Bushmechanic Mongrel 628 Trailbike

Hey Bushie,
About the Amsterdam street, i think you meant Nieuwekerkstraat, 'cause it means literally fuckkirkistreet, and there goes the reputation of the 5er BMW satnav
About the" alcohol map"i know for sure
But about the weight, are you meaning that it's streetlegal, with all the stuff on board?
That would indeed be very

Grtz Rens

p.s. About the sound thing, is badass the same as old fart !?

spanner said:

Hi Bushie,

Wish I could build stuff that quick Bushie but I seem to get tied up in the detail too much I suspect

Anyway how does it run with that lighter crank? interested of coarse if it makes much difference or should I try the lighter flywheel as well? as we have only removed around 10% so far.

Been studying the laser/electron beam welding scenarios for welding crank pin into the flywheels and it still not ideal for carburised parts, nothing is it seems, But may be helpful in other crankshaft designs.

Cheers spanner

Click to expand...

Interesting on the welding ...

the lightened crank is great .. not all that much difference it just feels "strong" in the way it responds to throttle input with light loads

under heavy load of course the 700 spins up quicker .. casue its got more grunt to deal with the load.

the light crank engine did fluff out on me once on the last ride but I was in 4th, going too slow over a creek and the pilot is a bit lean

I don't think that the crank is too light and if i had a lighter flywheel i would try that as well.

how does it go with engineering..something like ; Light weight, beautiful or quick to make, choose 2

got the Data logging with the WEGO working

looks like my guess of a 170 main to be safe was about right





graphs RPM vs AFR and TPS vs AFR, TPS is "analog input"

I'll put up some more graphs for a laugh when im happy with how the bike runs

10000rpm
I see you have finished the running in period

more pics these are off the 700 but its the same setup

spanner said:

10000rpm
I see you have finished the running in period

Click to expand...

LOL looks nasty right ?

it may be a bit of noise getting in there somewhere I didn't think it was 10 000

Interesting stuff Bushie, esp the TPS vs AFR.

Hey there Bushmechanic.

Some very interesting stuff going on there, I love it!

I intend to start some mongrelling of my own, and I didn't know where to post. I will start a new thread when I start the build, but first I would like to ask a couple o questions. I'm hoping the collective experience of the more experienced tinkerers/modifiers/butchers/mongrellers/engineers/wizards might help make my experience go a bit smoother...

Regarding the cylinder heads, between the 01-03 big valve and the later heads, do the big valve heads flow better, or why did the change to smaller valves? Between the two heads, which is better performance wise?

Let me explain what I hope to accomplish. I want to take a 2004 FE450 and make a rock crawler bike for technical riding. I was thinking of using something like maybe KTM 450 exc RFS 89mm piston, and have a liner made. That should put me at about 350cc more or less. Could also maybe use 525 RFS piston, to give me about 420cc or so. I haven't had a look at the deck heights to see if it will actually work, but I think it could be done. I'm hoping to have a tractor like power delivery, like on them 230crf honda's or some such thing. Obviously the 89mm piston will be much lighter, thinking of the crank balance factor and all that, but thinking of the honda 230 again, and they have heavy cranks with light pistons, will I achieve that ultra smooth power delivery like that?

With a tuned down engine like that, would I notice any real difference in low down throttle response between big valve or small valve heads? Will the head be too big? If I remember correctly 89mm and 95mm KTM heads are the same...

Also, carb size? I have 38mm DelLorto, 39 FCR and 41 FCR.

What other mods do the guys use on the 380 builds?

Any thoughts, guys?

Hi wardog

if you set up to use the fcrs you can choose between the 2 they are better carbs.

the bigger valves and head do flow more, for a tractor engine though if you are looking for off idle torque the newer head and bigger displacement engine could be a better choice.

the best "technical and slow" engine ive used is my 700, it makes a lot of off idle tourque and is very hard to stall. if I want "smoother" power delivery for a snotty hill I just put it in a higher gear

then when I'm on the way home its more fun than all the others put together.

if I had left the head alone unported with stock valves and used an LX2 or ktm 8/06 cam profile and a 39carb it would be even more suited to piddling around in rocks

I suppose it depends a lot on personal preference.. obviously you have a stack of parts in hand that can be made into about 400cc

for the best answers I would ask on the RFS section of KTMtalk they are RFS mongrel bike mad, almost any engine displacement and carb has been tried for almost any application.

RFS-Racing 4 Strokes - KTMTalk.com

you could also send Blunny on here a PM he is building a 380.

FCR Needle

made a needle today

surprisingly it was the easiest thing ive machined for this engine

used lineaweavers trick of starting with a large diam blank



used a center at first and cut the tapers in one pass



then cut the straights and put the grooves in





the tapers are halfway between dales needle and the honda NKBT

made it a tad oversize on the straight and sanded it down later

tested it then pulled it out and sanded it down a bit more ..... much easier than changing jets

took nearly 2 hours all up, works good

Nice " trick " again Mastahhh!!!

Grtz Rens

Dales needle with the honda NKBT imposed over it and dropped 2 clips

NKBT is the green needle,



in the bikes if you drop the nkbt 2.5 clips its very similar

2007 Honda CRF250R
NEEDLE SET, JET (NKBT) (16203-KRN-A01)

LINK| MotoSport

the one i made superimposed over the NKBT

I think that's a prototype for a wand.

Be aware Plumpbob!!! He could cast a spell on you
Maybe just to try it

Cheers Rens

yes rens it has magical powers, you point it at your lady of choice and she becomes immediately fascinated with procreation, unfortunately the target of her newfound obsession is rarely the owner of the wand LOL

I think it just needs to be a different colour ?

the idea with the needle was to have a more abrupt change from 1/8th to full open and have the straight fat enough to run a bigger PJ (#50)

what i was trying to do was improve the momentary lean spot that occurs when cracking the throttle from a steady 1/8th to WOT .. when there is no pump squirt to help at this point.

worked reasonably well probably needs even more difference on the needle between idle and wot

Bushie if you get around to turning those on the cnc mill, i would be interested
in trying one

spanner said:

Bushie if you get around to turning those on the cnc mill, i would be interested
in trying one

Click to expand...

FWIW spanner the honda NKBV is about the same .. $24

Honda Dirt Bike needle link | MotoSport

NEEDLE SET, JET (NKBV) | (OPTIONAL). (16205-KRN-A01)

Hey Bushie,

How is your prototype of witch broomstick doing?
And did you cast a spell on Sandra Yet? LOL

Grtz Rens