2100 swap

[richmo]

I replaced the MC 2100 with a rebuilt one (on a 79 AMC 304 )I got at oreilly's. I plan to rebuild the old one and use it later. The question I have is the old carb didn't have this fitting. I plugged it (it was open out of the box). Is this what I should have done? If not where does it connect? I can't find it in Chilton or Haynes. I am new at this and thank everyone who has helped and will help in the future.

 

[DHugg]

I replaced the MC 2100 with a rebuilt one (on a 79 AMC 304 )I got at oreilly's. I plan to rebuild the old one and use it later. The question I have is the old carb didn't have this fitting. I plugged it (it was open out of the box). Is this what I should have done? If not where does it connect? I can't find it in Chilton or Haynes. I am new at this and thank everyone who has helped and will help in the future.

RIchmo, I just put an O'Reilly's 2100 (JIMCO 1.08) on my 1980 AMC 304 . The port under the fuel bowl to the right of the right idle adjust screw is ported vacuum. It draws nothing until the throttle is cracked a little, then I see about 10 inches of vacuum for starters.

There is a longer port beneath and to the right of the choke housing, on the passenger side. That port is manifold vacuum and draws whatever is happening inside your intake manifold. I've plugged it. Any other opening that drops the intake vacuum on my vacuum gage I plugged. Your mileage may vary; this carb is sure different from the one I replaced.

With my AMC 304 , after puzzling so long about why a lot of folks wanted me to adjust the distributor for 10-12 degrees at hot idle, I think I finally broke the code today. If I adjust for TDC at idle, as soon as the throttle advance causes the ported vacuum, hooked to the vacuum advance, to suck on the diaphragm, I get a six-seven degree advance. When the RPM builds a little more, the first centrifugal advance spring, the weaker of the two springs, begins to add more advance. The bottom line is steady, smooth acceleration.

If I try to run with the distributor adjusted to even 5 degrees before TDC, I get a serious stumble as soon as the throttle is opened, and the more it opens, the more stumble and miss comes on until I can barely keep her rolling along at a brisk walk. I believe I am getting TOO MUCH advance from the reworked distributor and the vacuum advance canister set at its lowest spring tension.

I didn't mean to write the story of my life here, but I just worked over my whole ignition system after several months of painful, fruitless effort to tune the new carb for no miss-no stumble. I found the problems all in the distributor - the reluctor that triggers the spark wasn't staked to the shaft by the little steel "key' that was missing, and someone had put a small ball bearing in the vacuum line just in front of the vacuum canister input.

At least now I'm not ashamed to drive around the neighborhood with an engine that sounds like a junkyard refugee.

 

[richmo]

The one under the choke was plugged out of the box. So the one I was pointing at can be plugged? I am waiting for a kit for the choke heater box. I will let you know how it goes.

 

[DHugg]

Richmo, I have the under-choke vacuum advance port hooked to the vacuum advance canister, the big pipe at the rear base of the carb hooked to the PCV valve, and the choke pulloff hooked up with a hose to the port at the top rear of the carb as it was when I took the carb out of the box. Everything else is capped, with the exception of the power steering canister that comes off directly from the manifold vacuum.

And from what I earlier described, this is the best my engine has run since I got it from the previous owner.

 

[richmo]

My vacuum advance is hooked to a port on the driver's side front of carb. This is where the old one hooked up.

 

[Bent]

You can use the big one for power brakes or PCV. Or cap it.