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Discussion Starter #1
So I finished putting on the 44mm BBK.
I also installed the 68 jet, as well as moved the c-clip on the needle valve one notch down to run a wee bit richer. Last but not least, a fiberglass reed.

Now the issue I'm having is when riding, if I go from mid or full throttle and let go of the throttle to go back down to idle, the bike dies. But I can start it up again immediately after (even start it while rolling :p).
Another symptom seems to be when on acceleration if I twist the throttle a bit too quickly it's like a misfire and the bike loses power on a stroke, then lurches forward on another stroke.

Theory is:- jet still too small(anyone have recommended jet size on STOCK carb?)
-Float needles too high, and float bowl not refilling fast enough.
-unknown issue somewhere else...

Any input?
 

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Hooligan
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Sounds like top end reed flutter to me .... The reeds in your engine act as a one-way valve, opening to introduce the fuel/air mixture into the cylinder, then quickly snapping shut for the ompression/ignition/exhaust stroke. During TERF, when you have the throttle wide open (aka WOT), the reeds are flapping back and forth so fast that they can't make a good seal on the cylinder, resulting in loss of compression and of power. Solution: get new reeds, like carbon fiber or fiberglass (I run CF reeds in mine).

There's also a trick that one of our members came up with a while back if you have a second set of stock tin reeds. davation's cheap triple stage reed mod is located in the air-cooled how-to's section at the top of the page.
 

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Discussion Starter #3
The reeds I put in are brand new, if that is the case, I could trim the tin reed and mount it behind the fiberglass one?
This would apply a bit of pressure to ensure a proper seal right?
 

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Hooligan
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Well, actually, mount it in front of the new reeds, between the new reeds and the reed stop. Check out davation's mod, and you'll see how to properly set it up. I've done it to several bikes, and it works great.
 

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Discussion Starter #5
I understood where to put it :p
When I said behind, I was thinking in terms of air flowing in to the engine, and making contact with the reed first. I'll try this out today.

I can understand how it would explain the stutter in acceleration.
Could the reed thing explain engine cutoff when going from WOT to idle?
 

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Trained Chimp
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Reed flutter generally happens at a steady rpm. Usually wide open. It sounds like carb problems to me. Just my ¢.2
 

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When you go to a B/B engine you need a bigger carb and a better exhaust pipe than stock. For $20 Sam, will Swirl bore you carb form 12 to 14mm, I have two on his 3rd Stage race engines.
You could also be too rich or to lean at top speed. I have F/G reeds on my Red Head eng on the engine stand, there not as steady as CF reeds, think they are more for short track racing I believe.
 

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So I finished putting on the 44mm BBK.
I also installed the 68 jet, as well as moved the c-clip on the needle valve one notch down to run a wee bit richer. Last but not least, a fiberglass reed.

Now the issue I'm having is when riding, if I go from mid or full throttle and let go of the throttle to go back down to idle, the bike dies. But I can start it up again immediately after (even start it while rolling :p).
Another symptom seems to be when on acceleration if I twist the throttle a bit too quickly it's like a misfire and the bike loses power on a stroke, then lurches forward on another stroke.

Theory is:- jet still too small(anyone have recommended jet size on STOCK carb?)
-Float needles too high, and float bowl not refilling fast enough.
-unknown issue somewhere else...

Any input?


Pull the plug to see the burn...........Then do a compression test to see where the power lies............

Id upgrade the fuel system to 1/4" and do the petcock mod then Id regap the coil with a true .020" thick business card...New business cards arent .020"...they are .010".......

Pull the bowl off the carb after removing the carb to check float height and mod the mainjet tube where the float slides up n down on

Id also lighten the flywheel and the clutch pads aswell as add a rocket key

For the carb theres some things you can do other than the petcock mod to make them more reliable but it takes time and labor............
 

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Discussion Starter #10
-Coil gap was done already.
-Fuel line are aircraft tubing used on rotax engines.
-petcock is drilled straight through.
-I will be porting the carb myself in the fall when I have access to a reamer and mill.

I'll try the reed mod paired with the fiberglass reeds currently on the engine.
I don't have a compression tester, but I'll check my plug and match it to the Haynes guide to good plugs.
I'll make a small adjustment to the float fork and see what happens.
 

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Matty which notch on the needle is your c-clip now in? i'd do cams carb slide mod whilst messing about with the carb. i'd be pretty confident if you've done the petcock mod there shouldnt be a problem with refilling the flat bowl, fuel pours through the petcock once drilled, much quicker than i imagine the engine could drink it. Reeds is a good place to start, personally i'd probably refit the metal ones and test, just incase its the new reeds. i fitted some c/f reeds that made my bike run poorly, they were just poor quality and werent sealing properly.

Of course checking the plug has got to be the first step...
 

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You dont need any fancy tools like milling machines to work on these carbs,,,,,,,,,,,lol....You mostly need a drillpress,,chopsaw,,grinder,,files and a dremel set....................

Theres threads here at PBP outlining how to port the carb with a 14mm drillbit in a drillpress.....

I turned this one piece head into a 2 piece head with a hacksaw ,, dremel set,,and a couple of files

 

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Hooligan
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You forgot two other things he needs for all that, CAM2 - time and patience.
 

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Yeah, thats two things I am short of,lol,lol. When I have trouble I get my made in USA Du-All dead blow hammer and make adjustments, as needed,lol,lol.
Just ordered a short 420 chain from SP4L to fit my change from 17/38 gears to 16/28 gears on my X18. Stock chains way to long, and I don't want to cut the other one, so i can go back to stock gearing if needed.
 

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Discussion Starter #15
Matty which notch on the needle is your c-clip now in? i'd do cams carb slide mod whilst messing about with the carb. i'd be pretty confident if you've done the petcock mod there shouldnt be a problem with refilling the flat bowl, fuel pours through the petcock once drilled, much quicker than i imagine the engine could drink it. Reeds is a good place to start, personally i'd probably refit the metal ones and test, just incase its the new reeds. i fitted some c/f reeds that made my bike run poorly, they were just poor quality and werent sealing properly.

Of course checking the plug has got to be the first step...
Needle clip is third from the top I believe, I dropped it down one from stock after installing the BBK.
 

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Trained Chimp
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The needle clip only effects low to mid range. I habe had issues in the past of rc cars running away when you let off the throttle because they were lean. I would take Cams advise. Most of what I know I learned from him. Thanks Cam2. Hows the ankle? Are you out jumping rivers again yet?
 

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The needle clip only effects low to mid range. I habe had issues in the past of rc cars running away when you let off the throttle because they were lean. I would take Cams advise. Most of what I know I learned from him. Thanks Cam2. Hows the ankle? Are you out jumping rivers again yet?
The ankles good John............It gets its tender moments but Ill be ready to whip up on my KX450 but jumping over things is gonna wait for atleast a year.....Still deciding whether or not to convert it to a Supermoto and take the action to the asphalt..........

Im glad that what I know has a chance at teaching others how to cope with the chinese enigmas................Youre welcome JTC
 

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Trained Chimp
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My dad told me I was nutz for wanting street tires on my tt500bake in the day. I love those motard bikes. Such an aggresive look.
 

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Hooligan
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Convert it to a supermoto and bring it out here ... we got a great track just outside of town.
 
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