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Post by kostastmax on Feb 22, 2015 5:34:58 GMT -5
Hi there I have a Chinese scooter and yesterday I installed my 47mk bbk kit The engine starts fine and it works great My problem is that when I made my first ride I noticed that in full throttle the engine seems that can give power I think that I have to change main jet but what number?
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Post by jc33777 on Feb 22, 2015 8:17:38 GMT -5
Depends on what is in there now but you can try to start around 90
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Post by kostastmax on Feb 23, 2015 13:32:38 GMT -5
I opened the carburetor today an the main jet doesn't have any number. I think that I must buy a set of jets And also it is necessary to change the pilot jet also? Thanks for any help
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Post by jc33777 on Feb 23, 2015 15:41:25 GMT -5
Most of the time the pilot jet is ok but if you would like to change it around a little to see what results you get a good starting point is either 35 or 40 And here is a link to an affordable jet tuning kit www.partsforscooters.com/114-49-QMB139-Main-Jet-Kit?whence= $16 for a 10 piece kit $40 for a 50 piece kit
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Post by jc33777 on Feb 23, 2015 15:51:34 GMT -5
This might help some
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Post by kostastmax on Feb 24, 2015 13:55:14 GMT -5
Thanks for the help my friend I ordered the jet kit and I will make my tests when I will receive it
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Post by kostastmax on Feb 27, 2015 15:34:04 GMT -5
Today I received the main jet set and I made a try with number 90 I think that there isn't any serious improvement Should I try a bigger one or it might be something else?
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Post by humanshield on Feb 27, 2015 16:15:27 GMT -5
Hi there I have a Chinese scooter and yesterday I installed my 47mk bbk kit The engine starts fine and it works great My problem is that when I made my first ride I noticed that in full throttle the engine seems that can give power I think that I have to change main jet but what number? Hi, I don't mean to be rude but can you explain exactly what you mean? Are you saying the engine has no power at full throttle? I hate to assume I know what you mean. If that is what you are saying, then there are several things to look at. First of all, did it run fine before? (That would probably mean all the non BBK components are ok I would do the following..... 1). Check the valve adjustment again 2). Disconnect the airbox side intake boot going to the air box and see if it improves 3). Raise the needle by moving the clip to the lowest position and see if that helps 4). Check your compression and make sure it is good like 150psi or better 5). If you have a 18mm carburetor, consider going to 20mm more as I think of it
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Post by isurffl on Feb 27, 2015 17:06:38 GMT -5
Definitely buy a set of jets, I'd buy .90-1.15. I just installed a 47mm bbk a couple weeks ago and ended up with 1.05 to 1.15 in the sweet spot. 1.15 gives me best top speed (thinking I'm running a little rich but I like it that way). Every single set up is a bit different so you'll need to tailor it to your preference. Also need to play with the needle valve position and idle mixture screw and idle throttle position screw to tune. There's lots of info on carb tuning all over the place. Buy some extra spark plugs and read your plugs each ride until you're happy.
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Post by Fox on Feb 27, 2015 22:25:53 GMT -5
Today I received the main jet set and I made a try with number 90 I think that there isn't any serious improvement Should I try a bigger one or it might be something else? Maybe it's not fuel it's starving for but air. What's the spark plug look like? What color is the tip I mean? If it's really black then it's more air you need. Plug reading guide here: ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp Are you running a stock air box? If so try opening it up a little so it flows more air. There is sometimes a plug in the intake snorkel that you can remove. Sometimes it has a screen in it. If it gets better after removing any air restrictions then you can play with different jets and different air filter configurations. When all is said and done you want to see a nice brown spark plug. There is also a small rubber tube inside the air box that can be removed to allow for more flow. You can even drill holes in the air box to get even more air flow.
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Post by kostastmax on Mar 4, 2015 14:52:20 GMT -5
I removed the small rubber from the air filter and now I'm using main jet 98 It's working very good with this I will measure the top.speed with gps tomorrow To the scooter speedometer I can see easily 70kmh The only problem I have now is that when I'm with open throttle and I'm closing it to.stop most of the times the engine stops
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Post by 90GTVert on Mar 4, 2015 15:12:50 GMT -5
Could be needle clip position or you may be able to readjust the idle mixture screw and get it to work alright.
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Post by kostastmax on Mar 5, 2015 1:45:47 GMT -5
The needle is in the lower position now I will try again with idle mixture adjustment to see if I can solve the problem I saw your video for this but until now I can't make.it work properly I don't know what I'm doing wrong
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Post by 90GTVert on Mar 5, 2015 8:47:04 GMT -5
The lower position on the needle is the richest.
If you've got the right main jet picked out, then it sounds like there's just too much fuel as you let out. Could be the rich needle position. The needle changes a lot more than just letting off of the throttle though, so if you've found that it runs well from 1/4-3/4 throttle and transitions onto the throttle smoothly, then maybe you can solve it by adjusting the mixture screw or you may need to try a step leaner on the needle position. Could be that you need to do both. With a little fiddling and observing you should be able to sort it out so you have good power and good response as well as a steady idle.
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Post by kostastmax on Mar 5, 2015 14:45:32 GMT -5
Thanks a lot for all the info I.will make my tries tomorrow and I hope I will.make it
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