I had been having issues with the Dart getting warm in traffic. I had a jag clutch / fan that never seemed to pull a lot of air. I replaced it with the following, and a 1" spacer.

http://www.summitracing.com/parts/sum-g4917

Am running the stock 318 radiator, re-cored to 3 rows. Engine is stock/rebuilt 68' 383, with carb, headers, intake.

I have the initial timing set at 18 degrees, only the light spring, and total timing at 38. I have the vacuum advance hooked up adding 18 more degrees of timing. Hooked to manifold/lower port on Holley DP. I am thinking this might be too much timing as the car seems to be hesitating/breaking up from 2-3k RPM at light throttle. The exhaust is somewhat loud, I have looked at number 1 and 8 plugs, and no signs of detonation. I doubt I could hear it if it was. Plugs are a lightish tan in color. Carb is stock, stock jets, etc. etc.

If I get on the car it wakes up, and I am wondering if this is because vacuum drops and all that timing goes away.

I am going to mess with the vacuum advance, try it disconnected, see if the car acts different, etc. It won't idle as clean. Right now I have around 20" of dead steady vacuum with the can hooked up at about 950 RPM.

Anyone think I am hurting anything cruising around? Only way I know to dial this thing in...

Thanks

with all that timing it sure ain't retarded! & if no pinging you are OK in that regard. plug descrip sounds OK & unleaded burns with less color anyway. You might unplug the can & see if that miss goes away (might be too much timing) & the can capped will change timing and alter rotor phasing

Not sure on the part throttle hesitation... that said, ported vacuum for the vacuum advance generally seems to do best. No vacuum advance at idle = steady timing at idle which is usually good Also, 18 degrees initial plus manifold vacuum advance could be a lot of timing at idle/low speed.

No short term harm in disconnecting and plugging vacuum advance for a test run. After doing that, suggest you hook it to ported vacuum for another test.

Put a timing light on the damper while you rev it up till it starts missing/running ruff. I bet you will see spark scatter. Then disco the vacuum and recheck, probably smooth, but if not, you have at least determined its either mechanical or vacuum advance

I went through the same thing and cured it with a new MP distributor.

BTW, I just put the same Summit fan (18" version) for the same reason.
GOOD flex fans rock!

Thanks guys. I really don't want to give up the additional advance that I am getting at idle, helps with cooling, etc. Connecting to port vacuum will only make the can operate at cruise, which is where I am currently having the issue. Either way, to your point, I am going to fool around and see if disconnecting helps, that will at least tell me it is an ignition timing issue and not a carb issue. The vacuum at idle is stead and solid 19-20", so no worries of the timing jumping around. The car jumps to life off the starter (starts really easy), and now with the cooling issues solved I am feeling better about everything.

Is there a way to limit the advance from the can? I know you can adjust the "on off point" with an allen wrench, but is there a way to limit the amount of advance?

Thanks. This distributor is brand new. FWIW, I have had it for years, and didn't pay near what it is going for now.

http://www.amazon.com/ACCEL-59302-Performance-Replacement-Distributor/dp/B000CIE64Q

I had another thread on what I did to curve it over the weekend.

Agree on the fan -- this thing is really nicely made. Very pleased so far.

yes, epoxy strips of feeler gauge on either side of the "notch" in the arm to limit its travel into the can but just me I think you have way too much timing being on manifold. keep us updated

Thanks, will let you know.

Another thing you can do is to tighten the advance can spring down enough to where the beginning point is way late so that the vacuum advance is not "full on" at your cruise vacuum. Using one of those hand vacuum pumps is the easiest way to establish how much advance your combo likes. But trial and error with the allen wrench will get you there too. It will just take a bit longer to figure out.

And your mechanical advance does sound a bit much. How did you establish that as the best for your combo?

As a starting point, I use 32* mechanical advance and about 42* total with vacuum and tune from there. On the vacuum advance, I start a little low and add a couple of degrees at a time until the car starts to "surge" at cruise and then back it off until the "surge" is out of it.

run the vacuum advance to the timed port at the metering block.

i had a very light miss at part throttle on my truck, sounds similar to your miss.

i jetted the carb up a step and it solved it.

Are you running a fan shroud?

How I got here -- I am at 18 initial (not centrifugal) based on vacuum reading and adjusting the dizzy. Once that was set, I knew I wanted to be around 38 total (initial+centrifugal), so I pulled the dizzy apart and adjusted the centrifugal advance down to 20 degrees (10 degrees in the dizzy). While I was in there, I removed the heavy spring, leaving the light spring to help bring the advance in a little quicker. This is a stock build 383 with 906 heads, so not the most combustion-efficient setup, so I think it can take a little more timing. Vacuum reading with the can hooked up is about 20". I got this point after the initial timing was set, hooked the can up, and tweaked the idle mixture screws.

I have a mighty vac pump, and will play with the can next.

What I think might be happening, my cruise is 2-2.5k at 45-50 MPH (not exact) but close. So I am getting pretty close to full advance at this RPM, with the light spring only it was all in by 2500, so 38 degrees. Add another 18 on top of that with the can hooked to manifold and that is 56 degrees of timing at cruise. Might be a tad too much. I think low 50s is what to shoot for baseline and tweak per your surging adjustment comment.

A few options -- bring the initial timing down some, and readjust centrifugal to get back to 38 total. Attack can to port vacuum so that it does nothing at idle (which I want more timing at idle to help with cooling tooling around in traffic), or adjust some of the overall timing out of the can with the shims.

Either way, removing the can and/or trying port timing should tell me something. Either the car behaves the same way (which would mean it is likely carb related) or something changes (which should tell me it is timing related).

The other part of this is I am getting a whistling sound from time to time at idle/950 RPM. Vacuum leak? Not sure, vacuum signal is very steady at idle. Tracking that down too.

All part of the fun.

I am yes. It is the A-body shroud from mancinis. The lower holes did not align, so I had to modify, but it is on there. As you know this is a very shallow shroud and I really wonder if it does a whole lot of good. The closest point of the fan blade is 1.5" from the radiator core. Blades are about 1/2 in 1/2 out. I can grab a pic if you want later?

Well disconnected and plugged vacuum advance... didn't really make much of a difference with this hesitation/miss issue.

I am wondering if I should tune the hesitation issue out with the can connected or disconnected. Connected seems to make sense, since that is how I am planning to run it?

The carb has the stock jets (and everything else) 70s front 80s rear.

What to you guys suggest as a starting point for jets, pump cam (30cc), etc?

Does it miss all the time? If not when? hot cold what RPM and in hg does it start to miss at? reluctor gap. rotor phasing. plugs. plug wires. less likely (vac leak/lean jetting). I wouldn't think 70's is in danger of being lean but bumping up 4 sizes for a 1 hour test would be easy to elim that & might partly compensate for a vac leak just for diagnostic purposes.

RPM is 2-2.5k through 3-3.5k RPM at light throttle. I think there are some carb issues. If I take up to 3500 and jump on it, it stumbles and then pulls hard.

Would need to check reluctor gap. I am beginning to think this is more of a carb issue than a timing issue (at the moment).

Going to baseline the carb when I get some hours to mess around. Idle, transition slots/blades, fuel level, check for vacuum leaks, etc. etc. I know where the ignition timing is, so that is good.

Hey all. Its been a long time. I am re-baselining things on the Dart. I am running the billet Accel distributor. Anyone have any idea how much mechanical advance this distributor will provide with the slots opened up the whole way? My previous tune is listed above. 18 initial, about 20 mechanical, one, light spring, and then with the vacuum can hooked up around 18 more.

I've used a piston stop to verify TDC on the harmonic damper, insulating and rerouting some fuel lines, and a insulation plate to hopefully take care of the vapor lock issue I've had a few times.

Any suggestions on a baseline tune (lets start with ignition timing for now) for a pretty much stock 383 would be helpful too. 150 PSI cranking compression, stock cam, RPM intake, headers. After I get this set, I'll focus on the carb.

Thanks!

You might (1) set the initial with the "vacuum gauge method", (max vac in drive/idling then back off the INITIAL till the VACUUM drops 1 in hg & this is what the eng will see stoplight to stoplight & if it dont balk when cranking when hot you are good on the initial then (2) set the total (initial+springs) to 36 (38 in some cases), (the $25 FBO plate is the best deal in the house for this on a "regular" dist then (3) mix/match springs so that you are just under the pinging point at WOT up thru the gears on your hottest/driest (most likely to ping) day & peoples' hearing varies so give it a cushion, you want to be close to the pinging point but NEVER/EVER over it then (4) plug in the can to ported & adj the tip in with a 3/32 allen wrench till you are just under the pinging point in everyday driving under varying RPM/load conditions. there are manifold tuning afficionados but I ain't never tried it but some swear by it as opposed to ported. "Quicker/close" would be to set the initial to 20 then the total to 36 then work with the springs then plug in the can. First I would have the carb somewhat "close", at least not too lean

Interesting.
That photo shows a Mallory YH advance mechanism.
There are three adjustments that can be made internally.

Timing for your engine should be close to stock since its a stock engine. It can be tweaked from there but that's a good baseline.
Since yours is slightly hot rodded, looking at non-CAP '67 Plymouth specs, the initial timing should be 12.5* BTC. It should advance 6 to 10* by 1500 rpm.
After that it depends on whether it was the 2 bbl or 4 bbl version, and if we look at '68 specs 4bbl w/ (CAP) manual and automatic are different. What did your '68 start life as?