4t tuning thread

[Yow Ling]

I spoke to Brendan about this today, he had a similar problem with 1 bike and a new stator sorted it out. do you run a battery or capacitor?

[richban]

Pretty much, it used to suffer from the odd miss but I think that was due to not enough fuel in the tank as it never seemed to happen if I ran a higher level.

No clue what so ever. Never come across a problem like that.

[kel]

I spoke to Brendan about this today, he had a similar problem with 1 bike and a new stator sorted it out. do you run a battery or capacitor?

Neither a battery or capacitor.
Was thinking stator could possibly be the problem, will find a battery and give it a try.
Cheers.

[bucketracer]

If your still having problems Team ESE have an old oscilloscope you could borrow to check the AC wave form out of the stator and also from the rectifier to see how DC that really is.

[husaberg]

I have repaired a few FXR cranks. Seems there are 2 common failures.
Stiffies, where the bigend cage fails and the crank grinds to a halt, usually feels like fuel starvation or some tuning problem, then it siezes.

Then the less common but far more spectacular FXRmageddon, seem to happen at full noise, no warning just crunch. Seems to fuck the whole motor, hole through the top cases, sometimes the bottom, rod snaps in half, gear shafts bend. Sound familiar?

Attachment 245207

From What I have seen the Honda 125/200 rod could be adapted to fit they (The Honda) used to Seize/snap at the top but that was a problem that could be solve by a bronze bush.Of course there are yamaha rods 200 and 225 in slighly shorter lengths with 16mm pins as well as the ktm250 but they have short rods.the Honda rods to suit are available from Carillo. mmm....mmm.shiney bits

[kel]

Im off to India, which happens to be the home of the YZF-R15. Will be looking out for motors as I figure there will be plenty of write-offs knowing Indian traffic and driving technique (lack of). If anyones interested send me a PM and Ill keep you posted with what I find.
Kel

[gav]

India is also the home of the KTM 125 Duke built by Bajaj. Looks pretty cool.

[richban]

India is also the home of the KTM 125 Duke built by Bajaj. Looks pretty cool.

Made little bike. Must look at the engine more.

[richban]

Ok so been doing a bit of work on my old engine trying to make it work better. I changed the carb angel to get a more straight draft into the engine and that caused a little problem with the intake being to short. After a little search on the web I found a great little tip on making you own bell mouths. PVC pipe. I just heated it and pushed it over a small old bell-mouth and cut it to length. Worked a treat. Then ran it into a nice still air box. I had been meaning to sort a proper air box for ages and will never go back to open or slightly open carbs again. Makes jetting your bike very predictable. This is not a calculated plenum but just a big volume airbox with more than double the intake area of the carb. Keeps the shit out of the engine as well as drawing nice cool air. Cool air = more power its that simple. What is the correct intake length well here is a basic calculator to get it close. Cams and exhaust will have to match this to make it work proper of course.

I am buy no means an expert in anything to do with engine building but I have noticed what seams to work and what doesn't. Also the engine that I have been doing this on is now almost 3 years old and the same internally as the day it was build but keeps making better power with more development. It will be getting pulled down soon as I think is deserves a birthday.

http://www.bgsoflex.com/intakeln.html

I will post some pics of the PVC bell mouths tomorrow.

[timg]

Another one here http://www.velocity-of-sound.com/vel...alculator2.htm with a few more variables to suit your engine specs Cheers.

[Yow Ling]

Where do you measure the runner length from and to?

From the back of the valve ?

In general what effect does does the bellmouth velocity thing have on existing jetting?

[kel]

We did a whole heap of dyno runs with different length intake runners attached to the Kehin flat slide, the best result was with no bellmouth at all, the FXR/Keihin setup doesnt seem to like flared bellmouths. The intake length seemed to be best at approximately 175mm measured from the back of the valve but that maybe specific to our cams? The longer the intake length the earlier you produce peak torque (its not quite that simple but will do when considering the bikes space constraints) so less peak hp. I also run the airbox with no lid (wouldnt run with the lid on), the idea being to limit the crap the carb can suck in, not sure if it helped clean up the jetting or not? Was interesting to see Andrew Adlam runs the old Mikuni pumper I use to have, its a good carb and fairly easy to set up, glad I got rid of it
I believe Wallace has also done a fair amount of testing of FXR's with bellmouths and airbox.

[richban]

Where do you measure the runner length from and to?

From the back of the valve ?

In general what effect does does the bellmouth velocity thing have on existing jetting?

I think most of the time when people talk about runner length they are talking about the intake on a car that runs from the front of the car to the plenum / air box. Ram air style on a bike or like the monocoque old super bike can't remember who built it. Draws cool air from the back.

On existing jetting who knows. I have seen a cleaner power curve on the dyno after adding an open airbox to the equation. If you look at the standard FXR intake length into the air box including the rubber bit. I bet its really close to the equation below.

The simple equation for working out an intake length is 97000 divided buy peak power 11500 rpm = 8.4 inches / 213mm from valve centre. Apparently.

[kel]

If you look at the standard FXR intake length into the air box including the rubber bit. I bet its really close to the equation below.

Not that I looked at the formula but the original intake length to the airbox produced peak torque at 8500rpm, shortening the overall length to 175mm (or was it 185mm?) length lift peak torque to 10500rpm giving a handy increase in peak hp.

[richban]

Not that I looked at the formula but the original intake length to the airbox produced peak torque at 8500rpm, shortening the overall length to 175mm (or was it 185mm?) length lift peak torque to 10500rpm giving a handy increase in peak hp.

How long was the exhaust header?