need help with mc2100 1.21

[coas]

RE: Jeeps throwin codes...again

I've just installed the mc2100 1.21 venturi on my 258. I tried almost anything to make it work but still it hesitate, bogs down, puffing black smoke, running reach when accelerating running lean at cruising.

Changed the jet's from #48 to #46 and than to #50. now I'm back on #46 because the spark plugs were soot.

Changed the power valve to one with higher no, 9.65 instead of 7.5, and it's feel more responsive.


Changed the timing from 8- 24, no improvement.
everything is hooked up correctly and there is no vacuum leaks. the carb itself was dismantle and cleaned thoroughly even though its a remanufactured one. the float is set to 9/16 from top. the fuel pump deliver 5.5 psi. chock is set correctly and there is no hose lying too close to the manifold.

The engine was recently rebuilt w 4.0L head and HEI.

I'm just about tossing this one and look for the 1.08 venturi mc2100.

Any help will be appreciated.

 

[Platsmith]

I have heard that the 1.21 is a pain to tune. From all that I have read it has to much cfm for the motor. I just bought a 1.08 for my 258 and am trying to figure out which power favlve to get and how to do all my vacuum stuff. I want to make this as easy as a swap as possible.
It sounds like you are dumping way to much fuel and the venturi is to big. I would probly try to go to the other carb. sorry I can't help you with anything else. Did your jeep have the pulse air system. If it did what did you do with it?
Randal

 

[Junkpile]

RE: ABS Vibration no light

I couldn't help you with the specs on the tune, but it will work. It's only 350cfm. The 1.08 is fine for a mild 258, but it's going to hold you back if you want to take advantage of that better flowing cylinder head. What camshaft are you running? It's not a factory 258 grind is it? Header? What intake? It should be running better than that in the mid-high range, even if it is a little on the fat side for that engine.

The last 258 I messed with only had a "RV" type cam, Clifford intake, HEI, and a split header, and it ran pretty damn strong(and clean) with a 390cfm four barrel on it. We looked for a 1.33 motorcraft, but couldn't locate one.

The factory carb is rated to flow 280cfm.
The "small" weber is 300cfm, and the performance model is 400cfm(?)
The 390cfm Holley 4 barrel, along with the 350cfm and 500cfm 2 barrel are both used alot too.

Here's the CFM rating for the 2100/2150 as indicated by the venturi size
.98 = 190(cfm)
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

Good luck with it

 

[coas]

RE: cherokee leaf packs

Thx for the reply but since I post this I mange to gather a lot of info and the answer is that it's simply too large.
the CFM rating as you wrote is not correct mainly because of different flow test used by Ford compare to the other, Ford test flow at the top where as Holley and Weber at the base. meaning that the mc2100 is a lot bigger.
Or, it's better to look at it the dumb way: it came off a 351 CID V8, i.e. A lot more air, 30% more... compare to the 1.08 that is 15% larger. (since the flow is higher with V8 than in line 6 it's even worse)

Anyway, just bought from e-bay a nice MC2100 1.08 and that will end my saga with the 1.21.
Last, you cannot compare CFM of 4 bbl and 2 bbl, you need to compare the primary first to be in the range of 60-70 of the max engine CFM and than the secondary.
or use this: 2BBL CFM X 1.42=4 BBL CFM

Look for the information and the development of this at the following link, there is info on power valve as well:

http://www.jeepaholics.com/support/topic.asp?TOPIC_ID=40613

Thanks again.

 

[Junkpile]

electrical problems...

The problem isn't too many cfm, it's not having enough booster signal too accompany the available flow. It's the engine setup and the tune. That bigger carb can be made to work.

 

[coas]

Why won't it FIRE!!!!!!

The problem isn't too many cfm, it's not having enough booster signal too accompany the available flow. It's the engine setup and the tune. That bigger carb can be made to work.

I'll be happy to lern how to do it. and i'm not being cynical.

By the way, the Carter BBD is ony 195 CFM:
From Carter repair manual:

 

[Junkpile]

I had no idea that the factory carb was 195cfm. I must have read somewhere that it was 280 and just took it for the truth. Learn something new everyday I guess.


But the 1.21 still isn't too big for a healthy 258.

I didn't go to the site you linked......what do they say is the actual cfm rating of the 1.21?

 

[coas]

The 1.21 is supposed to be 351 CFM but, reportedly there is a difference in the testing method used by Motorcraft and the rest of manufacturer, MC, allegedly, testing the flow at the top whereas the other at the base.

someone is making a convincing mistake and all the others follow. so, all this CFM data is questionable.