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Thread: change pipe vs rejet for high altitude

  1. #1
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    Default change pipe vs rejet for high altitude

    I picked up a couple of Phazer IIs that were set up to run at around 1,200 ft elevation.

    I live a 4,000ft and will be riding mostly in the 6,000 ft range.

    both sleds came with pipes and the guy i bought them from said he would just swap pipes when he rode out here and did not have to change gets. Does this seem correct or should i be changing jets as well?

    thanks

    Brad

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    Hmm, interesting. So the previous owner would just swap out from the stock pipe to an aftermarket pipe when riding higher elevation to lean out the jetting with a more aggressive pipe?

    I'd be surprised if that worked very well if you want best performance out of them, as clutching comes into play as well. An aftermarket pipe will make more HP (they do require richer jetting and the previous owner's method would result in leaning out the jetting when at higher altitude) but results in it over-revving because the primary has weights set up for X horsepower but now it is making 5-8 HP more.

    Honestly if it were me, I'd run them both with the better performing aftermarket pipes and then jet & clutch for them. 4000'-6000' elevation change isn't going to require changing jetting between the two, just jet so that you get a nice cardboard brown burn on the plugs at 4000' and it'll be fine at 6000'. Maybe a bit rich but nothing that would be all that noticeable except for it being a bit "burbl-y" as I like to put it.
    03 Mountain Viper, SLP Triples, SLP Flo-rites, gas rack, low profile blue windshield, NO underhood air going to the air box, (& no more powder bog)

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    You could be alright on the mains, but those pz's like a 110 pilot at altitude, at least with my experience. I run mine 4-6k area and use the 143.8 mains. Without looking it up, 150's or 143.8 would be around that 1200 mark, but if you dont up the pilots you may have an issue on the first part of the throttle. Best way to keep those alive is not to stay the throttle for extended periods at low end and midrange. You need to frequently burp the flipper.

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    Sorry but that makes no sense.
    You recommend he "up" his pilots to jet for higher altitude? Up from a 95 stock size to a 110? Were the phazer ll's really really lean on the pilot circuit from the factory?

    Going up in altitude results in less air...fuel stays the same unless something is changed in the carbs...so his sleds will run richer due to air being reduced. It doesn't make sense to go richer on any circuit when jetted for a really low 1200' and then wanting to change to a 4000' altitude.
    03 Mountain Viper, SLP Triples, SLP Flo-rites, gas rack, low profile blue windshield, NO underhood air going to the air box, (& no more powder bog)

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    going to pull the jets and see tomorrow night. Met a local who has been running Phazers out here since they came out and he is piped with 127.5 mains and 100 pilot with no problems and runs crsip.

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    Quote Originally Posted by mod-it View Post
    Sorry but that makes no sense.
    You recommend he "up" his pilots to jet for higher altitude? Up from a 95 stock size to a 110? Were the phazer ll's really really lean on the pilot circuit from the factory?

    Going up in altitude results in less air...fuel stays the same unless something is changed in the carbs...so his sleds will run richer due to air being reduced. It doesn't make sense to go richer on any circuit when jetted for a really low 1200' and then wanting to change to a 4000' altitude.
    I have 4 phazers that I have ran piped and unpiped. I ride 4k to 6k, all the pipe sellers wont give you a straightforward jetting recommendation but say always to up the mains by 2 jet sizes. After you burn a few, you figure out why, and it boiled down to the pilot circuit. Once I upped the pilots, I never had an issue. Alot would depend on the current jetting and the statement of running stock pipe at altitude per the original poster. I read that as going back with the mains. 4-6 would be 135's and 150's at 1200 so with the stock pipe at elevation it would be over rich. Aftermarket pipe and you will be safe. And yes, the pz's are sensitive and need help when piped, and I would never not re-jet after swapping pipes.

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    Gotcha black dog, I thought you were referring to stock set up jetting.
    I had an '85 phazer with a PSI on it, can't remember exact numbers but know that I went up on the mains. I don't recall touching the pilots...but I was running it mainly at 6000'.
    I think he has a lot of room with the mains for an aftermarket, sounds like stock jetting will be pig-rich, but would yield to your knowledge of upping the pilot circuit. It's been 30 years since I had that phazer.
    Kinda sounds like you have it figured out axleater.
    Last edited by mod-it; 02-05-2020 at 02:01 PM.
    03 Mountain Viper, SLP Triples, SLP Flo-rites, gas rack, low profile blue windshield, NO underhood air going to the air box, (& no more powder bog)

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    151.3 is what it came with. Super fat even with pipe. Trying145 tomorrow.

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    Ended up at 141 and the plugs look like chocolate milk.
    Got a little bog right around 4000rpm or 30 mph. Going to experiment with primary clutch and see if I can make it pull through

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    Are you in a hilly or mountainous region?
    Current helix?
    Dannyboy

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