Advice needed for challenging daily commuting.

RB55

Active Member
Joined
Sep 18, 2019
Messages
168
Wow dude I know you're just trying to help a guy but you need to get your fact's straight other wise you will just confuse him.4 stroking has nothing to do with port volumes,the design or construction.4 stroking is solely due to being rich/over fueled and the spark not being strong enough to burn the complete charge within it's cycle.A 2 stroke engine having only 2 strokes to complete all the functions required cant retain left over charge and add more air in the next stroke,while the charge is introduced to the combustion area via the transfers the piston is on the down stroke of it's cycle and is done so with the pressure created by the descending piston,this pressure helps to expel any exhaust gasses left in the chamber weather fully combusted or not,it's impossible to add more air to it on the next stroke.So 4 stroking is solely due to being over fueled/rich and too weak of spark and the best way to solve this is by having the correct jetting so that the air/fuel mix can be fully combusted cleanly.
Then explain to me why when I heightened and enlarged the exhaust port of my 66cc HT, which was jetted at 0.61mm with the stock carburetor (extremely lean for HT and jetting below that would make the engine rev out of control and stop from being too lean) and had a free-flowing exhaust my 4-stroking almost disappeared compared to before, when it 4-stroked at all RPM ranges nonstop. I'm not making this s*** up, why would I anyway I have nothing to gain here lol. A rich air/fuel mix will make an engine 4 stroke but there's a reason why 4 stroking only occurs at high RPM and load. Most people who have issues with 4 stroking will say that it only happens beyond 3/4 throttle. If the issue was solely the air/fuel mix being too rich then why would it only happen at high RPM and load??? The air/fuel mix should be similar at all RPM ranges and if anything at high RPM the mix would become leaner because of the increased volume of air passing by the jet. The reason is because the messy porting on HTs is insufficient at high RPM and load to properly extract exhaust gasses and inject a fresh air/fuel charge. Therefore, at low RPM and load the engine will not 4 stroke since exhaust is leaving and fresh charge is entering properly but at high RPM and load the exhaust gases begin to build up inside the engine while an insufficient amount of fresh charge is entering the engine, leading to excessive dilution of an insufficient intake charge with exhaust gasses which prevents the charge from burning. An extra stroke is required to extract the exhaust gasses and suck in enough intake charge. Leaning out the air/fuel mix is one way to fix 4 stroking since the increased amount of air mixed in with the intake charge allows it to burn more easily even when diluted.

If you don't believe me, just look at this post: https://motorbicycling.com/threads/four-stroking-physics-and-fixes.49842/
 

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,160
Then explain to me why when I heightened and enlarged the exhaust port of my 66cc HT, which was jetted at 0.61mm with the stock carburetor (extremely lean for HT and jetting below that would make the engine rev out of control and stop from being too lean) and had a free-flowing exhaust my 4-stroking almost disappeared compared to before, when it 4-stroked at all RPM ranges nonstop. I'm not making this s*** up, why would I anyway I have nothing to gain here lol. A rich air/fuel mix will make an engine 4 stroke but there's a reason why 4 stroking only occurs at high RPM and load. Most people who have issues with 4 stroking will say that it only happens beyond 3/4 throttle. If the issue was solely the air/fuel mix being too rich then why would it only happen at high RPM and load??? The air/fuel mix should be similar at all RPM ranges and if anything at high RPM the mix would become leaner because of the increased volume of air passing by the jet. The reason is because the messy porting on HTs is insufficient at high RPM and load to properly extract exhaust gasses and inject a fresh air/fuel charge. Therefore, at low RPM and load the engine will not 4 stroke since exhaust is leaving and fresh charge is entering properly but at high RPM and load the exhaust gases begin to build up inside the engine while an insufficient amount of fresh charge is entering the engine, leading to excessive dilution of an insufficient intake charge with exhaust gasses which prevents the charge from burning. An extra stroke is required to extract the exhaust gasses and suck in enough intake charge. Leaning out the air/fuel mix is one way to fix 4 stroking since the increased amount of air mixed in with the intake charge allows it to burn more easily even when diluted.

If you don't believe me, just look at this post: https://motorbicycling.com/threads/four-stroking-physics-and-fixes.49842/
This makes no sense to me you're combining high rpm and load as if it has effect on how the exhaust gases get expelled? I have video on this site of stock engine's doing 10-12k with stock port timings and setups so I'll have to agree to disagree with that theory all together.Also I tried to tell you this before but 0.61mm is not lean jetting ,a number 71 drill bit fit's a number 68 jet (just) and it's measurement is 0.63mm so if your at 0.61mm that is like a number 67 jet and not lean but rather normal so again have to disagree there.
This bike in the video is stock and when I lift a bit and take the load off or ahead of getting on it just cruise speed is when you hear 4 stroking and this is proper 4 stroking and what you want to hear! It has nothing to do with load at high rpm the pressure waves take care of it at the rate witch matches the rpm regardless of load.
 

RB55

Active Member
Joined
Sep 18, 2019
Messages
168
This makes no sense to me you're combining high rpm and load as if it has effect on how the exhaust gases get expelled? I have video on this site of stock engine's doing 10-12k with stock port timings and setups so I'll have to agree to disagree with that theory all together.Also I tried to tell you this before but 0.61mm is not lean jetting ,a number 71 drill bit fit's a number 68 jet (just) and it's measurement is 0.63mm so if your at 0.61mm that is like a number 67 jet and not lean but rather normal so again have to disagree there.
This bike in the video is stock and when I lift a bit and take the load off or ahead of getting on it just cruise speed is when you hear 4 stroking and this is proper 4 stroking and what you want to hear! It has nothing to do with load at high rpm the pressure waves take care of it at the rate witch matches the rpm regardless of load.
First of all...
what you’re saying that “high RPM and load have no effect on how exhaust gasses get expelled” makes no sense. Physically speaking, less and less time is available for exhaust gasses to leave the engine through the port since it is open for a shorter and shorter amount of time as RPM’s increase. Just ask any tuner why they mess with camshafts and valve timings for max HP at high RPM. Or for that matter, why valve size, number, timing and lift makes drastic differences in a 4 stroke engine’s performance. And also why high performance cars have custom exhausts and engines with aggressive cam timing at high RPM (ex VTEC)?? Finally, 2 stroke tuners port engines for high RPM.

Yes a stock HT can hit 11K when you pull the clutch lever and rev it like hell. For that matter my weed whacker engine could probably do 12K. I don’t get your point. Also a properly tuned 2 stroke engine should never 4 stroke, period. I’ve plenty of mopeds and vespas with about the same CC engine as our beloved Chinagirl that never 4-stroke for a millisecond.

Lastly, I don’t know where your getting your numbers from jet sizes. You said “71 drill bit is 0.63mm” it’s actually 0.66mm. Stock HT jet is 70, meaning it’s 0.70mm - dropping down to 0.61mm means that the corresponding jet size would be 0.61. I don’t think you understand how jet sizing works.

25CB981E-0D54-4B4C-A3BC-465BEDAE1DD5.png
11A76C45-35DD-4827-A31D-EAE56E01BC05.png
 

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,160
First of all...
what you’re saying that “high RPM and load have no effect on how exhaust gasses get expelled” makes no sense. Physically speaking, less and less time is available for exhaust gasses to leave the engine through the port since it is open for a shorter and shorter amount of time as RPM’s increase. Just ask any tuner why they mess with camshafts and valve timings for max HP at high RPM. Or for that matter, why valve size, number, timing and lift makes drastic differences in a 4 stroke engine’s performance. And also why high performance cars have custom exhausts and engines with aggressive cam timing at high RPM (ex VTEC)?? Finally, 2 stroke tuners port engines for high RPM.

Yes a stock HT can hit 11K when you pull the clutch lever and rev it like hell. For that matter my weed whacker engine could probably do 12K. I don’t get your point. Also a properly tuned 2 stroke engine should never 4 stroke, period. I’ve plenty of mopeds and vespas with about the same CC engine as our beloved Chinagirl that never 4-stroke for a millisecond.

Lastly, I don’t know where your getting your numbers from jet sizes. You said “71 drill bit is 0.63mm” it’s actually 0.66mm. Stock HT jet is 70, meaning it’s 0.70mm - dropping down to 0.61mm means that the corresponding jet size would be 0.61. I don’t think you understand how jet sizing works.

View attachment 91913View attachment 91914
LOL your charts are not right!The number 68 jet,the number bit 71,and it's measurement!This is a 2 stroke not a 4 and time over area along with port volume is plenty to expel exhaust gasses to 12k stock I just showed you that!That's funny you don't think a 2 stroke shouldn't 4 stroke because in my 40+ years of building/tuning/racing 2 stroke engines in various forms all the factory tuners would set my stuff up that way! Are you doing 53 with a stock setup for 2 years now?
 

Attachments

  • 20191223_233745.jpg
    20191223_233745.jpg
    48.2 KB · Views: 65
  • 20191223_234107.jpg
    20191223_234107.jpg
    71.2 KB · Views: 71
  • 20191223_234741.jpg
    20191223_234741.jpg
    84.9 KB · Views: 66

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,160
Does no one else see the error's in the charts above? The first one has a #80 at the top of list and show's it's measurement in mm as being .3429 this is the smallest measurement of the list and the largest jet! The second chart shows all the jets coinciding with the drill number and that also is very wrong since the smallest numbered bit is number 80 and the largest is number 61 and we all know that a #61 jet is smaller/leaner than a #80 jet.
 

RB55

Active Member
Joined
Sep 18, 2019
Messages
168
Does no one else see the error's in the charts above? The first one has a #80 at the top of list and show's it's measurement in mm as being .3429 this is the smallest measurement of the list and the largest jet! The second chart shows all the jets coinciding with the drill number and that also is very wrong since the smallest numbered bit is number 80 and the largest is number 61 and we all know that a #61 jet is smaller/leaner than a #80 jet.
alright, idk what @Street Ryderz is using as his measurements. Wire gauge and jet size are NOT the same thing!!! If @Street Ryderz is using wire gauge drill bits, then he is correct. But wire gauge is not the same as jet diameter. @Street Ryderz said "we all know that a #61 jet is smaller/leaner than a #80 jet. " That is true HOWEVER the wire gauge scale is in REVERSE meaning that a SMALLER NUMBER actually designates a LARGER DIAMETER and a LARGER NUMBER designates a SMALLER DIAMETER. If you don't think this is right then look at the link below. So, how would a #61 jet be leaner then a #80 jet according to your wire gauge measurements??? It would actually be more than twice the diameter...

With jets, the jet number designates its diameter in mm. Again if you don't believe me look at this jetting article attached below. It states, "For example, a jet may be stamped (on its head) with the number 30. This indicates that the jet's size is 30 mm". For jet sizes below 1mm the jet number designates its diameter in hundreths (1/100) of a millimeter. Look at the capture below if you want proof.

Can we all agree on using mm instead of wire gauge? It's confusing as hell...

Also my 6 year old 2 stroke Echo weed trimmer (good quality) along with my two 2 stroke leafblowers (very bad quality) have never 4-stroked once in temperatures from -20F to 95F in KY with a 40:1 oil/gas mix. Even at full throttle for hours and hours and during warm-up. I use them heavily throughout the year for landscaping work. The same applies to my old 2-stroke dirtbike. So don't tell me that a 2 stroke engine should 4 stroke...if it does something isn't right unless the manual specifically states it should. Finally what you keep saying that "exhaust is removed from the engine the same at all RPM" is bogus. Just look at how the piston moves up and down through the exhaust port...as RPMs increase the piston will be below the top of the exhaust port for a shorter and shorter interval of time. A bone stock Chinagirl is heavily limited...porting alone will not double your HP but will still help. For example Zeda sells a ported version of their Zeda 80 which produces 2.9HP stock compared to the 2.4HP a stock Zeda 80 produces (all company's dyno numbers not mine). Now get a bigger carburetor, an expansion pipe/free flowing exhaust, increase compression on the head...and then porting will allow the engine to really breathe and run. A ported zeda 80 with a mikuni 18mm carb and an mz65 expansion chamber produces 4.75HP...the engine can suck much more air in and blow much more exhaust out. Why is it that so many people port these engines AND other 2 stroke engines to get more power?? plenty of 2 stroke experts do it...


jets.PNG
 

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,160
Wow you've got alot to learn! I don't use wire gauge's it's a numbered drill set with international standards,as your first chart claims to reference but is wrong!Next your a fool if you think jet numbers and mm are the same as they are not, the picture shows a dellorto #68 jet and the numbered bit 71 along with the micrometer showing it's actual measurement.What part of the bike in the video doing 53 is a stock engine did you not understand? Look up time over area for 2t porting because as rpm increase so does cylinder pressure and that pressure pushes the exhaust out faster than is needed in most cases,then look up what occurs during each stroke and the relationship the pressure waves play because your referring to amazon ad's and sh*t articles writen by unknowns like they are valid.Next go buy a numbered bit set from 61-80 as these are what is mostly used for jetting because obviously you don't use them or you would know your talking out your ass!Also by the way I have proof on the dyno that a stock engine can make 5 rwhp and just over 6 at the crank so again your way off!
 

CrazyDan

Well-Known Member
Joined
Jul 9, 2016
Messages
3,198
I hate meters and feet mixing. I wish the world went to a standard for distance, temps and weights. Meters and celsius and grams makes more sense, it's all easier for simpler folks to figure out. It's all divisible by 10. American measures seems like it tries to be hard, lots of americans have problems with it.
 

Street Ryderz

Well-Known Member
Joined
Oct 14, 2016
Messages
4,160
I hate meters and feet mixing. I wish the world went to a standard for distance, temps and weights. Meters and celsius and grams makes more sense, it's all easier for simpler folks to figure out. It's all divisible by 10. American measures seems like it tries to be hard, lots of americans have problems with it.
I couldn't agree more!
 
Top