Athlon ECU - Cold Start Problems
If you are experiencing cold-start problems on your CRF 250F or CRF 300F equipped with an Athlon ECU and Force Cam maps, this article explains how to correctly identify the cause of the problem and how to make the necessary adjustments to correct or significantly improve the motorcycle's behavior.
Before we begin, it is important to understand that the fuel maps we preload into the ECU are developed using our own test setups. In other words, we use the motorcycle's original components and/or parts that we know very well, such as Force Cam camshafts, the Belparts Force Cam Edition exhaust system, and other components.
When the same map is used with a different combination of parts, especially a different exhaust system, it is perfectly normal for some fine tuning to be required. The base map remains an excellent reference, but it may not match the airflow and exhaust characteristics of that particular setup exactly.
Because of this, symptoms may appear such as difficulty starting when cold or the engine starting normally and then stalling immediately afterward.
Starting and idle are two different things
This is probably the most important point in the entire adjustment process.
When starting the motorcycle, there are basically two stages:
- Starting: the starter motor cranks the engine until it begins running on its own.
- Idle stabilization: once the engine has started, it must remain running without stalling.
In the vast majority of reports involving a "cold-start problem", the motorcycle actually starts normally but stalls a few seconds later.
In this situation, the problem is not really the starting process itself. The problem is idle stabilization.
Understanding this difference is essential because the adjustments are made in different areas of the ECU.
It is a STARTING problem when:
The starter motor keeps cranking and the engine does not start, takes too long to start, or only starts if you slightly open the throttle.
It is an IDLE problem when:
The engine starts quickly and normally, but immediately afterward the RPM drops and the engine stalls.
Before changing anything, we strongly recommend taking screenshots or writing down the original map values. After several tests involving increases and decreases, it is very easy to lose track of the original settings.
If you need to completely restore the original map values, simply reload the original map file into the ECU. If you no longer have the file, contact us by email and request another copy.
1. The motorcycle takes too long to start or only starts with throttle
If the starter motor cranks for some time before the engine finally begins running, or if the engine only starts when you slightly open the throttle, this is a STARTING problem.
This normally happens because there is either too much or too little fuel during the first engine revolutions, usually at very low engine speeds of approximately 400 to 800 RPM.
The Athlon ECU has a dedicated area for this adjustment.
Go to:
Menu > Tuning > Start
Then open:
Starting Injection Time x Temperature (0 TPS)
On this screen you will find a graph that determines the injection time used during starting according to engine temperature.
You can modify only a specific temperature range or adjust the entire curve.
For example, if the motorcycle only has difficulty starting when cold, begin by working on the lower temperature points, such as 0, 20 and 40 °C.
If the problem occurs with both a cold and warm engine, you may need to modify a larger portion or the entire curve.
The main idea is to adjust only the area where the problem actually occurs whenever possible.
How to change points on the graph
The graph has a red dot indicating the currently selected point.
Use the arrows below the graph to move the red dot to the desired temperature.
Then use the + and - buttons to increase or decrease injection time at that point.
- + = more fuel
- - = less fuel
You can also select the size of each adjustment step, typically:
- 0.01 ms
- 0.1 ms
- 0.4 ms
By pressing the increment button, you select how much each press of the + or - button will change the value.
If you want to modify all temperatures at the same time, change the mode from POINT to ALL.
How much should I change?
During starting, a difference of only 0.1 ms is already significant.
Normally, changes of approximately 0.2 or 0.3 ms are already enough to produce a noticeable difference in starting behavior.
Depending on the setup, however, a slightly larger adjustment may be necessary.
Should I add or remove fuel?
This is the part that requires testing.
Because the CRF models do not originally have an oxygen sensor or lambda sensor, there is no simple way to immediately determine whether the engine has too much or too little fuel during starting.
There is also an important detail: both an excessively rich mixture and an excessively lean mixture can produce similar starting problems.
From our experience, however, a large percentage of starting problems encountered when using a different exhaust system are caused by insufficient fuel.
This happens because the Belparts Force Cam exhaust has its own flow characteristics, and our maps are developed around this behavior.
When a map developed for our setup is used with another exhaust system, the amount of fuel required during starting can change.
For this reason, as a first test we normally recommend adding approximately 0.3 ms to the starting injection time in the temperature range where the problem occurs.
Test the motorcycle.
If it improves but is still not perfect, add a little more fuel and test again.
If adding fuel produces no improvement or makes the behavior worse, return to the original value and begin testing in the opposite direction by reducing fuel.
Make small changes, test the motorcycle and observe how the engine reacts. With a little patience, it is usually possible to find the ideal point and achieve excellent starting behavior.
2. The motorcycle starts normally but stalls immediately afterward
If the motorcycle starts easily but the RPM drops a few seconds later and the engine stalls, the problem is related to IDLE, more specifically idle stabilization immediately after starting.
At this stage, two factors are especially important:
- The amount of fuel
- The amount of air passing through the idle system, controlled by the IACV
Both can be incorrect at the same time.
The Athlon ECU has a dedicated section for these adjustments.
Go to:
Menu > Tuning > Idle
We normally recommend starting with airflow because this is often the adjustment that produces the most obvious immediate response.
Open:
IACV Air Opening Curve x Temperature
This graph controls the opening of the idle air piston according to engine temperature.
Just like the starting table, you can modify individual temperature points or adjust the entire curve.
If the motorcycle only has trouble maintaining idle when cold, begin with temperatures such as 0, 10, 20 and 30 °C.
If the engine has difficulty maintaining idle regardless of temperature, you may need to work on a wider range or the entire curve.
How to adjust the IACV
Once again, a red dot indicates the selected point on the graph.
Use the arrows to select the desired temperature and then use the + and - buttons to increase or decrease IACV opening.
- + = more airflow
- - = less airflow
In this adjustment, the unit used is IACV stepper motor steps.
You can normally select increments of:
- 1 step
- 2 steps
- 10 steps
You can also switch from POINT to ALL if you want to change the entire curve simultaneously.
How much should I change the IACV?
We normally work with this adjustment in increments of approximately 10 steps.
A difference of 20 or 30 steps can already create a noticeable change in idle behavior.
The logic is simple:
More steps = IACV opened farther = more air entering the engine.
With more airflow, idle speed will generally increase and the engine will have an easier time remaining running.
If the motorcycle starts and then stalls immediately, increasing airflow can help significantly.
For example, you can test approximately +30, +40 or even +50 steps in the temperature range where the problem occurs.
Do not greatly increase airflow without correcting fuel
This is extremely important.
If you open the IACV significantly, you are allowing more air into the engine.
If fuel remains exactly the same, the mixture may become too lean.
For this reason, the best results are often achieved by adjusting air and fuel together.
Go back one screen and open:
Idle Injection x Engine Temperature
Here you can add or remove idle fuel according to engine temperature.
In this table, a change of only 0.1 ms can already produce a noticeable result.
As a practical starting point for a motorcycle that starts normally but has difficulty maintaining idle when cold, an adjustment that frequently works well is approximately:
- +30 to +40 IACV steps
- At 0, 10, 20, 30 and 40 °C
- At the same temperatures, add approximately +0.1 to +0.2 ms of idle injection time
This does not mean these values will be perfect for every motorcycle. They are simply a useful starting point for fine tuning.
Make one adjustment, test the motorcycle and observe its behavior.
If the result improves, continue refining in that direction. If it becomes worse, return toward the original setting and test the opposite direction.
Without an installed oxygen sensor, it is impossible to see exactly what is happening with the air/fuel mixture at that moment, so part of this tuning process must be performed by observing the engine's response.
Even so, with small adjustments and some patience, the idle can normally be tuned very well.
3. What if the IACV reaches its limit?
The IACV piston has a limited physical travel.
This means that eventually increasing the number of steps in the map will no longer produce additional opening because the piston has already reached its maximum position.
On most motorcycles, this is unlikely to become necessary.
However, on significantly larger displacement engines such as 310 cc or 360 cc, especially when using aggressive camshafts and operating in very cold ambient temperatures, the amount of air required to maintain idle can increase considerably.
If the IACV reaches its limit, there is still another way to allow more air into the engine: the throttle body butterfly itself.
When the throttle is completely released, the butterfly does not remain absolutely closed. It stays slightly open to help provide airflow for idle.
There is a mechanical stop screw that determines how far the butterfly remains open at its resting position.
Tightening this screw leaves the butterfly slightly more open when the throttle is released, allowing more air into the engine and increasing overall idle speed.
There is an important difference:
The IACV can be adjusted differently according to engine temperature.
The mechanical throttle stop adjustment, however, is global and affects operation at all temperatures.
For this reason, we recommend using the ECU's electronic adjustments first and only changing the mechanical throttle stop when it is actually necessary.
Important: whenever the throttle stop screw is changed, recalibrate TPS 0 in the ECU.
Quick summary
If the engine cranks for a long time before starting:
Adjust the STARTING section, especially Starting Injection Time x Temperature.
If the engine starts easily but stalls immediately afterward:
Adjust the IDLE section, especially the IACV and Idle Injection x Temperature.
Avoid changing several things at the same time. Make small adjustments, test the motorcycle and observe how the engine reacts. Once you find a direction that produces improvement, continue refining until you achieve the best possible operation.
This is one of the major advantages of the Athlon ECU's tuning capabilities: the base map can be adapted to the specific characteristics of each engine, exhaust system, engine build, fuel and operating condition.