Ajusting Carb / Ignition / Swm Tl.nw 320

[pschrauber]

I have some problems getting my carb / engine adjusted proper, I have not so much experience with the SWM and with the standard setup of the bike. When I got the bike it runned poor (coming from the alpes), the bike runned good in the middle but poor between idle and and mid throttel.

Any fiddling at the air screw did not really help.

I then changed the main jet to 100 now got good low to mid throttle but the bike is going lean, I believe.

Here a pic of the plug after 20 min to half hour of trail riding, (not trials riding), engine got quite hot I believe:

I adjusted the air screw slightly richer as I di not had any jets with me and went on with trials riding, it worked fairly well but wasn't the optimum, still a little bit on the lean side, (with bigger main jet!), the plug looked like this:

My carb set up:

Any Hints, I believe I should rather changing the main jet lift up the needle one notch, (now on second from top) and leave to 90 main jet and I think I have to replace the rubber seal of the idle jet (65) too, very old looking.

Any suggestions experience, may be I have some ignition set up problems?

Which kind of carb setup and ignition timing are you using?

Edited May 28, 2012 by PSchrauber

[woody]

These are the Dellorto settings from my 340 Bultaco

Pilot 40

Main 98

Needle tube AV264

Needle X2

Slide 4.5

Very similar.

I don't know which is the weaker needle, X2 or X1 but your slide is very weak at 6.0. Maybe that is most of the problem for running weak.

I can't remember the settings in my Jumbo now as I no longer have it, but the main jet was definitely not bigger than 100, so I don't think your main jet is the problem.

[pschrauber]

These are the Dellorto settings from my 340 Bultaco

Pilot 40

Main 98

Needle tube AV264

Needle X2

Slide 4.5

Very similar.

I don't know which is the weaker needle, X2 or X1 but your slide is very weak at 6.0. Maybe that is most of the problem for running weak.

I can't remember the settings in my Jumbo now as I no longer have it, but the main jet was definitely not bigger than 100, so I don't think your main jet is the problem.

Thank you for the information, I just found the settings while searching around at a Belgian site: http://www.trialclassic.be/images/SWM/reglagesUsine.jpg

So the setup should be OK, interesting as the bike came from the Alpes and was ridden in an altitude of 1500m! That it was used with the standard setup in this height is impressive.

So after figuring out that the main setup should be OK when I compare them I believe, - not sure -, that all these small issues like the missing seals and the small washers for the idle and mixture screws, the seal for the starter jet is worn out even the needle valve, (here the small rubber on top), shows wear / marks in the whole these misfits can get you in trouble... I replace them now and will fit new gaskets and will even replace slide needle and needle jet. The slide shows only very little wear as the cylinder inside the carb. Maybe this helps, if not I can at least strike the carb from the list.

The timing is Bohemian for me, noted in degrees, 21° ? Have anyone the specs in mm before TDC?

[zerorev3rev4]

Thank you for the information, I just found the settings while searching around at a Belgian site: http://www.trialclas...glagesUsine.jpg

So the setup should be OK, interesting as the bike came from the Alpes and was ridden in an altitude of 1500m! That it was used with the standard setup in this height is impressive.

So after figuring out that the main setup should be OK when I compare them I believe, - not sure -, that all these small issues like the missing seals and the small washers for the idle and mixture screws, the seal for the starter jet is worn out even the needle valve, (here the small rubber on top), shows wear / marks in the whole these misfits can get you in trouble... I replace them now and will fit new gaskets and will even replace slide needle and needle jet. The slide shows only very little wear as the cylinder inside the carb. Maybe this helps, if not I can at least strike the carb from the list.

The timing is Bohemian for me, noted in degrees, 21° ? Have anyone the specs in mm before TDC?

you need an old car type strobe light to check the timing one with adjustable degree,s on it is good ,or you might find a factory mark to align it to ,, personally id go bigger on the main jet and get the plug more brown looking 100 seems small for a 320 i am using 145 in a 175 trials bike , you will know if its rich as it will get spluttery then work down from there untill it cleans up ,its better to be slightly rich than lean especially if trail riding ,, the air screw is only for first 1/8" throttle position and will have no afect on higher revs

[b40rt]

Is it not a petrol screw, rather than an air screw ? ie out to richen the mixture.

Try oiling the air filter a bit more, crude but works.

[zerorev3rev4]

Is it not a petrol screw, rather than an air screw ? ie out to richen the mixture.

Try oiling the air filter a bit more, crude but works.

depends on what type carb is on it if the screw is in the rear of carb it tends to add air when opening which leans the mixture ,if to the front it tends to richen when opened ,but if its an amal mk2 and poss mk 1 it richens when turned in with the screw been at the front

[pschrauber]

depends on what type carb is on it if the screw is in the rear of carb it tends to add air when opening which leans the mixture ,if to the front it tends to richen when opened ,but if its an amal mk2 and poss mk 1 it richens when turned in with the screw been at the front

Yep, completly right, it's the Leerlaufgemischschraube: idle mix screw, and it's located to the engine, behind the slide so turning in is leaner, turning out is richer. (the type PHBH carb is used for the SWM, the type VHSB for for example KTM is vice versa).

Edited May 28, 2012 by PSchrauber

[woody]

Is it not a petrol screw, rather than an air screw ? ie out to richen the mixture.

Try oiling the air filter a bit more, crude but works.

On the Dellorto yes, fuel screw

[woody]

100 seems small for a 320 i am using 145 in a 175 trials bike

Jet numbers for one make of carb don't always correlate to another. 145 would be a massive jet in the Dellorto.

eg: The 350 Jumbo only used (approx) a 95. My 340 Bultaco with Dellorto uses 98. My 325 Bultaco with an Amal uses about a 150. My other 340 with an OKO uses a 115 I think

[pschrauber]

Aha ... fuel idle screw and air idle screw. we call them Leerlaufgemischschraube which doesn't express any difference, sometimes but very uncommen nowadays Gemischeinstellschraube for fuel mix screw and Lufteinstellschraube or air mix screw.

Here the PHBH mixture srew behind the slide towards the engine, (SWM):

And a VHSB with air mix screw, screw mounted towards the airfilter box side, befor the slide:

[pschrauber]

I found out where the issues where, beside of some faulty seals in the carburator that I replaced now:

I figured out that the decompression unit was sitting very loose, I always thaught I had a "just" a faulty exaust seal ... now I know where all the oil gume comes from ..

and why the bike is running so "different".

To thighten the decompression unit I had to deassamble half of the rear bike, as the unit is located under the headsteady and the bolt of the headstady on my bike was mounted from the side where the exhaust manifold is going ...

The faulty deco, I ad already cleaned up a lot of the slimy mess here and thghtend the bolt as good as possible, no room when the long cylinderhead srews are still mounted.

Maybe tomorrow evening I can get her running proper I hope.