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View Poll Results: which carb
weber 1 9.09%
mc2100 10 90.91%
stock 0 0%
Voters: 11. You may not vote on this poll

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post #1 of (permalink) Old 12-08-2007, 03:37 PM Thread Starter
 
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which carb is better

Trying to figure out what everyones opinion is on which carb is better for the 258. weber, mc2100, stock. Right now I am running the mc2100 and I am fighting with the accelarator pump, under hard load it is bogging down, thought about trying my luck with the weber.....
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post #2 of (permalink) Old 12-08-2007, 04:33 PM
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MC2100 is very highly rated, and seems to be easier to set up than the Weber. The Carted BBD gets a terrible rap, but my guess is that it's mainly because it comes with the external controls that can be tricky to get working properly. I like my little 1-barrel Carter YF, but you're not going to get much power out of it.

I think you're probably best off sticking with the MC. Bogging down under hard load isn't an accelerator pump problem; it's more likely jetting, if the carb is even the problem. Are you sure it's timed properly now?

The accelerator pump only comes into play when you initially open the butterflies. Air is less dense than gasoline, so when the carb is opened, the air can get flowing very quickly, but the gas takes a little while to get moving and catch up with the new amount of air. That causes a momentary lean condition, which the accelerator pump makes up for by adding a little extra squirt. But as soon as it adds that squirt its job is done and it plays no further role in events until you increase the opening again.

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post #3 of (permalink) Old 12-08-2007, 04:42 PM
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MC2100. Next would be a stock non computer controlled BBD (yes, with some tinkering it will work pretty good) and last would be the weber.

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post #4 of (permalink) Old 12-08-2007, 05:34 PM Thread Starter
 
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Quote:
Originally Posted by Jim_Lou View Post
MC2100 is very highly rated, and seems to be easier to set up than the Weber. The Carted BBD gets a terrible rap, but my guess is that it's mainly because it comes with the external controls that can be tricky to get working properly. I like my little 1-barrel Carter YF, but you're not going to get much power out of it.

I think you're probably best off sticking with the MC. Bogging down under hard load isn't an accelerator pump problem; it's more likely jetting, if the carb is even the problem. Are you sure it's timed properly now?

The accelerator pump only comes into play when you initially open the butterflies. Air is less dense than gasoline, so when the carb is opened, the air can get flowing very quickly, but the gas takes a little while to get moving and catch up with the new amount of air. That causes a momentary lean condition, which the accelerator pump makes up for by adding a little extra squirt. But as soon as it adds that squirt its job is done and it plays no further role in events until you increase the opening again.
Timing is good.......It is bogging down when the accelerator pump is engaged. So I would need smaller jets?
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post #5 of (permalink) Old 12-08-2007, 06:54 PM
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I did not vote.
But I agree with Jim, However my 76 258/YF generated more more power than my 81 bbd/258.

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post #6 of (permalink) Old 12-09-2007, 01:49 AM
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Well i cant vote on the MC i have never seen or tryed it. But i have had a Weber and it worked very well for me for many yrs..

The stock carb is only good to Shoot at.

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post #7 of (permalink) Old 12-09-2007, 05:01 AM
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Quote:
Timing is good.......It is bogging down when the accelerator pump is engaged. So I would need smaller jets?
So you push the pedal down and the engine bogs and sputters for a second or so, and then takes off and pulls well until you let up the pedal again? That's typical symptoms of a weak accelerator pump.

I guess you have the BBD, about which I know nothing specific. But every carb I can think of has a way to adjust the linkage that operates the accelerator pump. Usually you can move a link to a different hole on an arm so that the pumps moves more for a given movement of the throttle shaft, and that's probably what you need to do.

That's assuming that the pump itself is in good condition. They're either a plunger or a diaphragm. Other Carters use a plunger, so I'm guessing that your carb has one. They have a leather or rubber cup at the botton that makes a sliding seal inside the bore. If that cup is worn or cracked it won't work right.

Then there is a check valve that prevents the gas from flowing back into the float bowl when the plunger comes down; usually just a little ball over a hole in a little pocket. I can't imagine one going bad, but every rebuild kit has a new one.

Also, if the engine is running lean for any reason, like the float set too low or a clogged jet or emulsifier tube, or a vacuum leak, the accelerator pump could be working fine, but not have quite enough volume to fully make up for the lean condition.

Probably the best thing for you to do now would be to make sure you don't have a vacuum leak anywhere. Then adjust the accelerator pump linkage to increase the output, and if that doesn't do it get a good kit and rebuild the carburetor.

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post #8 of (permalink) Old 12-09-2007, 08:45 AM Thread Starter
 
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It is a rebuilt mc2100 on there right not.....under hard load it just stalls and cuts off........I unhooked the vac. advance and it doesnt it at a different spot in the rpm range like around 2000 or so........So maybe it aint the carb, maybe vac advance.....I have adjusted the accelerator linkage and it really doesnt get better or worse......pretty much stays the same.....I put a new diaphram in it and still the same thing.......
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post #9 of (permalink) Old 12-09-2007, 10:13 AM
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Quote:
under hard load it just stalls and cuts off.
That doesn't sound like an accelerator pump problem. Could still be timing related. Could also be that if you bought a rebuilt from a parts house it's not jetted or set up properly for your engine. Try the propane trick. RRich put up a brief description here: https://forums.off-road.com/jeep-shor...arb-gurus.html but there may be a more complete one somewhere else. If it is a carb problem, it's probably lean, in which case adding a little propane will perk it right up.

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Last edited by Jim_Lou; 12-09-2007 at 10:26 AM.
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post #10 of (permalink) Old 12-09-2007, 07:01 PM
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There are a few sizes in the MC2100 line. What size do you have?

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