TKR 2006 Settings NARAKU 70CC PISTON KIT MOTOFORCE CRANKSHAFT REED VALVE BLOCK (UPRATED) MOTOFORCE RACING INLET MANIFOLD YASUNI R EXHAUST (both restriced plates removed) 17.5MM PHVA CARB 95 main jet upto / 104 PRE-MIX oil Open air filter. Hi all , Hope some one can shed some light on my problem , I had a 70cc kit running on a 12mm carb with 72 main jet it ran well. I had a problem with the carb so upgraded to 17.5mm PHVA, the standard back box would not fit so i had to buy an open air filter. the bike started but only with the air mixture screw all the way in. i up jetted and it solved that problem bike starts np problem. How ever she seized up on me at about 40mph i started upjetting and have got all the way to 104, it still locks up and seizes. i modified the air box and fitted it back on. it seemed to make no difference. also put a new piston in after it had locked up a few times. i have tried a heavy mix of oil to fule also. but she just wont have it to long at to high revs. I did notes that when at WOT it BOOOORS out some what, and at low revs it crackles. it tried adjusting the needle to sort that but it didn't help. so many problems from this new carb. Please help.
Sorry to bump my own post. So after a few days of thinking .. my guess is i have not dont a good enough job when modifying the stock air box. I read an article stating that 17.5mm carbs dont like not having an air box on a 70cc kit. Whats is happening (I think) to much air is avalable for the engine with out the air box, so when im up jetting to a 104 to get the right air to fule mixtuer, it is futile, as the engine cant burn that amount of mixture. the locking up is becuase there is unburnt fule and air in the cylinder. Would this make sence?
its a round foam filter i had no clue when i bought it at the shop. ive just orderd a new backbox from pedparts, and a new needle.
this is better, new air box, 97 jet. Ive never seen another one of these bikes on the road . any one else got one?
I think so, The kit was already running well untill i changed the carb to 17.5mm. it was after that she kept locking up. i upjetted from a 95 all the way up to 104, with it still locking up each short run. I could only get a foam filter at the time OEM airbox did not fit. i changed the piston at this point. So im still trying to run it in with out lock ups. had a good short run yesterday but fule was low so will give it a run again today. Im not ragging it just taking it easy, low revs 20 -30 mph. So fitting an airbox and down jetting back to a 95 worked. the low rev crackle i had was a slightly bent jet needle. i also changed the crank and bearings. so that needs to bed in also.
You only need 2-3% oil ratio, adding more oil won't help. is the oil pump not working ? to late to say but start big and work smaller on jetting. Air leak ?
I have the oil pump blanked off as i use 5lts of fule 170ml 2t the green stuff not the red. Ithink you are right about the air leak, since i put the backbox on it dose sound like it could be ill fitting a bit and for a second letting in air. and jetting i may go leaner. say 80 rather than 95. thanks.
170ml of oil to 5 litres of fuel is an awful lot of oil really ... i use 125ml of oil to 5 litres of fuel 40:1 and thats quite oily really.
Interesting, do you think that amount of oil could be contributing to the engine seizing. it get a bit hollow and boggy before it stalls. back wheel some times locks. Im not sure down jetting will be the answer. but i thought a 95 jet might be to high. i sure am stuck lol. wish i kept the old carb now.
Have you taken the head off to see what your bore looks like? If your motor is seizing the wheel something is screwed
when you run premix, both oil and fuel has to pass through the main jet. oil will take up space that would normally be fuel, so your air/fuel mixture will be leaner. you have to increase your main jet a couple of sizes when you run pre mix, the more oil you add to the fuel the larger the increase in main jet.
@scubabiker I did take the head off yesterday the plug looks coffee color and is dry. piston had high carbon build up so to much oil is making it lean. @The Messenger That dose explain it running lean on a big jet, there are a few threads on the forum where people have had good results with an 80 jet, the kit was on a 72 jet on a 12mm carb and running with no problems.. So to much oil can give you false positives when trying to get the correct jetting.
