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Post by millsc on Jul 4, 2012 22:58:06 GMT -5
i put a performance exhaust on my scooter it makes the scooter slower or around the same i cant get over 6000 rpms i kept airbox and removed the hole restrictor it didnt really run at all until i took off the hole restrictor bogged out with both restrictors removed from airbox how to fix this? got an 85 jet in it tried 85 through 90 all the same could get 7000 rpms plus with stock exhaust and airbox with all restrictors
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Post by skuttadawg on Jul 5, 2012 0:58:10 GMT -5
You may need a carb with a larger venturi to have it tuned with the pipe and maybe even air filter upgrade .
Helps to know what engine you have , carb setup , exhaust system and if stock or a BBK
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Post by super9 on Jul 5, 2012 6:17:39 GMT -5
you may have to tune the cvt with the exhaust i had the same problems untill i modded the cvt
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Post by millsc on Jul 5, 2012 7:07:47 GMT -5
20mm carb taotao vip 63cc got exhaust off ebay
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Post by alwaysright on Jul 5, 2012 10:52:05 GMT -5
it is my opinion (and some experience) that unless you have a heavily modified scoot the exhaust will not do anything, you're not builing enough back pressure and actually robbing HP. that is why I still have the stock exhaust on mine, although with my mods I think I would benefit from perf exhaust, for the mild build such as you have I think you need to mod more to get anything out of the exhaust. If I were you I'd try a 72 or 83 cc kit, that should help, it it's still not helping I'm a huge advocate for scrappy's big valve head, that thing did wonders for my scoot.
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Post by millsc on Jul 5, 2012 11:47:34 GMT -5
makes sense i plan to get the 83cc kit wanted to put more miles on the scoot first only have 200 miles on it
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Post by mainepeace on Jul 6, 2012 7:38:43 GMT -5
Try to shoot a spitball with a normal straw, then try with one of the mega straws they use in bubble tea. You won't get the large straw to shoot any distance unless you have lungs of an ox. If you hook up an air compressor you will get more distance with the larger tube because there is enough pressure behind the spitball.
Same thing with the exhaust. You need the pressure wave to help evacuate the cylinder on the exhaust stroke or you will allow exhaust gases to stay in the cylinder and keep fresh air out, robbing you of power.
Greg
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Post by viral on Jul 6, 2012 8:50:32 GMT -5
Try to shoot a spitball with a normal straw, then try with one of the mega straws they use in bubble tea. You won't get the large straw to shoot any distance unless you have lungs of an ox. If you hook up an air compressor you will get more distance with the larger tube because there is enough pressure behind the spitball. Same thing with the exhaust. You need the pressure wave to help evacuate the cylinder on the exhaust stroke or you will allow exhaust gases to stay in the cylinder and keep fresh air out, robbing you of power. Greg This is not exactly true. You need SOME backpressure in order to take advantage of physics and draw the exhaust out of the cylinder, but in general less backpressure will help fuel economy and increase power. I can't see this hurting his performance unless he put on some stupidly wide "ricer" type exhaust you see on those Civics. |
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Post by millsc on Jul 6, 2012 9:16:04 GMT -5
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Post by millsc on Jul 6, 2012 10:45:42 GMT -5
i have an 85 jet with four hole cap removed from air box i only have 214 miles 365km on the scooter its not much slower i lost about 1000 rpms after the install goes 35ish on flat gps did 38 with stock exhaust and ran around 7000 rpms now wont go past 6000rpms so i lost 3 mph and a 1000 rpms looks and sounds better though ordered 4gram sliders hoping to get the rpms back
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Post by wile on Jul 6, 2012 21:40:31 GMT -5
I think your running to rich and that is why you lost the rpms. You have a bigger carb plus an 85 main jet, that is quite a bit fuel for a stock motor.
Wile
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Post by carasdad on Jul 6, 2012 22:11:28 GMT -5
My gf runs that exact muffler on her scoot. Free flow uni filter....that muffler...80 BBK...6 gram sliders....#82 jet....and can hit 49 mph (GPS) Sounds like your jet is too big....carb is too big...and engine displacement is too small.  |
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Post by wile on Jul 6, 2012 22:31:30 GMT -5
Exactly carasdad, to much ORANGE JUICE for a 49.? displacement motor.
Wile
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Post by carasdad on Jul 6, 2012 23:14:58 GMT -5
wile....exactly....too much Orange Juice....and not enough Vodka... As I have said before....a scoot set up like that....is like holding your little brother under the lake....and telling him to inhale...  |
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Post by wile on Jul 6, 2012 23:22:27 GMT -5
Good one carasdad, very good example of drowning the little thing.
Wile
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Post by carasdad on Jul 6, 2012 23:56:56 GMT -5
wile Sir....and drowning it he is ...he outta name his scoot...'Natalie Wood"...she drowned too...
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Post by mainepeace on Jul 7, 2012 8:07:38 GMT -5
It's not "backpressure", it's a pipe tuned so the reflections coincide with the exhaust pulses. You want the cylinder to completely evacuate on each exhaust pulse, or you will mix exhaust gas with the intake charge, resulting in less air/fuel to burn, robbing you of power. Also, the exhaust gases increase cylinder temperatures. A completely free flowing exhaust (or even an open header) will damage the engine and probably burn a valve because the exhaust airflow is not moving fast enough to vacate the immediate area of the head and the temperature dramatically increases. You need the exhaust VELOCITY to get the hot air away from the engine. On a racing vehicle its not much of an issue because the airflow of the moving vehicle will dissipate the heat (generally). However, in traffic situations the heat will build up quickly and damage the valves and warp the head eventually.
All this is just the exhaust header DESIGN and has nothing immediate to do with the air/fuel mixture.
The best way to tell if you need to rejet is to read the spark plug or use a wideband oxygen sensor.
Greg
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Post by millsc on Jul 7, 2012 10:03:53 GMT -5
I changed to an 80jet it had a 79 in it stock seemed to run lean with the 80 by the plug read but gave me 500rpms back and speed has returned but doesnt sound as smooth gonna get an 82 should be perfect
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Post by viral on Jul 7, 2012 11:44:30 GMT -5
It's not "backpressure", it's a pipe tuned so the reflections coincide with the exhaust pulses. You want the cylinder to completely evacuate on each exhaust pulse, or you will mix exhaust gas with the intake charge, resulting in less air/fuel to burn, robbing you of power. Also, the exhaust gases increase cylinder temperatures. A completely free flowing exhaust (or even an open header) will damage the engine and probably burn a valve because the exhaust airflow is not moving fast enough to vacate the immediate area of the head and the temperature dramatically increases. You need the exhaust VELOCITY to get the hot air away from the engine. On a racing vehicle its not much of an issue because the airflow of the moving vehicle will dissipate the heat (generally). However, in traffic situations the heat will build up quickly and damage the valves and warp the head eventually. All this is just the exhaust header DESIGN and has nothing immediate to do with the air/fuel mixture. The best way to tell if you need to rejet is to read the spark plug or use a wideband oxygen sensor. Greg OK Mr. Technicalities, you just said the same thing I did in about 5 times as many words |
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Post by wile on Jul 7, 2012 12:26:19 GMT -5
Nice going Mill,
And just so everyone knows 4 bangers are not very critical on backpressure like the 2 bangers are.
Wile
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