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Post by voorhees on Jun 2, 2011 6:35:24 GMT -5
Is 90 psi cold and 85 hot too low a reading for a 72cc BBK
2 stroke?
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Post by 90GTVert on Jun 2, 2011 8:00:33 GMT -5
Yes. Is this a new install or are you having problems after some time running it?
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Post by voorhees on Jun 2, 2011 8:07:45 GMT -5
Nuts! Yes, I installed the kit one month ago and began to experience a problem getting momentum from a stop in the past week. Just 400km on it....I supposed i'll pull off the plastic shroud and check the bolts. Other than that, i'll have to....blarg!
What PSI is healthy?
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Post by 90GTVert on Jun 2, 2011 12:35:48 GMT -5
I'd like to see at least 120psi. You might get lucky and it's a head gasket, if not you'll need to check over the cylinder, piston, and rings.
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hazza
Scoot Member
Posts: 27
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Post by hazza on Jun 2, 2011 15:13:10 GMT -5
I just finished doing my 70BBK and checked the compression yesterday, it was 110/115 so not fantastic but adequate.
I finally got it to run well today after putting the jet back to what it was before the BBK and it revs well and accelerates pretty good. Goes to show that an upjet is not always needed but you may need to tweek the needle to make it run a bit richer at mid revs.
Harry
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Post by reveeen on Jun 2, 2011 15:28:35 GMT -5
Harry: you have something wrong going on there.
Like the "performance pipe" that you do not have to jet for, a BBK (bigger engine) simply requires more fuel (as it is certainly supposed to be pumping more air), if it's not pumping more air you have timing "issues" (within the cylinder).
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theo547
Scoot Enthusiast
Posts: 497
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Post by theo547 on Jun 2, 2011 15:28:55 GMT -5
arnt you the lucky one harry ;( lol
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hazza
Scoot Member
Posts: 27
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Post by hazza on Jun 2, 2011 15:45:53 GMT -5
Hi reveeen, I did rejet for the pipe and increased the jet size by 10 from 47.5 to 58. It ran slightly rich on that jet so putting on a 70BBK probably was enough to lean it out sufficiently to run well. It still has the stock airbox but I have replaced the rollers and clutch springs. When I upjetted it ran like a pig and going back to the smaller jet made it run better thats all I know. I only know what works for my scooter, it doesn't mean that it will work for everyone though.  Harry |
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Post by 90GTVert on Jun 2, 2011 16:44:48 GMT -5
Polini's install manual for a sport kit only suggests raising the needle. Hasn't always been the case, but sometimes. I ran one for thousands of miles with no jetting change on a 49cc with a 70cc kit. It was a bit rich in fact. It is possible, not likely though. Most of the time I end up using larger main jets.
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Post by jmkjr72 on Jun 2, 2011 22:14:39 GMT -5
and the manual for the polini used to call for a 20% up jet
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Post by 90GTVert on Jun 3, 2011 6:51:43 GMT -5
Prob still does for some models. There are quite a few bore kits in sport alone that fit minarellis and I believe they use different instructions for some of them.
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Post by jmkjr72 on Jun 3, 2011 14:13:41 GMT -5
yeah but i need to know what size injector you need for kits now when are they going to put that in the directions
and the corsa kit talks about needing at least a 17.5 mm carb
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Post by 90GTVert on Jun 3, 2011 14:38:58 GMT -5
You better get busy selling EFI kits so Polini takes notice!
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