Starter Valves Sync, Valve Clearances and Fuel Economy

[dduelin]

The starter valves richen the fuel/air mixture for cold starts and have no effect on fuel/air mixture above off-idle rpm. If you look at the tiny starter valve passages that allow air flow when the butterflies are closed compared to the intakes when the butterflies open you see why. Honda's Programmed Fuel Injection system controls fuel/air mixture in the ECU based on sensor inputs from coolant temp, O2 in the exhaust, and intake tract air pressure.

 

[Dobby]

Filling up on the side stand, means a little bit less fuel than if you were on the Center Stand, filling up to the same mark. However, if your riding is at an average speed of 85 km/hr or 51 mph and if in the 5th gear. You should get some great gas mileage. 85 km/hr is about the sweet spot for a rebel 250. That engine loves 50 mph. I had a nighthawk 250, so that is how I know. There does not seem to be anything wrong with your bike.

Here is my 0.1c. Fill up your tank the way you normally do and go on a 450 km solo trip (225 km each way), possibly on the highway (to eliminate variables of stop and go and variation in speeds) and see where the flashing bar comes on. Maintain an indicated speed of 115 km/hr. You should be able to get close to 450 km.

One of my friends live exactly 210 kms away door to door, I guess it's time for a visit. Without stop and go traffic and maintaining a constant 115 kmh, I would expect even better mileage. The Roads we typically ride have a 80 KMH speed Limit anyway, but yeah, the wife's Rebel 300 kinda likes that speed. Anything more and she complains that it gets a little too buzzy. Meanwhile, My ST is gliding in 5th and I barely know the engine is running. It's just a bit confusing since nothing has changed except for the addition of a slightly larger windshield, yet I am down a whopping 80 KMS per tank. I am not sure if this means anything but when my last bar starts flashing, I fill up with 22.5 to 23 Liters. Always around the same amount. I understand it is a 29 liter Tank, so shouldn't it take a bit more?

 

[Dobby]

The starter valves richen the fuel/air mixture for cold starts and have no effect on fuel/air mixture above off-idle rpm. If you look at the tiny starter valve passages that allow air flow when the butterflies are closed compared to the intakes when the butterflies open you see why. Honda's Programmed Fuel Injection system controls fuel/air mixture in the ECU based on sensor inputs from coolant temp, O2 in the exhaust, and intake tract air pressure.

In that case, it could be any one of those sensors causing my fuel efficiency problem. I might be misunderstanding, but since the starter valves have no effect off idle, is it still worth synching them?

 

[Dobby]

Random thought, has Canada increased any non Dino base fuel to the gas pumps?

I wasn't aware that was a thing or whether there are any plans for that. Whatever it is, we are paying way too much for it. Last night I filled up at $2.10 per liter for 93 Octane. Regular was $1.80 per Liter. Robbery!!!!

 

[etalors]

One of my friends live exactly 210 kms away door to door, I guess it's time for a visit. Without stop and go traffic and maintaining a constant 115 kmh, I would expect even better mileage. The Roads we typically ride have a 80 KMH speed Limit anyway, but yeah, the wife's Rebel 300 kinda likes that speed. Anything more and she complains that it gets a little too buzzy. Meanwhile, My ST is gliding in 5th and I barely know the engine is running. It's just a bit confusing since nothing has changed except for the addition of a slightly larger windshield, yet I am down a whopping 80 KMS per tank. I am not sure if this means anything but when my last bar starts flashing, I fill up with 22.5 to 23 Liters. Always around the same amount. I understand it is a 29 liter Tank, so shouldn't it take a bit more?

1. Travelling at 115 km/hr in the fifth will increase your fuel consumption vs 85 km/hr in the fifth. You will notice the difference. But you should still get about 450 km. Try it.

2. When the last bar starts flashing there are 5 liters left in the tank. So filling up with 22.5 to 23 liters is about normal. Also, while the tank capacity is listed at 29 liters. No one has been able to fill 29 liters even when they ran out of gas. Most I heard on this form is about 27 liters or 7.3 gallons. I myself filled up with 7.1 gallons on the CS after I rode the bike 40 miles with the bar flashing.

 

[TerryS]

The starter valves richen the fuel/air mixture for cold starts and have no effect on fuel/air mixture above off-idle rpm. If you look at the tiny starter valve passages that allow air flow when the butterflies are closed compared to the intakes when the butterflies open you see why. Honda's Programmed Fuel Injection system controls fuel/air mixture in the ECU based on sensor inputs from coolant temp, O2 in the exhaust, and intake tract air pressure.

That's not quite the way I understand things; the starter valves just admit air around the closed butterflies, and provide idle speed control by allowing more or less air into the engine. For a faster cold idle, the starter valves are opened more to let more air in.

The FI system is reading intake air pressure and temperature along with engine revs, throttle position, coolant temperature and O2 sensor readings to determine how much fuel to inject; low coolant temperature instructs the FI system to make the mixture richer for cold starting, not the starter valves.

The starter valves are always open to some minimum extent and so would have a minor effect on airflow when the butterflies are open, although they are tiny compared to the full bore of the intake. If the SVs are grossly out of adjustment then it is conceivable that there would be slightly more or less air entering a particular cylinder, and that would make for slight mixture differences as the FI system applies the same injection volume to each (as long as the injectors all flow evenly...). The 5-way T connects all 4 intake vacuums so the MAP sensor is working on effectively an average air pressure.

Poorly adjusted starter valves give a rough idle as the cylinders will be wanting to idle at different speeds, but I doubt that would affect fuel use in any meaningful way