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Discussion Starter #1
ok so heres what i got, its a crf50 that i put in a 90cc yx motor, before this motor i had a 88cc TB race head kit. i am using that shengway that came with the kit, now that carb ran some what decent on that kit so i know the jetting for the 88 motor was ok, it was running the stock crf50 exhaust as well. well i had a few hours free so i installed the yx90cc motor in the 50 with a new fmf power core 4 exhaust (28mm it looks like)and through the 20mm shengway back on without changing any settings, at first the motor fired up and idled decently and reved freely, after letting it idle for about 1 minute, maybe 2, it died, and would not really kick back over. so i put the choke on full, and gave it 1/4 throttle while kicking it and this would get it started back up, but would then die out if i let off the throttle one bit. if it did die out it would take another 4 or 5 kicks with 1/4 throttle and choke on full to get her going again but as soon as i would let off, she would sputter and die.



now i am no certified genius but to me i think that it sounds lean on pilot and main. i didnt have time to pull off the carb bowl to see what jets are installed and i know i should have but does anyone have a base line or idea what jets i should be running. i tired to google search it and i found a guy whos story is simillar to mine only he had a lifan 90cc motor and same shenway carb and similar exhaust and he was running a 95 main and 38 pilot.



i am at sea level nearly, maybe 50 feet above, i am running a 20mm shengway (the one that comes with the tb88 RH kit), i am running a fmf power core 4 exhaust, and i am using a yx90cc motor with e22 head. bike now only starts with choke on full, but still dies out...



since the carb was dialed in decently with the 88 kit with stock crf 50 exhaust, it makes me thing it had the recomended jetting from TB. i figured the yx 90 wouldnt be too far off from jetting. i guess i was wrong, way wrong.



if anyone else has a similar china 90cc motor, what carb and or jets are you running?
 

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you could have dislodged some small spec of dirt in the bowl of your carb and now your pilot is slightly plugged.....but also check the valve lash....should do that on all new motors after initial run.....
 

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Discussion Starter #3
valves are still within spec. pretty sure the carb is clean but ill def check that agin when i get a chance. any recomendations on the jetting though? being that i wont even kick over without the choke being on, i am thinking its extremely lean......



one thread i found a guy says a 38 pilot, i think tb recomends like a 15 or 17 with there 88 kit
 

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if it ran fine on a 88 with a race head it should run ok on the 90......having to use the choke all the time tells me that the pilot circuit is restricted....clean the carb and then try.....
 

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Discussion Starter #5
ok, i was under the impression if the choke is on all the time in order for it to run, then the pilot was too lean
 

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do a plug reading first and that will tell u if ur lean or rich but it sounds like pilot circuit problem clean carb then warm bike up go back to house put a new plug in it and take it down the road in fourth or third gear wound out but not on limiter and pull in clutch and hit kill switch then walk it back to the house with it still off and let it cool a little and get a plug reading that will tell u the best of how bad its off
 

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well a safe way would be just to remove the carb and intake manifold to ensure there is not any splits in the gaskets or the insulator
 

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Have you tried adjusting the air/fuel screw? You may not need to switch pilot jets. I think the ShengWey carbs have air screws, so try turning it clockwise a half to full turn.
 

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Just a thought, but try checking the valve adjustment on the new motor?

If that's not it, you must have a small leak or plugged passage in the carb.

Ruled out bad gas or water in it, right?
 

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Discussion Starter #15
Tried air and fuel screw and no matter how much i let it out, no change. I checked valve adjustment but ill try again. What other carbs would u recomend ?
 

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If the engine bogs or dies when you hit the throttle from idle

its lean pilot condition.

We get tech calls about that all the time.



1)Install Intake manifold to head and carb, oil gaskets and tighten bolts lightly at first then torque then down gradually in a cross pattern to provide a good seal and avoid air leaks.

2)Make sure the carb is 100% clean, free of debris and you can see light thru both main and pilot jets

3)Double check you valve tappet adjustment .003intake and .004exh.

4)Make sure all electrical connections are tight and you have a good ground from the engine to the frame.

5)Check for good fuel flow and fresh fuel.

6)See our jetting guide and do a plug read.

TBolt USA, LLC
 

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Discussion Starter #17
this is getting a bit off topic i think, i checked valves, just checked carb, and everything is ok, this is def a jetting issue. i am more looking for someone with a 90 or 110cc china motor with this shengway carb to help gove me a baseline to start off with.



i think it maybe easier to call up piranha tommarow or maybe pitster and see what jets they use in there carbs they supply and or even buy a carb from one of them thats ready to go for this motor.
 

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deputyperk said:
this is getting a bit off topic i think, i checked valves, just checked carb, and everything is ok, this is def a jetting issue. i am more looking for someone with a 90 or 110cc china motor with this shengway carb to help gove me a baseline to start off with.



i think it maybe easier to call up piranha tommarow or maybe pitster and see what jets they use in there carbs they supply and or even buy a carb from one of them thats ready to go for this motor.


If its this bad its not a jetting issue. It will still run with the carb even though its set to the 88.



Are you sure your doing the valves correctly? Or did you make sure that the jets are spotless and clean them out with needles?



Its not jetting. possibly a bad ground like Tbolt said. Maybe a loose wire? check everything again.



it will run the way the carb is jetted
 

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fiddy4ever said:
if its this bad its not a jetting issue. It will still run with the carb even though its set to the 88.



Are you sure your doing the valves correctly? Or did you make sure that the jets are spotless and clean them out with needles?



Its not jetting. Possibly a bad ground like tbolt said. Maybe a loose wire? Check everything again.



It will run the way the carb is jetted


thank you !!!!!
 

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Discussion Starter #20
well theres only one ground on the whole bike, and that behind the carb and that seated properly, if it was a bad ground then the bike wouldnt start at all right?
 
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