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post #1 of (permalink) Old 02-12-2001, 05:59 PM
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Weber Carb and \'high\' altitude

This is about my Weber 32/36 set up. Here in Northern VA, my Weber is running great (at worst idles a little rough w/ occasional stall for the first 5 minutes when really cold out). When the engine is warm, I'm 100% w/ a perfect idle.

I went up to West Virginia's Snow Shoe mountain this weekend. In the morning up there, I couldn't get a good idle. Anything under 1000-1100 RPM and she would start to go rough and stall. Even after at operating temperature, with a solid 2 hours of traveling, she still wouldn't idle at all. So I had to 3-foot-it down the mountain (staying on the gas, keeping it always over 1100 RPM). I stopped maybe twice on the trip. When I made it home, I got off the gas, and she idled fine! No symptoms a day later either. Typical story of course!

I think I was running rich up there, but its not THAT high up. Plus, after 2 hours of coming DOWN it still did it. I didn't have the time to mess w/ the mixture screws to check for change.

My current guess is that I'm running rich HERE and being up in SLIGHTLY thinner air may have 'pushed it over the limit'. Not the most scientific guess. Only other factors would be: about 10 degrees colder there and maybe a bit more humid.

Any ideas guys?

Sam88Jeep

'88 YJ, 4.2L, 32/36 Weber, Jacobs Ign.
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post #2 of (permalink) Old 02-12-2001, 07:07 PM
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Re: Weber Carb and \'high\' altitude

I'd say you are just on the verge of rich. The reason it ran so badly on the return trip was probably related to it having fouled the spark plugs while running so richly. It took it awhile to get them hot and clean again. When you say after 2 hours, whas that 2 hours of driving after the mountains or two hours of drving coming down out of the mountains? I would assume that it would take travelling at normal pressure for at least 25-45 minutes depending on how good your plugs are to clean them well.

Nick Hagen
1995 Wrangler
3" suspension lift, 3" body lift
33" Mud Tires
TBI Chevy 350 followed by a Turbo 350 tranny.
post #3 of (permalink) Old 02-12-2001, 07:52 PM
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Re: Weber Carb and \'high\' altitude

Check your timing, you may want to advance it a bit and see if the problem clears up.

J just
E mpty
E very
P ocket!!

'85 or is it a '98?? Cj-7 33x12x15" BFG 2.5" Rancho 258 T-176 Almost EVERYthing Rebuilt or Replaced
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post #4 of (permalink) Old 02-13-2001, 01:41 PM
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Re: Weber Carb and \'high\' altitude

I did a routine plug replacement about 8 months ago. I gapped them really wide (say .55)... This was suggested by the Jacob's Ignition system I have in it. Would the wide gap do it?

As for the hours... It still performed bad after 2 hours coming down the mountain. The last 2 hours were at normal elevation, but I never slowed down to check for the stall during that portion of the trip.

Do you think my wide plug setting is the culprit? Jacob Ingition manual says to increase the gap by .20 or something like that.

I will check my mixture and timing though. That hasn't been checked in a long while.

Thanks again

Sam88Jeep

'88 YJ, 4.2L, 32/36 Weber, Jacobs Ign.
post #5 of (permalink) Old 02-13-2001, 01:47 PM
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Re: Weber Carb and \'high\' altitude

That's a little odd. My Weber runs pretty much the same at 6000ft. (my home) as it does at 12,000ft. It seems more immune to altitude changes than most carbs.

Brad
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post #6 of (permalink) Old 02-13-2001, 05:57 PM
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Re: Weber Carb and \'high\' altitude

Go back to the high end of stock. The Jacob's says to increase the spark because their system can jump it. However when you get a rich situation and the spark has a large gap to jump, it is more likely to follow wet fuel around the insulation and to ground. A larger gap does create a bigger, hotter spark under ideal conditions; hoever altitude and temperature changes can interfere.

Nick Hagen
1995 Wrangler
3" suspension lift, 3" body lift
33" Mud Tires
TBI Chevy 350 followed by a Turbo 350 tranny.
post #7 of (permalink) Old 02-14-2001, 01:19 PM
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Re: Weber Carb and \'high\' altitude

Hmm.. Maybe I'm not thinking this thru right. If its the plug gap and the plugs are grounding, then those exact enviromental conditions would have to happen in successive cylinders. If just one cylinder 'misses', it shouldn't be a bit deal.

Isn't it satistically improbable that a chance grounding is happening in successive cylinders every time I dropped below 1100 RPM? Granted, I guess at low RPMs, 2 successive misses would pretty much end in a stall.

I guess I'm reluctant to mess w/ the gap because I got 20.5 MPG on the trip out there....And can get that mileage semi-regularly on a constant-speed long trip. I don't want throw that mileage out the window.

Unfortunately I can't do a test because I'd have to travel out the mountains to recreate the symptoms.

Sam88Jeep

'88 YJ, 4.2L, 32/36 Weber, Jacobs Ign.
post #8 of (permalink) Old 02-14-2001, 05:40 PM
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Re: Weber Carb and \'high\' altitude

I guess as long as your engine runs fine around town you can leave it like it is. Knowing that you got 20.5 mpg changes things a little. You may just have a slight fuel leak in the idle circuits of the carb. This would make your idle mixture a little rich normally but when you went up in the mountains it was just too much. As to the way down, it just might have had trouble cleaning the plugs up. I guess the best way to tell for sure would be to take a plug wrench with you next time you make the trip and check one of your plugs after it starts running badly for awhile. The best way to tell how and engine is running is from spark plug condition.

Nick Hagen
1995 Wrangler
3" suspension lift, 3" body lift
33" Mud Tires
TBI Chevy 350 followed by a Turbo 350 tranny.
post #9 of (permalink) Old 02-14-2001, 06:22 PM
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Re: Weber Carb and \'high\' altitude

Actually I had one in the back (plug wrench, that is). Can't travel without my tools.
Ohwell, hindsite is 20/20.

Thanks for the thoughts.. I think I'm going to narrow my plugs a little and make the mixture a little leaner. Hopefully I'll get around the checking my timing.

I have no garage, so all this kind of stuff sucks when its 30 degrees outside.

Sam88Jeep

'88 YJ, 4.2L, 32/36 Weber, Jacobs Ign.
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