1996 Beta Techno 250 Carb Jetting

[chub35]

Been riding my bike this summer but am not happy with the carb setup, it is running very rich, signs of this are always being able to start bike without choke, spooge galore and have to rev like three to four long full throttle blast to clean up, then the engine loads up quickly after.

I am running 75:1 with very good synthetic two stroke oil (Motul). I do have a little experience with jetting motocross bikes but I see a big difference here, we can read a plug with the motocross as it is pinned out most of the time whereby the trials bike is running slower rpm's so thinking this would be tough to see through color. I have not checked which jet I am running or needle position but just thought I would ask for some advice. I am also 300 meters above sea level if that helps any.

I am thinking maybe just drop the needle one notch to start.

[lineaway]

 You should have a 145 main and a 27.5 pilot.

[chub35]

Ok will check, if the main and pilot are correct then I would assume either that the air filter is maybe not flowing well (it seemed a bit deteriorated when I cleaned and oiled it so ordered new one) or the needle needs to be dropped a notch. Does this sound right. Exhaust I just de-coked and repacked so I don't assume there is restriction, other than the new spooge LOL.

[chub35]

Well better late than never, LOL, had carb off last night as I was overflowing too much and checked the main jet (145) and pilot jet (30) needle circlip is in middle position of 5 slots, so it has two above and two below, air screw at about 1.5 turns.  The float level I am trying to find proper level, I have read two informs, one says arm should be level with float bowl mating facewhen carb upside down the other shows it to be pointing as per this picture, http://trialsport.com.au/beta/Manuals/mikuni/Side%20View%20-%20After.jpg I left it level, installed carb and turn fuel petcock on, fuel filled bowl then started coming from the one overflow, read some more and seems this could be siphoning effect that some betas suffer am going to try this

http://trialsport.com.au/beta/Manuals/mikuni/Mikuni.pdf fix for siphoning problem

 

Once I rode the beast this overflowing stopped so thinking it is definitely siphoning.

 

Now I am still concerned with the float level being too high, bike runs pretty good but to clean out it requires high RPM for at least ten seconds maybe a few times, then once ridden for 30 seconds or so loads up again, but runs fine, exhaust spooges bad.

 

my thoughts are try changing pilot jet to smaller size maybe 27.5 (see how it runs)

Changing float position to as per picture above

drop needle one groove

maybe add more air on air screw adjustment (1.75 turns out)

 

Please if anyone has any insight I am all ears. The bike otherwise runs good, starts easy (never have to use choke probably because it is so rich) low RPM operation is good but just hate the spooge dripping from the pipe all the time and never able to clean out easily with high revs. Thanks !

 

BTW, filter is clean :-)

 

[2stroke4stroke]

Apart from anything else the spooge will have gathered in the silencer so you won't be able to tell if anything you do has had any effect on that until you take it apart and clean out the excess oil. The resulting necessary repack will also improve running.

[dan williams]

To stop the siphon just nipper a hole in the vent tubes above the float bowl. No need for modifications. As long as the hole is above the level of fuel in the bowl the siphon stops.