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782 Posts
Discussion Starter · #61 ·
Can never do better than 34 mpg on mine.

The pushbutton timing profile is kinda cool.

I have a brand new set of chicken strips to throw away. 馃檮 I never drag the pegs.
How fast do you ride normally? I have to be above 70 MPH to get below 40 MPG.
Even two back to back runs of the Tail showed 41 MPG.

10,006 Posts
How fast do you ride normally? I have to be above 70 MPH to get below 40 MPG.
Even two back to back runs of the Tail showed 41 MPG.
I try to limit it to 75, but I'm full throttle a lot.

782 Posts
Discussion Starter · #63 ·
Now that it's cold (35-40F), my cold start ignition retard need some adjustment. With cold starts in 65F+ temps, it kept the choked RPM to around 1500-1800. Now with the drop in temperature, I'm seeing it creep above 2500 RPM even with the retard on. Additionally, I found the bike is a little hesitant to come up to idle if I tried starting it with the retard engaged. That was an easy fix of starting it without it, and turning it on once it was running.

Now I'm thinking about abandoning the -10 setting for a second ignition table designed for cold/choke running. I haven't needed the stock ignition setting for anything other than to turn off the decel pops. That did prove invaluable during VERY LONG downhill runs while traversing the smoky mountains. I was riding as a group, and they weren't all that excited about 2 miles of backfiring....:)

I could really use a third timing map! :)

782 Posts
Discussion Starter · #64 ·
I've been making some more adjustments, to try to tune in the cold/choke start.
With my timing table, I was using a -10 degree retard for cold starts. The problem was the idle would sometimes settle at 1500, sometimes at 1000 and sometimes at 3000. It was difficult to ride because it wouldn't decelerate when releasing the throttle if the RPM was around 2700-3100.
The bike always did this on choke with the factory timing, but I feel I had made it worse.
Before, I recall it wanting to hold 2200-2500 on choke.

Well I rode today in ~40F weather, riding for about 15 minutes with the choke on and the -10 degree switch set.
Every red light, the RPM would climb to 3000. If I held the brake and partially released the clutch, I could get the engine to settle at a lower idle.
But I had to drag the RPM down to almost 1000 to get it to hold low. A slight bump of the throttle and it'd rise up to 3000 again.
I logged my whole ride to see what it was doing and try to improve it's behavior.

What I found was on normal (no choke) rides, the engine vacuum at idle is around 60-65 kPa.
Engine braking had a vacuum around 40-50 kPa.
Cruising at 60 mph had a vacuum around 88-90.
I set up my table for 59-100 kPa, with everything 50 kPa and lower all treated the same.
At 100 kPa, I use stock timing.
Anything below 100 kPa (part throttle) I advance the timing.

Riding with choke, those numbers were all shifted with idle being around 85-87 kPa.
Engine braking had a vacuum around 82-84 kPa.
Cruising at 60 mph had a vacuum around 95 kPa.
I set up a 2nd table for 78-101 kPa, with everything 75 kPa and lower all treated the same.
At 101 kPa, I use stock timing.
Anything below 101 kPa, I retard the timing to offset the effects of the choke.

My first attempt worked great at most RPMs.
It started quickly, whereas trying to start with the -10 enabled resulted in a slow clime in RPM from cranking speed to idle speed.
It was EXCELLENT at holding the idle between 1450-1650 RPM.
A cold start sounds like a fuel injected bike now, firing right up and idling right where it's supposed to!
Above 2200 RPM, the RPM dropped at closed throttle like I expect. Maybe slightly slower than normal, but FAR better than stock.
However between 1650-2200 RPM, the RPM was very slow to drop.
I had mis-judged the kPa for closed throttle in that RPM range and didn't have enough ignition retard programmed in.

I tried riding the modified table without choke on and it's still reasonably ridable.
Because of the retarded ignition, partial throttle feels like you're riding with the brake stuck on but it retains a smooth throttle feel with just a touch of roughness as you roll off the throttle.
The exhaust is a bit louder as well, both from retarded timing and from having to add throttle as compared to proper timing.
At full throttle, the two tables are identical.
The idle speed still holds around 1100 with the "choke" table and no choke.
This is an improvement as well, from accidentally leaving my -10 switch enabled.
In that case, the idle would fall below 900 due to idle ignition timing being so far off.

I made some adjustments in the 1650-2200 RPM range to fix the slow RPM drop.
I also modified the idle timing a bit to try to hold more closely to 1500 by retarding the timing at 1700.
I also pulled a bit more timing from the gear change vacuum levels (82-84 kPa) to try to get the RPM to drop faster from 3k.
I'm planning a test ride tomorrow.

As a side benefit, I feel like pulling so much timing results in a faster engine warmup.
That would be difficult to prove, as I have no way of logging temperature, as well as uncontrolled variables such as weather and traffic and a heavy right wrist.
My main goal was to make riding with choke feel more like riding without choke, and if I could warm up the engine faster, that's a bonus!

Idle into a moderate acceleration to 3rd, followed by a stop.
Notice the RPM doesn't drop smoothly after 3rd gear but rather rolls down to 2100 and hangs out before falling to 1600?
Rectangle Slope Plot Font Line

Here are gear changes with my normal table and no choke. A very snappy drop from 3200 RPM.
Rectangle Slope Plot Font Parallel

This is my normal table with the choke off, showing the RPM drop to idle. That's my goal for on-choke riding, only idling at 1500.
Rectangle Slope Plot Font Parallel

782 Posts
Discussion Starter · #66 · (Edited)
The choke should always raise the idle on this carb, if all is working correctly.
Yes, but I don't like how much it raises the idle. It makes it difficult to ride when the RPM hangs too high.

I tried my new timing today, and the RPM now falls sharply with a closed throttle, just like no-choke behavior!
I have it set to hold a higher idle when on choke (1500) instead of normal (1100).
High enough both to remind me it's on choke, and to give it some breathing room if it stutters when I crack the throttle.

Compare this with the final image in my previous post.
Water Rectangle Slope Triangle Parallel

I am running -2 degrees timing at 1500 vs 5 stock timing.
The timing falls to -5 at 1700 to both aid in RPM dropping, and to hold the RPM from climbing at idle as the engine warms up.
The timing goes up to +7 at 1300 to keep the RPM up when the engine is cold.

The idle is very steady over these 90 seconds.
Rectangle Slope Font Parallel Circle

For the rest of the timing table, I moved up the throttle point where the timing is still pulled back. Cruising top gear at 30 mph (2700 RPM) the timing is about 8 degrees on choke and 21 off choke. Stock timing would be about 19 degrees. You can really feel the retarded timing now. She'll still accelerate if you get into the throttle, but mid throttle is a bit sluggish. It's a good reminder for me to take it easy while she's warming up.

Timing comparison between no choke with "no-choke" timing (21-22 degrees) and choke and "choke" timing (3-8 degrees, peaking at 10 with some throttle.
I switched timing tables and threw on the choke while cruising at 30 mph.
Rectangle Water Slope Font Parallel

She purrs like a FI bike now when cold.
The ultimate would be to put a sensor on the choke itself to automatically trigger the alternate table!
Of course then I'd want a temperature driven servo to auto disengage the choke when the engine warms up...


782 Posts
Discussion Starter · #67 ·
I rode again today, with a temperature of 33F.
Here is the first 2.5 minutes of my ride, with the cold start happening just after 290 seconds from when I started logging.
It's idling right around 1500-1600. It's 1500 at first start, rising to 1600 as it warms up a bit.
At around 425 seconds (2 min 15 sec since starting), I turned off choke and the idle settled at 1020 +/-50.
By the time I arrived at my destination, the no-choke idle had risen to about 1160 +/- 50.
Rectangle Water Font Slope Parallel

I'm quite satisfied with how it runs on the choke now!
I am getting the crisp drops in RPM and the rock steady idle speeds I鈥檝e been looking for.

I did some follow-up research on retarding ignition timing:
1. It's undebated that retarding timing from optimal results in less power, assuming everything else remains the same. This means less fuel is turned into power. It is either spit out unburned, or it's turned into additional heat.
2. It's commonly known in hot-rod circles that having no vacuum advance can cause an engine to overheat at idle. It is not known if this is due to more heat in the engine itself, or more heat in the exhaust manifold/header raising the under hood temperatures.
3. Retarding the timing raises the exhaust gas temperature.
4. Some OEMs retard the ignition timing at start up to heat up the O2 sensor faster.

All of this points to retarding ignition adds heat to the exhaust. However, there's nothing to say it adds heat to the engine itself. Until I found this page. It shows some engine with the cylinder temperatures and pressures plotted against crank angle. It shows that in that particular engine, moving the timing from 45 BTDC to 0 BTDC resulted in a 25% increase in exhaust gas temperature (from 1720 C to 2150 C). Integrating the area under the pressure curve and under the temperature curve, shows a 33% reduction in total power and a 10% reduction in cylinder heat exposure with retarded timing. If one were to retard the timing AND increase power to match (greater throttle opening), the cylinder temperature would be increased by 33%. This doesn't even take into account the additional heat absorbed from the exhaust through the exhaust valve (cooled by the valve seats) or the exhaust manifold.


782 Posts
Discussion Starter · #68 · (Edited)
I'm having issues now coming off idle where the ignition coil dwell time will drop from 15mS to 6mS and cause a misfire. It shows up in hotter weather as the coils become less effective with greater temperature.

Stock dwell time is 15mS at idle and 2.5mS at redline.
Here's the dwell time I was running:
Dwell time: 10,000 uS
Dwell dynamic addition: 30%
Max dwell time: 12,000 uS
Min duration of discharge: 3,000 uS
Max rpm for dwell by lobe: 600 RPM
Rectangle Slope Plot Font Parallel

I made some adjustments to try to fix the issue and this was the result.
Dwell time: 12,000 uS
Dwell dynamic addition: 30%
Max dwell time: 14,000 uS
Min duration of discharge: 5,000 uS
Max rpm for dwell by lobe: 900 RPM
Eye Rectangle Slope Plot Font

It increased the average dwell time below 3000 RPM from 12mS to 14mS, and slightly increased the lowest dwell time from 5.5mS to about 6.5mS.
However it caused a decrease the dwell time near redline from 4mS to 2mS.
I realize now that's due to the change in Min duration of discharge from 3,000 uS to 5,000 uS.
At 8700 RPM, it has to fire a spark every 6.9 mS. If I take away 5 mS for "duration of discharge", that leaves only 1.9mS of charge time.
That starts to have an effect at 4200 RPM in the first graph and as early as 3200 RPM in the second graph!
I also noticed that bumping up the Max rpm for dwell by lobe to 900 RPM caused it to struggle to recover if the RPM ever dropped that low.
I think it's because it removes the ignition advance and it drops from 5 degrees advanced to 0 degrees.
Cranking RPM is ~250 on my bike so I figured 300-400 is a good range.
That way it retains an extra long dwell time during low voltage cranking to help with hot starts, but then quickly jumps to it's running timing to get the RPMs up on startup.
I'm going to pull down the max dwell time to 12mS because I don't like how it sometimes goes as high as 18-20mS at idles now.

I'm going to try another change to see if I can resolve this issue.
Dwell time: 12,000 uS
Dwell dynamic addition: 30%
Max dwell time: 12,000 uS
Min duration of discharge: 1,000 uS
Max rpm for dwell by lobe: 300 RPM

The manual is translated into English and not everything is super clear.
I don't fully understand these two settings:
Dwell dynamic addition - dwell addition to compensate uneven engine running at low RPM [%].
Compensation - frequency compensation of the phase error of engine position inputs. The phase error is due to the frequency dependency of trigger level of input and the delay that occurs when processing the input signal. The phase error is mainly dependent on the number of lobes of the pickup system of the motor position.

I have them set at 30% and 11 respectively, but I really don't know what they do, especially "Compensation".

Water Rectangle Slope Plot Font

The dwell time seems to drop to just under 1/2 of the "Max dwell time" when I crack the throttle.
I was seeing it drop to 5.5-6.0mS with a 12,000uS max and 6.5mS with a 14,000uS max.
The stock system looks like the coils only needed 8-9mS at idle, so 2x8 = 16,000uS. Add a little extra and go with 17,000uS max.
I'm going to increase the Min duration of discharge to 4,000uS for 3mS dwell at 8500.
This helps reduce the dwell time at midrange, as this will limit dwell time to 11mS at 4000 RPM.
When I looked at the load/heat in the coils, it would actually peak at 4500-5000.
Stock timing at 5000, it charges for 8mS every 12mS or 67% of the time. At idle, it charges for 15mS every 50mS or 30% of the time.
I can afford to drive them longer near idle without worrying about heat produced.
Reducing the Max rpm for dwell by lobe to 300 was an improvement over a setting of 900, and possibly an improvement over 600.

I'm going to try the following:
Dwell time: 12,000 uS
Dwell dynamic addition: 30% (I think this setting adds up to 30% to the dwell at low RPM)
Max dwell time: 17,000 uS
Min duration of discharge: 4,000 uS
Max rpm for dwell by lobe: 300 RPM

EDIT: Here's the results of that test.
Plot Rectangle Slope Parallel Font

Almost there! Still a bit of off-idle hesitation, but less than before.
I'm satisfied with the high RPM dwell time.
With gas being high, I'm not going to go out of my way to make sure I hit those RPMS for logging purposes anymore.
I'd like to lower the average dwell time at idle, while bringing up those 6.5-7mS points.
I just did the math and at 300 RPM, if the dwell time is the length of the lobe (20 degrees), it's only going to be 11mS of dwell time!
300/60 = 5 revs per second or 200mS per rev. 200 * 20 / 360 = 0.011.
I'm actually shortchanging my dwell time at cranking RPMs, And here I thought I was helping.
That explains why setting that value to 900 RPM was so terrible as it made the dwell time 3.7mS.

I'm going to try the following:
Dwell time: 11,000 uS (Hoping to lower the average dwell time)
Dwell dynamic addition: 30% (Still not sure how this affects things, but 30% is the maximum allowed value)
Max dwell time: 20,000 uS (This seems to affect the minimum values seen)
Min duration of discharge: 4,000 uS (Limit mid to high RPM dwell time)
Max rpm for dwell by lobe: 100 RPM (Effectively disabled since cranking speed is ~300 RPM)

EDIT: Here are those results.
Rectangle Slope Plot Font Parallel

I did bring down the average dwell in the 2000-3500 range.
Meanwhile the values around idle have increased, with the minimum climbing to about 7-8mS!
The hesitation was improved, but still present.
I was hoping for 9mS, but I'll take what I can get.
20,000uS is the maximum value the software will allow for Max dwell time, but increasing that did seem to improve things.
Ignore the <2mS values. Those are from messing with the kill switch while it's running and aren't real world values.
Cold (well, cool...it's 75F in my garage) and hot starts are good.
The coils are still being driving a bit hard in the 2500-5000 range (as compared to stock), with peak heat happening at 3500 RPM.
But the values I rode with last year drove them a bit harder in that range and they survived just fine.

About all I can do from this point (in order) is:
Try reducing the Dwell dynamic addition to see what effect that has.
Fix my grounding ignition to gain back 0.7 Volts I lost from my wiring.
Regap my plugs a bit smaller, and closer to stock gap size.

EDIT: Here are the results, this time only looking at 1000-4500 RPM as I'm fine tuning the lower ranges.
Rectangle Slope Line Font Plot

The values are shown as: Red, Black, Green.
Dwell time: 11,000 uS - 11,000 uS - 10,000 uS
Dwell dynamic addition: 30% - 15% - 10%
Max dwell time: 20,000 uS - 20,000 uS - 20,000 uS
Min duration of discharge: 4,000 uS - 4,000 uS - 4,000 uS
Max rpm for dwell by lobe: 100 RPM - 100 RPM - 100 RPM

This tells me the Dwell dynamic addition percentage changes at what RPM it takes effect.
Overall, the black settings seemed to respond best.
Green gave me a bunch of outliers in the 1500-2500 range that didn't show up with the black settings. No idea why that is.
It also drives the coils a bit less than stock in the 2000-2500 range.
Lastly, the additional dwell with green tapers off around 1000 rather than 1250 for black, or below idle speed.

I'm going to stick with the black settings and now focus on the wiring and plug gaps.
As seen in post #10 in this thread, the stock coils don't charge much more after about 8-9mS at idle, and that's where the black settings are getting me at a minimum!
There really isn't anything more I can do to improve the ignition dwell time at this point.

P.S. Ignitech stopped responding to my emails after I told them about my logging program.
I still recommend purchasing this unit, but I think I offended them through my work :ROFLMAO:.
I did notice that the unit has a built in hourmeter that gets sent back with the data packets somehow.
I hope to update my logging program to record that data as well.
Who knows what other data is sent back. Each data packet is 152 bytes and I only know what 14 of them are for!


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