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Post by oldgeek on Feb 24, 2014 6:51:25 GMT -5
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Post by poppysteve on Feb 25, 2014 12:41:02 GMT -5
Hi,
So if I was going to buy a PWK OKO carb, what size should I get for a 54mm BBK 90cc (~100cc)
I've read go get 28mm for 86-90cc, but that seems like a huge jump from my current 19mm.
This is for an ATV application, so lower end and wider power is better, then a tiny peak.
My experience is larger is better on high rpm, but lowers the low rpm power..
Options are 19, 21, 24, 26, 28, 30mm
Thanks!
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Post by 90GTVert on Feb 25, 2014 12:53:10 GMT -5
19-24mm would be my choice, prob 21mm. I use 21mm Dells on my 90-110ccs for the most part. If it's more race oriented, then maybe 24-28mm. 21mm has given me good cooling, good power, and reasonable fuel economy. I used to use 24-25mm on my street 90-100cc, but fuel economy was never as good and there was no power benefit that I could discern.
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Post by poppysteve on Feb 25, 2014 13:26:11 GMT -5
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Post by 90GTVert on Feb 25, 2014 14:22:22 GMT -5
I think those are too large to work with the stock airbox and intake, but it's been a long time since I've had a PWK around. If the numbers Parts For Scooters lists are correct for the 21mm it's not gonna work with the stock stuff. They say 49.5mm on the inlet side, stock airboxes work with around 36-38mm. They list 34.5mm on the outlet side and I don't recall the ID of the stock intake, but I don't think it's that big. The intake I had with an OKO 21mm, this was 8 years ago and I was new to modding scoots so I can't really remember fit details, was like PFS part 169-125. Those reeds don't like to fit the cases without filing down the screws or filing the reed opening or using a reed spacer though. 2strokd had one that looks just like it, though from another vendor (still prob the same thing), leak at an intake port and need sealing. The carb itself is larger too IIRC so it may change fit in the frame of the scooter. Plus the cable needs to be reconfigured or replaced becasue it's no longer a screw on fitting like stock. |
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Post by 90GTVert on Feb 25, 2014 14:36:36 GMT -5
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Post by poppysteve on Mar 3, 2014 10:53:19 GMT -5
Well Poop.. Rushed a bit too much.. New reduction gear, new starter relay. Motor would stumble for 5-10 seconds but never catch. Still original cleaned carb, both mixtures 2.5 out.. Checked compression, only 60.. Re-torqued head, still 60. Pulled head and checked rings.. fine.. Reinstalled everything and stripped a head nut.. M7-1.0 Flanded nut, NOT in local supply. Picked up some M7 nuts and washers. Pulled the stripped headbolt, re-tapped and die'd everything. Installed the headbolt upside down ( original stripped section now at the case ). Torqued all to 10, 13, 15 SNAP.. Snapped the headbolt on the bottom left.. The worse spot.. SO HATE these cheap a$$ headbolts so order new better looking ones, and flanged nuts.. Pulled the jug and there is a little stub sticking out.. Tried Vice grips.. Na.. Filed 2 flat sides, re-vicegrip, not a budge.. Only have maybe an 1 inch arc between the pickup and the connecting rod/frame.. EZ out time.. And time to think.. Measured the 2 jugs, 50mm (90cc) [77.66mm] and 54mm(100cc)[77.33mm]. Check the 2 heads, the new 54mm head ( Part number 633141 ) has a very deep recess ( 5.9mm ). Well crap.. this must be a 'stroked head'.. 90cc stock is 42mm, 110cc is 48mm. I'm NOT stroked, at least not yet..  SO.. can I use my 50mm head on a 54mm jug? Do I need to get the 54mm head machined down? Anyone know which head will work with a 54mm jug and stock stroke? The piston diameter is 53.85mm. Some pictures... www.dropbox.com/sh/ska5vuiecerfrum/RmbUM2OJWhThanks! |
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Post by 90GTVert on Mar 3, 2014 11:27:03 GMT -5
If the head is too far recessed you could have it milled. One approach would probably be to figure out what is needed to end up with around 0.9mm squish clearance. Then it could be used without a gasket for the tighter side of squish settings or a gasket could get you maybe 1.2-1.4mm squish if compression is a bit high the other way. The longer and more in depth approach would be to go over everything including port durations, measuring current clearances, finding the volume of the combustion chamber and piston crown displacement, deck height, etc... and calculating compression ratios, playing with timings, and figuring out exactly what you need before having any work done to the head. Lots of work, but you may end up with a better end result. You can use a 50mm head with a larger bore. It's not ideal, but as long as there's sufficient clearance it can be done. Here's a 54mm head. www.maximumrpm.com/index.php?p=product&id=30&parent=3 |
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