back to the basics...

[bubba22349]

Hesitation from a stop is most of the time related to the accel. pump shot. Look at the front of crab and the throdel linkage there is a cam there to talor the duration of the squirt and amount the cam has two positions so you can change it the other setting is the clearance between to change how soon the pump shot starts. Check that sometimes it starts too soon sometimes too late and that with the length of time of the shot. Experiment with those settings. One other thing I have found that a vacuum advance can sometimes cause a stumble if it's not working correctly too so you may need to experiment with when it comes in. Good luck looks like you heading in the right direction and solved several problems

 

[MPGmustang]

Asa, I already have the DUI... it replaced the LOM before I swaped to a 2bbl.

a pump shot will add gas, making it richer, mabye I have it running rich on idle cause it was fine before (my cousin and I tried to get rid of a little hesitation). the pump shot I have is a 19.5 or a 26.5 shot, I have it on 19.5 right now. do I need more or less?

with stronger springs I am able to run more initial timing, and that has given me 10 hg on vacuum @ 700rpm, that's the most I have ever had at idle. and this is with 15-16* initail.

 

[bubba22349]

a pump shot will add gas, making it richer, mabye I have it running rich on idle cause it was fine before (my cousin and I tried to get rid of a little hesitation). the pump shot I have is a 19.5 or a 26.5 shot, I have it on 19.5 right now. do I need more or less?

Bogs or hesitation can be caused by way too much fuel and not enough, without seeing it or hearing what it's doing it would be just a guess on if you would need more or less. You should try first going one direction using just the linkage adjustments and try some different colored cams or step up to the 26.5 shot.

 

[MPGmustang]

just an update, the whole engine idle/smoothness is drasticly changed, once I set the idle it STAYS there, the think I changed was the vacuum canister and put both silver springs in from mr gasket #929 then set static timing to ~19* static... the acceleration is much smoother, the crusiing is much nicer. overall the car is quieter, and power is everywhere... the silver springs are one step higher than what was there... and it's HUGE difference. I'm at 10' of vacuum at idle where as before I was down to 5-6 and very rough idle.

IMO all street machines should have this kind of timing. I'm sure I'm not perfect and I don't know the max timing I can use yet as I'm going slow and haven't ping'd since I swapped the springs...

the vacuum canister has 22* of advance, the static is 19*, mech IDK but according to the chart it's 10* @ 4K rpm.. so it's slow!!! most of the advance while crusing will be ~5* at 2600 rpm, so cruise timing is 22+19+5 =46 that's if I have a 15" of vacuum but I'm probably closer to 10" vacuum while crusing so maybe i'm closer to 40* timing while cruising... I bet I can go more initial... as long as I don't ping I don't see why not try'n more... unless one cna have too much static timing?

Here's the instruction sheet... spring curve is down low. **side note, I'm using the stock DUI weights, so my curve could be more aggressive as mine look heavier vs what comes in the kit.
http://www.mrgasket.com/Portals/0/downl ... i_929G.pdf

 

[CobraSix]

I would be hesitant to say all street machines should be at 10*. There are too many factors. During the summer I run at 6 degrees and have a smooth idle. It increases my mileage a little by tuning it down some. When it turns cold, I end up setting timing to 10*, otherwise it can stall when the engine is cold if the chock is off.

But you are right...I like tuning my engine to the lowest possible initial timing that gives good vacuum and smooth idle.

I don't recall what cam you are running, but 10" of vacuum still seems a bit low. Should be closer to 18" unless you are running a very aggressive cam.

 

[MPGmustang]

Slade-
my cam is CSC 264/274 110* .450 it say's it's to get 15" of vacuum, which it does at 1200rpm, currently idle is 800rpm with 10" vacuum, at 2k feet above sea lvl in 110* summer dry heat (0% humidity) with 19* initial/static timing it is currently running the smoothest at idle I've ever had since the 2bbl head mod. I even have low RPM torque again like I used to have with the stock motor.

no ping yet!! (nock on wood)

here in AZ timing is opposite, it seems I retard it for summer and advance the timing for winter. it might have to do something with the humidity and temp.

 

[CobraSix]

It's typical to have to change your timing and carb idle settings through the year. I have to do the same. I run 10-12* BTDC when the morning temps are below 50*, else the choke warms up faster than the engine and it'll die. When the morning temps are over 70*, I cut it back to 6-8*. My vacuum never changes more than 1-2". You should be able to get to 15" at something lower than 1000 RPM. If not, don't overlook a vacuum leak still existing somewhere. Your cam isn't aggressive enough to cause you to lose so much vacuum at idle.

 

[69.5Mav]

don't overlook a vacuum leak

I agree that a vacuum leak could still be present.

How ever, in Phonix at 2000 feet above sea level he won't get more then 13 ", based on a maximum of 15" for the cam.

my cam is CSC 264/274 110* .450 it say's it's to get 15" of vacuum

You loose 1" of vacuum for every 1000" altitude gain.

Dose your carb have a power valve? If so it might not be acting correctly with such a low vacuum.

With low vacuum you might want to give this post a read.

Manifold vs Ported Vacuum
viewtopic.php?f=1&t=63354

It's located in the sticky section.

 

[MPGmustang]

the power valve is open @ 3.5 inches, and the acceleration cam squirt is around 19.5 cc, can bump it up to 25cc, but think it's good where it is.

13" is possible but I have AC on, and that lowers it to 8-10 vac, when off it bumps back up to 950rpm and 11vac ish... maybe 12...

I bet I can run more timing. I'll try that.