Just thinkin' With all of the Gen 1 vmax being smog exempt , I was thinking that the coast enrichment valve is not needed. Would deleting them improve fuel mileage or even simplify jetting? I so far have not heard this topic discussed. What say you all? Stay warm . Wayne B
coast enrichment valve
- Thread starter wayne billings
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I know that when you are coasting that is a high vacuum....a lean condition. I know that in the past, I've had a slight issue with my enricheners. I would get a bit of a lean pop on de-acceleration. I wonder if the enricheners are strictly for things like that, and not for mileage...etc?
Great fodder for ponder this cold winter night
No mechanical engineer here, but like the two-stroke's oil injection pump, it serves a purpose. A lean condition, whether two-stroke or four-stroke, can cause problems for the motor's operation, That's why before EPA regulations, bikes would be tuned to be slightly-rich instead of being leaned-out.
Two-strokes, in the pre-mix days, when the engine main bearings, the piston/cylinder wall and the conn rod bearing surfaces were lubricated by the oil in the gasoline, could go dangerously-lean if the throttle was snapped-shut. That limited the amount of oil going to the bearings, whether ball, needle, or plain bearings. Damage to those bearing surfaces could result. An example, a bike running at high RPM, and then the throttle snapped-shut, causes a lean condition to the bearing surfaces, just what you don't want. Seizures could result. An experienced two-stroke rider, who has developed a knack for listening to the sound of the engine, will hear the difference in the pitch/RPM of the engine, as it runs momentarily lean, when the fuel tank empties on the 'main' fuel tank setting, and requires a quick flip of the lever to the 'reserve' fuel setting. "It was running nice and crisp, just-before it seized!" The racer who heard the tell-tale change in engine sound, as the engine went too-lean, would quickly pull-in on the clutch lever, to avoid a seized engine from high-siding him onto the track. In the days of the 500 cc two-stroke racers, with their ability to run at insane speeds, such an ability to sense impending seizure and to pull-in the clutch lever, preventing the seizure from locking the rear wheel, could mean the difference from having a spill, because a spill could possibly bring an end to the rider's season, and just having a DNF, and pulling-off the circuit because of that engine seizure. 'Fast Freddie' Spencer and 'King Kenny' Roberts were two American racers whose ears and other senses were allegedly capable of sensing the 'about to seize' moment, when they would pull-in the clutch lever, to avoid the bike throwing them onto the racetrack.
The design of the oil injection pump was to always provide a supply of oil to the engine's surfaces needing lubrication, but early designs of the oil injection didn't do any better, until the engineers set the oil delivery properly for 'closed-throttle' operation. Many riders and racers would eliminate the oil injection pump and just run pre-mix. Webco had a good business selling oil pump blank-off plates for Japanese two stroke bikes. This author was one of their customers for use on a RT-2 360cc single Yamaha converted from dual-purpose use to strictly off-road use.
The bike below is not mine! It still has the oil injection cable, see it running diagonally into the right side of the engine block behind/below the cylinder 'jug.'
Probably the best way to test the elimination of the fuel/coast enrichment valve's function would be to use an exhaust gas sensor probe, and to monitor what the air/fuel ratio goes to on trailing or closed throttle. I suspect that the throttle response of the bike with it, is better-than without it, as the rider transitions from closed-throttle, to open throttle. Many a motorcycle or 4-wheeled vehicle has been plagued with 'soggy' throttle response, and a bad reputation in the marketplace, because of it. The coasting enrichment valve was obviously an expedient way for the performance-oriented VMax to avoid such issues.
Two-strokes, in the pre-mix days, when the engine main bearings, the piston/cylinder wall and the conn rod bearing surfaces were lubricated by the oil in the gasoline, could go dangerously-lean if the throttle was snapped-shut. That limited the amount of oil going to the bearings, whether ball, needle, or plain bearings. Damage to those bearing surfaces could result. An example, a bike running at high RPM, and then the throttle snapped-shut, causes a lean condition to the bearing surfaces, just what you don't want. Seizures could result. An experienced two-stroke rider, who has developed a knack for listening to the sound of the engine, will hear the difference in the pitch/RPM of the engine, as it runs momentarily lean, when the fuel tank empties on the 'main' fuel tank setting, and requires a quick flip of the lever to the 'reserve' fuel setting. "It was running nice and crisp, just-before it seized!" The racer who heard the tell-tale change in engine sound, as the engine went too-lean, would quickly pull-in on the clutch lever, to avoid a seized engine from high-siding him onto the track. In the days of the 500 cc two-stroke racers, with their ability to run at insane speeds, such an ability to sense impending seizure and to pull-in the clutch lever, preventing the seizure from locking the rear wheel, could mean the difference from having a spill, because a spill could possibly bring an end to the rider's season, and just having a DNF, and pulling-off the circuit because of that engine seizure. 'Fast Freddie' Spencer and 'King Kenny' Roberts were two American racers whose ears and other senses were allegedly capable of sensing the 'about to seize' moment, when they would pull-in the clutch lever, to avoid the bike throwing them onto the racetrack.
The design of the oil injection pump was to always provide a supply of oil to the engine's surfaces needing lubrication, but early designs of the oil injection didn't do any better, until the engineers set the oil delivery properly for 'closed-throttle' operation. Many riders and racers would eliminate the oil injection pump and just run pre-mix. Webco had a good business selling oil pump blank-off plates for Japanese two stroke bikes. This author was one of their customers for use on a RT-2 360cc single Yamaha converted from dual-purpose use to strictly off-road use.
The bike below is not mine! It still has the oil injection cable, see it running diagonally into the right side of the engine block behind/below the cylinder 'jug.'
Probably the best way to test the elimination of the fuel/coast enrichment valve's function would be to use an exhaust gas sensor probe, and to monitor what the air/fuel ratio goes to on trailing or closed throttle. I suspect that the throttle response of the bike with it, is better-than without it, as the rider transitions from closed-throttle, to open throttle. Many a motorcycle or 4-wheeled vehicle has been plagued with 'soggy' throttle response, and a bad reputation in the marketplace, because of it. The coasting enrichment valve was obviously an expedient way for the performance-oriented VMax to avoid such issues.
Good morning This coast enrichment (CE) is more interesting than I thought. These I my thoughts . I grew up in Calif. , the smog capital of the U,S. . Between c.a.r.b and EPA. the car and cycle mfg's. had to jump through a lot of hoops to pass the rigid standards of the day. That being said I can say that Yamaha could have built a carb for the max that would have been sufficient for the job without the Ce valve. However when I look at the valve circuitry it seems like quit a task to eliminate or isolate it from the rest of the system . That is all my brain can come up with for now. Happy days. Wayne B
