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Post by endru on Jun 8, 2013 22:00:56 GMT -5
So this weekend I installed my 83cc BBK from scrappy's. It was a great feeling to get it all put together and have the scoot start right up  Absolutely no problems from the starter, which I've heard can be difficult with the BBK's. But... after letting it idle a good 20 minutes to warm up and let the rings initially seat, I went to take it for a test run and found that it won't accelerate. It revs up enough to engage the clutch and then wants to go, but suddenly bogs, sputters and hesitates but stays running. My idle in fact is really steady, although adjusting the A/F screw and even the idle screw don't have much of an effect on the idle like they did when it was stock. I've done my own troubleshooting all day and haven't solved it yet. I adjusted from my initial #  jet down to a #92 and #  , all of which didn't have a significant effect. Then I was sure the timing chain must have been off one link, but when the flywheel T lines up with the crankcase tab, the two smaller holes on the cam are perfectly parallel to the head and the large whole is perpendicular like they should be. Sprayed carb cleaner around the intake and exhaust while it was running to check for leaks, nothing noted. I would check compression if I had a gauge, but I'm willing to go out and get one if all else fails. What else could it be? Here are all the other relevant (and maybe some irrelevant) details: It's a Puma Amor, Uni-style filter, performance exhaust, valves at .004" and .005", stock carb, #35 idle, stock head, stock CDI, orange coil, 5 gram sliders, 1500 rpm clutch springs and contra spring, iridium plug... I think I got it all ;D Thanks everybody in advance! |
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Post by millsc on Jun 8, 2013 22:41:25 GMT -5
5 grams with a 1500 contra spring is way light, need to go up to 7 grams at least if you weigh 190 or less, you probably are over reving bad, spinning wheels and not going anywhere. 5 gram weights with a 1500 contra sping is like running 3 grams on a stock spring. more power needs heavier weights to balance the power to stay in the powerband
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Post by skuttadawg on Jun 8, 2013 22:41:43 GMT -5
May need a larger idle jet . Idling it not suggested on a new build nor is that how you break it in . To break it in ride at midrange while going up and down in speed .
Now you want to try a smaller MJ as when I did my BBK I tried too large of MJs and it would sputter even had gas drops come out of the UNI tried a smaller MJ and tada no sputter and the fun began . How many MMs is your carb ? Checked for intake or exhaust leaks . Do a plug chop to see how the jetting is
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Post by lykos23 on Jun 9, 2013 5:45:45 GMT -5
Congrats on the bbk install! Like Skutta says, you should only be idling it long enough for the engine to warm up, not much longer than that. 5 minutes tops maybe. Though I've read elsewhere that you need to make sure the engine is warm before taking a ride anywhere with a new bbk. You can safely bump up to a 38 idle jet, it's what I use, makes for easier startups, etc. Right now I'm using a # main jet and it seems to be working though I have yet to do a plug chop. #  should be safe too, but I'm not quite sure. You may want to temporarily switch to the weights that came with the kit as they are heavier. I myself have 3 4g and 3 9g weights which seems good for my setup and weight but a lighter rider needs more weight from what I've read. Definitely listen to Millsc. The ones that came with my kit were 8.6g roller weights. I got 45mph on flats now, you should be able to do similar with your identical bbk  Good luck! |
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Post by ej132 on Jun 9, 2013 9:11:28 GMT -5
So if I sometimes have to give it some throttle to get it started I probably could go up to a #38 pilot jet for easier starting?
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Post by lykos23 on Jun 9, 2013 9:32:51 GMT -5
[replyingto=ej132]ej132[/replyingto]That's what I did. Still gotta adjust the a/f screw for first-try-starts, but the #38 worked wonders for me because I have a free flow filter.  Note: you should only need to get a 38 if you up the displacement of your scooter. If not, then a longer 35 should be fine. |
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Post by endru on Jun 9, 2013 20:22:50 GMT -5
Hey thanks everybody! Tomorrow night I'll change the weights using my roller kit. I knew I would need a weight change after installing the bbk, I was just hoping to get everything working properly before then. I don't really think the weights are the problem though. I'm only revving until maybe 3.5k rpm at most before it sputters. With these weights and springs I should at least be getting 25 mph before over revving becomes an issue... I'm barely hitting 10 mph and it's hesitating, sputtering and skipping. skuttadawg - So the carb I have is stock, which I'm guessing is 17mm but I'll need to measure tomorrow to make sure. Do smaller carbs in general require smaller jets for the same displacement engine application? My thinking is that a smaller carb won't move as much air, so it would require smaller jets to keep from running rich. I'm really encouraged by your example with using jets that were too large. Would yours sputter and not gain speed, or just sputter while at the speed you wanted? My next smallest jet is an #  . I'd prefer to try an # first, but if the # seems to solve the problem then I'll buy an # and do the plug chop. An exhaust leak is possible, I'll order a new gasket just in case, as well as a #38 pilot jet. @lykos - I'm glad you chimed in, I fee like we're in the same boat in a lot of ways. You were on the old skuttadawg site too, right? So what size carb are you using with your main jet? Thanks again, I'll update again after I make these changes. Can't wait to go riding and do the "real" break-in. |
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Post by lykos23 on Jun 9, 2013 20:26:56 GMT -5
[replyingto=awhitlock]endru[/replyingto]Yup, been a member since the day after I got my Great Leap in January I'm using my stock carburetor. Hitting 44.93mph on flat ground |
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Post by endru on Jun 9, 2013 20:37:19 GMT -5
[replyingto=lykos23]lykos23[/replyingto]Can't wait! That used to by my straight downhill, wind at my back, head tucked top speed. Hopefully that and even better then with the gears and an a9 cam.
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Post by lykos23 on Jun 9, 2013 20:41:56 GMT -5
Can't wait! That used to by my straight downhill, wind at my back, head tucked top speed. Hopefully that and even better then with the gears and an a9 cam. I don't have the a9 cam or taller gears yet, AND I'm overweight at 267lbs. You should have no problem hitting these speeds once we find your problem. |
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Post by skuttadawg on Jun 9, 2013 22:53:00 GMT -5
Yeah larger venturi means more air which requires larger jets . Too big of a venturi and the engines vacuum is not enough to optimize it . Look at the sparkplug I bet it is wet and dark from too much gas
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Post by endru on Jun 10, 2013 21:35:07 GMT -5
Okay here's the update. I first pulled the plug and yup it was running rich. That was a good call skuttadawg. Downjetted to a # and I saw a lot of improvement. It was still popping and hesitating, but it would pick up more speed than before. Suspecting an exhaust leak, I put on the stock muffler. It dampened a lot of the popping sound but it was still hesitating and higher rpm's. With the stock exhaust, I could hear some popping coming out of the air intake. Put in 8.5 gram rollers from my kit. It put me well below my power band, but at least now I was hitting 30, though it was still taking me as much time as before to get to that point. The nice part about that was that I could really isolate when the problems were happening. Low rpms are great, right up until just after the clutch engages. After that the engine starts feeling sick, and then if I briefly crank full throttle it sounds and feels really unhappy. I'm stunned because I messed around with all kinds of jet sizes and all kinds of weights and it never caused me these kinds of performance issues. I guess it could still be to rich... but jeez I was running an #80 with my stock kit no problem. I'm still suspecting an exhaust leak, so my next step is to get a new gasket ordered and try that out. Now for the happy side of the story. I was finally able to get my new gears pressed. I had trouble finding a machine shop that would do it. The first guy took a look at them and saw how tight the fit was and just said "there's no way that'll work, I'm going to decline." No amount of convincing would get him to even attempt it. The next machine shop the guy wanted to charge me $25 to have it done. When I balked and said it was a 10 minute job max, he literally shoved them back at me and said "see you later then." I asked him what his hourly rate was and he said $50... guess math wasn't his strong point. I was pretty hopeless by that point. I went to the last place and the guy was super friendly. He took me back with him and he had me help him position it under the press. It went right in like butter, It was 6 minutes from the time he punched in until the time he punched out. And then to make things even better, he decided to not even charge me.  I was ecstatic. ;D |
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Post by endru on Jun 12, 2013 21:48:49 GMT -5
I have 7.5 g in rollers from my weight tuning set in right now and the speed has improved like expected, but the skipping is still there. I even got a new exhaust gasket and sealed it with exhaust gasket sealant. It runs pretty smoothly at lower speeds and rpms, but the problem still shows up at higher rpms. So with 7.5 g weights, as soon as I hit about 30 mph, I can hear popping coming out of the air filter and the exhaust, and the scooter skips and hesitates. The most interesting thing was when I took it down a hill, at about 35 mph it was popping and cutting out rapidly, about once every second. It honestly felt like I have a rev limited CDI or something, even though it's the same CDI as before, and I'm pretty sure it wasn't limited back then. So maybe the CDI is malfunctioning. What caused it I don't know, but the issue just feels like a timing issue. An main and 38 idle jet are in the mail, at least now I won't be running quite so lean. |
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jet down to a #92 and #
, all of which didn't have a significant effect. Then I was sure the timing chain must have been off one link, but when the flywheel T lines up with the crankcase tab, the two smaller holes on the cam are perfectly parallel to the head and the large whole is perpendicular like they should be. Sprayed carb cleaner around the intake and exhaust while it was running to check for leaks, nothing noted. I would check compression if I had a gauge, but I'm willing to go out and get one if all else fails. 
should be safe too, but I'm not quite sure. 
. I'd prefer to try an #