High Allitude jet settings
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High Allitude jet settings

  1. #1
    Member The Chaz's Avatar
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    Default High Allitude jet settings

    Could someone give me a base number to start with for holley jets size. I am running at 5100ft (vs San Diego) and it is so rich I get popping and very brown plugs.
    Also is there any need to change the timing at this altitude?

    Thanks

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    Member Rogers daycruiser fan's Avatar
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    I will ask my freind that races jets tomorrow when I see him, we are going to tune my boat after a carb rebuild.
    !!

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    Senior Member H20MOFO's Avatar
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    Quote Originally Posted by The Chaz View Post
    Could someone give me a base number to start with for holley jets size. I am running at 5100ft (vs San Diego) and it is so rich I get popping and very brown plugs.
    Also is there any need to change the timing at this altitude?

    Thanks
    As a rule you can get away with more timing at altitude.
    Another Hot Boat refugee

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    Senior Member 1975sleekcraft's Avatar
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    Quote Originally Posted by The Chaz View Post
    Could someone give me a base number to start with for holley jets size. I am running at 5100ft (vs San Diego) and it is so rich I get popping and very brown plugs.
    Also is there any need to change the timing at this altitude?

    Thanks
    brown plugs is ideal air fuel mix.

    look into timing!

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    We just got back from racing in Burley Idaho, around 6000' corrected elevation, we went down 2 sizes on the primary and secondary jets. Hope that helps.

  8. #6
    Senior Member bp298's Avatar
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    i can't recall "popping" resulting from being too rich. i've gone from sea level (mission bay) to 5500 d/a (texas), and have only changed hispeed bleeds 2 sizes. and that's all i do.
    if you idled the boat around for any length of time before putting it back on the trailer, the plug condition you are looking at reflects a/f conditions at idle, not wot. 7 years ago at chowchilla, with d/a over 5000', a friend kept chasing what he thought was a rich condition at wot by reducing jet sizes (he got it so lean it was popping like crazy), but the plugs were not indicative of wot because at chow there is a long shutdown area where you are running at reduced rpm for awhile. he never adjusted idle/midrange metering, until he talked to his engine builder after that weekend and found out he was lucky he didn't burn it down.

    exactly what rpm does it start to pop? exactly what rpm does it stop? my suggestion would be to check everything. popping can be caused by a lot of different things, ignition related or fuel related. and it can be ignition related and not manifest itself until rpm is raised under load (don't ask me how i know). possible problems are mostly easy fixes once you figure it out, but it's not necessarily a good thing to run it that way.

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    Senior Member bajadad's Avatar
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    I set my jetting at Parker, 78'S primaries, 82's secondaries 750 holley on a stock 460,performer rpm intake, ot headers,10 initial 28 total on timing. went Lake Elsinore yesterday and ran good, not as good as at Parker. Had a small popping at idle, and not as responsive. Parker elevation is 430ish, Elsinore is 1430 elevation.

    Maybe a little more timing? plugs look good, tan in color.

  10. #8
    Member The Chaz's Avatar
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    Quote Originally Posted by bp298 View Post
    exactly what rpm does it start to pop? exactly what rpm does it stop? my suggestion would be to check everything. popping can be caused by a lot of different things, ignition related or fuel related. and it can be ignition related and not manifest itself until rpm is raised under load (don't ask me how i know). possible problems are mostly easy fixes once you figure it out, but it's not necessarily a good thing to run it that way.
    It pops through all RPM ranges, however it doesn't really start until about 1200 and gets progressively worse. I took it to Lake Almanor which is 4505 alt and I got about 300 more RPM's. The popping was the same however. It also wants to(will) stall if I get out of the throttle too fast. It will cough and sputter, but can sometimes be saved if I flutter the gas.

    I am wondering if something could be plugged in the carbs to make the popping. I am running BTW 2 Holley 600's chokes removed and vacuum secondaries on a tunnel ram. Cam is custom ground Clay SMith (I forget the numbers and would have to dig out the cam card if necissary but lets say "medium" lift and duration with solid lifters, roller rockers, studs, guide plates. Compression is 9.7ish and I run 91 octane from the pump. There has been no change to the engine since last year when the coil burnt out except changing to a MSD Blaster 2 coil. I run MSD dist and 6-AL box.

    Could I have blown out the power valves with the back fireing? I am a noob when it comes to the carbs, the rest of the work and build on the boat I did myself

    One other thought, would "dirty" air filters cause the problem I will be checking this one today as I plan to try again.

    Thanks again for suffering through this long read and offering any advice.



  11. #9
    Senior Member ol guy's Avatar
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    There alot of variables there!! First I would do a compreesion check and make sure you are within a good range! Second if you have back-fired the carbs mutiple times then the power valves are probably gone. I raced the 460 Ford for years and know that they are prone to valve train issues.( wihich is why I would use cheby valve train ) . Also one qwik question! does pop out the exhaust or intake??? M

  12. #10
    Senior Member bp298's Avatar
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    pull the cap off the msd and make sure the center post (carbon) is still round and protruding down like it's suppose to. not unusual at all for msd caps to wear out. also, use a timing light, and verify that timing is where it's supposed to be, all the way up the rpm range. if timing starts bouncing around when the popping starts, you'll know there's something going on with the distributor or msd box. msd boxes do not like bad grounds, which can create all sorts of wierd symptoms. make sure all those grounds are good.

    i just have a very hard time believing the symptoms you are describing are carb related. not saying absolutely they aren't, but for this to just start happening out of the blue, altitude or not, it just doesn't sound like a carb issue... also not saying your carbs wouldn't to be rejetted either, just sayin...

  13. #11
    Member The Chaz's Avatar
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    I took it out today and got the same thing...


    So I decided to check the compression while I was sitting on the beach. All cylinders w/in 2lbs of each other @ 92lbs on one compression stroke. No problems there.

    #7 and #8 plugs looked "oily" or perhaps sooty.

    Pulled the scoop and filters and looked like hell in the carbs Black soot on EVERYTHING. Sprayed some carb cleaner all in it.

    pushed the throttle and noticed that the rear carb was not spraying
    Cleaned it out, had some gasket material blocking it.

    Fired it up and remarkably better throttle response(of course) but still popping

    Checked the cap for wear, nada, it has maybe 3 hours on it.

    Decided to rotate the wires 1 place so I could get more advance than before, (tunnel ram hits the cap) wouldn't start. Went to put the wires back and noticed that #7 and #8 were reversed

    I must have checked the firing order 3 or 4 times since this started and each time missed that. WTF I feel stupid.

    Got in started and idled perfectly. Mashed the gas and 5250 RPM's and a hole shot I never dreamt of having; only had a worn out impeller before.

    It did stumble a bit after maybe 30 mins of lake touring with my family just before it went on the trailer so I may have some junk in filters, but I think problems are solved for now.


  14. #12
    Senior Member H20MOFO's Avatar
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    Quote Originally Posted by The Chaz View Post




    I took it out today and got the same thing...


    So I decided to check the compression while I was sitting on the beach. All cylinders w/in 2lbs of each other @ 92lbs on one compression stroke. No problems there.

    #7 and #8 plugs looked "oily" or perhaps sooty.

    Pulled the scoop and filters and looked like hell in the carbs Black soot on EVERYTHING. Sprayed some carb cleaner all in it.

    pushed the throttle and noticed that the rear carb was not spraying
    Cleaned it out, had some gasket material blocking it.

    Fired it up and remarkably better throttle response(of course) but still popping

    Checked the cap for wear, nada, it has maybe 3 hours on it.

    Decided to rotate the wires 1 place so I could get more advance than before, (tunnel ram hits the cap) wouldn't start. Went to put the wires back and noticed that #7 and #8 were reversed

    I must have checked the firing order 3 or 4 times since this started and each time missed that. WTF I feel stupid.

    Got in started and idled perfectly. Mashed the gas and 5250 RPM's and a hole shot I never dreamt of having; only had a worn out impeller before.

    It did stumble a bit after maybe 30 mins of lake touring with my family just before it went on the trailer so I may have some junk in filters, but I think problems are solved for now.

    92 LBS is less than ideal.....
    Another Hot Boat refugee

  15. #13
    Member The Chaz's Avatar
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    Where should I be? It will hit 120 on the second stroke... never really cranked it for multiple revolutions to see where it tops out.

  16. #14
    Senior Member GT Jets's Avatar
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    Quote Originally Posted by The Chaz View Post
    Where should I be? It will hit 120 on the second stroke... never really cranked it for multiple revolutions to see where it tops out.
    Crank until peak pressure is achieved (typically three or four revs). 120 shoud be really close.

    GT
    GT


    Quote Originally Posted by Quickjet View Post
    Put a 300 on the back of it, Flywheel it and a nosecone. $15,000 later you'll have a 65 mph pile of shit......

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