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Post by 90GTVert on Sept 2, 2016 20:03:16 GMT -5
You're not looking for the stoichiometric mixture for high load/max power. You shouldn't be doing that with a 2T or 4T. Max power is going to be rich of that point. Stoich is supposed to be the proper amount of air and fuel present for complete combustion, but in the real world you need more fuel around because your combustion isn't going to be perfect and it helps to keep engine temps in check. Stoich is fuel dependent, so I don't see why it's not roughly 14.7:1 for a 2T or a 4T. Max power for a 4T is typically 13-13.5:1, but it varies to some degree from engine to engine. Air cooled engines may like an even richer tune for cooling purposes. I try to keep my TaoTao bouncing the wideband around from 12.5-13.5 WOT (it never stays steady). For a 2T, I would guess you want to stay around 12-12.5:1 for WOT tuning, because the 2T is igniting the mixture twice as often at a given RPM and at greater risk of running hot. Maybe it still makes max power around 13:1... but will it overheat in the real world WOT on a long stretch?
In reality, if I had a dyno I would be comparing engine output to air/fuel ratio with jet changes and that would tell me what my engine liked. Pretty much the same way I tune on the street, using MPH and RPM notes with jet swaps so I can see what truly works vs what meets any spec from a book, person, or elsewhere.
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Post by eclark5483 on Sept 2, 2016 21:35:50 GMT -5
I agree with you 100% Brent. We were shooting for a stoich of 12 on the dyno, we got it in the high 12's but experienced plug fowling and oil saturation on the muffler probe. Going by what others experienced using a 32:1 ratio in the tank with a deleted oil pump, I have concluded that 32:1 is too much oil. On my configuration, it was ran with 64:1 in the tank and the oil pump was still in use as well. The alleged output has been stated to be anywhere from 70:1 to 50:1 on the pump. Using the 70:1 assumption with the 64:1 in the tank, gives me around a 33-34:1 ratio where I had experienced the same fowling others had on just premix. At this point, I am not ready to say that a jet change is needed because of the oil that was in the tank was of course affecting the fuel being delivered. But what I CAN safely assume, is that my oil ratio needs to be lowered to prevent the fowling.
I expect that the stoich will change dramatically next week when we run it with 100% fuel in the tank, and just the oil pump for oil delivery. I think the next run will give us the best indication of whether we need to up the jet size or not.
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Post by 90GTVert on Sept 2, 2016 21:46:55 GMT -5
I'd toss the oil pump in the trash can, mix it at 40:1 with a good oil, and then see what's up. 40:1 should be safe for most setups and I haven't had anything sputtering and over-oiled from 40:1... scooters, midbikes, chainsaws, weedeaters...
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Post by humanshield on Sept 2, 2016 21:47:56 GMT -5
He blinded me with (2 stroke) science  |
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Post by eclark5483 on Sept 3, 2016 0:54:23 GMT -5
I'd toss the oil pump in the trash can, mix it at 40:1 with a good oil, and then see what's up. 40:1 should be safe for most setups and I haven't had anything sputtering and over-oiled from 40:1... scooters, midbikes, chainsaws, weedeaters... That will possibly be something I may look into doing later on down the line. For now though, I'm leaning more towards keeping the pump and zero premix in the tank for one key reason... The Spree is for my son with Autism. I would then be placing him in a situation where he would need to figure out how to do the premix every time he put gas in. A long term goal for my boy is to step him up to a bigger scooter, but at this point, he only wants to drive the Spree. Doing premix for him till he finally gets the courage to try a bigger bike is no big deal, but then I may be faced with a reality that he simply will not do that. In which case, what I ultimately might have to end up doing, is removing the BBK and taking the Spree back down to it's stock configuration. But again, I can agree with 40:1 as the probable safe bet for the BBK. If the pump is in fact, putting out 50:1 like some have claimed, then it won't be too far away from a 40:1 ideal range, and with that, I'm guessing a good squirt of oil in the premix container should be good to go. I know I have seen some "claim" to get better revs when they delete the pump, while many other's argue that the pump is NOT bad at all and just gets a bad rep. Pump .vs Premix gets ALOT of debate and alot of pros and cons from people who will swear by one or the other. I think for the most part, Honda makes a damn good bike and I have much faith in the pump. If it was a TaoTao 2 stroke with a pump though.... yeah, that pump would have been gone before even taking a first ride. I just wish there was more data out there for these older scooters so calculating precise premix would be easier. But, one problem at a time is the way to take it. For now, I just need to get the BBK WOT stable and idling correctly. |
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Post by eclark5483 on Sept 5, 2016 1:14:15 GMT -5
So 90GTVert what RPM do you think I should try finding stoich at? This next run I'm going with 100% fuel in the tank, and just the pump supplying lubrication. I'm not gonna be crazy enough to try rapping it out to 9,10,11 grand. So here's where I'm thinking.. The last time it got it's best run, it achieved 35mph@4300rpm. I'm thinking I repeat and take it back to 35 or 4300rpm, whichever comes first. Figure 35 is a perfect top cruise speed for most needs, so that speed is probably the speed I want to see the BBK producing it's best burn with the lowest achievable stoich. Or should I do it at a lower speed or rpm? I plan on getting lubrication worked out after first getting ideal stoich. 64:1 in my tank saturated the plug, and ran me too lean. I'm thinking of.. after finding ideal stoich, then add small cc's of injector oil into the tank and swish it around look at readings, and right when it goes a bit higher on the stoich, stop and record cc's used and calculate for 1 gallon of gas and proper premix ratio... It's alot of work, But I think I am doing it right by first finding optimal rich, then focus on optimal lubrication. Using Honda GN2 Injector oil, BTW. |
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Post by eclark5483 on Sept 5, 2016 2:37:54 GMT -5
Oh and 90GTVert can you or somebody check my oil ratio math. I think 120:1 added oil is the safest bet, but 100:1 might be more optimal?  |
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Post by 90GTVert on Sept 5, 2016 5:47:58 GMT -5
Id' forget 4300RPM. Something was wrong with the tach function on that run. On sound alone, there's no way that's 4300RPM. Watching the vids side by side, it's even more apparent. I tune WOT however fast it will go first and worry about anything else later. Others do it differently. You may have to take a different approach on a dyno?
The ones I checked look OK.
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Post by eclark5483 on Sept 5, 2016 17:34:56 GMT -5
Id' forget 4300RPM. Something was wrong with the tach function on that run. On sound alone, there's no way that's 4300RPM. Watching the vids side by side, it's even more apparent. We do know, or can safely assume, the plug was fowling out from oil saturation. might that have skewed readings? Tach lead was touching MLM in video 2 and got hot and smoked, that's why test was halted. |
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Post by 90GTVert on Sept 5, 2016 21:29:31 GMT -5
If the sensor could be fouled, that would throw off air/fuel readings. Otherwise, I don't see what oil fouling would change in the sensors.
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Post by eclark5483 on Sept 6, 2016 2:49:48 GMT -5
It didn't change the sensors, it just made the plug fowl. And yes, he did have to readjust the tach clip after getting it hot on the muffler. I agree videos 4-5 are more of an actual representation of RPM's, nice catch.
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Post by eclark5483 on Sept 6, 2016 11:11:50 GMT -5
Well, it hit just a bit over 40 today. NOW we can conclude that it not only needs a bigger main, but a bigger pilot. I went with 128:1 in the tank for this run. No filter, no airbox lid. It appears the BBK has more to give.
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Post by 'O'Verse on Sept 6, 2016 12:30:11 GMT -5
Really nice. That actually sounded like a more powerful tune. For a spree!
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Post by gsx600racer on Sept 6, 2016 18:45:29 GMT -5
Id' forget 4300RPM. Something was wrong with the tach function on that run. On sound alone, there's no way that's 4300RPM. Watching the vids side by side, it's even more apparent. I tune WOT however fast it will go first and worry about anything else later. Others do it differently. You may have to take a different approach on a dyno? The ones I checked look OK. Thanks Brent. For a brief moment, I thought my ears were deceiving me. |
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Post by eclark5483 on Sept 6, 2016 19:46:24 GMT -5
Yep, it was a setting for the Dyno he had wrong. Wasn't sure if it was 90 or 180 on a 2 stroke. Shawn's a 4T guy.
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