|
Post by mrhooper on Dec 11, 2016 21:12:16 GMT -5
Intalled a a9 cam shaft on a sunny scooter and i up jeted to a 85 . Now I'm not getting to top speed, it only goes about 25. But there is no bog and the valve have been adjusted. Could this be a timing issue ?
|
|
|
Post by humanshield on Dec 11, 2016 21:23:32 GMT -5
Yes it could. If you're off by even one tooth it will make a big difference.
50cc Sunny correct?
|
|
|
Post by mrhooper on Dec 11, 2016 21:38:23 GMT -5
Yes it could. If you're off by even one tooth it will make a big difference. 50cc Sunny correct? Yes a sunny 50 cc
|
|
|
Post by mrhooper on Dec 11, 2016 21:42:24 GMT -5
I'm at sea level what size jet would you guys recommended for a A9 cam
|
|
|
Post by humanshield on Dec 11, 2016 21:42:26 GMT -5
Go back and recheck the timing. It's not hard to miss a tooth. Actually it's pretty easy. I've done it hundreds of times and I can't say I "never" miss a tooth...but them my peepers are not what they used to be.
Also, is this has no other mods correct? Just the cam?
Now I can also tell you this.....the A9 cam will drop your compression a bit. If you were compression deficit before the cam, you might be too low now. After rechecking the timing, check your compression. Below 140 would be on the low side...180 up on the high side. (give or take). I've seen TaoTao 50's run with only 70psi compression.
You DO NOT want any headwind with that setup. All downhill would be better.
I Installed a 50mm BBK on mine over 4,000 miles ago and the compression was actually too high for my tastes. The A9 brought it back down to my liking beautifully. It was REALLY hard to start before the cam. A great hand in hand set of modifications.
|
|
|
Post by humanshield on Dec 11, 2016 21:49:43 GMT -5
I'm at sea level what size jet would you guys recommended for a A9 cam I'll ease out now and let others chime in......good luck! The more opinions the better....usually.
|
|
|
Post by mrhooper on Dec 11, 2016 21:55:28 GMT -5
Thanks but I have a uni air filter and a white brothers racing pipe.
|
|
|
Post by 90GTVert on Dec 12, 2016 7:35:04 GMT -5
|
|
|
Post by humanshield on Dec 12, 2016 16:17:17 GMT -5
Ah... I also have a Uni filter
|
|
|
Post by mrhooper on Dec 13, 2016 1:51:37 GMT -5
Thanks for your guys responses i have changed to a 95 jet it runs better but still feels "flat" I belive the rings are worn so I will perform a compression check
|
|
|
Post by 90GTVert on Dec 13, 2016 11:59:26 GMT -5
You might want to try a few more jets before tearing it down, unless a compression test gives a poor result.
|
|
|
Post by greggkinney on Dec 14, 2016 19:42:07 GMT -5
Go back and recheck the timing. It's not hard to miss a tooth. Actually it's pretty easy. I've done it hundreds of times and I can't say I "never" miss a tooth...but them my peepers are not what they used to be. Also, is this has no other mods correct? Just the cam? Now I can also tell you this.....the A9 cam will drop your compression a bit. If you were compression deficit before the cam, you might be too low now. After rechecking the timing, check your compression. Below 140 would be on the low side...180 up on the high side. (give or take). I've seen TaoTao 50's run with only 70psi compression. You DO NOT want any headwind with that setup. All downhill would be better. I Installed a 50mm BBK on mine over 4,000 miles ago and the compression was actually too high for my tastes. The A9 brought it back down to my liking beautifully. It was REALLY hard to start before the cam. A great hand in hand set of modifications. hate to sound dumb but could you explain a little how or why the cam affects the compression. Education is the key
|
|
|
Post by 90GTVert on Dec 15, 2016 10:54:19 GMT -5
hate to sound dumb but could you explain a little how or why the cam affects the compression. Education is the key It's not a dumb question by any means. Camshafts can alter dynamic compression. There are two compression ratios that get mentioned with four-stroke engines. Static compression and dynamic compression. Static compression is what most people think of when they think of a compression ratio. It's what most manufacturers and build sheet specs will quote. Static compression ratio is basically just the ratio of the total volume in a cylinder and head above the piston at bottom dead center (BDC : the bottom of the stroke or piston travel) compared to the volume above the piston at top dead center (TDC : the top of the stroke or piston travel). For example; if you have a 50cc cylinder and a head with a 5cc combustion chamber, you'd have 55cc above the piston at BDC. In reality, you have to figure in gasket thickness/volume and piston crown volume and so on, but this is a simplified example. When the piston is at TDC, there's only the 5cc of the combustion chamber left above the piston. Again, you'd have other factors and maybe the piston doesn't reach the top of the bore so there's more volume there and so on, but that's not all necessary to know about to get the basic idea. So your piston is trying to compress 55cc at BDC into just 5cc at TDC. 55 divided by 5 gives you and 11 to 1 (11:1) compression ratio. That's the static compression ratio. Static compression ratio is not affected by the camshaft. It is only influenced by things like cylinder and head volume. It's what compression would be if everything were simple. Dynamic compression ratio recognizes that things aren't so simple inside of a working engine. Static compression ratio assumes that the cylinder is sealed from BDC to TDC on the compression stroke, but that's not how it usually works. In reality, the intake valve isn't usually closed at BDC on the compression stroke so the cylinder is not sealed. Dynamic compression ratio uses the volume above the piston when the intake valve is closed for it's calculation instead of using BDC. The later the intake valve closes, the lesser than volume will be if all else is the same. So you may only have 40cc total instead of 55cc in the previous example. Compress 40cc into the 5cc at TDC mentioned in the past example and compression ratio drops to 8:1. So in that case, 11:1 would be the static compression ratio and 8:1 would be the dynamic compression ratio. Because swapping camshafts can change the timing of the valves, camshaft swaps can alter dynamic compression ratio. For the 2T folks, dynamic compression ratio can be compared to effective or corrected compression ratio, that uses the exhaust port closing point for it's calculations. Hope that makes some sense.
|
|
|
Post by jkeney on Dec 15, 2016 16:02:26 GMT -5
I have put the same a9 cam in three bikes now and each time it woke the top end up a little. I recommend that more people use the stock 5cc head with their bbks and the loss of compression becomes negligible, the bike will be easier to start, and most likely last longer. Also don't use the thicker head gaskets that sometimes come with the kits. I swear I can tell a difference in two bikes with same displacement and supporting mods using thin vs thick gaskets.
|
|
|
Post by jkeney on Dec 15, 2016 16:04:09 GMT -5
I have put the same a9 cam in three bikes now and each time it woke the top end up a little. I recommend that more people use the stock 5cc head with their bbks and the loss of compression becomes negligible, the bike will be easier to start, and most likely last longer. Also don't use the thicker head gaskets that sometimes come with the kits. I swear I can tell a difference in two bikes with same displacement and supporting mods using thin vs thick gaskets. I do not mean the bike will be easier to start with a bbk, stock head , and stock cam.
|
|