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Old 07-15-2014, 10:54 PM   #1
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MC2150 flat spot/lag

Have my 2150 with 1.08 venturis installed and have a "flat spot" and lag at mid throttle and up to W.O.T. Anyone have this issue with theirs. Timing is at 9 degrees and it's nuttered. Thanks

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Old 07-15-2014, 11:06 PM   #2
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Quote:
Originally Posted by 90yjjeepin View Post
Have my 2150 with 1.08 venturis installed and have a "flat spot" and lag at mid throttle and up to W.O.T. Anyone have this issue with theirs. Timing is at 9 degrees and it's nuttered. Thanks
9* with the vac advance unplugged and at 700rpm? Incorrect jet size or wrong power valve could also be the issue. Tell me your elevation, and any engine upgrades or mods.

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Old 07-16-2014, 12:14 PM   #3
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9* with the vac advance unplugged and at 700rpm? Incorrect jet size or wrong power valve could also be the issue. Tell me your elevation, and any engine upgrades or mods.
Yes, 9* with vac advance unplugged and 700rpm. I'm at sea level on the coast of NH. Just nutter bypass and Team Rush conversion, no other upgrades. Got the carb from GRONK in Colorado and supposed to be set up to my elevation and it has 1.08 venturis.
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Old 07-16-2014, 12:30 PM   #4
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So what size jets?

If you do not know you can pull the top off the carb and look under the float there should be two brass plugs in the bottom of the bowl a good size flat tip will unscrew them just be careful and do not strip them lastly take a look at you float if it is bad then it is filling with gas and not floating also look to see if you have a spring on the float if it is installed wrong it can cause an issue like you describe.

Lastly if you pull a spark plug and look at it if it is all black jets are probably to big if all white your timing is off or the jets are to small it both

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Old 07-16-2014, 12:45 PM   #5
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Can't remember what jets are in it. It's been a few months since I got it. I'll have to look for my paperwork, and if not, Ill have to pull it apart and check them. It's a new carb so I would hope that the float isn't bad.
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Old 07-16-2014, 01:32 PM   #6
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Can't remember what jets are in it. It's been a few months since I got it. I'll have to look for my paperwork, and if not, Ill have to pull it apart and check them. It's a new carb so I would hope that the float isn't bad.
Float wouldn't be bad, just might not be retained right or set at the right level. At sea level, the float should be 1/2" from the top of the float bowl. You should also have #47 jets at sea level with a 7.5lb power valve. Try setting your timing to 8* btdc at 1600 rpms with the vac advance unplugged and see how that runs
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Old 07-16-2014, 02:46 PM   #7
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Not to be overly nit picky but it is not a new carb just rebuilt. And I am not saying the rebuild was done wrong but sometimes the float can have a crack in it which let's gas collect in it which weights it down.

Just overing some potential items to investigate.

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Old 07-16-2014, 03:19 PM   #8
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Thanks for the info c5wagner. It's raining here today so I'll have to get into it after it stops. And yes, 89Saharagreen I know its not a "new" carb... it has new parts in it. I was just thinking it might have to be fine tuned or maybe accelerator pump adjustment. I'll look into all the info you guys provided. Thanks again!! Guess I should get out my vacuum gauge too.
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Old 07-19-2014, 02:30 PM   #9
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Well, found my paperwork. Says it has 48.5 jets and doesn't say what power valve it has. Guess it's time to tear into it and see what I find... NOT what I was anticipating when I got it.
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Old 07-19-2014, 03:00 PM   #10
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Well, found my paperwork. Says it has 48.5 jets and doesn't say what power valve it has. Guess it's time to tear into it and see what I find... NOT what I was anticipating when I got it.
Get a rebuild kit for a 2.8l v6 mustang since that will come with the right power vavle. Jet size should be 47 for a stock motor at sea level to 3500ft elevation. 46 for above that until 7000ft. If you have oversized pistons like .030 over 48 should be fine.
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Old 07-20-2014, 01:30 PM   #11
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Found it has a 7.5 lb power valve with one 48 jet and one 49 jet... also found brass threads under the jets when I pulled them out... I don't like seeing stuff like that, usually not a good sign. Anyway, I'm gonna order 47's for it and see what happens. Thanks again for the info!!! (Also e-mailed Gronk... we'll see if I get a response) My YJ is my D.D so unfortunately I have to keep it "driveable"...
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Old 07-24-2014, 06:11 PM   #12
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Well... got my new jets (47's) and installed... this thing is still falling on its face on acceleration. I'm pretty sure this thing is thirsty for fuel on acceleration (leaning out) badly. Anyone else have any input where to go with this thing??
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Old 07-24-2014, 07:51 PM   #13
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Is it only on acceleration? The first post said mid throttle to WOT. If accelerating issues, you can fool around with the accelerator pump linkage.

Could also be too much fuel being dumped into the motor causing hesitation. Did you adjust for peak lean vacuum after you set the timing? My vacuum reading at idle and warmed up is 22 inch/Hg and I'm at 4500 ft elevation.

If it was running lean, your temperature gauge would show your engine running warm, and your plugs would also show if you're too lean or rich
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Old 07-24-2014, 10:51 PM   #14
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Is it only on acceleration? The first post said mid throttle to WOT. If accelerating issues, you can fool around with the accelerator pump linkage.

Could also be too much fuel being dumped into the motor causing hesitation. Did you adjust for peak lean vacuum after you set the timing? My vacuum reading at idle and warmed up is 22 inch/Hg and I'm at 4500 ft elevation.

If it was running lean, your temperature gauge would show your engine running warm, and your plugs would also show if you're too lean or rich
Yes, by mid throttle to WOT I was meaning acceleration. Accelerator pump linkage is adjusted to top position on throttle arm, there's no adjustment available on pump arm. I tried the other positions on it and its worse. Only thing I haven't checked was plugs yet... I'll have to read them in the a.m.I think my vac reading was like 23" I can't remember exactly, it was 2 days ago that I read vac.
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Old 07-25-2014, 01:21 AM   #15
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Yes, by mid throttle to WOT I was meaning acceleration. Accelerator pump linkage is adjusted to top position on throttle arm, there's no adjustment available on pump arm. I tried the other positions on it and its worse. Only thing I haven't checked was plugs yet... I'll have to read them in the a.m.I think my vac reading was like 23" I can't remember exactly, it was 2 days ago that I read vac.
You adjust the pump arm by bending it, I'll have to post pictures showing them adjusted in the morning. There's also the area where it connects on the throttle shaft where you can adjust the pump too
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Old 07-27-2014, 12:35 PM   #16
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Ok, so after much reading and reviewing and checking everything over multiple times, I found what seems to be the outer part of my crank pulley has slipped causing my timing mark to be off by quite a bit. Adjusted timing with my vacuum gauge at manifold vacuum and even though I already had 20" vacuum, I was able to advance it and get it to 22" of vacuum and my issue is 95% gone. So now time for minor carb adjustment and should be good. Thank you guys for all your help, MUCH appreciated!!!!!

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