quite simply does any one know what jet size to use in a holley carb at around 3000 ft above sea level? tried to call holley support but apparently were super busy as i ended up on hold for around 15 minutes thanks for any help all
CK5
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holley jet sizes
- Thread starter 84bigblue
- Start date
670 cfm, im guessing your suggestion still applies?
on a second note, trying to kill two birds one stone here, i finnally got my drive shaft extended and everything out back together down there and when i whent to take it for a test drive i noticed the tranny gear shifter is stiff/hard to shift into reverse/drive but when driving it seems to shift fine and it has not done this before any one have any thoughts
sounds good ill start with that then thanks for the help =]
scpaul
1/2 ton status
If the vehicle will run and can be driven, put a new fresh set of plugs that you will be using (gap them yourself) drive it around like you normally would for an hour or so depending on how it's driving, then pull your plugs and read them. There has to be a chart for reading but it's probably pretty old. If when it's up to running temp. and idling and it smells rich the idle circuit needs adjustment. I doubt if it's still done the old way. Have you got many mods? Your gear ratio, altitude, gas octane, etc. There's so many things that go into jetting a carb that it's the kind of thing that until you get more used to it, you're better to read plugs and maybe change plug heat range and possibly gap.I know that you know this but the smaller the jet # the less gas. If it bogs when you open the back barrels, you might have to adjust the accelerator pump stroke. Get your jets and plugs right first unless it isn't driveable. My email is in my profile.
Man, it's nice to be able to talk old skool stuff that I used. I just hope that my memory keeps working. Paul
Man, it's nice to be able to talk old skool stuff that I used. I just hope that my memory keeps working. Paul
thats some good info man thanks! this is my first holley and only second carb but im slowly learning haha i was going to throw new plugs in anyways so ill be sure too keep an eye on them. theres still alot iv got to learn so im sure you an email from me at some point haha thanks again
scpaul
1/2 ton status
Blue, do you know the history of the engine? You might want to look at how stable your timing is. Put white out, chalk,fingernail polish, paint or anything so you can really see the movement of the timing mark. If the timing is moving very much, depending what you want or can afford, you might want to think about the timing too. Sorry
Any of the other old timers on here might give him a hand too. I know that I've forgot alot.
Paul
Any of the other old timers on here might give him a hand too. I know that I've forgot alot.
Paul
iv been told that sbc 350s like around 36 degree of total timing on a couple of different forums right now iv got it set at 31 degrees as that was the highest i could set it with out it seeming like to much and let my initial timing fall where ever it may (was also told that total timing is more importent then initial timing and if you dont know your mechanical advance to just set the total and let the inital fall where it does) from what i remember the last time i checked and set it my timing was pretty stable. as for the history of the engine iv never opend it up to tell exactly whats been put in there although you can tell its got a pretty good cam. i was told by the previous owner it was a 350 but also had a guy recognize the truck before i painted it claiming that he built the engine (he knew the bottom was blue and the top orange to what ever credit that gives him haha) saying that he built it to be a 383 stroker. never opend her up though to find out
You say reverse/drive, so I'm guessing its an auto. If so, take it in steps.
Try disconnecting the shifter at the base of the column outside and make sure the lever moves free and the shift rod is not bound up between the column and the transmission.
You will feel a lot of tension on the rod when you try to disconnect it if its bound.
Then, Chock Your Wheels, and take the rod loose from the transmission with the truck sitting on level ground, and try running the shifter on the transmission through the gears by hand, to make sure the internals in the transmission feel ok, and the lever is not bent and hitting the side of the transmission.
If its a manual, check your clutch to make sure its releasing all the way.
scpaul
1/2 ton status
This is going to sound a little flaky but, keep in mind that I ran some pretty wild cams, compression, heads, etc. Once you get so far with engine mods you can just about throw the book in the can. Don't do it though. Once we got it close, carb & plug wise, we would retard the timing until it started kicking against the starter, then advance about 2 or 3 degrees. That's where we would re- start our tuning, plugs, carb, timing, and on until our times started slowing then back up a little of what it was we did last. Then if you want to really max it out, then go back to what's left and work with them and so on. If this is a daily driver you might want to back it all down just a little. This kind of tune is what we did for comp. Keep in mind that the most electronically controlled device was our FM radio or the Fm to AM converter, it plugged into the 8-track. Look it up. Paul
the over all goal of this truck build is to be as much of a daily as it is a trail and mud truck, ill admit that while i have been around chevys basically my whole life this is very much so my first rodio with this old of a chevy (only 21 so grew up with fuel injection hahah) this place has been amazing to search through and learn alot so id really like to just say thanks to all of you for the advice and learning experince
scpaul
1/2 ton status
Blue,
How are you doing with the truck? Good I hope.
I've been looking around for some of my old manuals and magazines. I haven't found so much as a mailing label. If I haven't over looked them; possible, my wife threw them away. I had boxes that dated back to the 70's with a few from the '60s. I know it's old info but, sometimes you might find something you can use. I haven't even seen my jet box and that's strange. I'll keep looking, maybe I'll get lucky. If you can find it, there was a list that told you which wire drills to get a certain number jet. You could start with a small jets and work up. Once you figured out what you needed, then you could buy a set that is properly marked and throw the other ones away or at least put a tag on it so you don't grab it by mistake.
Best of luck to you, Paul
How are you doing with the truck? Good I hope.
I've been looking around for some of my old manuals and magazines. I haven't found so much as a mailing label. If I haven't over looked them; possible, my wife threw them away. I had boxes that dated back to the 70's with a few from the '60s. I know it's old info but, sometimes you might find something you can use. I haven't even seen my jet box and that's strange. I'll keep looking, maybe I'll get lucky. If you can find it, there was a list that told you which wire drills to get a certain number jet. You could start with a small jets and work up. Once you figured out what you needed, then you could buy a set that is properly marked and throw the other ones away or at least put a tag on it so you don't grab it by mistake.
Best of luck to you, Paul
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This is a cut and paste from what I used to figure it out. Read last sentence for jet setting
First, why are changes necessary? If the carburetors are set for sea level perfomance (400m / 1312'), the proper
fuel:air mixture has been established. As you increase altitude, the actual density of the air decreases. There is less
oxygen available and the fuel:air ratio is changed. There is too much fuel / too little air. So jetting has to be
adjusted to bring back the proper ratio. If the altitude change is temporary, you might choose to let it be, or just
make adjustments in your volume control screws. But if the altitude change is great enough, or the time spent at
altitude is long enough, you may want to swap out your jets.
When carburetors are tuned for altitude driving and then brought down in altitude, the opposite happens due to
denser air.
Is the car running too rich, or too lean? Unburned gasoline will leave sooty deposits in your tailpipe, turn your spark
plugs black and cause popping in the carbs and backfiring through the exhaust. When lean, the spark plugs will be
light grey or white, carbs will spit back, and the car will run hot.
High Altitude Adjustments 101 Driving a carbureted internal combustion gasoline engine at higher altitudes requires a bit of adjustments to the air/fuel mixture and a slight increase in the engine timing. Generally most vehicles are set at sea level and will operate somewhat smoothly up to 6,000 feet in altitude. The deal is, there's less air up there, so you need to "lean out" the mixture to maintain the proper fuel/air mixture. That's the theory, but in my practice, it's not absolutely necessary. The reason -NOT- to adjust the mixture is that if you don't richen it out back in the lower altitudes, you'll be too lean, and... too lean is more likely to damage your engine than too rich. Leaner mixture burns much hotter. Final adjustment for high altitude is your engines base timing which will need to be increased. To perform this adjustment you will need a proper end wrench to fit your lock down bolt at the distributor. Most distributor lock down bolts are either a 9/16th or 1/2 inch (15mm or 13mm). Loosen the lock down bolt just a bit and then turn the distributor to the right just a little then tighten it back up It's a little hit and miss but that slight adjustment should do the job without changing jets and/or pulling the carb apart. If you must lean out the jets, normally turning them in will lean them , turning them out will richen them. Try the timing adjustment first.
Be prepared to find only lower octane fuels available. Problems will be compounded by lower octane fuels (85, 87, and 91). Consider octane boosters.
Consider advancing the timing a few degrees. Adjust to where your idle smooths out then test drive. If you detect any pinging or knocking just retard the timing. Usually you will adjust the idle speed a little to compensate for the timing increase.
RECOMMENDATIONS
Winter time low ambient temps make a machine run leaner. Removing that free flowing filter and switching back to the stock restricted one will allow less air and more fuel. Cold temps make the AFR leaner, so less air = more fuel thus a richer AFR
HOLLY JETTING
2. Carburetors are calibrated at 70° at sea level. Decrease the jet size, one number for every 2000 ft. increase in altitude.
First, why are changes necessary? If the carburetors are set for sea level perfomance (400m / 1312'), the proper
fuel:air mixture has been established. As you increase altitude, the actual density of the air decreases. There is less
oxygen available and the fuel:air ratio is changed. There is too much fuel / too little air. So jetting has to be
adjusted to bring back the proper ratio. If the altitude change is temporary, you might choose to let it be, or just
make adjustments in your volume control screws. But if the altitude change is great enough, or the time spent at
altitude is long enough, you may want to swap out your jets.
When carburetors are tuned for altitude driving and then brought down in altitude, the opposite happens due to
denser air.
Is the car running too rich, or too lean? Unburned gasoline will leave sooty deposits in your tailpipe, turn your spark
plugs black and cause popping in the carbs and backfiring through the exhaust. When lean, the spark plugs will be
light grey or white, carbs will spit back, and the car will run hot.
High Altitude Adjustments 101 Driving a carbureted internal combustion gasoline engine at higher altitudes requires a bit of adjustments to the air/fuel mixture and a slight increase in the engine timing. Generally most vehicles are set at sea level and will operate somewhat smoothly up to 6,000 feet in altitude. The deal is, there's less air up there, so you need to "lean out" the mixture to maintain the proper fuel/air mixture. That's the theory, but in my practice, it's not absolutely necessary. The reason -NOT- to adjust the mixture is that if you don't richen it out back in the lower altitudes, you'll be too lean, and... too lean is more likely to damage your engine than too rich. Leaner mixture burns much hotter. Final adjustment for high altitude is your engines base timing which will need to be increased. To perform this adjustment you will need a proper end wrench to fit your lock down bolt at the distributor. Most distributor lock down bolts are either a 9/16th or 1/2 inch (15mm or 13mm). Loosen the lock down bolt just a bit and then turn the distributor to the right just a little then tighten it back up It's a little hit and miss but that slight adjustment should do the job without changing jets and/or pulling the carb apart. If you must lean out the jets, normally turning them in will lean them , turning them out will richen them. Try the timing adjustment first.
Be prepared to find only lower octane fuels available. Problems will be compounded by lower octane fuels (85, 87, and 91). Consider octane boosters.
Consider advancing the timing a few degrees. Adjust to where your idle smooths out then test drive. If you detect any pinging or knocking just retard the timing. Usually you will adjust the idle speed a little to compensate for the timing increase.
RECOMMENDATIONS
- gentle leaning of mixtures
- mild advances of timing
- keep rpm's high
Winter time low ambient temps make a machine run leaner. Removing that free flowing filter and switching back to the stock restricted one will allow less air and more fuel. Cold temps make the AFR leaner, so less air = more fuel thus a richer AFR
HOLLY JETTING
2. Carburetors are calibrated at 70° at sea level. Decrease the jet size, one number for every 2000 ft. increase in altitude.
rayfin
Registered Member
- Joined
- Jan 3, 2016
- Posts
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- Reaction score
- 21
The short version.
Hahah for sure all good info regardless
Team208Motorsports
Its Magic Bitch
Real short version. EVERY ENGINE IS DIFFERENT preset calibrations mean nothing except to what they were pre set to.
