Good follow-up video. I was a bit vague in my comment about low speed running. Probably I meant low rpm running. Or running the bike below ideal power band. I’ve found with air cooled 2 strokes and Less than perfect expansion chamber designs you can get excessive diffuser wave vacuum pulling charge into the exhaust and baffle wave not scavenging it efficiently. This gives you oily exhaust no matter how perfect the jetting and timing. And oil ratio. This results in that mid throttle mid rpm bog which you feel in many bikes just before power and can often mostly tune out with carb but not fix completely without altering porting or expansion chamber further. Most riders just ride around this by clutching or dropping a gear but sometimes it’s necessary to ride in that rpm and throttle opening. There’s a trade off with air cooled 2 strokes I think around controlling piston crown temps and lubricating bottom end at all degrees of rpm and throttle opening and yeah we can’t always eliminate entirely the spooooooge. I think the other viewer talking about octane and oil build up. The higher octane burns in a more controlled way. This suggests he should advance ignition timing for 91 to gain performance benefit of achieving the same peak cylinder pressure as the 85 for more complete burn. The downside of his 85 octane is detonation and the potential for carbon formation due to higher combustion temperatures. Peak cylinder pressure is always the goal with the only limiting factors being heat and detonation.
With a typical expansion chamber the top 25% of the RPM range is when the return baffle wave creates more dynamic engine compression. Blow that range the baffle cone and its return wave make power worse because the wave returns and its "pressuring" ends before the piston closes the exhaust port. So instead of causing a higher dynamic cylinder compression, it forces some of the intake charge back down the transfers, reducing the delivery ratio. So the compression loses its dynamic value and there's less air/fuel to burn and so the combustion temp is less and then more oil can survive (not burn up) and contribute to spooge. Look at my video about pipe design for street/trail bikes that can't be kept in that top 25% RPM and so need a modification to the baffle cone.
Hi Michael, great video as always. Do you have or know where I can get the SDS info for Honda GN2 premix. I can't find it anywhere. It's non synthetic and I'm using it in an FL350 air cooled with a BR9ES plug. I have a feeling the flash point would be too low. This thing has no spooge anywhere at 32:1, even right at the pipe connection to the cylinder. I have idled it for 5 minutes before and took the top end off, there was a 3/16" puddle of oil in the crankcase (it was well loaded up) According to that it should be getting enough oil I'd assume. The GN2 bottle says right on the label that it's made for this machine. Thanks for reading.
I can't find any data sheets on it. Being fully mineral oil I'd want to know how much of it is group 1 oil, if there is any. That's because group 1 is like nothing, because it instantly vaporizes off hot metal. But the lower bearings like it. I personally wouldn't use any oil that has its data hidden from the public. That implies they have something to hide. But mineral oil is prone to spooge so you should use my "combination tuning method" to check your jetting and timing.
@MichaelForrestChnl Thanks for the info. I'll check the jetting again, I've done it several times. But I'm almost out of GN2 so I'll probably go with Klotz Original techniplate. And I'll jet it while using that. Thanks Again.
Dont care that my bike spoodges, running Motul 800 60:1. just wipe tail pipe with a rag before washing it. Had several 300's over the years and they never wear out if you run them slightly rich/cool on Motul 800.
Good follow-up video. I was a bit vague in my comment about low speed running. Probably I meant low rpm running. Or running the bike below ideal power band. I’ve found with air cooled 2 strokes and Less than perfect expansion chamber designs you can get excessive diffuser wave vacuum pulling charge into the exhaust and baffle wave not scavenging it efficiently. This gives you oily exhaust no matter how perfect the jetting and timing. And oil ratio. This results in that mid throttle mid rpm bog which you feel in many bikes just before power and can often mostly tune out with carb but not fix completely without altering porting or expansion chamber further. Most riders just ride around this by clutching or dropping a gear but sometimes it’s necessary to ride in that rpm and throttle opening. There’s a trade off with air cooled 2 strokes I think around controlling piston crown temps and lubricating bottom end at all degrees of rpm and throttle opening and yeah we can’t always eliminate entirely the spooooooge.
I think the other viewer talking about octane and oil build up. The higher octane burns in a more controlled way. This suggests he should advance ignition timing for 91 to gain performance benefit of achieving the same peak cylinder pressure as the 85 for more complete burn. The downside of his 85 octane is detonation and the potential for carbon formation due to higher combustion temperatures. Peak cylinder pressure is always the goal with the only limiting factors being heat and detonation.
With a typical expansion chamber the top 25% of the RPM range is when the return baffle wave creates more dynamic engine compression. Blow that range the baffle cone and its return wave make power worse because the wave returns and its "pressuring" ends before the piston closes the exhaust port. So instead of causing a higher dynamic cylinder compression, it forces some of the intake charge back down the transfers, reducing the delivery ratio. So the compression loses its dynamic value and there's less air/fuel to burn and so the combustion temp is less and then more oil can survive (not burn up) and contribute to spooge. Look at my video about pipe design for street/trail bikes that can't be kept in that top 25% RPM and so need a modification to the baffle cone.
Hi Michael, great video as always. Do you have or know where I can get the SDS info for Honda GN2 premix. I can't find it anywhere. It's non synthetic and I'm using it in an FL350 air cooled with a BR9ES plug. I have a feeling the flash point would be too low. This thing has no spooge anywhere at 32:1, even right at the pipe connection to the cylinder. I have idled it for 5 minutes before and took the top end off, there was a 3/16" puddle of oil in the crankcase (it was well loaded up) According to that it should be getting enough oil I'd assume. The GN2 bottle says right on the label that it's made for this machine. Thanks for reading.
I can't find any data sheets on it. Being fully mineral oil I'd want to know how much of it is group 1 oil, if there is any. That's because group 1 is like nothing, because it instantly vaporizes off hot metal. But the lower bearings like it. I personally wouldn't use any oil that has its data hidden from the public. That implies they have something to hide. But mineral oil is prone to spooge so you should use my "combination tuning method" to check your jetting and timing.
@MichaelForrestChnl Thanks for the info. I'll check the jetting again, I've done it several times. But I'm almost out of GN2 so I'll probably go with Klotz Original techniplate. And I'll jet it while using that. Thanks Again.
Dont care that my bike spoodges, running Motul 800 60:1. just wipe tail pipe with a rag before washing it. Had several 300's over the years and they never wear out if you run them slightly rich/cool on Motul 800.