Dellorto Setup for the Lineaweaver LRX2 Cam

I have been running one of Dale Lineaweavers LRX2 cams in my 2000 501 for 18 months now. I initially tried to use my standard jetting but had an over rich condition below 5000 rpm that I could not resolve my self so I asked Dale for some jetting help.

If you have a Lineaweaver LRX2 cam in your Dellorto equipped Berg and have some questions about carb setup this may help you.

I was experiencing 'Intake Reversion', caused by a high overlap cam and a very short intake manifold. On a high overlap long duration cam the intake valve is still open as the piston is starting to compress the intake charge and the air/fuel mixture starts to back up, some of it blows back through the carb venturi (at higher throttle settings and lower rpm) and then gets sucked back through the venturi adding more fuel to it on the next intake cycle.. creating a rich mixture. On an automobile engine, you have long intake runners so this is not a problem for them. In the case of your Husaberg, you only have 5-6 cm of intake manifold so some of the fuel laden air can pass back through the carb venturi into the air box. On 2 strokes, the reed cages permit more agressive port timing. Try running a big bore 2 stroke with a bad reed sometime and you will experience a super rich condition the same as I was on my Berg.

Here is how to fix it on your bike with the LX2 cam if you are still using the Dellorto.

Throttle Slide #4.5 (you can modify your OEM 4.0)

needle K51 clip #1-2-3, I am using clip #2 at 3000-4000 ft

needle jet DR 272

pilot jet #35

main jet #170

main air bleed #53 drill = 0.059" = 1.499 mm

pilot air bleed #60 drill = 0.040" = 1.016 mm

fuel screw 1.5 to 2 turns

The throttle screw will have to be adjusted to get the idle set.


Regards,

Joe

JoeUSA said:

I have been running one of Dale Lineaweavers LRX2 cams in my 2000 501 for 18 months now. I initially tried to use my standard jetting but had an over rich condition below 5000 rpm that I could not resolve my self so I asked Dale for some jetting help.

If you have a Lineaweaver LRX2 cam in your Dellorto equipped Berg and have some questions about carb setup this may help you.

I was experiencing 'Intake Reversion', caused by a high overlap cam and a very short intake manifold. On a high overlap long duration cam the intake valve is still open as the piston is starting to compress the intake charge and the air/fuel mixture starts to back up, some of it blows back through the carb venturi (at higher throttle settings and lower rpm) and then gets sucked back through the venturi adding more fuel to it on the next intake cycle.. creating a rich mixture. On an automobile engine, you have long intake runners so this is not a problem for them. In the case of your Husaberg, you only have 5-6 cm of intake manifold so some of the fuel laden air can pass back through the carb venturi into the air box. On 2 strokes, the reed cages permit more agressive port timing. Try running a big bore 2 stroke with a bad reed sometime and you will experience a super rich condition the same as I was on my Berg.

Here is how to fix it on your bike with the LX2 cam if you are still using the Dellorto.

Throttle Slide #4.5 (you can modify your OEM 4.0)

needle K51 clip #1-2-3, I am using clip #2 at 3000-4000 ft

needle jet DR 272

pilot jet #35

main jet #170

main air bleed #53 drill = 0.059" = 1.499 mm

pilot air bleed #60 drill = 0.040" = 1.016 mm

fuel screw 1.5 to 2 turns

The throttle screw will have to be adjusted to get the idle set.


Regards,

Joe

Click to expand...

The secret is in changing the throttle slide from a 4.0 to a 4.5, and in opening up the air bleed jets. This was a progressive series of changes, the slide change was done next to 2nd friom the last and had the biggist effect in controlling reversion effects at partial throttle settings. I had been using a 33 pilot, and clip #1, but after the slide change I needed to richen up the bottom end (35 pilot) and mid range (clip #2).

My OEM settings were:

Throttle Slide #4.0
needle K35 clip #3

needle jet DR 270

pilot jet #33

main jet #190

main air bleed did not measure prior to drilling it to the size Dale recommended

pilot air bleed did not measure prior to drilling it to the size Dale recommended

fuel screw 1.5 to 2 turns

I have been asked if the changes will work with the OEM cam. I don't know, but doubt it. The slide change may be the biggist factor. The air bleed jets are pressed into the carb body and are not removeable, but they can be drilled out, and the body threaded to fit what ever standard series of air bleed jets you have available.

Dale is the best source of information on these details.

I have also been asked how to modify the slide.

If you remove the slide and measure the height of the cutaway arch it will be 4.0mm from the bottom of the slide. You want to machine enough material off of the the outside of the slide to aise the arch to 4.5mm.

Do not remove any material from the bottom surface of the slide or the face of the arch where it intersects the bottom of the slide. Keep the cutaway "flat'from the peak of the arch to the intersection of the arch with the bottom of the slide.

To achieve the new cutaway you will have to change the angle it makes to the plane of the slide base.

The Height is measured to the peak of the arch, at the outside diameter of the slide. I will post some pictures in my gallery.

My Gallery

Regards,

Joe

Taffy said:

hi joe

great advice on work done fella. thanks from all here for that. definately one for the 'owners doc' that one!

Q; you have a small drilled hole at the back of your slide? i don't believe that this is standard either! how big a hole is drilled here and who did it? you? dale?

coronaberg had had this done to one of his carbs and he siad it was the best of the three he owns (carbs that is!).

you went the opposite way to me with your slide cutaway..... nice to learn new tricks!

regards

Taffy

Click to expand...

Hi Taffy,

The hole in the slide is OEM, and is blocked off. It appears to to be a passage to the needle. The only mod to the slide is the cut to raise the arch to 4.5.
The Carb came stock on my 2000 501, that I purchased new. I watched Eric and his mechanic Brett uncrate it and prep it for me.

Aside from the LRX2 cam and these carb changes the engine is stock except for the KTM 400SX piston I installed. It raised the compression from 11.8:1 to ~12.4:1 and definitely increased the bottom end and mid range torque. It was a fluke! I needed a piston due to some trash that got backwashed into the crankcase when I had a transmission bearing fail and the reed got jammed open by a piece of the bearing ball retainer. The only piston I could find was the KTM, and it only cost $204.22 including the pin, clips and rings. Part number 590.30.007.000, year 2002
Regards,

Joe