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post #1 of (permalink) Old 12-18-2005, 12:40 PM Thread Starter
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Carb. Adjustment?

Well my jeep is up and running again with only a few bugs to work out. The shop I took it to said I needed a new carb. I don't believe it as they couldn't really give me a reason. So me and my limited knowledge and haynes manuel have been tinkering with it. I checked the jets on the front and one was out almost 5 turns(Passenger side) and the drivers side was only out maybe 1 1/2 turns. I turned them in and backed them out to two turns on both. Now as I understand I should be able to crank the engine and turn them in until the rpm drops and bring them back out till it picks up where it was. Well this makes no difference in fact I can turn them in or out almost all the way. What gives here? I think it should make more difference than that. Any thoughts and help is greatly appreciated.

Matt
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post #2 of (permalink) Old 12-18-2005, 12:46 PM
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Re: Carb. Adjustment?

Use a vacuum gauge.

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post #3 of (permalink) Old 12-18-2005, 01:26 PM
 
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Re: Carb. Adjustment?


OK, I haven't been following this...
What kind of carb, on what, in what, ect...???

If you have a vacuum gauge, and you can't tune a carb or diagnose an engine without one, Try here, http://www.junkyardgenius.com/tools/vacgauge.html

The only reasons for the idle mixture screws to not be functioning are,

1. Some dummy cranked them in until the nose of the needle twisted off in the adjustment passage.
Remove the screws and check for a point on the screw.

2. The passage is clogged with crap from an imcomplete cleaning before rebuild, or clogged with crap from inadiquate fuel filtering.
Remove screws and try carb cleaner with that little plastic tube attached to the nozzle.
If the passage fills up and the can doesn't have enough pressure to blast the blockage out, leave the passage full, then use a blow gun and shop air!
You aren't going to break anything...
Once the passage is open, rebuild the carb.

3. Some 'Smog Years' had carbs the screws worked backwards.
Lean was out, in was rich.
Since we don't know what carb you have, we can't tell you if this is the case...

4. Float level so high that fuel is flooding the idle passages.
Adjusting float level should have been done immedately after carb install.
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post #4 of (permalink) Old 12-18-2005, 01:37 PM Thread Starter
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Re: Carb. Adjustment?

It is a MC 2100 on a 304 in a 73 cj 5. I had to replace the powervalve due to a really nasty backfire and it hasn't been the same since.

Matt
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post #5 of (permalink) Old 12-18-2005, 01:42 PM
 
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Re: Carb. Adjustment?

Now we are getting somewhere...
I have a '73 CJ-5 with factory V-8 also.
I'll have a look...



First Picture,
1. This is a clean air vent.
It's intended purpose was to supply clean (and cold) air for the choke regulator.
If it's not hooked up properly with NEW hose, cap it like in the picture.

2. Choke regulator.
Adjust as necessary, instructions on the end of the canister.
Ford had a bad habit of the end of the bi-metal spring slipping off the choke flap arm, so you may want to check that.

3. Ported Vacuum.
This is the vacuum port that's supposed to supply your distributor.
Make sure it has NEW hose or is capped.

4. Idle adjustment screw.
Take the screw out, make sure it has a point on it.
If it doesn't, you are in for a rebuild and new screws, if it does, squirt some carb cleaner in the hole and see if it drains quickly.
Cleaner with the little plastic straw works well here so you can really get down in the hole.

If it drains and the screw has still got a point, replace the screw, GENTLY screw in all the way until it bottoms out, then back out 1-1/2 turns for an adjustment starting point.

5. This will be the large manifold vacuum port.
NEW HOSE to where ever it's going... PCV or brake booster, ect.

6. Factory ID tag.
If you have one of these, the carb probably hasn't been opened, or the guy that did it actually knew what he was doing.
This is the little bugger that will get you the correct parts.
If you ever buy a used carb, look for this tag, and look to see if it looks like it belongs there...
(IE: grease smudged where it mounts, rubs from vibration on the zinc carb bowl parts, ect.)



Picture 2.
4. Idle Adjustment Screw.
This one is out of sight under the float bowl.
Same drill as above for this screw.

6. Factory ID Tag Again.

7. Accelerator Pump Housing.

8. Small Manifold Vacuum Port.
Make sure this is plugged with a NEW hose or a NEW cap.
this can not be left open.

9. Not shown, New base plate gasket...
You must not allow any leaks at the base plate of the carb.
Don't over tighten the bolts or you will warp the baseplate of the carb and leaks will happen!
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post #6 of (permalink) Old 12-18-2005, 02:08 PM Thread Starter
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Re: Carb. Adjustment?

Hey what is your opinion of a holly 500cfm carb on this engine? I had one offered to me for only 100.00. there's nothing wrong with it the guy thats got it took it off to put 4barrell on his truck.
Matt
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post #7 of (permalink) Old 12-18-2005, 02:41 PM
 
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Re: Carb. Adjustment?

I think most are better off with the Motorcraft carb than the Holley. Comparing both bone stock the motorcraft works much better on inclines. If you are at all mechanically inclined, I would take the carb off, disassemble it looking for problems, clean it thoroughly and adjust the float height. Specs vary depending upon the year, but a good service manual should have the information for your year's float height and teardown procedure.

When its working properly, you should definately have a point at which screwing in the idle mixture screws makes the mixture so lean it stumbles then stalls. You can make it run far richer than it needs and not see that pronounced of an effect unless you are using a vacuum gauge. Keep the two screws in synch, and work slowly and systematically to find the peak lean vacuum. Ie, the leanest point at which it will produce peak vacuum at idle. But don't bother with any adjustments unless you know the carburetor is working properly and the float bowl and fine passages are not full of crud.
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post #8 of (permalink) Old 12-18-2005, 04:19 PM Thread Starter
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Re: Carb. Adjustment?

Thanks guys

It's coming off this week as soon as school gets out.

Matt
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post #9 of (permalink) Old 12-18-2005, 05:53 PM
 
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Re: Carb. Adjustment?



Holley is a good carb, very tunable.
I run them off road all the time, but you will have to do some mods. Easy enough if you know what to do.


If you take a good look at the MC 2100 you will find out it is a copy of a Holley...
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post #10 of (permalink) Old 12-18-2005, 07:31 PM Thread Starter
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Re: Carb. Adjustment?

Thats my problem I really don't know what to do. I'm ok with everything but major engine stuff. I guess I'm afraid I'll mess it up good. I'm gonna pull the carb off and rebuild it or at least try. I figure if I can put in a whole wiring harness surely I can do this too.

Thanks Matt
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