Problems with my new carburetor

the inside of the delorto carb has a brass tube running up a down through it right next to the slide. this tube is your venturi, there are two holes in it. you need to widen up these holes, or add a third hole between them.
(word of warning: the proprietor of that site seems to have some beef with the owner of this forum. I am not trying to start anything by posting this, I could care less about this guys problems with whoever, but this guide on this carb is a good one regardless)

edit: heres a better link to less of a dickhead
SHA page

as I understand things (beware: I am not an expert I may be wrong) the dellorto SHA carb relies on this venturi tube AND the main jet to control fuel air mix (there is also an idle mixture adjustment screw, but thats for idle and fairly self explanatory) according the the guide I linked if your altidue is requiring a richer mix it may be better to add another hole than simply re-jet the carb.

the jet will control your maximum allowable amount of fuel for full throttle, but the holes in the tube meter the gas entering the engine further by using the throttle slide.

for example my SHA had a point in the throttle where the slide uncovered the top hole, at this point the bike would get a sudden increase in power (while accelerating hitting this point felt somewhat like shifting your gears but the bike was a single speed)

this is because the carb is leaning out the mix slightly as I increase throttle until the top hole is uncovered then the mix becomes rich again.

so assuming your engine has enough flow overall to deal, you mentioned that the carb has dropped your power so I am assuming that the engine does have the necessary flow, adding a third hole (or widening the bottom hole, which is a riskier idea you can cover the new hole, if widening doesn't work you need to rebuild your carb to go back) will remove this 'step' in throttle response, and when at full throttle you will have more gas entering the engine, you can think of this as allowing the carb to meter out the amount of fuel you have re-jetted for.

all of this having been said, before you do anything at all.
TAKE THE CARB OFF THE ENGINE AND LOOK INSIDE IT. when you pull the throttle double check that the top hole is uncovered, I managed to assemble mine once where the slide didn't move right, you may have done the same.
I made this bit red because I re-read this post and the super important bit is at the bottom. redness is easier than editing.

ֹֹ_Tal_ said:

even tryed to change the jet to the jet of the standart old NT carburetor and still same result..

Click to expand...

The jet in the NT is a 70
The jet in your Runtong? carb is probably also a 70

Try a 65 or 66 jet before you start messing with your carb.

it can, then again so can a few hundred feet of altitude.

before you do anything drastic compare the two jets to make sure they are different (there also tends to be quite a bit of wiggle room in the actual sizes of jets supplied with these parts from what I've read on here) if you have two the same it may be more worthwhile to purchase a pin-vise drill bit set in order to solder and re-drill your jets (from what I've read on here this method is generally considered much better than buying jets and trying to find the right one because you can just start small and drill a wider hole to re-jet the carb, saves some money that way.)


also considering that brass and solder are both very soft metals you probably only need the drill-bits not the pin vise itself to get the job done.

ֹֹ_Tal_ said:

going from 70 to 65 can do such dramatic difference?

Click to expand...

I am at sea level and yes they run good when you go from a 70 to a 66.
I have rejeted quite a few.

A few hundred feet in altitude makes no difference.

I use drill bits to measure my jets.

okay so here is a much better link than the one I posted before that is talking about the same stuff (beware this is writen by someone who is trying to prove how cool they are, just ignore that and look at the facts.)
Delorto SHA

Thanks for the link GoreWound, good interesting info.