arthurmoto1

There was a lot of work with 250 ccm engine but it is almost finished now. But I can not attach new photo because of 171 kb size restriction. I'll try later to give you more information. I personally have final race of MotoRallyCupUkraine during next three days and then could pay more attention to this topic. Cheers!

My friend have got broken leg when he was landing on paratrike because of invisible concrete part in grass. That is why it was some delay. But everything is OK with small engine. He is just flying around. It was paramotor race once this year because of COVID and we have got 2 place but it is obvious that we need more power. So the next stage is to finish 250 ccm engine.

There are bad news- the leg was broken during landing because of concrete part in the grass. And good news - there is new front end with suspension now! But I can't attach photo... something is wrong.

There is some progress with large engine

https://www.youtube.com/watch?v=mW5zVN4G8mE

Hi everybody! So have good news, it was first fly yesterday. Everything is OK. The trouble with carb was solved with additional fuel pump. Engine is powerful but needs some changes in transmission. So wait for video! Cheers!

First fly short video https://www.youtube.com/watch?v=7S07EzjMmos

Sorry we have some delay because of paratrike building. Fortunately the trike has had the first sky time yesterday! Wait for video and for news soon.

Good news! It flyes but engine is a real beast! I think we have to make something to switch off one cylinder in the fly because it is too powerful. Wait for video. It is enough to have the engine just idling to move but 1/2 throttle seems to make possible to turn trike over!

Thanks a lot! The same idea I was talking about.

OK! Yesterday I was trying to find the solution of the carb issues and have found that it has very simple design. Such carburetors like Walbro are intended for use with not modified engines that have RPMs not higher than 6000 preferable less. They have only two metering systems, one for low RPMs and another for high. But this statement is not correct. It means one for lower and another for higher RPMs. So in reality you can adjust this carb on the middle range 4000-4500 RPMs but it will be lean on 7000 RPMs. Or you can tune it on 7000 RPMs but it will be rich on 4000 RPMs. You know the common motorcycle float type carburetor has needle for mid range and main jet for top range and in many cases accelerator pump. Google says the only solution is to use additional low pressure pump but I don't think so. So solution is to add one more jet for high RPM range.

And there is a problem with Walbro carburetor at 4000 rpms. It is so rich that the mixture explodes just inside the chamber! Under 3500 and higher 5000 rpms it's OK.

We were trying to use our old style exhaust but it is not suitable for such wide exhaust port timing this cylinder has. And you can see 250 cc motocross chamber for comparision.

Hi everybody! So good news! I was trying to check the dimensions of chamber and the decision was that it was too short. We are trying the engine to be the best at 7000 rpms but that pipe was suitable for 12000 rpms. OK! Yesterday some parts were welded additionally and the result is suitable but not perfect. It is very strong on 7800 rpms but not lower.

I was trying to add video but something went wrong. Once again. https://www.youtube.com/watch?v=7FdBpMeSFIs&t=31s

Hi! Bad news! The first start of this engine was with the use of our old style exhaust and was absolutely great. But with new chamber we have lost approximately 1000 RPM of high range. So it is needless to say how difficult now is to make changes to produce new matrix and so on. But the aim of this project is to develop the best race engine ever and to win every championship and cup stages we can participate this year in our country so we have to make everything quickly. I have video but sorry the language is Russian. You can see the weight of the engine. I'm going to make English version after exhaust repair to show you. Cheers!

The next step is to add the silencer.

And at last we have nice chamber.

So you need matrix and 100000 kg oil pump to make hydroforming pipe. We take two sheets of 0.5 mm steel and weld them carefully together then pump them with oil inside the matrix. This is the photo of the first attempts.

Next step is expansion chamber. Everybody knows to make good power it is necessary to have 1/2-valve design and do not use mild steel. We decided to use temperature resistent stainless steel and hydroforming process. It was some period of tests and now we have obvious sucess. Wait some days and I'll show you photos.

The rollers have to be done with proper accuracy and after the binding the ends of tube (20 cm) are junk.

Sorry it's too late! My buddy gave it back to the metal workshop. But I can tell you it is very simple and consists just of three rollers and motor that drags the tube. Your task is to move the middle roller with the screw during the process. And the tube is of 52 mm diameter and 1 mm thickness (I was wrong about 1.5 mm).

You can see next step.

Yes this is stainless tube with thickness of wall approximately 1.5 mm. This is not a huge task to roll the tubes ourselves and we have DIY hand tool I'll show you soon.

Yes that's it! Actually the tubes are paper thin but of large diameter. But the is a problem they react on welding so much we have to correct geometry every time after welding.