Johansson´s Pocketbike

[Johansson]

Yup, the rear spring is quite stiff so the swing moves only a couple of centimeters.

//Anders

[Johansson]

The tank is finally finished, it turned out pretty good without any warping from the welding. After some sand blasting it looks very nice, it will be painted later in the same colour as the frame so it melts in better.

The bike is now ready for a test run, I use the 12V ignition module from the jetcart so I won´t have to use my crappy oil burner transformer. I don´t know if I have time to run it tonight, but rest assured that I will let you know about it...

Except for the shop air hose the only thing external is the battery which will be an internally mounted motorcycle battery as soon as I have measured how much the pumps consumes, the battery must be able to keep the bike going as long as there is fuel left so at least 20 minutes battery power is needed.

//Anders

[Fricke]

That tank is looking great!

By the way I got the right coil with the mail to day... Damn it´s small... The ignition plug cap is bigger then the coil!

So if I survive tomorrow... I think it should be done and in the mail back to You by the end of next week... I need a few days to proper burn in the circuit and test it...

[Nick]

My god that is a professional job mate!!!
Really smart!

Cant wait for the final assembled start up and run!

Are you gong to freepower this little beast?

Nick

[Johansson]

Thanks!

I tested the bike this evening with mixed results. The combustor modification didn´t work at all, it is even worse now with instant flameouts as soon as I release the starter button. The good thing was that the starting system worked perfectly and that the tank was as good as leak-free, only two tiny leaks on top of the tank.

I will have to re-design the entire hole pattern to get this baby running, it is not practical to make any more modifications to the existing flame tube so I am going to cut away the hole area and make a new one with an improved pattern. I am at this point in need of some good advice before making another flame tube since my design capabilites obviously are limited...

To be sure that is was the combustor that was the problem I tried to remove the plastic in front of the intake and the exhaust cones in two separate runs, but the problem remained the same. The P2 gauge peaked at only a couple of psi before flame out and judging from the sound it didn´t spool up as much as it did before altering the flame tube. My guess is that the engine got about the right amount of air before, but it entered at the wrong place and in the wrong direction for the combustion to remain stable.

I am going to take a break from the bike now, I have probably worked 50 hours on it this week only so I will have to get some rest... ;-)

//Anders

[Jmitchell]

No

You must finish it, by tomorrow.

I can't wait any longer!

[Johansson]

Jmitchell: Ha ha, alright then. I will try to rebuild the combustor during next week and run it before the weekend. Happy now when you´ve ruined my vacation? *LOL*

Nick: Yes, I will start making a power turbine on the bike this winter assuming that I´ve got it running properly on pure thrust first. I have a clear idea of how it will be done, but I will save that until later...

//Anders

[Fricke]

Anders -

Sadly that´s what comes with development... But anyway... You´ve done a really good job! Converting to ballbearings, a vapo-fuel system... and managed to get it all to fit in a "whimpy" pocket bike... Now I have to get myself a pocket bike and start building - damn You! =)


Back to redesigning the combustionchamber...

But.. We have our jet-karts to race later this year... If you can get the cart to Terra Scaniae.. I´ll have at leat 400 L fuel... =) And a lot of beer... And I get my thumbs out of my XXXX =)

[Zippiot]

Just how close is the exhaust to the tire?

[Fricke]

Close enough! =)
Dragsters do "burn outs".
Anders dont need to... He has constant burn outs! *LOL*

[Zippiot]

It definitely resembles that.

Make sure you can duct the exhaust towards you opponsts tires too.

Just as background, any idea how much horsepower this thing will put out?

[Johansson]

The rear tire is out of the "line of fire", I am more concerned with the disc brake and its rubber suspension. I am concidering removing the rear brake and just use the front one while thrust driven, I won´t do any rear wheel stunts so there is no need for it anyway... ;-)

It is hard to say just how much HP I can get from the engine, but John told me earlier that I could expect ~25hp if I make the power turbine good enough so even if it turns out to be half that number it will be more than enough to scare the hell out of me while riding it!

//Anders

[NickC]

25hp is a lot on a bike like that. I used to race Metrakits before i started 125gp. The Metrakit has 12" wheels so it's sligthly bigger than your bike and made ~26hp with a 72cc motor with a long stroke and raised ports for a top end based powerband. It would hit 100mph and accelerated pretty well too, if you geared it for like a 70mph top speed you could pull wheelies without leaning, just sitting back a little. When I had it geared for like a 45mph top speed it would wheelie real easy.

For your flame tube design, do you have the NTC program Jet Specs? It's pretty cool, I got it after seeing their NT5 perform so well. If you want I could send you their reccomended falme tube design.

What does vapo-fuel system mean? like a carburetor? so is there just little jets in there the air passes over like in a valved puslejet?

[Nick]

Anders,
you must have your work cut out just keeping up with the email/forum entries this little marvel has generated :-)

Its lucky the days are sooo long up there at the moment :-)

Hats off to you mate!

(mmmmm....wondering.... A. how much flights to sweden are and B. can i persude my employers they should give me the time off?.....:-) )

Im sure a slight re-jig of the flame tube, same dilution values but differently placed holes will cure the flame out problems and as you say the start up mechanism works great!.

I have some ideas ref the power turbine i'd like to discuss with you when you have time.

I reckon John is the man to give you advice about the flame outs!

Cheers

Nick

[Johansson]

NickC: I guess that I will have to extend the wheel base to avoid tipping over with all that power. JetSpecs is of little help here since it is designed for propane fueled GT´s, it gets a bit more difficult with liquid fuels unfortunately...

Nick: Keeping the forum updated is just as much fun as the actual building, since my friends here at home couldn´t care less about my stupid projects it is great to get a digital "pat on the back" once in a while to keep the spirit up if things are going slow. Without the advice I have got from mostly John and Fricke this project would not have gotten this far at all, so my computer is a vital part of the bike project.

John has been so kind to give me detailed directions on how I should rebuild the existing flame tube, so I will do that next week and try to run it again and see how it performs. What would we jet-heads do without him? :D

We can discuss the power turbine later, I will focus on the gas producer at the moment and try not to let my mind go ahead of things...

//Anders