Hey Kalli, Ya, the timing before all the upgrades was at 6 degrees and though it didn't run great, it did run... Now that said, what we found when we pulled motor apart could only be explained as a half-*** rebuild. 1 mis-matched piston replacement, 2100 autolite carb and original cast intake that had been welded to fis a crack (or something like that)...Right now, believe it or not, I can't see a noticable difference in performance and I have driven other comparable 289 based Mustangs and the difference is obvious...That said, I was careful to match all parts and given the various leads produced in this thread, I struggle to understand why it performs so poor. If it was valve or cam related, I would expect the vacuum to show as such. I'm sure it's not timed right on, but still can't explain the significant loss of power...I'll retime it and set to to 10-14 degrees initial and see what the total come out to...Other than that, any other suggestions?

 

I am answering before reading any other answers... so if I repeat sorry, I want to keep my ideas unmolested...

My first reaction is to wonder if your carb is a vac secondary, if so maybe the secondaries are not opening right or at all.

Second reaction is that maybe you should "borrow" another carb of a known value (one that is running on a similarengine now)and see if it makes a difference.

My third reaction is to wonder if it may be possible that the timing chain was set up on the wrong marks,,, possibly set up on the "retard 4 degrees" mark, or worse yet off a half tooth. I know that you said it was triple checked, but if it was wrong three times and overlooked...

My 4th thought is that the distributor is not advancing properly or at all as the RPM rises.

As always with these dinosaurs, the problem will be with fuel, timing, or ignition....

Damn,, that does not help to narrow things down much does it!

<<Edit: went back and read a little, what ratio rear end did you end up with after the 6 to 8 swap?

Might be something to look into...... maybe the gearing is something way too high...

 

JMD...LOL...Nothing wrong asking...So, timing chain is spot on. I even went to the extent to lay a laser level to ensure they were lined up...As for the Carb secondaries, thats worth looking into as is the distributor not advancing....With repect to the dist advance, how can I trouble that? Before I left the country, I took her out for a ride and noticed that at, what appeared to be WOT, acceleration seemed to flatten at around 60, but the RPM's continued to increase...

As for the rear-end, she still has her original 7.25 with 3.20 gears and does seem to work fine...I have a bolt in 8 inch that I just acquired but need a few other accessories first (brakes, rims, etc)...In all honesty, I expected to be spitting gear teeth by now, given what I did to the motor....

 

While everything engine related has been discussed at great length....

Are you sure your rear drum brakes aren't locked up/parking brake set? Jack up the rear of the car and spin the tires to make sure. I'd hate to see you struggle through all of these engine "issues" only to find out your rear brakes are malfunctioning.

Does the torque converter/transmission feel okay?

Dave

 

Rear brake lock was considered and eventually ruled out...Tranny and converter are new (though that doesn't mean anything) feels/shifts fine...

 

This makes it sound like the trans is going. Might be slipping and thats why it seems down on power.

 

Trans is sound...no slipping, shifts fine and consistant with the expected shift points...

 

Sorry, just realised why you mentioned that....Why I stated that was the thought that possibly my total advance or vacuum advance was not set right...Would that cause this?

 

just to mention:
a) yah. the car should go better than that. definetly
b) it should go that good that your 7.25 will break eventually so great you got yourselves sorted for that eventuality
c) look into those things first we mentioned
Tad: throttle plate not fully opening
JMD: secondaries not opening. maybe the quickest check would be to have them fully open constant just to see if it makes a difference
and mine: set the timing right:
you said you have electronic ignition, so no need for adjusting dwell or points (correct me if that's wrong)
then as mentioned. I'll explain again, then you might understand why exactly what is measured:

1. Disconnect the vacuum advance hose as distributor side and block the hose with screw or similar.
set timing to 8 degrees at around (you can guess the rpms without tach). nice slow idle
2. now check if the mechanical advance is working. this is the one that increases advance the higher you rev.
the way to do it is just to slowly increase rpms and you should see your timing mark move towards advance
the furthest it should go is around 32-35 degrees. all this with ac still disconnected and plugged
3. in idle connect your vac advance hose again. the timing should stay at 8 degrees if it jumps by more than 5 degrees you are using the wrong port on the carb for vacuum pickup.
4. maybe change your fuel filter. A clocked up one will cause same

again as you said it's backfiring through the carb so my #1 culprit with good compression is wrong ignition timing

at the same time get some break cleaner or wd40 and spray that around the carb (NOT INTO THE CARB OR INTAKE). if you see the idle go up or down while doing that you have a vacuum leak. so the engine is sucking air where you're spraing. If that happens mixture is far too lean which can cause similar

work through that list and let us know how you get on

 

I know Im digging this one up, but happens when you havent been on the forum for a while. Just wondering how this one turned out?
I think this might be on the money.
It won't hurt your engine to try setting your firing order over to the 82 and later order.