Engine Trouble BT80 running rich and nothing fixes it

[Karl Snarl]

mmmm not really. If its still 4 stroking its definitely not lean. 28:1 is dumb rich, youll never seat your rings with that much oil. Bearings are plenty fine running dry at 1000 rpm for hours on end. As soon as bearings are initially coated they're good to go to full rpm. Anyone that builds real motors will go balls out for a few heat cycles and then you're good to go.

As to OP, its still 4 stroking because the offset intake, those intakes are so restrictive and they dont allow the fuel to stay atomized. When the fuel travels though the intake, it adheres to the walls and turns it into little drops of fuel instead of the mist. Thats what caused the 4stroking. A china offset will never run correctly.

i dont wanna go to much into this, cause some people have a huge problem with physics. so i'll keep it all simple and not to much sciency talk or math. the fuel doesn't drop out on the walls do to layered flow. the air is not just flowing in one stream in the intake, it is flowing in layers from the outside in. the middle layer being the fastest, and the closest to the intake being more still ( it's moving, just not how you would think it is, science stuff i'm not gonna get into unless you wanna pm). the fuel will not turn in to drops on the inside of it unless your running like a 10 foot ( exaggeration) intake. an it wold only drop out because there is very little flow happening in a super long intake. an break in is more than setting the rings. the reason you use so much oil then is because you are coating the bearings and soaking the metal. i run 28:1 to 32:1 (some i've gone all the way to 16:1, just to much smoke for the small gain in power for me i get almost no smoke until i hit around 20:1 then its not to bad still) in all my bikes, for more power mainly, better ring seal. and running at 28:1 is not gonna hinder ring seat at all. not one bit. i've been building engines for over 30 years and not very many people actually understand what break in really is. 28:1 is not rich at all, it's actually pretty lean, meaning you need a larger jet. thing is, tht extra oil in there is gonna save you money and time in engine longevity when you are beating on it. an the cost of oil, well its good extra protection. when breaking in, you wanna wot a little here and there, just dont hold it to long. you are trying to coat all the metal ( which suspended oil in the air at a high flow is not gonna drop out very well), so you wanna vary the throttle a lot. you are trying to get the rings to match the walls, cover the all surfaces with oil ( bearings included) an stress the metal a bit ( not kill it) so it all seats in. by running a higher ratio of fuel in the beginning, you are lowering the life of all parts. once everything is coated and soaked in, then the ratio can be raised with out worrying if you are lowering life expectation of the parts. i've got bikes with over 5000 miles on them, still run like brand new. very little wear on the walls and rings after break in. if i was doing it wrong, i'm pretty sure i would have noticed after 30 years of building engines.

 

[Karl Snarl]

mmmm not really. If its still 4 stroking its definitely not lean. 28:1 is dumb rich, youll never seat your rings with that much oil. Bearings are plenty fine running dry at 1000 rpm for hours on end. As soon as bearings are initially coated they're good to go to full rpm. Anyone that builds real motors will go balls out for a few heat cycles and then you're good to go.

As to OP, its still 4 stroking because the offset intake, those intakes are so restrictive and they dont allow the fuel to stay atomized. When the fuel travels though the intake, it adheres to the walls and turns it into little drops of fuel instead of the mist. Thats what caused the 4stroking. A china offset will never run correctly.

also you might not actually be 4 stroking. i'd have to see your bike, but i'm betting you are running to lean. or you have a super restrictive exhaust. besides, you want a little bit of 4 stroking, when you are going on a flat and transfer to a slope, you want power, not a lean run condition. which is what happens with these 2 strokes if you set it to not 4 stroke at all on a flat. when sitting with out the clutch engadged, if you can rev your motor to the moon, you're running way to lean and gonna burn tht motor up. an tht is a fact.

 

[Member 30059]

i dont wanna go to much into this, cause some people have a huge problem with physics. so i'll keep it all simple and not to much sciency talk or math. the fuel doesn't drop out on the walls do to layered flow. the air is not just flowing in one stream in the intake, it is flowing in layers from the outside in. the middle layer being the fastest, and the closest to the intake being more still ( it's moving, just not how you would think it is, science stuff i'm not gonna get into unless you wanna pm). the fuel will not turn in to drops on the inside of it unless your running like a 10 foot ( exaggeration) intake. an it wold only drop out because there is very little flow happening in a super long intake. an break in is more than setting the rings. the reason you use so much oil then is because you are coating the bearings and soaking the metal. i run 28:1 to 32:1 (some i've gone all the way to 16:1, just to much smoke for the small gain in power for me i get almost no smoke until i hit around 20:1 then its not to bad still) in all my bikes, for more power mainly, better ring seal. and running at 28:1 is not gonna hinder ring seat at all. not one bit. i've been building engines for over 30 years and not very many people actually understand what break in really is. 28:1 is not rich at all, it's actually pretty lean, meaning you need a larger jet. thing is, tht extra oil in there is gonna save you money and time in engine longevity when you are beating on it. an the cost of oil, well its good extra protection. when breaking in, you wanna wot a little here and there, just dont hold it to long. you are trying to coat all the metal ( which suspended oil in the air at a high flow is not gonna drop out very well), so you wanna vary the throttle a lot. you are trying to get the rings to match the walls, cover the all surfaces with oil ( bearings included) an stress the metal a bit ( not kill it) so it all seats in. by running a higher ratio of fuel in the beginning, you are lowering the life of all parts. once everything is coated and soaked in, then the ratio can be raised with out worrying if you are lowering life expectation of the parts. i've got bikes with over 5000 miles on them, still run like brand new. very little wear on the walls and rings after break in. if i was doing it wrong, i'm pretty sure i would have noticed after 30 years of building engines.

Talk as much math as you want, it's called Poiseuille flow, I'm a mechanical engineer so this is a basic fluid dynamics concept. It absolutely does form drops. It may not be visible drops but on a molecular level it is, this is basic adhesion/cohesion. Every single restriction will cause a higher friction factor for the airflow, hence adding the larger boundary layer within the tube. It's not completely de-atomized to drops but with these intakes, it does add decrease atomization efficiency, enough to make a difference for sure. With a 95% certainty bet that if a different intake was used the 4 stroking symptom would clear up instantly.

Running lots of oil is a very old school way of thinking, which makes sense given your background. In your times' oil was not nearly as developed as it is now. Today synthesized oil technology has gotten to the point that you can even run 100:1 reliably all day long, which many do. Sure old conventional oils need the really heavy mix, but those oils are a thing of the past. Catching up with the times, a good quality synthetic can be run at 40:1-50:1 from the start, they're literally formulated for these ratios at break-in. I have about 400+ engines to prove it to, many with thousands upon thousands of miles as well. I have many china girls making 8+ hp running 10k all the time, WOT pulls, and the cylinders look flawless. What I'm trying to point out is the heavy oil mix isn't needed for break-in, in fact, it hurts long-time performance, you can run less oil at ZERO sacrifice of reliability nowadays. Sure your mix works for you, but I'm sure they would be running a lot better if you went a little leaner from the beginning. Can't even count how many engines I've seen fail from too much oil, its ridiculous.

 

[Street Ryderz]

Talk as much math as you want, it's called Poiseuille flow, I'm a mechanical engineer so this is a basic fluid dynamics concept. It absolutely does form drops. It may not be visible drops but on a molecular level it is, this is basic adhesion/cohesion. Every single restriction will cause a higher friction factor for the airflow, hence adding the larger boundary layer within the tube. It's not completely de-atomized to drops but with these intakes, it does add decrease atomization efficiency, enough to make a difference for sure. With a 95% certainty bet that if a different intake was used the 4 stroking symptom would clear up instantly.

Running lots of oil is a very old school way of thinking, which makes sense given your background. In your times' oil was not nearly as developed as it is now. Today synthesized oil technology has gotten to the point that you can even run 100:1 reliably all day long, which many do. Sure old conventional oils need the really heavy mix, but those oils are a thing of the past. Catching up with the times, a good quality synthetic can be run at 40:1-50:1 from the start, they're literally formulated for these ratios at break-in. I have about 400+ engines to prove it to, many with thousands upon thousands of miles as well. I have many china girls making 8+ hp running 10k all the time, WOT pulls, and the cylinders look flawless. What I'm trying to point out is the heavy oil mix isn't needed for break-in, in fact, it hurts long-time performance, you can run less oil at ZERO sacrifice of reliability nowadays. Sure your mix works for you, but I'm sure they would be running a lot better if you went a little leaner from the beginning. Can't even count how many engines I've seen fail from too much oil, its ridiculous.

Mechanical engineer huh ?I think your off a bit No? where did you get your off set intake from,every one I've seen is around 17mm I.D. and with a 14mm carb is just fine as most of these are stock or mild builds being asked about.The bend in the reed setups and extended intakes are the same thing just matched to the dia's being used!You are aware the engine doesn't really suck in the air right? Whats this magic oil your talking about,and do some research the scooter guy's run from 16-20:1 and kart guy's at 16:1 for a reason!

 

[Member 30059]

Mechanical engineer huh ?I think your off a bit No? where did you get your off set intake from,every one I've seen is around 17mm I.D. and with a 14mm carb is just fine as most of these are stock or mild builds being asked about.The bend in the reed setups and extended intakes are the same thing just matched to the dia's being used!You are aware the engine doesn't really suck in the air right? Whats this magic oil your talking about,and do some research the scooter guy's run from 16-20:1 and kart guy's at 16:1 for a reason!

Yes I am a mechanical engineer. The junk china offsets that most beginners use are these https://bicyclemotorworks.com/product/40mm-offset-intake-manifold/ the ID is closer to 15mm or so, they're no good. Reed setup intakes are fine, much less bends and are a straight shot to the reed. Opti2, redline, ipone, amsoil, the list goes on and on for good synthetic oils. Sounds like you need to do some research for yourself too. Look on any aprilia forum, 2 stroke R&D groups, etc and they run pretty lean mixes (iron cylinders aside).

 

[Street Ryderz]

Yes I am a mechanical engineer. The junk china offsets that most beginners use are these https://bicyclemotorworks.com/product/40mm-offset-intake-manifold/ the ID is closer to 15mm or so, they're no good. Reed setup intakes are fine, much less bends and are a straight shot to the reed. Opti2, redline, ipone, amsoil, the list goes on and on for good synthetic oils. Sounds like you need to do some research for yourself too. Look on any aprilia forum, 2 stroke R&D groups, etc and they run pretty lean mixes (iron cylinders aside).

Opti2 the oil that meets the lowest standards avail today,go on! Dude when you wanna talk REAL engines performance built go ask the people whom hold the records in small 2t classes none use less than 20:1 Fact,wanna talk to me and others like your the new school and know better get your facts straight! Some of here have been racing 2t's for decades and know what's going on currently as well!Hell I'd like to see one of your ten year old china girls with more than 10k on it,but wait what am I saying you haven't even been around long enough to do that LOL.

 

[Member 30059]

Opti2 the oil that meets the lowest standards avail today,go on! Dude when you wanna talk REAL engines performance built go ask the people whom hold the records in small 2t classes none use less than 20:1 Fact,wanna talk to me and others like your the new school and know better get your facts straight! Some of here have been racing 2t's for decades and know what's going on currently as well!Hell I'd like to see one of your ten year old china girls with more than 10k on it,but wait what am I saying you haven't even been around long enough to do that LOL.

I and a million other people would beg to differ. Theres better oils out there, but opti2 is one of the best easily available oils there is. That is flat out false LOTS of high power engines running less oil than that. The big hp kart motors running a lot dont last too long, theyre rebuilt all the time. Why is it you have such a hard time accepting that someone may be doing something better than you? There are a lot smarter poeple that you in this world. Just because you're old doesnt mean you know absolutely everything, it just gives you more time to be stubborn and make it miserable for everyone else. Give it up old man, you're not always right.

 

[Member 30059]

I do agree that more powerful engines often have to run a heavier mix due to the extremely high rpm, but many dont. Ans regaurdless of what high hp engines are running, we're talking about a bt80. One of the slowest 2 strokes in existence, a daily cruiser motor. Hes not going 20k rpm plus, so theres no reason to run the extra the oil. A simple leaner mix will do him better than cheech and chong coming out the exhaust

 

[Street Ryderz]

I and a million other people would beg to differ. Theres better oils out there, but opti2 is one of the best easily available oils there is. That is flat out false LOTS of high power engines running less oil than that. The big hp kart motors running a lot dont last too long, theyre rebuilt all the time. Why is it you have such a hard time accepting that someone may be doing something better than you? There are a lot smarter poeple that you in this world. Just because you're old doesnt mean you know absolutely everything, it just gives you more time to be stubborn and make it miserable for everyone else. Give it up old man, you're not always right.

LOL what are you doing better than anyone? These are the simplest form of engine out there and nothing your doing is new! What happened to your 14k+ 18hp engine? last I saw it only turned 11,7 and surely wasn't making any where near 18hp,Funny how the ktm 65 does 76 easily with only 16hp still had a 64t gear !

 

[Member 30059]

LOL what are you doing better than anyone? These are the simplest form of engine out there and nothing your doing is new! What happened to your 14k+ 18hp engine? last I saw it only turned 11,7 and surely wasn't making any where near 18hp,Funny how the ktm 65 does 76 easily with only 16hp still had a 64t gear !

Not saying me specifically, just in general. Its obvious your ego gets the best of you sometimes. Why are you talking about my am6, to change the subject?? Its great FYI, finally have a clutch sorted that will actually hold the power. So far 12k is where im pegged, likely from the stock cdi is way to advanced up high. Were getting there. I am still confident on the 18hp, or at least damn near close to it. Theres literally no comparison of speed to ktm65. It has a 6 speed trans. However its max rpm is around 12.5k and makes about 15-16hp. That's definitely comparable to where im at. And funny you mention the ktm 65, you know the engine that is manufacturer suggested to run 60:1. Huh interesting. Not saying I would run 60:1 but hey ktm knows best