Yamaha ET250 Modification

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Desertduler

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Here is a modification which I did last year and I am still waiting for my buddy to bring his kart over to my shop so that we can install the engine and I can set up the jetting and test out this modification.
Then we will race together out on the dry lakebed and see if he can out run my my flying red pig.
https://www.youtube.com/watch?v=ha7NNU4ep9A
https://www.youtube.com/watch?v=2e6jmg-aKEg
https://www.youtube.com/watch?v=hSRbon_5Lss
https://www.youtube.com/watch?v=-0B0EgJ2j5A
https://www.youtube.com/watch?v=nn1v3BvmA5M
https://www.youtube.com/watch?v=Tb8_WzWCG_U
https://www.youtube.com/watch?v=ymCECBAVrmU
https://www.youtube.com/watch?v=Qm2IX0Zopho
 
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Desertduler

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landuse said:
Nice going. Hopefully he brings his kart around soon
Click to expand...
Matter of fact he is going to bring it by tomorrow so we can install the engine and I will set up a baseline for the jetting because a reed valve induction engine requires a richer mixture than a piston ported inducted engine due to the fact of a reed valve engine does not have the intake reversion and fuel standoff in the intake tract that a piston ported inducted engine has. During the intake cycle of a piston ported engine the engine draws in partially the atomized air fuel mixture that was spit back out of the intake tract during the previous intake cycle thus adding to the air fuel mixture that the carburetor is producing by itself at that time where as a reed valve inducted engine has the reed valves that act like one way check valves which do not permit reversion during the intake cycle so the engine is drawing in just air from the atmosphere and not any atomized fuel stand off so in order to achieve the correct air fuel mixture we need to go way richer most certainly the main jet. For instance I use a 34 mm Mikuni carburetor on my Rotax 277 that I converted over to reed valve induction and the main jet that was in the carburetor for the piston ported induction was a 180. After the conversion to reed valve induction I had to use a 270 main jet if I did not change the jetting the engine would have seized at wide open throttle in no time at all.
 
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Desertduler

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Snow in my location has put a delay in engine testing. I will post again as soon as I can with this modification.
 
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Here we were able to test out this engine today a little. The owner/driver said that there is a huge difference in power. We will soon be able to take our karts out on the lake bed and test them against each other and I will make a helmet cam video of our racing each other.
https://www.youtube.com/watch?v=_g6dVMeC7iM
 
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NewbCarter said:
Interesting how smoothly it pulls thru the whole rev range .
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By converting this engine to reed valve induction the engine has a wider power band which we need with one gear ratio. The gearing is quite tall for use on the lake bed which is a wide open place. This engine with the tall gearing that it had when it was piston ported induction had terrible bottom end power and the engine would load up and sputter and hardly move until it was able to pick up enough speed to get close to higher RPM's. I have this engine jetted way rich at the moment as a safety measure right now and I will drive it myself and set up the jetting on the dry lake bed and we will go from there with more testing and compare how well this engine runs now racing against my reed valved 277 Rotax.
Before when we raced against each other I could give him a huge head start on a large course and I was able to catch and pass him within a couple of laps because of my engine had a wider power band
than his engine at the time. We will see what happens.

---------- Post added at 05:15 AM ---------- Previous post was at 05:07 AM ----------

In this video (which I am sure some of you have seen already) If you look real hard way ahead of me you will be able to see how far of a head start I gave my friend when his engine was piston ported. You do not have to watch the entire video to be able to see how long it took me to catch and pass him. I will use this video as a reference in this thread as a before and after modification. You can skip in the video to 2:27 and see the difference between my reed valve inducted Rotax 277 and his engine when it was piston ported. There is a huge difference in the low through mid range power delivery and that is why I could reel him in plus I weigh 70 more pounds than him.
https://www.youtube.com/watch?v=FaTL65TtVaI
 
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NewbCarter

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Hmm .. how doable ( or more precisely worth ) is this for smaller engines ? Im yet to fix up the KT100 i have ... tho it doesnt seem to be the best platform for modding ...

Only thing id do on that engine now is a muffler of some sort:kewlsmiley:
 
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Desertduler

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NewbCarter said:
Hmm .. how doable ( or more precisely worth ) is this for smaller engines ? Im yet to fix up the KT100 i have ... tho it doesnt seem to be the best platform for modding ...

Only thing id do on that engine now is a muffler of some sort:kewlsmiley:
Click to expand...
Most piston ported engines can be converted to reed valve induction.
It is not a easy task but for me it is worth it. I did this for my friend so that we both can race together and his engine will be more competitive.
There are other karts that race with us too with different engines.
Yes he needs a muffler but ear plugs work too! :thumbsup:
 
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We have set a date of April 7 to head out to the dry lake bed and I will dial this engine in.
Then we will do some racing on a course that we will lay out and we will be able to compare how much better this engine performs after this conversion. I will be taking out my red kart with my modified Rotax 277 engine and I will also take with me my Wife's yellow screaming rotary powered kart.
 
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Desertduler said:
We have set a date of April 7 to head out to the dry lake bed and I will dial this engine in.
Then we will do some racing on a course that we will lay out and we will be able to compare how much better this engine performs after this conversion. I will be taking out my red kart with my modified Rotax 277 engine and I will also take with me my Wife's yellow screaming rotary powered kart.
Click to expand...
Postponed due to rain. :censored:
 
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