago discussing strobe timing a T140E where Stuart said the following:


"Stuart
...If I understood John Carpenter correctly when he explained it, the amp. components form one advance curve, that's then modified by the pick-up supplied for each model of bike - e.g. a Rita on a triple or 650 twin shouldn't be 38°-fully-advanced 'til 6,500 rpm."
 

SteveA

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Reference the attached document, the pick up is simply a coil. Meaning, it does not have any capability to advance the ignition. The advance circuit is part of the main module function.

Don't invent functionality.

Secondly, you will find reference to incorrect wiring affecting the advance. Fully retarded rather than advanced. Here are the words from the document:

'The Pickup is just a coil of wire and can be measured with a Mutimeter.
200-450 ohms - C and Low C types (270 ohms average)
1500-2000 ohms for the 2PU type.
600-700 ohms for the 5PU type ( Triumph factory fit)
If the pick-up leads are reversed by mistake, the ignition will still work and will not be damaged but the ignition point will be fully retarded (No advance) The engine will be appropriately poor in performance, maybe hard to start.'

Personally, when I saw mention of lack of rpms in a higher gear, my thought was of the ignition not advancing, not doing too much of it!

My RITA experience is limited to an ex Norton works unit. I knew it had an advance circuit for one simple reason, the unit exhibited no advance at all, because the works team in their wisdom had jumpered it out on the PCB. I discovered this when I drew the circuit out for my reference some time in '77 or '78. I am sure I still have that drawing somewhere.

Running fully advanced is fine for a race bike with no kick start, and bear in mind that a lot of racers in the '70s ran point ignition with the advance unit welded up and set fully advanced. Because the AAU had a habit of exploding, I know, had that happen, and it is why I got the RITA in the first place. I was able to fit the reluctor in the otherwise unusable camshaft.

However, given the options, and being very happy with the cheapest Pazon on my short stroke, and fully supporting FE's comments on cost, just bin it! What else should we do with old electronics :rolleyes:
 

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NickZ

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I’m using my RITA with rebuilt module using this board from Rex’s.
View attachment 100986
Thanks David. I actually bought one of those a while back to have as a spare.
Have you strobed the timing of your RITA on the Norton? If so, does yours act like it is supposed to, meaning advance tops out near 28 deg at high rpms?
 

NickZ

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I know Mistral could alter the ignition advance characteristics to suite different bikes, (e.g. they also made RITA kites for the Moto Morini 350) so perhaps it’s not the correct unit for a Commando?

Has it ever run properly?
As far as I know, I am the 3rd owner of this 1972 750 Combat Interstate. It sat idle for many years partially disassembled before I bought it 3 years ago. I believe the engine was rebuilt and the RITA installed as part of that rebuild, but the bike was never finished and hadn't been run. I finished it and got it running about 2 years ago. It seemed to me to run 'OK' but I was expecting a bit more performance. When I compare it to my stock 1971 750 Roadster, it seems to have similar performance in gears 1-3, but a little bit less torque at lower rpms, but it bogs down in 4th while my 1971 will continue accelerating till I chicken out. I should also mention that the 72 has 21 tooth sprocket and the 71 has 20.
So, to answer your question, I haven't felt sure that it was running 'properly', so I haven't ridden it that much, but wanted to get thru break in to see if things would sort out. I've put about 800 miles on it and the performance has not changed significantly.

Apologies for the long answer to your short question.
 

NickZ

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There was a Thread on the BritBike forum some time ago discussing strobe timing a T140E where Stuart said the following:


"Stuart
...If I understood John Carpenter correctly when he explained it, the amp. components form one advance curve, that's then modified by the pick-up supplied for each model of bike - e.g. a Rita on a triple or 650 twin shouldn't be 38°-fully-advanced 'til 6,500 rpm."
38* at 6,500 rpm is close to what I am seeing, but I don't follow how the pick-up can change the advance curve, other than to move the point at which it starts advancing forward or back.
 

Tornado

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I believe the Combat motor runs better at 28 degrees fully advanced vs the 31 degrees of the standard motor.
Agree that the data would suggest a Triumph unit.
Given the modest price of the Pazon for instance I'm also in agreement with Ed. For the cost of a couple of hours at workshop rates would pay for it easily.
I haven't tried the Vape unit on a Norton yet, but I haven't heard any negatives about them either.
My Vape-Wassell EI has been on my 850 MKII for four yrs now. Put about 14 K Miles on it and everything has been just fine. Well made, nice instruction booklet with good diagrams from various setups. Has a fully epoxy encased stator unit so little to no risk of fracturing wires within, an issue with older Boyer's.
 
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