MC2100 jet size for street use?

[GL49]

Hey all! I've got a '74 CJ5 with stock AMC 304 , T-18 , and 3.73 gears. Pretty much the only upgrades done have been a 2" suspension lift and 31" BFG's. I knew the V8 wasn't going to be easy on gas, but at $3.49 and rising, I wasn't too happy with the 12.5 mpg at my last fill up. Checked the carb (an MC2100 1.14 off a '63? Galaxie) and found that it currently has .054 jets, making it run rich. Does anyone have any suggestions for jet sizes on a rig that sees mostly pavement, with the occasional weekend trip to the hills? I'm thinking somewhere between .044 -.047 based on research that I've already done.

 

[NorthwestCJer]

I ran 47's on my 74. But I was 1.08 ventury that came on the jeeps.


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[IOPort51]

Makes no difference, trail or street. Trial and error, What is in it now? Does it smell rich?? Running lean can burn valves and in general make things run hotter.If you wanted fuel economy you may not get much if any better than you have. But if you do I know we all would love to hear about it.

 

[GL49]

Like I said, I'm not expecting to get Geo Metro milage here, but if I can increase it at all, I'd be happy Right now its running, .054" and very rich. Spark plugs are dark, and not the good golden brown kind of dark either. I have no problem at all starting it after it has set overnight, even with no choke. According to the tag, I think it originally came off of a 352, so I should be able to go down a few jet sizes.

 

[IOPort51]

I am pretty sure I am also running 47s in my 1.08. My carb came from a 63 Galaxy also 289 I think. I think it had 52 in it originally. I would try a 47 and check the plugs. I would also think about some ignition mods. Make sure you can actually burn what you put in the cylinder. It is always just one thing after another.

 

[GL49]

I went ahead and ordered some 46's, so I'll see how that works out. If they end up being too lean, I'll just throw the old 54's back in and try again. I'll let you all know how they run!

I don't think I'll do anything with the ignition right now, since it has a brand new distributor. Plus I'm trying to keep the drivetrain pretty much stock. Maybe sometime in the future when I'm not living on a college student's budget!

The Transmission is out right now because I was having a terrible time getting it into 2nd, so I won't be able to test drive it for a few days but hey, at least I know what my spring break project is For right now, this is where it sits...

 

[jeremy5780]

Keep me updated, I have a mc2150 on the way I bought of eBay . I'm replacing a VERY finicky holley 390!

 

[Jimbos76cj]

I don't think I'll do anything with the ignition right now, since it has a brand new distributor. Plus I'm trying to keep the drivetrain pretty much stock. Maybe sometime in the future when I'm not living on a college student's budget!

If you increase your spark energy and get better burn out the gas your dumping into it right now your economy will increase. Jeep's are pretty well known for thier not so great igntion system. Id look into an upgrade. It can be easily upgrade for pretty cheap. there are plenty of great write ups on it. If you increase even 2mpg you will be up to about 15 mpg. On a 20 gallon tank thats about 40 miles extra or $9 saved.. 25 tanks will pay for a HEI dizzy

You can also do some thing like the stealth HEI for really cheap.

 

[GL49]

If you increase your spark energy and get better burn out the gas your dumping into it right now your economy will increase. Jeep's are pretty well known for thier not so great igntion system. Id look into an upgrade. It can be easily upgrade for pretty cheap. there are plenty of great write ups on it. If you increase even 2mpg you will be up to about 15 mpg. On a 20 gallon tank thats about 40 miles extra or $9 saved.. 25 tanks will pay for a HEI dizzy

You can also do some thing like the stealth HEI for really cheap.

I'll look into my different options, thanks!

Stealth HEI, I'm assuming thats an HEI system that simply looks like a conventional system?

Jets came today, but the Transmission won't be back until tomorrow (fingers crossed!), I'll post again in the next few days once everything is back together and driving!

 

[Jimbos76cj]

Yeah the stealth HEI is for places that have inspections. You pull the guts out of your ignition box and install and wire a chevy HEI module into it. When its done it looks almost like a stock box. Or I was looking at o'Reily's yesterday and they sell a MSD Street fire CDI box. This will give you so much more power over the HEI or stealth HEI.

I picked up my MSD 6a off craigslist for $75 lightly used. some times a little money up front will add up in the long run.