This was fun. Hopefully there will be more of these and follow up vids of you going over the questions/answers

Man, this has been on my bucket list for so long. Q1: A B C Q2: C Q3: A B C Q4: A Q5: A B C Q6: A B C Q7: B C Q8: A B C

I allready have your calculators, just finished a build with balanced cranck, ported cylinder, retarding the stock ignition with capacitors, stock tweacked carb and chinese clone exhaust and it rips really hard, all the numbers match with the performance I got, would be nice to show you all the infos on the build and see your thoughts on it so I decided to answer the quiz! In order of greater importance Question #1 A, B, C detonation is THE main limiting fator, squish volume can control velocity in low and mid range and affect temps as well Question #2 C, B, A it depends more on the port map, for example, I use the common base numbers to estimate the volatility and velocity of the gas Question #3 B, A, C if the carburetor is too large, the airflow velocity will be too low. This will not create enough suction at the needle jet, and the engine will not get enough fuel. Question #4 A I think mineral and synthertic oils are fast burn, castor is definitely not fast burn Question #5 A, C, B Question #6 C, B, A love the return wave visualization from your calculator, helps a lot! Question #7 B, A, C Question #8 A, B, C It really affects the return wave strenght

i think all are correct for all the questions i read. I do want to purchase a calculator anyway so I'll be emailing you shortly

How to buy all calculate

how much deegres should 2 transfer ports be to give decent performance with 185 degrees exhaust port

I have spent a bunch of time in your web site - just a massive amount of interesting information I was wondering for KTM TPI bikes if you would just stick to the recommended motorex cross power 2 or use something else that’s easy to purchase? Again thank you for all the great information

Flying my Paramotor I got an engine out and landed in a football field. While descending i pull started it so many times I bruised my arm pretty bad. Ended up being a sliver of plastic that clogged my main jet. The engine would not start because the main jet was clogged.

I've independently confirmed this idle off idle tuning, going down rabbit holes and then empirically testing these concepts with my specific application, ABA testing needles, float height, etc. I confirmed it with a wide range O2 lambda sensor. Michael Forrest is a 2 stroke treasure and should be supported. I have experience as an automotive engineer calibrating engines, if you aren't that experienced here, he has a bunch of tools to help figure this stuff out.

You speak the truth, you've done empirical testing which is of great value unlike a lot of the book reader repeaters with no actual real experience on the topic. I greatly respect your knowledge and experiences. To add from my experiences: My experience is with calibrating car engines, learned by doing on two boosted cars of mine, hundreds of flashes and hundreds of hours tinkering, with successes like making 500 bhp with a 2.4L ecobox engine. That landed me a job doing engine development in the dynos professionally where my engine projects all used cylinder pressure transducers and hope someday these become affordable (like they come standard on factory cars). In addition we used a powerful tuning aid that is the wide band O2 lambda sensors to measure lambda and AFR. I also used this tuning privately and in addition engine tuning companies require access to wide range O2 readings. I thought I was clever bringing O2's into 2 strokes, however I have recently found a flaw with my approach in using 4 stroke automotive AFT targets for 2 stroke small engines. I may be able to accurately measure AFR, however I don't actually know what AFR is good for each load with a 2 stroke or with my 2 stroke engine model. In addition, there could be an offset in my AFR measurements based on the location of the O2 sensor (in fat part of pipe). I run a Paramotor that spins a propeller, the propeller spinning on the ground making static thrust is a very good analog of in-flight loads. Recently I found a hole boring through my piston from detonation, right above the spark plug. I've been running 93 octane + boostane making it 100 octane fuel. On my Dyno stand with the O2 sensor, I targeted about 14.7:1 at idle and cruise rpms, and 12:1 at WOT. I correlated these numbers with the EGT readings. There is good correlation when you are near stoichiometric AFR, however EGT can read high if you are too rich. New piston on order and going to get back on the Dyno stand to develop / validate more rich tunes at higher loads.

on my Facebook forum "Two Stroke Tuning/Modifying" Nick Rhine had this to say; "spot on knowledge. How I have jetted my race bike engines I have developed for 50 plus years. Over 200 Championships and three 2 Stroke world titles. The World titles were won at Glen Helen by the way." He told me that he jets for the sweet spot on a medium sized uphill. kzfaq.info/get/bejne/fMt0Z7J0q96tj2Q.html

a dyno won't show the true peak horsepower unless the jetting is changed to match the load of the dyno, or the load of the dyno is changed to match the jetting of the bike. I think dynos are a useful tool but i wouldn't use one to select the main jet.

Also it is possible that the type of engine oil used can close the gap between those two peaks, possibly an all synthetic oil, or an all group two oil, or like the Kawasaki oil which is a combination of the group two and synthetic. dragonfly75.com/moto/oilpower4.html

This comment was from the previous version of this video. @markburden6265 : "Great video Michael....thumbs up dude ....top end jetting feel is so important..I run castor and jet with feel uphill ....everything is a compromise...I jet for engine life as well as performance." My reply : "yes, jetting is a combination of getting good peak power without ruining reliability. I forgot to include that if you happen to jet it so lean to get peak power that it causes the oil to start burning on the piston, and you don't want to change to a more heat resistant engine oil, then it's probably because the squish velocity is too low."

What I recently found out is that the motorcycle "typical timing curve" applies only to engines with a squish band head which increases the air/fuel swirl speed as RPM increases which accelerates the combustion. Heads without a squish band (like our stock ones) need an ignition curve that maxes out and then maintains that advance thru the rest of the RPM range. The latest Jaguar CDI allows you to select that curve for a stock head. This also applies to heads with too much squish clearance which has too little squish velocity. Also the higher the engine compression, the less advanced the timing needs to be. The stock CDI has timing that is suited to an engine with low compression and no squish velocity (due to lack of a squish band) although its spark voltage is too low for my tastes. More spark voltage means less misfires. This increases engine power. There's a study on this subject linked to on my CDI page.

I would like to ask your opinion about Klotz Supertechniplate. I see on your website that you won't use your ratio calculator for it because it has artificially increased viscosity. In one of your videos you show it as a really good oil. I assume that is 80% PAG group 4 oil and 20%castor. I also assume that there are no group 1, 2, or 3 oils in it because it will mix with alcohol. I appreciate your drive in all you do concerning proper mixture in all conditions, keep up the good work!

Is there a downside to just retarding ignition? besides for loosing a bit of low end of course. Currently low on funds and that custom Cdi sounds expensive, though I’m sure it’s worth it. Just trying to keep detonation down for cheap. Thanks a bunch , your videos and website are the best source of knowledge for 2 strokes and these little bike engines. Hope you are do well.

HOW DO YOU ADVANCE THE TIMING

if someone have cavity in tooth should he remove it or kill the bacteria is enough?

Of course the synthetics have about twice the viscosity as group 2 mineral oil at upper cylinder temps and so you have to add twice as much group 2 oil to the gas than what you'd add with synthetics. I use Synplus on my air cooled street bike at 27/1.

👌

If any of you think this is crazy, using a pure mineral oil in a dirt bike, please consider that many people have successfully used Yamalube 2R in motocross bikes and it's only around 67% group 2 oil and 29% group 1 oil. It has no synthetic in it. Also Golden Spectro is a classic old time racing oil and its mostly group 2 oil with a little group 1 oil in it. It has no synthetic in it. I'm afraid that once again we've been the victims of oil manufacturer propaganda and general rider misconceptions that are shared amongst riders.

Of course rich jetting greatly contributes to spooge, but if you're using an oil with synthetic but you don't have any spooge then either 1) your silencer is catching it all, 2) your jetting is too lean. Some spooge is normal, I just don't want the excess amount that synthetics cause. My engine is air cooled which gets hotter than water cooled but using Synplus gives me long engine life. It's all about the NGK heat range. That indicates how hot the engine is getting. If you're not sure about your heat range then just look at the color change line on the ground electrode. It should happen halfway along the electrode. Closer to the end means the heat range number is too high, and closer to the threads means the heat range number is too low.

As pertains to the jetting chart; I am surprised that the main-jet is relatively non-responsive per 10% move as many others on the chat are.

does that calculator work for Keihin carbs also??

Clear, concise and directly to the point. Great presentation, as always. Thank you for sharing with the world. I bought an Artic Cat M1000 with a twin 999cc 2-stroke engine. Specs say 162HP and 120lbs/ft of torque. I stripped the sled all the way down and salvaged the engine, electronics, and all sub systems to build a super powerful minibike. Looking forward to using your software to build the header pipes. Thanks again.

I just tested the #3 porting engine and it only got up to 7300 RPM. The angle of HP increase needs to be around 20 degrees past 7300 on my setup but the graph shows 15 degrees which is why it couldn't go farther. So if I want to go faster I need to lower the RPM range of the pipe by lengthening its header so the pipe boost can assist the porting power there. This has been a great example of how things sometimes are backwards from what you think they will be, and how there are exceptions to the rule. Before this I would of always said that raising the ports will increase the high RPM power, but in this case raising the transfers lowered the blowdown too much. Also raising the transfers raised the pipe powerband by around 250 RPM according to my pipe calcuator, which moved the pipe powerband even farther away from where it needs to be. It's very important to synchronize the pipe and porting.

what do you recommend for joinig the sheets at home? I`m gonna try a brass rod with mapp torch. Do you know a better alternative?

I haven't experienced this; but I have experienced the UFO's. Infact I coppied them using quick metal that you Kneed. Then dremel shaped it. Certainly changed the exhaust note to very crisp. Yamaha RD 350 air, already fitted with chambers. Even more crackle. Yet to test ride.

What Is the price for the CDI ?

What I should of included: 1) motocross bikes usually already have near ideal porting, 2) the pipe length sets the top RPM so usually it needs to be shortened but mine was already the right length to allow 8000 RPM max, 3) the porting calculator uses more info other than the exhaust port, including transfers/boost widths and duration, compression ratio of engine and crankcase, and it estimates the port durations just based on conrod length and mm above ports (to the TDC location).

What Is the price of the CDI

Oh my god! My Yamaha TZR and my old post on facebook:) 2:48. I have learned a lot since then and also run an EGT probe. I have learned that 2 storke world is filled with know it alls and black magicians. Thank you for that video mand yes, back then I was a complete noob.

God you talk so slow. Nice video though learned a lot

Excellent vid

my bike is oil injected.... so i error a bit rich havent fouled a plug in 5000 miles . 74 kawi G5 100cc

Shaved head to increase squish really woke up my ktm 380. Made jetting the bike exponentially easier as it smoothed out power dips throughout rpm range. Was years ago and dont remember the numbers of what was removed so dont ask me!

@2:39 DGY Sports (now extinct) formerly located in Downers Grove, Illinois, USA, corrected my overly-rich 1998 Kawasaki KX250 by inorming me via the telephone to raise the needle-clip one position. Night and day difference. It too, for a mediocre rider such as me, had from idle to 7500 RPM grunt. I could take off in fourth gear on hardpak-with inadvisable slipping of the clutch. I was told by DGY that Kawasaki, though the KX, brand new, came with NO WARRANTY, neither expressed nor implied, off the showroom floor. The factory set the bike up rich so that minions such as me would foul the sparkplugs in lieu of blowing up the engines. Gosh-I miss that bike....😐

Why do people install a piston with the intake window in the CR250R engine which is a case reed engine?

The Solution website: www.dragonfly75.com/eng/

Hi do you do a perfomance cdi for the kx125a ?

I sell an expansion chamber calculator for $25 (dragonfly75.com/moto/portsMS.html) and I can do all the computer work for you for $75. My email is [email protected]

Stainless steel wool. My stock Ax hits the power band at about 7k rpm, where it pulls much harder, but I also lowered the gearing (13x42). Then I have another AX118 with an FMF enduro pipe with a very long belly and shallow cones. That pipe makes it downright violent at about 4k-5k rpm, but is gutless after 7k and won't even rev past 7k in 4th on a long, steep downhill. How high did yoh AX rev with no load?

Interesting video but it makes me worry a bit. I used your 2 stroke exhaust calculator to design good allrounder pipe for my suzuki Gp125. It has the same stock exhaust as that AX100 you showed in the video. Would I be better off leaving the stock pipe on or continuing with the custom one?(I already tacked the sections together but will need to sacrifice the stock pipe for the initial bend) And what is your opinion on rasing the compression ratio of the Gp125 from 6.9:1 to 10:1.?(it's a dome chamber with no squish band). Keep up the good work Mr!

You are a very smart person Mr. Forest. Thanks for sharing some of your vast 2-stroke knowledge.

I believe that’s why exhaust ports were widened with bridge ports and chamfering to allow exhaust pressure to reduce enough to open the transfer ports.

fucking hell man. Spend 3 hours going through this bullshit website. this shit is not on there.

For how much time you put into this, your website is fucking awful man. use square space or something. I cant find a fucking t hing

There is no link anymore to these