why you are losing power with the 14/12p sha clone runtong carb

Jimmy Bloodmaker

Active Member
Nov 24, 2018
through extensive testing of different store's RT carbs, this is what i have found.

most of them seem to have a bleed tube / atomizer tube with the wrong fuel curve. they work awesome on the 49cc but tend to run to lean or rich on one side with a 66cc. even seen them run perfect on a 4 stroke. which got me investigating. with a little bit of modification, it will run with the stock bleed tube. how i got a few to run great, was i covered and redrilled the holes ( over finding the right tube with the right holes). i drilled two tiny holes instead of just one, but made them half or so the size of the big hole they replaced. and i made the top hole slightly smaller, but more oval ( exaggeration, just slightly out of round circle) than before. i then flattened the slide bottom slightly. they usually come angled. then after this i noticed how much crispier, but hotter my engine ran. it is burning fuel much more efficiently. so now there is three holes in the bleed tube instead of two, and the slide is slightly flatter on the air side of it. to combat the extra heat from better burning, i added extra oil to the mix. instead of running at 32:1 like i would for a nt carb, i went up to 24:1, an power increased, not smoke though. so i went up a bit more to 20:1, slight increase in smoke, dramatic drop in temp, increase in power. just a bit of smoke on start up, an a wisp after warming up. without running the extra oil, i noticed faster wear on the rings and cylinder walls( all other wear seemed pretty much the same). i have a snake cam and record and compare the footage at predetermined intervals. there is a bit of spooge in the pipe when running higher oil content, but the pipe can be cleaned with gas every few months of riding. all of my experimenting has been done with lucas synthetic 2 stroke oil on engines over 500 miles. all engines had been slightly ported on all ports and custom intake and exhaust. while the rt will give you twice the mileage almost, it also starves the engine a bit for oil. causing premature wear, but awesome power and fuel mileage. so my advice if wanting to run the RT carb, add a bit of extra oil to the mix, or you will burn your rings up quicker than normal. i've got engines with over 3000 miles on them and still the stock rings, etc. still running like they did when they first broke in. i attribute it to the extra oil, because i really beat the crab patties out of my bikes. without the extra oil, i had to replace rings much more often. when i do rings, i do the whole cylinder, so it gets a bit costly.

edit: another reason i added more oil, well i ran out of jets. my smallest was a #59 and it was still a bit to rich. not wanting to buy more jets ( i have handfuls of them, lol), i just went to 20:1 to see what would happen.

javy mcdees

Active Member
Jul 30, 2018
wow! I ran them carbs for about 6 months and finally bought a Dellorto and glad I did cause it runs way better more power than them little carbs. I had always went back to the stock jetting that ran the best compared to anything else used, compared to the NT carb the RT carb was superior but I had to buy like 6 of them to get 2 good ones and in the end the good ones still broke at the clamp. I also used 100:1 mix the whole time with them carbs and still run 100:1 now. Them carbs are a waste of time but that is only for the newbies to find out.