the motorcraft 2100-2150 2-bbl carb. and related posts

[CJ BRIAN NJ]

hey guys im having a carb issue with my 79 CJ7 carb. its a motorcraft 2100(or 2150 no id tag) on a fresh tight AMC 304 that has plenty of power and runs great . it wont idle unless i manually push the choke almost completely closed. im not sure how the idle circuit is designed in these carbs but i know on some the vaccum sucks a little gas from the bowl to keep it idleing . but i only see gas in the carb when i pump the accelerator pump . i have ran a few gallons of super unleaded through it with fuel system cleaner and that didnt get me anywhere. is there a port or circuit in the carb throat that i can see the idle gas getting pulled in to the motor

here is the description i put in my build thread to help you guys understand my problem!

it only gets gas from the accelerator pump there is no gas getting to it at idle so it dies. if you pump the gas petal it runs great very strong and revs out quick and clean.it just wont pull fuel at low rpms. should i be able to see any gas moving in the carb like i do when i pump the throttle. the pump squirts strong and nice and even in both barrels but if i dont keep pumping the venturis go dry and i dont see any gas in the carb throat then it konks out. i know in some carbs you can see the idle gas being sucked out of the bowl or idle circuit but i see nothin!


Read more: http://www.jeep-cj.com/forums/f98/1...g-restoration-13704/index5.html#ixzz2DDHtzZh4

 

[CJ BRIAN NJ]

feel free to post any other info that is helpful when dealing with these carbs! specs , diagrams , pics , tip anything! i searched the forum and didnt find a thread about these carbs and i know alot of us have them so share some knowledge!

brian

 

[alpha6]

Here is a really good link on how everything works on the mc2100. http://street2mud.com/webfiles/MC-2100 set up for a 258.pdf. Page 11 has really good instructions on setting idle speed. Hope that helps.

 

[IOPort51]

http://c805745.r45.cf2.rackcdn.com/motorcraft_2100_4100_manual.pdf

if this won't load let me know.

One of the moderators has started putting together a pretty comprehensive Motorcraft tech page. From what I have heard it just needs a bit more editing. I , for one, am looking forward to it.

 

[IOPort51]

Have you tried adjusting the idle jet screws??

 

[mtnwhlr]

Have you tried adjusting the idle jet screws??

You said it won't idle unless you close the choke that sound like it is way lean.

 

[elwood blues]

One of the moderators has started putting together a pretty comprehensive Motorcraft tech page. From what I have heard it just needs a bit more editing. I , for one, am looking forward to it.

Yes, I know, I need to finish the MC2100/50 thread



CJ BRIAN NJ;
I agree with what the other 2 said, the only thing in the idle circuit that makes any sense is the idle/air mixture screws. Typically 1 1/2 turns out is a good place to start. The .pdf that IO attached has a good procedure in it for adjusting idle. I would suggest using both a vacuum gauge and a timing light. If your timing is off, that will also greatly affect your idle. Set up your timing according to specs, I don't remember what it should be for a AMC 304 , somewhere between 8 - 12 degrees BTDC, that's where the timing light comes in. To get your timing exactly spot on, use a vacuum gauge at the same time, your manifold vacuum should be between 17 - 19 in Hg.

Here are a couple of diagrams for explaining the idle circuit and the load circuit in the MC2100;

Idle

Load

Let us know, we'll help you get it dialed in

 

[alpha6]

Yes, I know, I need to finish the MC2100/50 thread

Giddy up!!! I have my 2150 sitting on the bench and plan to start the replacement this Wed. Not to rush you or anything.

 

[CJ BRIAN NJ]

Giddy up!!! I have my 2150 sitting on the bench and plan to start the replacement this Wed. Not to rush you or anything.

thanks everybody i have saved all your info and i will let you know how it goes! im ordering a kit and a new choke setup my choke weas removed and zip tied open so i gotta get it setup properly before and rebuilt and maybe that will fix everything. it just runs so damn good on the accelerator pump that i didnt want to tear it down but i guess thats the way to go . as soon as the kit comes in i will go through it step by step and take pics. i like making tutorials with pics and easy to follow directions so guys like me can get greasy and keep there jeeps out of the shop.

 

[IOPort51]

I never once mentioned a name.



@ CJ Brian: check for vacuum leaks. This will show up when you have no response to the idle jet adjustment.

Yes, I know, I need to finish the MC2100/50 thread



CJ BRIAN NJ;
I agree with what the other 2 said, the only thing in the idle circuit that makes any sense is the idle/air mixture screws. Typically 1 1/2 turns out is a good place to start. The .pdf that IO attached has a good procedure in it for adjusting idle. I would suggest using both a vacuum gauge and a timing light. If your timing is off, that will also greatly affect your idle. Set up your timing according to specs, I don't remember what it should be for a AMC 304 , somewhere between 8 - 12 degrees BTDC, that's where the timing light comes in. To get your timing exactly spot on, use a vacuum gauge at the same time, your manifold vacuum should be between 17 - 19 in Hg.

Here are a couple of diagrams for explaining the idle circuit and the load circuit in the MC2100;

Idle

Load

Let us know, we'll help you get it dialed in

 

[CJ BRIAN NJ]

I never once mentioned a name.



@ CJ Brian: check for vacuum leaks. This will show up when you have no response to the idle jet adjustment.

will do i checked it with a can of starting fluid a while back but i could have missed something.

AND I FORGOT A REALLY WIERD SYMPTOM IN MY DESCRIPTION ! WHEN I GET THE JEEP TO IDLE WITH THE CHOKE FORCED CLOSED AS SOON AS I ROCK THE JEEP A LITTLE BIT IT DIES! EVEN IF I SIT MY BIG *** ON THE SEAT KINDA HARD THAT IS ENOUGH TO MAKE IT STALL. IF I GRAB THE WHEEL AND ROCK BACK AND FORTH AND GET THE JEEP ROCKING A TINY BIT SHE STALLS OUT. MAYBE THE FLOAT IS STUCK OR ITS WEDGED IN A WIERD WAY OR THE PIN FELL OUT ?? IT REALLY DIES QUICK WHEN YOU SHAKE THE TRUCK HARD BUT EVEN A GENTLE ROCK WILL MAKE IT SPUTTER AND DIE. IF I KEEP PUMPING THE GAS IT STAYS RUNNING AND EVEN DRIVES WELL BUT I CANT KEEP THE PETAL IN ONE SPOT IT NEEDS TO BE PUMPED TO STAY RUNNING :::::::::::((((((((( REALLY ODD AND IM PRETTY GOOD WITH CARBS ESPECIALLY WHEN THEY ARE THIS SIMPLE AND OLD .FROM A 3.5 BRIGGS AND STRATTON TO A BIG BLOCK WITH TWO 750 DOUBLE PUMPERS AND EVEN THE HOLLY PROJECTION RAIL I HAD ON THE CHEROKEE STRAIGHT6 I CAN USUALLY FIND FUEL PROBLEMS PRETTY QUICK SO IM STUMMPED ! IM SURE WHEN I GET IT ON THE BENCH I WILL FIGURE IT OUT JUST GOTTA GET A KIT!

THX BRIAN

oh and sorry about the lack of puncuation and capitolization i type slower than i think so i gotta just type it out quick sorry , i know some people hate it but i gave up the office and desk 10+ years ago so to me typing always feels like work to me

thx

 

[alpha6]

Set up your timing according to specs, I don't remember what it should be for a AMC 304 , somewhere between 8 - 12 degrees BTDC, that's where the timing light comes in. To get your timing exactly spot on, use a vacuum gauge at the same time, your manifold vacuum should be between 17 - 19 in Hg.

What's the best timing to set for a I285 with a MC2150...right now I have it set on 8 BTDC but was wondering if there is a tighter adjustment

 

[mtnwhlr]

Up as high as we are we need to run more timing. I run 10-12 BTDC AS long as it's not pinging you are fine.

 

[IOPort51]

I find this to be a rather elusive number, I run about 12 BTDC and I am pretty close to sea level.

What's the best timing to set for a I285 with a MC2150...right now I have it set on 8 BTDC but was wondering if there is a tighter adjustment

 

[elwood blues]

You shouldn't be adjusting your timing for elevation, my timing here in Williamsburg VA (86 feet above sea level) should be the same at my parent's house in NW PA (~1800 feet) as it would be in CO.

What needs to change is your carburetor settings. Holley Carbs recommends to go down 1 jet size for every 2000 feet in elevation. Here on the coast, I ran size 47 jets with the best results in my 1.14 venturi MC2100 on 87 unleaded.

That would put me down to 44's in CO. You may need to play with your jetting, it's okay to run different sized jets together, that isn't going to hurt anything. I.e., a size 44 and a size 45 together.

It is my opinion that you guys in CO shouldn't be running a 1.08 venturi, you should probably be running a 1.02. If you're going to run a 1.08 you should try to find one with the altitude compensator on them. The look like this;

In theory, it works like this. As you go higher in altitude, you have less O2 in the air so the standard carb runs richer.

To off set that, the carb has an atmospheric pressure sensitive circuit (HA circuit) that is normally closed at sea level and as you go higher, the reduction in pressure gradually allows the vavle to open and it exposes an air inlet port in the carb. This then leans out the mixture in the carb by injecting more air to compensate for the thinner air at high altitude.

The problem is finding on of these gems, I've only found them on eBay, and usually not cheap.

 

[alpha6]

Thanks Elwood. Right now I am running 45's. at idle I am at 820 rpm's set at 8 BTDC. Engine is smooth and lots of power 1st through 4th. Once I switch to Overdrive on the highway, I have no acceleration left and the slightest hill I lose speed and have to shift down to 4th again to gain up. I am going to reset the timing to between 10 and 12 BTDC...hoping for more power.compression in that 5th gear. Next step would be to drop jet size like you suggest. Thoughts? Sorry CJ Brian for hijacking your thread.

 

[elwood blues]

Thanks Elwood. Right now I am running 45's. at idle I am at 820 rpm's set at 8 BTDC. Engine is smooth and lots of power 1st through 4th. Once I switch to Overdrive on the highway, I have no acceleration left and the slightest hill I lose speed and have to shift down to 4th again to gain up. I am going to reset the timing to between 10 and 12 BTDC...hoping for more power.compression in that 5th gear. Next step would be to drop jet size like you suggest. Thoughts? Sorry CJ Brian for hijacking your thread.

That sounds like a good plan. Don't get your head wrapped around that +10 to +12 BTDC number, a lot of people do, it's only a number. You need to time your engine to how it runs best.

I recommend to everyone to use not only a timing light, but a vacuum gauge at the same time. Get your timing close to with the light but fine tune it with the vacuum gauge. You should be running 17-19 in Hg of vacuum at idle.

Also, I would try to get your idle at or below 800 RPMs.

 

[elwood blues]

oh and sorry about the lack of puncuation and capitolization i type slower than i think so i gotta just type it out quick sorry , i know some people hate it but i gave up the office and desk 10+ years ago so to me typing always feels like work to me

It's okay, we forgive you I really think that something is up in your idle circuit and a good rebuild will help. Let us know.

 

[alpha6]

One last question Elwood, where is the best place to hook in the vacuum? Coming off the distributor would make sense... It has been so long since I did all my own engine and vehicle work I have forgotten lots. I am really enjoying doing it again and with all the insight on Jeep- CJ and it's members, it makes it tons easier. Thanks guys!

 

[elwood blues]

No, not off of the distributor, that is ported vacuum. You need to find manifold vacuum, off of the PCV of EGR valves would be the best place.