Combat performance issue - RITA

SteveBorland said:

Ah, thanks for the clarification Steve, that makes (I think!) sense.
Tricky stuff this lecrticity, it'll never catch on
Seriously though, it would be very interesting if someone could post pictures of a known Norton Rita reluctor. Both the Trident and the Ducati reluctor profiles seem similar to the naked eye, but they both use rather more advance than the Norton head requires.

Click to expand...

You might be looking at this from the wrong end.....

Yes, the Triumph engines typically use 36 degrees fully advanced compared to a Norton at 31 with an electronic ignition (28 with points). As you say, due mainly to cylinder head and piston crown designs.

I am not sure the amount of advance in the ignition system itself changes 5 degrees.

What we set when installing an ignition is the end point of the advance curve, the fully advanced figure. If I set full advanced at 36 degrees instead of 31, I have advanced the timing 5 degrees at full advance, but I have also advanced it 5 degrees at static, no advance, so the 'static' timing figure is also increased 5 degrees!

Using the same box (twin cylinder) on a Norton I may have say 5 degrees as a static figure, installed on a Triumph I will have 10 degrees static.

Happy New Year!

Update on original post:

The issue was to determine if the RITA electronic ignition is somehow affecting the high end performance of this 72 Combat. The original RITA was strobing at around 40 degrees at higher rpms (4500 & above) when set per the Mistral Engineering instructions, which is much higher that the 28* called for.

My approach was to replace the original RITA circuit board with one from Rex's Speed Shop which is billed as a modern replacement. After some fitment issues with the replacement that are documented in previous posts #40 & #56, I installed the Rexs unit on the bike. The installation instructions call for a static test of the main power portion of the circuit consisting of turning the ignition switch on then off again, which should produce a spark. It did not, even though it did spark on my bench test, and the original RITA unit would produce a spark with this static test. After a great deal of time and energy spent to isolate this problem, I determined that it is an idiosyncrasy of the interaction of Rexs unit and the ignition switch, because even though it fails this static test, the installed Rexs unit functions properly when performing the static test of the trigger circuit (touching the white/purple pick-up wire to -V to produce spark), produces a spark on the bike when in normal operation (ignition switch on and the reluctor activating the pick-up), and the bike starts and runs. I could have saved a lot of time if I just ignored the first static test.
So, after all that, I strobed the timing and the result is pretty much identical to how the original RITA performed. Which means, it still is advancing around 40* at higher rpms. I can conclude that the problem is not the RITA circuit board itself.

I did a test ride, and when accelerating in 4th gear it topped out at 4500 rpm and would go no higher. This seems to correlate with the strobed timing measurements where the advance seemed to jump from mid 20* to around 40* at 4500 rpm. Similar performance with original RITA unit.

Next, I will try retarding the ignition to have it at around 28* at the higher rpms. I'm not sure what the advance will be at lower rpms (probably not on the scale) but we will see.

If that doesn't resolve the issue, I'll try replacing the reluctor rotor. The one on the bike had to have tabs filed to get the air gaps within the spec. It is possible that affected the advance operation.

After all this reading I would simply pull it and fit a Boyer MK 1V , at $150 , who needs the hassle . If that does not cure it , I'd pull the timing cover to make sure the timing chain is fitted the proper 10 rollers apart using the punched timing marks on the sprockets .

The point of strobing is to set the max advance to the required figure, 31 degrees at 5000rpm.

If you haven't adjusted the timing at the pickup, it won't be any different to how it was with the original RITA pcb!

Torontonian said:

After all this reading I would simply pull it and fit a Boyer MK 1V , at $150 , who needs the hassle .

Click to expand...

If I wasn't such a stubborn SOB I would do just what you say... put a Boyer in, and I have one on the shelf. That might be where I end up, but my nature won't let me go there till I find the reason the RITA is not working.

Torontonian said:

If that does not cure it , I'd pull the timing cover to make sure the timing chain is fitted the proper 10 rollers apart using the punched timing marks on the sprockets .

Click to expand...

Good suggestion, but as I noted in my original post, and in an earlier thread, I've already had the timing cover off and verified valve timing is set up properly.

SteveA said:

The point of strobing is to set the max advance to the required figure, 31 degrees at 5000rpm.

Click to expand...

SteveA said:

If you haven't adjusted the timing at the pickup, it won't be any different to how it was with the original RITA pcb!

Click to expand...

That all makes sense to me. Except that the documentation from MIstral Engineering that came with my RITA called for a different procedure. Since that did not produce good results, I did try to set it as you say. I will be making another attempt at doing that.

Update:
My intent was to get things set up such that the advance would top out at 28* at higher rpms. Since it appeared to be advancing to around 40*BTDC, I retarded the static timing around 10*. Started the engine and strobed the timing. At 2000rpm advance was 16*BTDC; at 3000rpm it increased to 22*; At 4500rpm it was 24* but it would jump up to approx. 40* and the back again to 24, over & over.

So, it appears that what I was observing is not that the timing would advance up to 40* steady state, but rather that at some point near 4500rpm something causes the advance to cease the steady increase with rpms we expect and begins jittering between what it should be and 40*. I went back and verified this behavior with static timing set for the normal 28* as well.

Another data point... I initially mistakenly adjusted the static timing by moving the air gap adjuster rather than rotating the stator plate. This configuration strobed about 15*BTDC at 5500rpm with no observed jumping to 40*. I did a road test and the engine seemed strong all the way to 5000rpm in 4th gear before I had to back it off. Not sure what this means, except that it further reinforces my current belief that the problem is something with the pick-up / reluctor function. I feel certain that the electronics of the circuit board have been ruled out because the system performs exactly the same way in this respect with both the original RITA board and Rexs replacement board.

My next step will be to swap out the reluctor with the spare I have, making sure that its taper seats correctly into the cam. If that does not fix it, I will swap the stator & magnetic pick-up also.

Looking foward to the results...
Carry on....

L.A.B. said:

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.

Click to expand...

I don’t believe this is a correct statement. The rotor is one solid piece and has no advancing mechanism The reluctor is only a magnetic trigger.

Use a strobe powered by something other than the bike’s battery.

Try another strobe lamp.

ILLF8ED said:

I don’t believe this is a correct statement. The rotor is one solid piece and has no advancing mechanism...

Click to expand...

Yes, but as already discussed earlier in this thread, it is possible that its shape could perhaps alter the advance characteristics.

ILLF8ED said:

The reluctor is only a magnetic trigger.

Click to expand...

The rotor is the "Reluctor"...


...however, there's more than one RITA "pickup" used with the same AB11 amplifier and the difference in resistance could possibly change the advance characteristics...

"2 P.U. Type. Basically hexagonal in shape and full encapsulated. Normally used only on racing machines.
The standard "C" type used on Trident and Suzuki three-cylinder.
The low "C" type used on most other road machines.
The 5 P.U. Pickup and Reluctor used on OEM Triumph twins when the AB11 amplifier is used. This Pickup is also compatible with the AB5 amplifier - OBSOLETE

4. The shape of the triggering poles on the reluctor are different for Fixed Ignition and Automatic Advance/Retard. It should therefore be noted that a four-stroke Reluctor will not run a two-stroke satisfactorily on Fixed Ignition as at 3. Please ask our Technical Department if considering a non-standard application."
"Replacement Lucas Rita reluctor (pick-up or trigger unit). This is the ‘C’ type that measures 200-450 ohms."

The fact that replacing the AB11 box electronics resulted in no apparent change to the advance curve would seem to indicate that the complete pickup assembly may have some influence over the advance curve, however, I admit I don't have all the answers but have only read discussions elsewhere.

L.A.B. said:

Yes, but as already discussed earlier in this thread, it is possible that its shape could perhaps alter the advance characteristics.


The rotor is the "Reluctor"...


...however, there's more than one RITA "pickup" used with the same AB11 amplifier and the difference in resistance could possibly change the advance characteristics...

GENERAL INFORMATION ON LUCAS RITA IGNITIONS

"2 P.U. Type. Basically hexagonal in shape and full encapsulated. Normally used only on racing machines.
The standard "C" type used on Trident and Suzuki three-cylinder.
The low "C" type used on most other road machines.
The 5 P.U. Pickup and Reluctor used on OEM Triumph twins when the AB11 amplifier is used. This Pickup is also compatible with the AB5 amplifier - OBSOLETE

4. The shape of the triggering poles on the reluctor are different for Fixed Ignition and Automatic Advance/Retard. It should therefore be noted that a four-stroke Reluctor will not run a two-stroke satisfactorily on Fixed Ignition as at 3. Please ask our Technical Department if considering a non-standard application."

Luca Rita Reluctor ‘C’ Type

www.rexs-speedshop.com

"Replacement Lucas Rita reluctor (pick-up or trigger unit). This is the ‘C’ type that measures 200-450 ohms."

The fact that replacing the AB11 box electronics resulted in no apparent change to the advance curve would seem to indicate that the complete pickup assembly may have some influence over the advance curve, however, I admit I don't have all the answers but have only read discussions elsewhere.

Click to expand...

....it could....

Well, I guess it 'could', but sincerely, I remain unconvinced.

The only potential effect I see is that narrowing the end reduces its impact on the magnetic field, which might make the trigger pulse more precise.

But I still don't see how that varies in a controllable way with rpm!

Pick ups themselves definitely vary the trigger pulse shape through variations in core and windings. But again 'in a controllable way with rpm!' I doubt that.

NickZ said:

Another data point... I initially mistakenly adjusted the static timing by moving the air gap adjuster rather than rotating the stator plate. This configuration strobed about 15*BTDC at 5500rpm with no observed jumping to 40*. I did a road test and the engine seemed strong all the way to 5000rpm in 4th gear before I had to back it off. Not sure what this means, except that it further reinforces my current belief that the problem is something with the pick-up / reluctor function. I feel certain that the electronics of the circuit board have been ruled out because the system performs exactly the same way in this respect with both the original RITA board and Rexs replacement board.

Click to expand...

Yes, I am sure the air gap will have an effect. Yes, I think you have ruled out the circuit board.

That leaves, pick up and reluctor?

Or have you checked that you don't have an alternator/rectifier/regulator problem? (Or potentially a range of connection and earthing problems)

What is happening to battery voltage when this 'jump' occurs?

This is an analogue system and supply voltage will affect it!

(Cue someone telling me the amplifier has an in built voltage regulation circuit....I will need some convincing guys)

Monitor the voltage. Another test is to temporarily run the electrics as total loss. Disconnect the alternator and regulator from the circuit and test.

It will run plenty long enough on a fully charged battery!

"48022B although quoted as a Norton Commando number does not appear to have any speciality for the Commando, directly replaceable with 47270A and 47270B. ALL RITA amplifiers have 5 wires coming out of the box. Black-Negative. White/Yellow-Positive. White/Black-coil switch. With originally a 3 pin Lucas/Rist plug, and a separate lead and 2 pin for the pickup White/Orange, White/Purple. The case of the amplifier has another Black wire that is connected to the vehicle Earth. The advance curve is dictated by the 'shape' of the reluctor, but the total height of the advance curve can be reduced from inside the amplifier (Different coloured panels on the box). For racing."

Regarding the question as to whether the advance curve is established by the electronic circuit of the AB-11 unit or a function of the reluctor (rotor) and magnetic pick-up, I offer the following, based on the reference cited by @SteveBorland in his post #78. This on the Britbike website:

https://www.britbike.com/forums/ubbthreads.php/topics/32497/re-lucas-rita-notes


I think that reference gives a very clear explanation of how the system works. You can read it for yourself on the site, and I have reproduced the very useful diagrams here.



It basically says that the circuitry functions mainly as an amplifier and a switch. It amplifies the waveform produced by the magnetic pick-up, who’s magnetic field is modified by the rotating reluctor. The amplified waveform triggers the switch function when it reaches the required voltage level. The waveform is riding on top of a bias voltage which the circuitry makes proportional to engine rpm. The higher the rpm, the closer the base waveform voltage is to the trigger voltage, meaning less time will elapse from the start of the waveform pulse to the trigger, resulting in more advance relative to lower bias voltage (rpm).

Given that as the means of increasing advance with rpm, it follows that the shape of the advance vs rpm curve would be determined by the shape of the leading edge of the pulse waveform. It seems very reasonable to me that the shape of the “piece of metal” making up the reluctor could determine characteristics of the waveform. Things like reluctor base circle diameter and tab height above that along with the curvature in between could determine things like the rate of onset of the leading part of the pulse and the length and slope of the ramp to the peak, which I believe would determine the amount that it can advance the trigger and how it approaches the max advance as the trigger voltage is approached by the start of the pulses as rpm increases.

The idea that the AB-11 is standard and the pick-up / reluctor is specific to the desired advance characteristics is supported by this reference:


This shows that RITA was (is?) available for many different bikes. The diagrams show a variety of pick-up and reluctor configurations. I don't know how accurate these drawings were meant to be, but I can see differing dimension / geometry between various models (I'm referring to the reluctor tab size & shape, not the number or angular relation of the tabs).

Triton Thrasher said:

Use a strobe powered by something other than the bike’s battery.

Click to expand...

Strobe was powered by separate battery.

Triton Thrasher said:

Try another strobe lamp.

Click to expand...

Worth trying. I'll see about getting ahold of another.

SteveA said:

What is happening to battery voltage when this 'jump' occurs?

This is an analogue system and supply voltage will affect it!

Click to expand...

At the frequency the advance is jumping around, battery effect would be hard to determine without an oscilloscope. My DVM shows nothing out of the ordinary.

SteveA said:

Another test is to temporarily run the electrics as total loss. Disconnect the alternator and regulator from the circuit and test.

It will run plenty long enough on a fully charged battery!

Click to expand...

Good idea! Eliminate alternator/rectifier/regulator from the equation.

You have a lot more patience than I. That Rita would have been in the trash a long time ago!

Nick,
How is this coming. I had my combat out on the interstate a few days ago. It still has a problem getting past 80mph. Noteworthy that mine still had the same issue when using a TriSpark ignition.

ILLF8ED said:

Nick,
How is this coming. I had my combat out on the interstate a few days ago. It still has a problem getting past 80mph. Noteworthy that mine still had the same issue when using a TriSpark ignition.

Click to expand...

Thanks for checking, I have been a little slow on reporting progress.

I swapped out the stator and magnetic pick-up with a replacement unit that I have. Set the air gaps with the original reluctor. Set static timing at 28*. Strobed timing. Similar performance as before: 21* indicated at 2000rpm and 40 ish at 5000rpm. Not jumping around as much though. Retarded static timing to 15*. It now strobes 30* at 5000+rpm. Left it set there. Road test showed that rpm kept increasing past 4500 in 4th gear. Couldn't go past 5000rpm because of traffic.
I buttoned everything up with the modern replacement RITA electronics (Rexs), replacement stator and original reluctor.

Conclusion: I believe there were 2 issues. First, the Mistral RITA set up instructions result in way too much advance at higher rpms. This was easily resolved by setting up for the correct advance at high rpm, as was suggested by some folks earlier in the thread. The other is that it appears there was a problem with the original RITA stator & magnetic pick-up assembly that caused quite a bit of jitter at high rpms.

However, while the 4th gear performance is better than before, I still feel that it may be less than what I experience with my stock 71 750 Roadster. There is the difference in 21 vs 20 tooth sprocket, but come on man, this is supposed to be a Combat!

Now that I feel the ignition timing is ok, I have moved to carburation. The bike has 32mm Amal Mk II carbs jetted same as called for MK I on Combat engine. A WOT roll-off test indicated that it was lean. I swapped the 230 mains for 240 and there is now no surge on roll-off, but I also sense no difference when the throttle is moved from above 3/4 to fully open.

That is where I am now. I am going to try different needle positions. It is currently on center position. I'm going to move them 1 notch richer. I realize that shouldn't affect the WOT performance, but that is the next thing I can experiment with.