No power under load

[Ironmerganser]

Ok..so I have it all put back together. Starts up and idles great, but getting down the road, no power under load. Can't get above 30 mph.

AMC 258 i6 / 4.2l with new carb. Its as if it is running too rich. Spits and spitters under load and kicks out black smoke. New Plugs, wires, cap and rotor.

Any help is greatly appreciated!!

 

[fzsk4p]

What is all back together ?

What kind of carb ?

Fill us in with some more details.

 

[Ironmerganser]

Sorry.....had a build thread going. Got the new wiring harness in. Everything works, just have no power under load. Starts up and idles great, just when I am moving down the road, once I hit about 30mph, I have no more power, and if I come to a hill....forget about it.....it chugs and kicks out black smoke.

Stock carb....I think it is the MC-2100. It is a reman carb though.

 

[Casuall454]

The MC 2100 comes in 2 models high and low altitude. The high is for elevations over 4000 feet attached is a pic of a 2100 set for high altitude.

 

[IOPort51]

MC2100 is not stock on the AMC 258 i6 / 4.2l . what Transmission do you have??

 

[Ironmerganser]

OK. i am pretty sure I don't have the high altitude one.

Not sure on the Transmission designation, but it is the 3 speed. Is there more than one? Sorry...first Jeep....still learning as I go.

I got the timing set correctly last night. Everything looks to be up to snuff there. I think I may try a new coil and ignition modual today and just see if that works. I was planning on replacing them anyway.

As I am accelerating, it is as though it just starts missing at higher rpms. Got up to about 40mph last night once the timing was set correctly but still dropping out once I get there. No more power.

 

[JR74CJ5]

Couple questions...

• Have you tracked down and hooked up all needed / capped all un needed vac lines?
• When you set timing did you remove the vac advance?
• When you set timing did you go off book timing or "runs good" timing?
• How are you adjusting your carb? Evenly? Close both off complete and start at 2-3/4 turns out each? etc?

It's a 79 correct, so I assume you have to "SMOG" it? Not sure at your location...

If so it becomes a little more difficult, but still should be the same... What i would do is: (this is what i do on my AMC 304 , so may be a little different for you)

If any of this seems wrong, it could be just suggestions, and i haven't visited your build thread to see distributor type, etc that may make a difference in how you do the following...

1. Close mixture screws on carb all the way down (don't over tighten, just close), then turn them both out to 2-3/4 turns. If it idles ok and doesn't die, go to # 2. If not try to adjust the idle screw out (faster) if that doesn't help try adjusting the mixture screws again a little further out. (1/4 or 1/8th at a time depending on how it's sounding / running...) once you get it to idle without dieing
2. Disconnect vac advance, and set the timing to the recommended setting. (Book Timing) If it still runs ok, continue, if not re adjust like step 1
3. reconnect vac advance, and set Idle to (for me 750 RPM's) what recommended for your jeep.
4. See how it's running.
5. Fine tune the mixture and idle form there... Sometimes smog legal is not optimal performance... So you may want to reset after smog'ed etc.

Tips:

• I use a small (2-3") piece of rubber fuel line to fit over my mixture screws to be able to easily adjust the carb mixture without a screwdriver.
• Points may need some adjustment, again if its that type of distributor
• Have you checked your fuel filter out? Clogged filter could be a problem?

That's all I got for now... Hopefully a nice place to start, and hopefully applicable to your rig? Not an expert by any means, so please correct me if I am wrong fellow Jeepers.


~ JR

 

[Ironmerganser]

Thanks for all the great info JR74CJ5!!!!! I will try all of this tonight when I get home.

 

[CJim7]

Does this thing have a catalytic converter?

 

[Old Dog]

If it's blowing black smoke I'd start with a carb adjust.

 

[Ironmerganser]

Thanks for all your help guys, it is really appreciated, but I threw in the towl tonight. Its 100 degrees here in Omaha and I was sweating and leaning over teh engine bay. The wife came out to see if I had it fixed yet. I told her I was just about fed up with it...and no..still not right.

She says.....and this is why I love this women....."Why don't you just do that rebuild and 4.0 head thingy you have been talking about?". I looked at her, dropped my tools and gave her a big kiss. She is right, I am planning on doing that anyway. Why not just do it now and quit messing with it.

Again, thanks for the help guys. The next time I post, I will be posting about the new engine!!!!!

 

[JR74CJ5]