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Altitude?
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ragphoto
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PostPosted: Thu Nov 13, 2008 12:06 am    Post subject: Altitude? Reply with quote

What is the best way to adjust my car for altitude? I've read about advancing the distributor and also been told to just adjust the mixture on the carb. Which way is best and any suggestions?
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Bruce
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PostPosted: Thu Nov 13, 2008 1:24 am    Post subject: Reply with quote

Change the jets.

How much elevation change are you talking about? What carb?

ROT is to reduce the jets by 5 for every 5000'.
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ragphoto
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PostPosted: Thu Nov 13, 2008 4:59 am    Post subject: Reply with quote

Im already traveling and dont have extra jets. I will be going through all kinds of altitude. In the next couple of days I will be around 7000 feet. Am I screwed?
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li_gangyi
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PostPosted: Thu Nov 13, 2008 6:51 am    Post subject: Reply with quote

If you're already jetted properly, moving to higher altitude for awhile shouldn't hurt your car, it'll run richer (no good for MPG). You will most likely observe a loss of performance because of the thinner air also.

In short, no you're not screwed.
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bon2198
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PostPosted: Thu Nov 13, 2008 9:22 am    Post subject: Reply with quote

you can also re-adjust air fuel mixture. the higher you go the less air for the car to breathe.
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wompninja
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PostPosted: Thu Nov 13, 2008 4:31 pm    Post subject: Reply with quote

I'm in Salt Lake City that's 6500 ft and I have the stock jets in and I have no problems at all even when I go skiing which gets me up to about 8000 ft. I wouldn't worry about it unless you have to pass emissions at 7000 ft Very Happy
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mnussbau
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PostPosted: Thu Nov 13, 2008 6:10 pm    Post subject: Reply with quote

bon2198 wrote:
you can also re-adjust air fuel mixture. the higher you go the less air for the car to breathe.

I'm assuming you have a 30PICT/3, 34PICT3, or H30/31 carb with two adjusting screws in the side.

If the car runs badly or is hard to start, try turning the volume screw (the smaller of the two screws) in/clockwise 1/8 turn or so and wait 10-15 seconds. Keep making slight adjustments until the idle speed maxes out. You should be able to tell this by ear. That should be the best setting for that altitude. REMEMBER HOW MANY TURNS YOU MADE! Then turn the big screw (the bypass screw) in or out until the idle is 850-900. Again, you probably don't have an idle meter so just set it by ear. When you get home reset the volume and bypass screws back to where they were.
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ragphoto
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PostPosted: Thu Nov 13, 2008 7:34 pm    Post subject: Reply with quote

Thanks all.. Im at about 8000 feet right now and my car was running like a dream. It was however plenty warmed up. I drove from Brownsville Texas to Guanajuato Mexico today. Ill see how it starts in the morning.

Thanks again for the tips
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bon2198
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PostPosted: Thu Nov 13, 2008 9:35 pm    Post subject: Reply with quote

Make sure you stop in Chihuahua, best damn Tequilla ever!!!!!!!!!!!!!!!!
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ragphoto
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PostPosted: Thu Dec 25, 2008 4:04 am    Post subject: Reply with quote

OK, I made it through Mexico and Central America with no problems at all. Over 9000 pretty hard miles. However, in Ecuador, Peru and Bolivia I will be driving well over 10,000 feet quite a bit. Should I re-jet the carb or can I still just adjust the mixture? Two questions. about a 34 pict 3.

1. Which jets do I replace? The main jet or Idle jets?

2. Someone posted here to turn the mixture screw clockwise when adjusting the mixture, I thought it was a counter clockwise turn to let in more oxygen, which is it?

3. I'm not sure whats in there now. What size jets should I get?

and

4. How do I change the jets. Do I need to take the carb off or apart?

Thanks
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ragphoto
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PostPosted: Thu Dec 25, 2008 6:46 pm    Post subject: Reply with quote

Any ideas anyone?
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Cuog
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PostPosted: Thu Dec 25, 2008 7:47 pm    Post subject: Reply with quote

clockwise I think richens it if I recall correctly, test each direct and drive around the block to see which sounds better.


To rejet You'll have to open the carb. Don't really need to change the idle jets its more the main jet since thats the one that really matters when you're driving.
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mnussbau
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PostPosted: Thu Dec 25, 2008 8:12 pm    Post subject: Reply with quote

Not an expert on this, but I think clockwise lets less fuel in, so it leans it out. At high altitude there's less air, so to compensate you let in less fuel. Try it clockwise until you get the fastest idle, turning maybe 1/8 turn at a time and then letting it settle down.
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PostPosted: Thu Dec 25, 2008 8:56 pm    Post subject: Reply with quote

When I turn it clockwise (tighten) it starts to die. Then I usually loosen it about two and a half turns for the proper adjustment, right?
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Cuog
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PostPosted: Thu Dec 25, 2008 9:02 pm    Post subject: Reply with quote

Of it runs properly its correct. The absolute proper thing to do would be a rejet, but since you're traveling its probably necessary to do so. A lot of times I've found tuning the carb by ear to be the best when dealing with altitude adjustments.
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Jimmy111
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PostPosted: Fri Dec 26, 2008 7:07 pm    Post subject: Reply with quote

You will have difficulty as you pass 8,000 ft. especially now that it is hot down there in SA. The car will still run but it will start to run hot, loose power and smoke a lot.I did a race over the andes earlier this year and needed to change my jets at 5000, 9,000 and 12,000 ft. When you hit 16,000 ft in Peru you will loose most of your power no mater what you do simply due to the lack of Oxygen and the motor will over heat. You will need to go for a while and then stop. Just be aware that in most places in the mountains in Peru there is no gasoline available. You got to bring your own.
How did you pass the Darrian Gap?
Good luck.

By the way. Some of the VW parts houses in Peru carry the altitude compensator for the solex carb.
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Bruce
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PostPosted: Fri Dec 26, 2008 10:50 pm    Post subject: Reply with quote

Cuog wrote:
Of it runs properly its correct. The absolute proper thing to do would be a rejet, .

Those two statements contradict each other. It is simply not possible to have the correct A/F ratio without changing the jets.

As you drive up in elevation with a carb, two things are happening. The density of the air is decreasing, meaning less oxygen for every liter of air your enigine draws in. Then because your carb can't compensate for the reduction in oxygen, the A/F ratio it delivers becomes richer. A rich mixture has more fuel than is needed for the amount of oxygen. The extra fuel can't burn, so it passes through the engine out the tail pipe as unburned HC. In effect, the extra fuel puts out the fire.
Those two things are what takes away hp. You can only change one of them, the A/F ratio by changing jets. Fiddling with mixture screw is virtually worthless when trying to alter the A/F ratio over the whole range, since it's effect is at idle, and just off idle.
By changing the jets, you will regain some of the lost hp due to altitude change.
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PostPosted: Sat Dec 27, 2008 7:09 am    Post subject: Reply with quote

Thank Bruce for that! I am not sure what size jet I have in there right now, I am guessing 135 or 140... What size jets would you recommend to take along just so I cover all the bases? I was guessing 140 down to 120 or 115??? My car seemed to run just fine at around 8000 ft. in Mexico. I will be getting up over 15,000 in Peru and Bolivia. I think I will certainly have to re jet. Also, Is it necessary to remove the whole carb to re jet it. Seems like a hassle and Unfortunately, I have stripped threads on the front post. I managed to get it on there just tight enough to keep it air tight and it has been working perfectly since Missouri, but every time I remove it I risk pulling that fron post all the way out and not being able to get it back on tight.

Thanks
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Mexicanmafia
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PostPosted: Sat Dec 27, 2008 10:09 am    Post subject: Reply with quote

when i took my bus thru the rockies it got up to 12k feet and i just advanced the timing like 10 degrees and it did fine.
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PostPosted: Sat Dec 27, 2008 10:32 am    Post subject: Reply with quote

There is a huge difference between 12 and 16000 feet
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