Carb questions?

First thought would be to check the float level. Have you checked this yet?

thanks,
json

I would trying increasing the main jet size.My
02 fx feels a little lean on top and it is stock.

same symptoms here and it turned out that up 10 on the MJ did the job. (FE400e) 195 to 205 in my case.

Taffy

possumdth,

What main jet are you using at the moment?

And I will ask some really stupid questions:

When specifically are you experiencing this problem? Does WOT alone cause this problem or is it at high rpm?

If it is at WOT, does it happen immediately or does it take a bit of time?

As you say it happens in 4th or above, does the problem go away temporarily when you change gear?

The reason I ask is that it could be the main jet, the float level, or some other fuel supply problem, or you could simply be over-revving the engine where it will produce similar behaviours - these engines produce peak power well below the rev limit!


Taffy,

I'm extremely surprised by the need for a 205 on a 400, especially if used with an enduro exhaust system. I've only known an older 501 with full race exhaust system to need anything over a 200 and even that was only just needing a 205.


Cheers,
Simon

simon

so was i quite frankly but the proof of the pudding was in the thrash up 'n down the field at welney wash. don't forget that i had gone from DR266 to DR270/272 (can't remember) to richen the midrange.

i always maintained that i had never finished testing. indeed i had about 4 two-taper needles ready to try.

the dell orto book has some long formula that i should have done that basically says that the ET won't pass anymore fuel if it is too small. even if the MJ was pulled out. i didn't do tthe calculi.

i'm happy to fax you my tests if you give me a fax number.

Taffy

Hi,

I would say the right jets for your bike were:
DR 270 (272 is too big), 185-190, pilot jet 33.
A friend of mine has got the same model and it runs
very well.
I had a lot Husabergs and it didn´t make a sense to use
a main jet >200, even with fully race exhaust systems.
With a DR 272 it took too much fuel,
so I changed that to 270. It should be right for several
models. But you know, each dellorto carb is different to
another! You have to try and error, just test it.

Greetings from Germany

PS: Another problem maybe the climatic zone you´re living.
During summer or on holidays in warmer regions we sometimes
have to change some jets. So its no general validity what I said
above.

Oppssss.

Here IS an issue I have been trying to sort out for what seems to be a decade....
Many pipes have been puffed in the garage in order to solve this painstaking problem.

You see, my old ´96 501 had the excact same problem Mr. possumdth is mentioning and my 2001 550 is also just the same.
When I open the throttle AFTER a long sprint in the upper gears, 5th and 6th it hesitates and sputters forever, until I have reached about 1/3 throttle.

It´s just like the damn bike has run out of fuel.

I had the chance to speak to a very friendly Husaberg mechanic who was wrenching for a swede (Jörgan Karlsson) in the GP´s and Motocross des nations (at Zolder) last season.

He said it had taken them nearly one season to get the jetting of the Dell Órto vergasser spot-on for their use:

This is his description;

Main Jet; 195 (200 st)
Jet Needle; DR274 (DR272 st)
Needle jet; K51 (K 35 st)
Slide; 45 (40 st)
Pilot ; standard, 33

I have tried this combo and the bike is really fantastic with these settings ( I had to back the fuel screw out 3 turns besause of exessive heat when idling)
Note that this has no effect on said hesitation.

He also said that they ENLARGEDED the chamber where the main jet sucks it´s fuel to ELIMINATE the hesitation after full throttle in the upper gears. (our problem)
I still have´nt tried this.
Has anyone ?

Somehow I think that jetting changes will not eliminate this hesitation.

Any clue, MR Lineweaver ??

In my "humble" opinion ,

Heimir Bardason

HeimirBardason said:

Any clue, MR Lineweaver ??
Heimir Bardason

Click to expand...

Hi Heimir,
A lean top end with the as delivered OEM carburetor is quite common.

A simple test:
Completely remove the main fuel jet and test top end performance.
If the engine runs clean during wide open throttle and remains capable of reaching peak rpm under load then major internal air bleed modifications are required in order to bring the main jet back into play.

Kindest Regards,
Dale

Ps
Most often after proper modifications I end up using a Keihin or DJ #170 main fuel jet.

Thanks for your promt answer, Dale.
I am not quite following you ;

"When I open the throttle AFTER a long sprint in the upper gears, 5th and 6th it hesitates and sputters forever, until I have reached about 1/3 throttle."

Completely remove the main fuel jet and test top end performance.
If the engine runs clean during wide open throttle and remains capable of reaching peak rpm under load then major internal air bleed modifications are required in order to bring the main jet back into play.
-------------------------------------------------------------------

But main jet affects from half to full throttle openings Dale. How can the main jet have affect when I am starting to give throttle ?

Are you suggesting I take the main jet completly out and take Brutus for a spin that way??

Have you heard og riders englargening the vicinity of the main jet ?
Is it possible for the main jet to starve for fuel, all else being ok?

Kind regards as ever,

Heimir Bardason

Heimir,

A high rpm misfire upon light reapplication of throttle following closed throttle deceleration is often the result of a lean low speed circuit.

My earlier post was aimed toward those using a main jet larger than a #180.


Fuel delivery nor air flow is linear. A setting which delivers the optimum mixture during 3K rpm quarter throttle operation is likely to be off considerably during quarter throttle 7.5K rpm operation.

Dale

Taffy said:

i'm happy to fax you my tests if you give me a fax number.

Click to expand...

Thanks for the offer taffy but I was just expressing my surprise, nothing else.

Simon

HeimirBardason said:

But main jet affects from half to full throttle openings Dale. How can the main jet have affect when I am starting to give throttle ?

Click to expand...

Heimir,

In theory this is the case but in practice all the jets overlap. Indeed changing the main jet can and will affect starting and idling - even transitions.

HeimirBardason said:

Are you suggesting I take the main jet completly out and take Brutus for a spin that way??

Click to expand...

I can't speak for Dale but I've only known this test to be carried out on the dyno rather than while riding.

Cheers,
Simon

heimar is suprised i went to a DR272 and in the next post the factory ran with a DR274. don't know what else they did to the carbs etc other than the fact that the factory would probably run a leaner mixture than me (not lean for their engines - just the figures themselves would be leaner).

as said, i never finished off the testing and in a new thread here i invited anyone to help finish them off.

no offers :cry: :cry:

i was about to try a set of two-stage needles and try to get to the bottom of the relationship between the ET and the MJ.

time overtook me and all along i was gagging to get the FCR working.

Taffy

Thanks for your input dear friends of the round table.

Reading your good input I still cannot put a finger on the problem.

To put my and I presume Mr.possumdth jetting problem in perspective again:

When applying throttle after a long pull in the high gears the bike kesitates for 2-3 seconds (no kidding !!)
This hesitation only clears itself when throttle has reaches 1/2 to full throttle again.

If I use full throttle straight away the hesitation is less but still 1 second ! ( plus or minus something of course)

The fuel runs freely from the tank into the vergasser.

The lucky one with the right answer to this "riddle" wil get a hug and a kiss from my wife anywhere he / she wants.......................)

Desperate ?

Yes I am

Best regards,

Heimir Bardason

Heimir,
Simply raise the needle, install a larger pilot jet and go test.
If the stumble is reduced you know you were lean for that particular throttle position and rpm combination.

As stated in an earlier post: "Fuel delivery and air flow are not linear". The perfect mixture setting for light throttle / low rpm will not be correct for light throttle / high rpm. In addition the fuel mixture goes lean during deceleration from high rpm. Opening the throttle from decel will create yet a leaner mixture creating a stumble.

If by chance the stumble becomes worse simply drop the needle and reduce the pilot jet size one step beyond your base setting.

Hope this helps.
Best Regards,
Dale

Dale,

Thanks for your post.
As always, you can be depended upon a reply.

At long last I have understood ;

""In addition the fuel mixture goes lean during deceleration from high rpm. Opening the throttle from decel will create yet a leaner mixture creating a stumble.
""

This sentence broke the ice.

And now, straight for the garage and rip the Dell´Orto apart.

Change the pilot, take a spin, raise the needle, take a spin, puff my pipe, take a spin and so onwards and upword.

My wife sends a BIG kiss.

Heimir Bardason