Trying to sort out timing 77 2.7

[egertk]

My 1977 2.7, which has no smog equipment and SSI's (otherwise stock as far as I know) likes to surge a bit when I decelerate, I can hear/feel it missing sometimes. I just adjusted the valves again, only two were out of spec from the last time I checked them (I do it with each oil change) so I thought I'd take a look at the ignition timing. All ignition components are new within maybe 2000 miles. Timing at idle... is about 5-10 degrees BTDC? It's not falling on any mark on the pulley. My distributor has the vacuum retard diaphragm, timing when I rev it up appears to be ballpark correct, but it bounces around a bit around the 35 mark. I unhooked the vacuum line to the vacuum retard, and plugged a long fresh line on there and sucked... I had to really exert some effort to get it to actually impact the timing though. Points were set to 0.012, and the dwell is reading about 34 degrees right now. It's got the stock CDI box on it. Any ideas? Just from my searching on here and the fact that it takes a lot of vacuum to get the distributor to retard timing I'm suspecting the distributor might be in need of a rebuild? Any other thoughts or suggestions?

If that is the case, what's the best place to send out my distributor to for rebuild?
Thanks!

[moneymanager]

There are a lot of people, including me, whose motors run just fine with no vacuum retard, which is basically an emissions device which has little impact on performance. I'd look elsewhere to fix the surge.
35° at 6000 or so sounds just fine with stock compression.

[egertk]

Even hooked up though, at idle, I'm at 5-10 BTDC rather than 5 deg ATDC which I believe is how it should run with the canister hooked up? (I only got it to pull timing if I unhooked it and sucked on the end of the vacuum line with all of my might) Good to know I can unhook it and eliminate that from my troubleshooting though.

[moneymanager]

When all is said and done, advance or not at idle doesn't matter much. It's the number at high revs that you really care about. And you're fine on that score.
Did disconnecting it make any difference in performance, or fix your surge problem? I'm betting it was pretty much irrelevant. But if it did fix the surge, leave it off and enjoy!

[egertk]

Nope, disconnecting it makes no difference.

[T77911S]

if you are 5-10BTDC at idle, it sounds like your retard is not working or your timing is way off.


make sure you are using Z1. the 77 had several marks. TDC, 5 ATDC and 15ATDC. at least for my non-cal car. since you have the smog crap removed, i would go with non-cal specs.

check the vac retard at idle by removing and connecting the vac hose, no need to suck. if the timing does not move, either the vac diaphragm is bad, the dist is bad or you do not have the hose connected to the correct port on the throttle body (TB). even though you may not use this retard, i would check it, could be an indication of bad dist.

next, with the vac hose removed, check timing at full advance. this will also check to make sure the mechanical portion is working.

personally i liked the way the engnine idles with the retard connected and timing set to 0TDC, which is spec for non-CA cars. the idle has a deeper sound to it. the retard is all gone by about 11 or 1200 RPM so i just think of it as another advance. the choice is yours as to if you use it or not. the other bonus i found with the retard, and you may like this with SSI's is you can run the mixture a little richer. with retard, the idle will not surge or dip when you let off the throttle. the richer idle mixture will make it richer at WOT which you may need with the SSI's.

for a miss you need to look at the CIS and air leaks. (since ignition is new)
first i would do a compression to make sure that is good.
then i would go through and check/fix air leaks. you can have a smoke test done or just replace common leaky parts. injector sleeves, Orings, rubber boots on the runners, vac hoses,
intake gaskets, just to name some parts.
then i would check fuel volume and spray pattern out of injectors. you could also pull plugs and check for ones that are very different from the others.

an air leak at one cylinder can really mess up the overall mixture, just as an injector that is dumping too much fuel, or in my case, not enough.

you also need to check fuel pressures just to make sure they are correct.
altough FP's do not make it miss, they need to be correct before making any mixture changes.

this sounds like a lot of work but look at it as a 30year maintenance. once done, you will have a great running car that you will not have to do anything to for a long time.

[egertk]

Thanks for the feedback! Next time I get a chance I'll try to snap a picture of where the vacuum is hooked up. I have replaced the o-rings on the injectors also. I think next I'll pull them and check their spray pattern. I did notice the car revs when it first first up, just for a moment, like the minute it first up it revs up to maybe 2-3k rpm before settling down into idle. Is that a sign of a leaky fuel injector?

My pulley has 4 marks for cylinder #1, it looks like the first (far left) is 15 atdc, then 5 atdc, then Z1, then 35 btdc. Like I said at idle, it bounces around at about 10 degrees BTDC (i've got a timing light where you can dial in the amount of timing), so it's not on any of these marks. Once I rev it up towards 6k, it does advance to about the 35 BTDC mark, but again it bounces around a little bit.

I'll start looking at my fuel system... might pull the distributor to see if I can clean it up a bit inside and smooth out the internal mechanisms.

[egertk]

Is there a diagram like this or a walk-through for tear down for a 77 distributor? Or could somebody highlight any differences when I go to clean mine up.
Thanks,

[Joe Bob]

Surging at idle in my experience is vacuum related or 02 sensor issues.....if on decel, it's sucking in air....could be the injector seals, good idea to replace them anyways if the injectors has some slop.

[T77911S]

those are the correct timing marks.
if the timing mark is bouncing and the engine runs smooth, it could be a worn dist shaft. check this with the nut tight on the dist.

when i would mess with the timing o my car, the engine would cut off and on when i would move the dist.
i pulled the dist and cleaned where anything was grounded, starting with the points, then the plate to the dist body and especially the dist shaft that touches the engine case.

[E Sully]

This thread goes over the same model distributor.
73.5 MFI distributor service

[egertk]

Not sure I'm being clear enough on what's happening with where my timing is showing up with respect to the timing marks. I made a rough image to show you what's happening.


Thanks Ed for the link!

[94teener]

FWIW - ('77 911s) when I pulled my dist. and checked it out - the advance plate was totally frozen. Did an R&R on it at that time - its actually fairly easy job and wouldn't hurt unless you know its all good. You can just pull the cap and see if you can move the plate by gently prying it with a screwdriver. Lube it and put some oil on that felt thing in there, etc. Vacuum hose is plugged on mine as I understand it should be - mechanically advances at high(er) rpm.

[T77911S]

i understand what is going on. your retard is just not working.

it is not connected to the correct port most likely since you can get the timing to move.


you dont need it, i prefer it but thats me. most on here do not want it. you can set your timing to 32-35 degrees full advance and not worry about idle timing.

the prefered way is really to set idle, then check full advance. dont try to adjust it while at 6k.

[egertk]

Exactly! (As they say... a picture is worth a thousand words) It's connected to a T right now, I haven't spent time following that T back at all to see where it's connected to.

[moneymanager]

Your car is timed perfectly, is behaving exactly as a well worn 40+ year old machine should. My timing bounces around a bit too, even though the distributor has been gone over from stem to stern. I still doubt there's anything wrong with your set up, but it costs under $200 to have your distributor cleaned, checked and tweaked if needed.

[egertk]

Thank you all for the feedback! Good to know it's behaving as it should
I think I'm still going to pull it and clean it just for piece of mind, check the axial play of the shaft, and replace the broken dust cover.

[T77911S]

the dist should not be Teed. there is a diagram floating around that shows it
teed with the thermo time switch(TTS), that is not correct. the WUR is Teed with the TTS and decel valve(DV). i want to say my dist went to a port on the front of the TB, just below the throttle plate and the WUR goes to the rear of the TB. the WUR has vacuum all the time except at WOT.

[egertk]

Finally had time to snap a picture of where the vac line to the distributor originates. It starts here, and then leads into a T junction, one line goes back by the WUR, though I'm not exactly sure where. I'll have to pull out my heater aux motor and hoses in order to trace that down, but the other junction leads into the distributor.