Carb and Timing issue

[lah2420]

On to the next problem!! I've had my MC2100 on for about a tank and a half of gas now. Starts great. Runs better than the Weber did. But it flat out sucks gas. The first full tank got less than 10 mpg. The Weber got 12 to 15, depending on how I drove it. The Carter before that got 15 to 17. I seem to be going the wrong way.

I don't know if this is related. Right after I put the MC2100 on, I had to reset my timing. It was running about 10* btdc and the motor was running hot. I set it to 8* and the temp went down. I then found that I had a major vacuum leak at the EGR. The leak is now fixed and that is when I filled up to actually check my mileage.
I checked the timing after that tank of gas and found the timing was 4* btdc. Could the vacuum leak have caused my timing to change like that? And would the timing issue cause that much of a difference in the gas mileage? Sorry for the long way around to the questions, but I wanted to cover everything that has been done so far.

 

[Thord]

when you timed it did you unplug the vaccum line from the distributor advance and plug it? and rev it up to the proper rpm for timing, i believe 1600 or 1800?

 

[lah2420]

Yes I did. Now here's a good one. I checked the timing this morning after I warmed it up to normal temp. It was 9*. I then checked it this evening after driving home from work. It was 6*. I think it wants me to go crazy.

 

[Thord]

huh?!?!? is the distributor somehow slipping??? i had one that would lock up and swing around but never heard of one adjusting doing that. do you have the self adjusting timing sychronized distributor system (SATSDS)???? :lol:

dude i give

 

[lah2420]

Since this is an 87, they went through and put in a conglomeration of parts from 86 and 87, as well as whatever else was on the floor of the factory. You might have just hit on the experimental distributor system that AMC was trying, without success, to develop. I wonder if they Chrysler will buy it back from me? I think it was actually the DCOM (Drive Owner Crazy Module).

 

[lah2420]

OK. I bypassed the ECM today. Warmed it up. Set timing. I ran out of adjustment at 9* BTDC. I ran it down the road a couple of miles and back. Checked timing. It was about 3 or 4* BTDC. What else could cause this? When hot, timing drops. When first started and warmed up it is fine. It has TFI and MC2100. I fixed a major leak at the EGR. I blocked off the EGR with a plate to make sure the vacuum leak wasn't through the EGR. I am also plugging off the vacuum advance line before checking.

 

[lah2420]

You'll love this one. I stood on my head in the engine compartment to try to see why I could only advance my timing to 8*. Guess what happens when the vacuum advance body makes contact with the corner of the motor mount. It still decreases timing by 4* after the motor gets hot, but at least I can set it so it stays at 8 or 9 now after it warms completely up.
Now, does anyone know what part number power valve to get for the MC2100? I'm hoping that will be part of my gas mileage problem. It has what I assume is the original type single stage in it.

 

[Thord]

i bought this power valve for my 2100 from advance auto parts. its a holley but advance can special order it, took like 3 days. part number 125-85. its a single stage that opens at 8.5 in HG. also order a new gasket for the power valve cover. i didnt see it on their website, if you need the PN i can look up my reciept.

later gl