Altitude issues with MC2100 carb

[illegalFSJ]

Well, I live at 2000 feet, and work at 6500 feet, which makes for a large altitude difference with every drive to and from work. The carb seems to run somewhat rich and rather poorly at 2K feet, but really, really badly up at the mountain. I think it's rich because of all the black exhaust and the truck barely running. And I got about 7mpg on the last tank. Yesterday, coming down, I had to keep the gas pedal all the way to the floor just to keep the engine from stalling out. And when I came to an incline, the jeep moved uphill at about 2 mph, with the gas pedal on the floor. The engine just would not rev up.
So, is it normal that a carb would run richer at altitude? And how do I fix this? Do I have to rebuild, or is it just an adjustment?
It must be altitude because back at 2K feet, the truck is running OK again, not great, but acceptable.
Any ideas are very appreciated. Thanks.

[Don S]

illegalFSJ...
... Been there done that and it sure did happen to me…
… Your spark plugs are fouled with carbon. Does your 2150 have the altitude Compensator? If so it may need a light duty cleaning. Try adding 2 degrees to the timing. Try to lean out the carburetor a little and make sure the air cleaner is working correctly with a clean filter. Make sure you have no vacuum leaks.
... the link below has some sure-fire answers...
link> CARBON & FUEL ADDITIVES (http://groups.msn.com/JEEPTECH101/jeeptech.msnw)
…
It works for me... http://www.michiganjeepers.com/forums/images/graemlins/rock.gif Take care ;) and… CUL.. ds..
- - - - - - - - - - - - - - - - - - - - - -
1976 406 MC4300 TH400 QT TruTrac 2" lift 31x10.50s duel Optimas
It’s taken us over 261 Colorado Mountain Passes since 1985-
BRC#30093 link> Blue Ribbon Coalition JOIN and save your TRAIL (http://www.sharetrails.org/)
http://groups.msn.com/isapi/fetch.dll?action=MyPhotos_GetPubPhoto&PhotoID=nGwAAABMFpTDRtacZBUx4ywyLKrzYkIl*zJaWIPM1A J4l6juZsDWTsK!GahB5tXiF Ice on Engineer Pass near Ouray Co.
link> 2003 OURAY FSJ Invasion Info and High Altitude Tips (http://groups.msn.com/ATexasOklahomaJeepClub/ouraycotopic.msnw)
link> Acronym and Abbreviations for 4x4 Gearheads (http://groups.msn.com/NISSAN4X4TRAILS/acronymlist.msnw)

[illegalFSJ]

My carb has no altitude adjustment, as far as I know - it's the 2100, not the 2150. It's just the 2150 that has the alt. adjustment, right?

By adding 2 degrees to timing, do you mean, moving from 8 BTDC to 10 BTDC or the other way, to 6 BTDC?

I checked out the link. I've never heard of adding 2-stroke oil to the gas tank. Is this really what it's advocating? Is this really a good idea? If so, I'm willing to give it a try.

By leaning out the carb, is that just turning the front screws a bit to the left?

Thanks.

[AzFrank aka Desertson]

It would be best if you got a MC2150.The High Altitude comp automatically mixes a metered amount of air into fuel/air mixture to prevent a over rich condition. They were standard stock equipment on Jeeps sold at over 4000ft in elevation.

[ December 21, 2002, 06:00 PM: Message edited by: AzFrank aka Desertson ]

[illegalFSJ]

I did a bit of searching around to find out what the base settings are supposed to be on the idle screws. It seemed as though 7/8 of a turn out was a good base setting (?)
Anyway, I checked and mine were about 2 full turns out, so I set them to 7/8 out and we'll see tomorrow if she does any better going up the big hill.

[Don S]

Originally posted by illegalFSJ:
My carb has no altitude adjustment, as far as I know - it's the 2100, not the 2150. It's just the 2150 that has the alt. adjustment, right?

right

By adding 2 degrees to timing, do you mean, moving from 8 BTDC to 10 BTDC

yes

I checked out the link. I've never heard of adding 2-stroke oil to the gas tank. Is this really what it's advocating? Is this really a good idea? If so, I'm willing to give it a try.

By leaning out the carb, is that just turning the front screws a bit to the left?

worry with carb. last

Thanks.
..
illegalFSJ:...
... In my engine the out board oil is able to keep the large porcelain area of the plugs clean enough to prevent the leakage, from fouling, of electrical current. If the electrical current can’t leak it’s forced to jump the gap.
... If your plugs are already fouled it might take 75 miles of highway driving for the oil to clean the plugs. If the plugs are fouled then there is bound to be more deposits in the head and cylinder areas that can cause pre-ignition. We had a long thread about this about a month ago.
… I’ve been using upper-lubes for over 50 years and will continue until they pry the bottle out of my cold dead hand…!!! :eek:

Good luck and http://www.michiganjeepers.com/forums/images/graemlins/wave.gif … CUL.. ds..
- - - - - - - - - - - - - - - - - - - - - -
1976 406 MC4300 TH400 QT TruTrac 2" lift 31x10.50s duel Optimas
It’s taken me over 261 Colorado Mountain Passes since 1985-
BRC#30093 link> Blue Ribbon Coalition JOIN and save your TRAIL (http://www.sharetrails.org/)
http://www.fullsizejeeps.com/jeeps/files/1963-1983-Wagoneers/76401.s.jpg ALL American Pure Cast Iron
link> 2003 OURAY FSJ Invasion Info and High Altitude Tips (http://groups.msn.com/ATexasOklahomaJeepClub/ouraycotopic.msnw)
link> Acronym and Abbreviations for 4x4 Gearheads (http://groups.msn.com/NISSAN4X4TRAILS/acronymlist.msnw)

[illegalFSJ]

I'll give it a try - Thanks for all your help Don!

[Stuka]

You could just tune your carb for a between altitude. Thatss what I did with my edelbrock. I live at 2750 and work at 5000, its a 11 mile trip to work. I set my carb for between the two, and my plugs are always tan.

EDIT: my 65 stang has a 2100, and i did the same thing and it works out just fine.

[ December 22, 2002, 11:25 AM: Message edited by: Stuka ]

[illegalFSJ]

Good news - it turns out that the PO had been screwing around with the carb and the mixture screws were all way out. I drove it to work yesterday, and the truck did tremendously better. Still dying when I hit the brake, but not flooding out like before. I'll be happy with this for awhile until I get tired of driving with one foot on the brake and one on the gas.

[Langdon]

Illegal, just a tip with the 21XX carbs...the mix screws only adjust for idle mixture. You have to change the jets to affect the main circuit mixture :cool: