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Unread 04-03-2013, 05:38 PM   #1
YJMonster
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YJ MC2150 Help

Hello,

I recently put a new Motorcraft MC2150 Carb on my jeep and I am experiencing some hesitation on acceleration. I checked and I am getting good spray from the Accelerator pump nozzles. I also have done the nutter bypass before I changed the carb and the Timing is set at 8 degrees. I was also playing with the Choke and mixture settings and that does not seem to help the issue. A quick question about the choke settings though. Someone told me the marks on the top of the choke housing are to set it lean or rich but I am not sure which way is lean and which way is rich. It Idles great so I would not think it is a vacuum leak. Any help is much appreciated.

Thanks in advance.

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Unread 04-04-2013, 09:05 PM   #2
YJMonster
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I believe that I am runing rich as I went to the pump today to realize I am getting about 13 MPG when I used to get 15-16 on the carter. I changed a few things around today, hopefully they wil make things a bit better.
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Unread 04-04-2013, 10:24 PM   #3
Jax89Jeeper
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Was this carb from the ebay guy? If so... I can tell you his base tune hardware is probably wrong. Start by making sure your idle screws and float level are set properly and back off on the accel pump. If you are hessitating on acceleration, you are surging too rich on the transition circuit.... If you are getting crappy mileage, your main circuit is probably too rich which could also contribute to loading up on aceleration This may require stepping the jets down a size and/or going with a lower rated power valve. Tell me the details... Location, jet size, power valve size, idle screw settings, and timing. Are you using a vac guage to tune?
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Unread 04-05-2013, 10:13 PM   #4
YJMonster
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Thanks for the reply, yeah it was from the ebay guy. I believe they were 48 jets, They may be 46 but I have to check he only sent a paper stating the Jet size nothing else really. I am not sure of the powervalve size and as for the Mixture screws I have been adjusting them so I would say about 5 turns out I think. The timming is at 8 Degrees BTDC right now and I am in Southern California in the inland empire area, about 30 miles inland from Los angeles.

Thanks for the help.
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Unread 04-06-2013, 10:35 AM   #5
Jax89Jeeper
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Quote:
Originally Posted by YJMonster
Thanks for the reply, yeah it was from the ebay guy. I believe they were 48 jets, They may be 46 but I have to check he only sent a paper stating the Jet size nothing else really. I am not sure of the powervalve size and as for the Mixture screws I have been adjusting them so I would say about 5 turns out I think. The timming is at 8 Degrees BTDC right now and I am in Southern California in the inland empire area, about 30 miles inland from Los angeles.

Thanks for the help.
It sounds like you are a bit far out with the needles.... Typically the srews are no more than 2.5-3 turns out. #48 jets should be about right for your elevation (not too far above sea level). One question I did not ask: is this the 1.08 venturi version? Being from the ebay guy, it should be, but this can greatly affect tuning so it is worth verifying. Timing is about right, though 8-12 BTDC is acceptable, I have mine set at 10 BTDC. If are not using a vac guage, get one and learn how to use it... it will help get everything sorted out, from the carb to the timing. You will need to check vac to get the proper power valve as well.

It may make it easier to start by tellIng you my set up : #48 jets, 7.5 inHg PV, the needles around 2.75 turns out, float set to 7/16", timing at 10 BTDC, and idle set around 650-700rpm with engine vac running 21-22. Considering your similar elevation (Although in that area the mountains and hills come into play) you should not be too far off from my settings. My carb came from the ebay guy with #50 jets and a 9.5inHg PV and gave me a way too rich base tune.
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Unread 04-14-2013, 10:12 AM   #6
YJMonster
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I went ahead and picked up a VAC gauge from harbor freight and tested it today. The first thing I noticed is that it would not climb past 16 PSI when I first plugged it in. I then decided to start by advancing the Timing to 10 DBTDC. After that it was in the green at 18 PSI. And that made an instant difference in the power and hesitation. I still have a slight hesitation sometimes but I think I need to continue playing with the tune for now and make sure there are no leeks and once everything is dialed in if I am still having a hesitation problem I am going to replace the power valve. Can you think of any reason why the pressure will not climb past 18PSI?

Thanks for all the help
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Unread 04-15-2013, 05:29 AM   #7
vadslram
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Make sure your vac lines are run correctly for your carb and Dizzy combo. When you stomp on it you lose vacum and it will change the timing.
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Unread 04-15-2013, 05:47 AM   #8
Beachcruiser
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Quote:
Originally Posted by Jax89Jeeper View Post
It may make it easier to start by tellIng you my set up : #48 jets, 7.5 inHg PV, the needles around 2.75 turns out, float set to 7/16", timing at 10 BTDC, and idle set around 650-700rpm with engine vac running 21-22.
I set my own up, but it's almost identical (save for #47 main jets).
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Unread 05-10-2013, 07:11 PM   #9
YJMonster
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Finally Able to get back to it, I will be resealing the carb tomorrow as there might be a small vac leak at the manifold to carb gasket, I will also look into getting a new power valve. Do I have to look for a motorcraft brand. Is there an online vendor for the power valve, will the Holly one work? I am not sure if they are universal?

http://www.carshopinc.com/product_in...FelxQgodUxMAOw
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Unread 05-10-2013, 08:14 PM   #10
4.7stroker
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You have to set your idle mixture screws with a vacuum gauge.
There are plenty of write-ups on how to tune that carb, the sequence MUST be followed step by step with no short cuts.
Setting it up on manifold vacuum for the vacuum advance is also better than ported vacuum.
Installing a 81 pre smog distributor with a set of light centrifugal advance springs will bring in full timing bt 2200 rpm to give you the most power down low.

Dwayne
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Unread 05-11-2013, 05:37 PM   #11
YJMonster
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Yeah I already set the timing and adjusted the mixture screws with a vac gauge from a manifold vac line. I still have a slight bog but my choke is also screwed up and the guy did not include a fast idle screw in the kit. I will be changing the choke, reseating the carb t get rid of a vac leak and re-tuning it but I was wondering for future reference if I still have an issues if the Holly PV will work or if there is somewhere specific to get one for the motorcraft.
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Unread 05-11-2013, 11:12 PM   #12
Jax89Jeeper
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Yes Holley will work... The MC carbs were made by Holley and share many parts. NAPA should be able to easily cross reference the part numbers for you.
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Unread 09-21-2013, 11:38 AM   #13
drespecki
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Quote:
Originally Posted by Jax89Jeeper View Post
Was this carb from the ebay guy? If so... I can tell you his base tune hardware is probably wrong. Start by making sure your idle screws and float level are set properly and back off on the accel pump. If you are hessitating on acceleration, you are surging too rich on the transition circuit.... If you are getting crappy mileage, your main circuit is probably too rich which could also contribute to loading up on aceleration This may require stepping the jets down a size and/or going with a lower rated power valve. Tell me the details... Location, jet size, power valve size, idle screw settings, and timing. Are you using a vac guage to tune?

Hi...not to hijack but have a question... I am running a CJ7 with the 4.2 and have the DUI hei installed.. My 2150 is one of the new ones from the ebay guy and has the 7.5 PV and 47 jets.. I had a hesitation upon accelerating and am thinking I need a 6.5 PV and 46 jets?
Any better recommendations? I am at about 2600 feet +
Thanks...
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Unread 09-21-2013, 12:54 PM   #14
c5wagner
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Quote:
Originally Posted by drespecki View Post
Hi...not to hijack but have a question... I am running a CJ7 with the 4.2 and have the DUI hei installed.. My 2150 is one of the new ones from the ebay guy and has the 7.5 PV and 47 jets.. I had a hesitation upon accelerating and am thinking I need a 6.5 PV and 46 jets?
Any better recommendations? I am at about 2600 feet +
Thanks...
Since you have the hei dizzy, you should have the #47 jets, but I would try downsizing the power valve. I would also play with the accelerator pump linkage to get it right for your vehicle. Also, advance the timing to about 10-12* for your elevation.
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Unread 09-21-2013, 01:37 PM   #15
drespecki
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Go with the 6.5 PV? No change in the jets then... I was having a hesitation when giving it a firm, more aggressive push of the gas pedal..
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