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Post by oldgeek on Oct 7, 2023 20:28:41 GMT -5
I finally got some motivation late afternoon today so I tried to tune a bit, because I really wanted to ride it. I went back to an old tune that had worked pretty well and tweaked it just a hair better than it originally was.
I went for a ride down the blvd, cruising sucks down there since they close off 1 block and everyone has to detour around it so it is a real cluster. The tune is pretty good as long as I keep RPM's up and the clutch is not too hot. I have to run it like a light switch because part throttle is not to good in certain places. If I roll off of it too slow there is a nasty lean spot sometimes. I think the biggest problem is that the clutch warms up and then starts coming in just a tad too soon , so it bogs for a bit on takeoff. Top speed is down to 65, likely because I have lighter sliders in to bypass the gutless low end of the pipe. Temps stayed between 120F and 130F, RPM's are around 10500 at WOT. It will make the front wheel very light from a roll pretty consistently, the wheel may even be coming off the ground for a moment. It is loud and a blast to ride.
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Post by 190mech on Oct 8, 2023 5:41:08 GMT -5
That pipe could be giving you some tuning problems also as it appears to have a very steep headpipe angle that will cause mixture from the 'A' transfers to be drawn into the exhaust port causing a lean condition at part throttle. That cylinder port layout should be giving you a lot of wheely producing torque .. I think Jennings had a good graph in his tuning book about this problem also.. Ya got any other pipe around there to test??
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Post by oldgeek on Oct 8, 2023 7:24:14 GMT -5
That pipe could be giving you some tuning problems also as it appears to have a very steep headpipe angle that will cause mixture from the 'A' transfers to be drawn into the exhaust port causing a lean condition at part throttle. That cylinder port layout should be giving you a lot of wheely producing torque .. I think Jennings had a good graph in his tuning book about this problem also.. Ya got any other pipe around there to test?? That must be what is going on. The pipes I have that physically fit this motor are the PG short, which would be a poor choice, the V8 pipe which is said to be good for up to 90cc, and the Piece of a Peace pipe which needs some repairs. Autotech355 on feebay has a V8 pipe good for up to 125cc Take a look and see what you think of it. V8 pipe for up to 125cc EDIT: I think scooter tuning has the same one cheaper. I may email them and check to see the inlet size on that one. |
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Post by 190mech on Oct 8, 2023 18:57:51 GMT -5
I have a home brew pipe I'll send you if you like..
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Post by repherence2 on Oct 8, 2023 19:49:47 GMT -5
I have a home brew pipe I'll send you if you like..
C16 spec Peace Pipe....?
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Post by oldgeek on Oct 8, 2023 20:01:17 GMT -5
I have a home brew pipe I'll send you if you like.. What is the header ID? I've got 32mm coming off of this cylinder |
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Post by repherence2 on Oct 8, 2023 20:12:04 GMT -5
finally came back to the Forum. Oldgeek, try looking into a Venturi Divider. i was reading your thread and seen that you have been having problems sorting out the Polini PWK. i encountered problems with the Chinese Oko knock off carbs and the genuine Taiwan OKO PWK carbs. my solution was a Venturi Divider that i first seen on Rich's Taylor'd Porting website. i made my dividers out of aluminum plate. i have also experimented with clear polyethelyne plastic from the hobby shop. for large PWK carbs, the Venturi Divider makes a big difference in my experience when tuning the PWK type carbs. the way i see it, the flat slide face fucks up the air flow and vacuum characteristics versus a round slide. i am just saying this because my experience tuning a Polini CP24 was much easier than tuning a 26 and 28 PWK carb. i think the Slide makes a big difference when it comes to low throttle performance. ever since i started using a Venturi Divider on my large PWK carbs, 26mm-28mm Knock-off and genuine OKO, i have had no problems with the PWK carb. I liken it to something like VTEC on Honda's or "reverse VTEC". from 0 to 1/2 throttle, you get better velocity and vacuum with the Divider. similar to VTEC, the intake profile as far as velocity is concerned, changes. when you run the divider, low to mid throttle is a lot smoother because of the way the air flows and the amount of vacuum the divider induces from 0 to 1/2 throttle. it is So much Easier to tune a large PWK when it has a venturi divider. from 0 to 1/2 throttle, the way the air flows with a divider increases the vacuum and the air is less turbulent because the incoming air is not hitting the flat face of the D slide on the PWK carbs. all i am saying is this, i think your tuning troubles with the PWK carb would be solved with a Venturi Divider. i know it works for me.  vertical and horizontal diffuser i made out of hobby polyethylene plastic.  aluminum diffuser plate.
diffuser in the PWK carb
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Post by oldgeek on Oct 8, 2023 20:19:40 GMT -5
finally came back to the Forum. Oldgeek, try looking into a Venturi Divider. i was reading your thread and seen that you have been having problems sorting out the Polini PWK. i encountered problems with the Chinese Oko knock off carbs and the genuine Taiwan OKO PWK carbs. my solution was a Venturi Divider that i first seen on Rich's Taylor'd Porting website. i made my dividers out of aluminum plate. i have also experimented with clear polyethelyne plastic from the hobby shop. for large PWK carbs, the Venturi Divider makes a big difference in my experience when tuning the PWK type carbs. the way i see it, the flat slide face fucks up the air flow and vacuum characteristics versus a round slide. i am just saying this because my experience tuning a Polini CP24 was much easier than tuning a 26 and 28 PWK carb. i think the Slide makes a big difference when it comes to low throttle performance. ever since i started using a Venturi Divider on my large PWK carbs, 26mm-28mm Knock-off and genuine OKO, i have had no problems with the PWK carb. I liken it to something like VTEC on Honda's or "reverse VTEC". from 0 to 1/2 throttle, you get better velocity and vacuum with the Divider. similar to VTEC, the intake profile as far as velocity is concerned, changes. when you run the divider, low to mid throttle is a lot smoother because of the way the air flows and the amount of vacuum the divider induces from 0 to 1/2 throttle. it is So much Easier to tune a large PWK when it has a venturi divider. from 0 to 1/2 throttle, the way the air flows with a divider increases the vacuum and the air is less turbulent because the incoming air is not hitting the flat face of the D slide on the PWK carbs. all i am saying is this, i think your tuning troubles with the PWK carb would be solved with a Venturi Divider. i know it works for me. vertical and horizontal diffuser i made out of hobby polyethylene plastic. aluminum diffuser plate. diffuser in the PWK carb I do remember you telling about the divider before and I have been kicking around how to build one since I have been wasting so much time on tuning this carb. I have no doubt it will help get the carb dialed in easier. How is it attached? Looks like a bit if a PITA to make one. |
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Post by oldgeek on Oct 8, 2023 21:08:41 GMT -5
I really enjoy having a fast scooter to ride again!
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Post by repherence2 on Oct 8, 2023 21:35:06 GMT -5
I do remember you telling about the divider before and I have been kicking around how to build one since I have been wasting so much time on tuning this carb. I have no doubt it will help get the carb dialed in easier. How is it attached? Looks like a bit if a PITA to make one.
i totally get it.
yes it does take some effort to make the pattern out of card stock. i use a Compass/Divider to transpose the contour of the carb mouth.
if it is a 28mm carb, i cut out a strip of card stock to the "carb size". so if it's a 28mm carb, i cut a strip of card stock that is 28mm wide. i draw a center line at 14mm. then i take a grade/elementary school compass and use it as dividers. i set it to 1/2 diameter of the carb, i use that to transpose the contour of the carb mouth. if the carb is 28mm, i cut card stock to 28mm width. then i inset it into the carb throat. using a compass, you put the hard point on the carb mouth side and the pencil/graphite point on the center line side. while running the hard point of the compass along the carb mouth, you transcribe that contour onto the card stock.
if not, the other option i thought of would be to use clay of plastocine get a mold of the carb mouth, and then you cut to the clay in half to get the carb mouth contour profile and trace that onto card stock to get a pattern.
what size PWK carb is your POLINI?
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Post by aeroxbud on Oct 9, 2023 3:58:49 GMT -5
Would you be possible to get a small contour gauge into the carb mouth?
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Post by oldgeek on Oct 9, 2023 6:16:29 GMT -5
I do remember you telling about the divider before and I have been kicking around how to build one since I have been wasting so much time on tuning this carb. I have no doubt it will help get the carb dialed in easier. How is it attached? Looks like a bit if a PITA to make one. i totally get it.
yes it does take some effort to make the pattern out of card stock. i use a Compass/Divider to transpose the contour of the carb mouth. if it is a 28mm carb, i cut out a strip of card stock to the "carb size". so if it's a 28mm carb, i cut a strip of card stock that is 28mm wide. i draw a center line at 14mm. then i take a grade/elementary school compass and use it as dividers. i set it to 1/2 diameter of the carb, i use that to transpose the contour of the carb mouth. if the carb is 28mm, i cut card stock to 28mm width. then i inset it into the carb throat. using a compass, you put the hard point on the carb mouth side and the pencil/graphite point on the center line side. while running the hard point of the compass along the carb mouth, you transcribe that contour onto the card stock. if not, the other option i thought of would be to use clay of plastocine get a mold of the carb mouth, and then you cut to the clay in half to get the carb mouth contour profile and trace that onto card stock to get a pattern. what size PWK carb is your POLINI? 28mm |
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Post by 190mech on Oct 9, 2023 7:23:51 GMT -5
This pipe ID is 29.2mm..
A piece of solder makes a good contour gauge...
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Post by oldgeek on Oct 9, 2023 7:25:31 GMT -5
This pipe ID is 29.2mm.. A piece of solder makes a good contour gauge... Genius! |
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Post by 90GTVert on Oct 9, 2023 7:42:09 GMT -5
Never heard of a contour gauge before. Looked it up. Now I've found another tool that I suddenly need. lol repherence2 : One thing that I never saw you answer is, how is it attached? I've seen some that appear to be epoxied in. Some that look like they notched the carb mouth and made the divider wide enough to fit the notches there. Others were a whole bell mouth design. Your pics kinda look like they're just sitting in there, but I'd think they could at least rotate that way. |
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