An older thread, but the topic is always a good discussion item.
As of late, have been asking about this very topic at morning coffee with the old guys who have been mechanics for quite some time. Mentioned the symptoms on start and Bruce - a recently retired but good all round mechanic - seems to think the injectors are causing me a lot of this grief. I reviewed my thread and Tony also has some sage advice as well.
Started doing more research on the internet into fuel injectors and the types available. For my '85 LTD FI model, the fuel system specs are:
With the engine not running the pressure should be 2.4-2.7 kg/cm' (34-38 psi).
At idle (1,000 ±100 rpm). The pressure should be 2.0-2.4 kg/cm^ (28-34 psi)
The specified capacity is 630 cc (21.3 oz.) per minute minimum, OR 37.8 liters per hour minimum OR 10.0 US gals/hr minimum.
The injectors for this bike were cleaned and flow tested. Flow rate at 40 PSI was 65/66 ml (CC) with a resistance of 2.5 ohms.
Taking all this into account, the injectors are low impedance, peak and hold injectors. Peak and hold injectors are also generally high flow injectors. A downside to having low impedance injectors is that they are generally more expensive than high impedance injectors.
The following is probably in regards to a car FI system, but the theory and premise should be the same - "The Peak current is the amount required to quickly jolt the injector open, and then the lower Hold current rating is used to keep it open for as long as the ECU commands. These require the extra kick from the higher current to keep the opening and closing time of the injector stable at the higher fuel flow rate. With this type of driver, 12 volts is still delivered to the injector, but due to the its low resistance, the current in the driver circuit is high. How high? Using Ohms Law we can calculate the current rating (12v/2 ohms = 6 amps). This is substantial current flow and a Saturated Injector cannot handle it. The drivers also come in two values; 4 amp peak/1 amp hold, and 2 amp peak/0.5 amp hold."
The high impedance injectors are termed saturated injectors. High impedance injectors have a resistance between 10 and 14 ohms. Low impedance injectors have a resistor pack.
This web site:
https://www.hondata.com/tech-low-high-i ... -injectors recommends using high impedance injectors.
Went to another site, a Honda civic forum:
https://www.hondacivicforum.com/forum/e ... tion-9292/ and there is some good information there. Post #1 is very informative and gives more clarification on injectors to be used. Using this post as a guide, the flow rate specified by Honda for the '85 LTD could support up to 126 HP, fuel pp flow rate divide by 5 - good approximation.
Here are the conversions that can be used:
Conversions
660cc per minute is approximately equal to 65 lbs per hour which is equal to approximately 126 hp.
lbs/hour = cc per minute / 10.2
lbs per hour = HP / 2.04
cc per minute = lbs per hour x 10.2
cc per minute = HP x 5
HP = cc per minute / 5
HP = lbs per hour x 2.04
Another site that is good information is:
https://www.promracing.com/injector.php/ It's a guide to sizing fuel injectors. Using the site calculator, and 124 HP, it recommends a fuel injector size that flows 19 Lbs/hr. Even at a flywheel HP of 100, the recommendation is for an injector with a fuel flow of 19 lbs/hr.
Have perused the Supplement for this bike and the schematics illustrate that there is a resistor unit for the injectors. This site:
https://performancefuelsystems.com/Injec ... Corner.htm indicates that using high impedance fuel injectors in a low impedance fuel injector circuit since the amperage needed to open the high resistance injector is lower and within the limits of the peak-and-hold driver circuit. It is not recommended to use low impedance fuel injectors in a high impedance fuel injector circuit.
Have to take all this information and try to make some sense of it all. The other issue is finding the specs on fuel injectors that you find on line so that I can find a fuel injector that is close to the amount of fuel required without having more fuel flow than necessary.
Cheers
