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Post by jspringator on Sept 22, 2008 15:43:46 GMT -5
What does the vacuum line to Carburetor do? I'm betting that is what holds the throttle open while you are coming to a stop. I'd like to plug it.
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Post by paranoid56 on Sept 22, 2008 18:22:19 GMT -5
plug it and see what happens
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Post by lankeeyankee on Sept 22, 2008 23:15:59 GMT -5
The vacuum is used for many different reasons on an engine, but not to "Hold the throttle open" thats controlled mechanically not by vacuum. What does the vacuum line to Carburetor do? I'm betting that is what holds the throttle open while you are coming to a stop. I'd like to plug it. |
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Post by mx5tc on Sept 23, 2008 1:25:46 GMT -5
The vacuum is used for many different reasons on an engine, but not to "Hold the throttle open" thats controlled mechanically not by vacuum. What does the vacuum line to Carburetor do? I'm betting that is what holds the throttle open while you are coming to a stop. I'd like to plug it. The stock 24mm CV carb on most 150cc scoots has an air cutoff/air bypass valve (activated by high manifold vacuum) located on the "starboard"/right side of the carb. This valve is an emissions control device which supposed to reduce "emissions" which occur at high manifold vacuum with a closed or almost closed throttle. Hardly new technology, the Zenith Strombergs on my 1971 Volvo 164 had the same bypass valves! The bypass valve shouldn't have any impact on WOT, steady idle, steady cruise or acceleration. If you want to "bypass the bypass valve", remove the intake manifold vacuum line from the valve, plug the intake manifold line and put a plug/cap on the bypass valve fitting. Take your scoot for a test drive and see if you notice any difference. I suspect the only difference you will note is that the scoot will come down to idle speed a little faster when you let off the throttle. FWIW, the "aftermarket" Keihin 30mm CVK and the "OKO" Taiwanese/Chinese clones thereof do NOT have an air bypass valve. Makes for a cleaner engine compartment, especially if you have replaced the vacuum fuel petcock with a manual one. LankeeYankee, I'll bet ya an expensive beer (hard for me ta do, cause I'm cheap) that Jsprings scoot will come down to idle faster with the vac line to the bypass valve plugged and the vac inlet to outlet plugged! Mitch |
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Post by lankeeyankee on Sept 23, 2008 23:32:17 GMT -5
Yo what up Mitch Hmm betting beer on scooter tuning. In this section with all the vacuum I am going to say you know more about this certain topic. I have messed with CV carbs for many years and most with no emmisions control. So I am going to give you a beer for all the information you just provided to me. Cheers! to ya in a huge 48OZ Stien. ;D The vacuum is used for many different reasons on an engine, but not to "Hold the throttle open" thats controlled mechanically not by vacuum. The stock 24mm CV carb on most 150cc scoots has an air cutoff/air bypass valve (activated by high manifold vacuum) located on the "starboard"/right side of the carb. This valve is an emissions control device which supposed to reduce "emissions" which occur at high manifold vacuum with a closed or almost closed throttle. Hardly new technology, the Zenith Strombergs on my 1971 Volvo 164 had the same bypass valves! The bypass valve shouldn't have any impact on WOT, steady idle, steady cruise or acceleration. If you want to "bypass the bypass valve", remove the intake manifold vacuum line from the valve, plug the intake manifold line and put a plug/cap on the bypass valve fitting. Take your scoot for a test drive and see if you notice any difference. I suspect the only difference you will note is that the scoot will come down to idle speed a little faster when you let off the throttle. FWIW, the "aftermarket" Keihin 30mm CVK and the "OKO" Taiwanese/Chinese clones thereof do NOT have an air bypass valve. Makes for a cleaner engine compartment, especially if you have replaced the vacuum fuel petcock with a manual one. LankeeYankee, I'll bet ya an expensive beer (hard for me ta do, cause I'm cheap) that Jsprings scoot will come down to idle faster with the vac line to the bypass valve plugged and the vac inlet to outlet plugged! Mitch |
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Post by mx5tc on Sept 24, 2008 0:50:24 GMT -5
Hey Lankee,
I can't wait to collect it and buy ya one in return! Ya got me good the other day on CV needles and how they impact midrange steady state cruise mode so I owe you a beer too.
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Post by lankeeyankee on Sept 24, 2008 21:45:19 GMT -5
Hey Mitch No Biggy man, I am learning from you and reading your threads. Not to get off the topic of talking about scooter tuning but since the CV carb is very popular also in motorcycles I have spent years tuning them for jet kits installs, after market exhaust and overall performance. On my VMAX I was only getting 24-25 MPG when it should get 35-38 with the mods I have done to the engine. I lowered my needle one notch and now I am getting 32 MPG. I have never had to change pilot jets out. with basic CV carb tuning the tricks are in the main jet, needle, and slide spring pressure. I just changed out my main from a 105 up to a mikuni style 115. The scoot now is smoother, quiter and the top speed has increased 2 MPH. The biggest difference is going up hills it tends to pull them better now. I left the 34 Pilot in. The bad thing I was getting 79-81 MPG now I got 67MPG. This is not my goal with the scooter I am trying to get it back atleast in the mid 70MPG. I am going to increase my spring pressure to hold the slides down until WOT when needed. Any ideas on increasing the MPG? I may drop the header pipe and smooth the exhaust port out along with matching the header with the port. My Main Goal with this scoot is MPG!!! Tossing ya a cold one ;D Yankee Hey Lankee, I can't wait to collect it and buy ya one in return! Ya got me good the other day on CV needles and how they impact midrange steady state cruise mode so I owe you a beer too. |
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Post by mx5tc on Sept 25, 2008 0:24:10 GMT -5
Lankee,
The fuel economy issue is sticky. I suspect what is happening on your scoot is that you now have the right mixture for best power at WOT but are too rich for midrange and less than WOT cruise. I wish I had a real Mikuni or Keihin CV needle to compare to the one in my clone 24mm CV. I'm wondering if a needle with more taper (look at the various profiles that Keihin has) would still give you the right WOT mixture while providing a leaner and more economical mixture for midrange and cruise. Has anyone figured which Mikuni or Keihin needle series can be swapped into our carbs??
I am trying to figure out a way to "hack" my stock exhaust/muffler with an 02 exhaust bung so I can use my Innovate wideband o2 sensor and really understand what air fuel ratio is through out the RPM range so I'm not guessing. Innovate's website has some interesting carb articles (http://www.innovatemotorsports.com/resources/carb-central.php) demonstrating how to get both WOT performance and fuel economy out of carbed motors. Same principles hold true for scoots and CV carbs; the challenge is going to be finding interchangeable needles that will fit and figuring out how to modify the existing air bleeds. Drilling out air bleeds isn't for the faint of heart, but hey these are basically throwaway carbs anyway!
Mitch
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