[Custom10]

"get an adjustable start point can and the crane limiting plate in there would be my advice"

as noted earlier by cobalt, I second that one...

[oldbogie]

Originally Posted by kyle86

The problem isn't that it's pinging at cruise, it's when I accelerate from cruising. Like If i tip into the throttle a little to speed up. It dosn't do it going uphill either, it's got to be a light acceleration like I'm going to pass someone, but not in a hurry. And it's a very light detonation sound that only lasts for a second. If I hammer it off cruise, I might get one ping if even at all. It doesn't ping any at WOT which I think it would do if it was too lean, that's why I'm thinking vac advance.

As far as the engine,
383 stroker
9.8-10:1 compression - zero decked with .041 gasket
67 cc heads pro topline sr/torkers 2.02 1.6
XE284 advanced additional 3*
Holley 300-36 dual plane intake
holley 750 carb, vacuum secondaries
turbo 350, 3.73 gears
Initial timing 15*, total timing 32* ported vacuum

The numbers on the vacuum can are AR-10

Thanks!

This probably shows the mixture drops lean when the throttle is opened, this is common with a big cam as the air flow dies momentarily and fuel falls out of suspension. With no continuance of detonation once mixture velocity picks up, I'd say you need more accelerating shot and maybe the power valve needs to come in sooner (i.e. a higher vacuum).

You will, also, have to figure out if the secondary opening drops the mixture lean as well; although vacuum secondaries tend to be more graceful than mechanical in this regard, it still could be a problem. The Q-jet suffered in some applications with this to where they put enrichment ports just above the closed air valve so when it would start to open it would pull some extra fuel. Holley, of course, has the "famous" double pumper for the same reason. You could either add this feature if it isn't on the carb, or increase the secondary metering a couple jet sizes, or put in a stiffer spring to slow the secondary actuation a bit.

Bogie

[kyle86]

Originally Posted by oldbogie

This probably shows the mixture drops lean when the throttle is opened, this is common with a big cam as the air flow dies momentarily and fuel falls out of suspension. With no continuance of detonation once mixture velocity picks up, I'd say you need more accelerating shot and maybe the power valve needs to come in sooner (i.e. a higher vacuum).

You will, also, have to figure out if the secondary opening drops the mixture lean as well; although vacuum secondaries tend to be more graceful than mechanical in this regard, it still could be a problem. The Q-jet suffered in some applications with this to where they put enrichment ports just above the closed air valve so when it would start to open it would pull some extra fuel. Holley, of course, has the "famous" double pumper for the same reason. You could either add this feature if it isn't on the carb, or increase the secondary metering a couple jet sizes, or put in a stiffer spring to slow the secondary actuation a bit.

Bogie

I just thought of something. My carburetor occasionally feels like it's getting air in the accelerator circuit at idle. It will hesitate, BUT if I give it a few revs in neutral, it kind of gets the air out, then I have a nice clean rev from there after. I've already replaced the acc pump diaphram, tightened down squirter nozzle, replace metering plate gasket. It usually only does it when the engine is cold and clears up after a while of driving. Think this could be related?

[kyle86]

Oh also made a little J looking limiter plate out of some scrap kind of like the pic Cobalt327 posted. I took about half the travel out. I'll drive it some and see if that helps any.

[cobalt327]

Your AR10 can starts in at 3-5 in/Hg, all in by 9 in/Hg with 11º-13º total.

[oldbogie]

Originally Posted by kyle86

I just thought of something. My carburetor occasionally feels like it's getting air in the accelerator circuit at idle. It will hesitate, BUT if I give it a few revs in neutral, it kind of gets the air out, then I have a nice clean rev from there after. I've already replaced the acc pump diaphram, tightened down squirter nozzle, replace metering plate gasket. It usually only does it when the engine is cold and clears up after a while of driving. Think this could be related?

Could be, there should be a check valve in that circuit that keeps the fuel behind the nozzles from draining back to the pump chamber. It it's missing or failing, the passages of fuel will empty so the next time you use it you'll have to pump the accelerator till those passages fill before they will squirt into the air stream.

Bogie

[eloc431962]

Along with everything else what octane fuel are you running?


Cole

[cool rockin daddy]

"Your ported vacuum of 20" seems high"

Agree. I would put a con in that provides 15 and see what happens.

[cobalt327]

There are two check valves per accelerator pump circuit in the Holley. One is a rubber umbrella inside the pump chamber (if a newer carb) or a ball retained by a brass bail if an older carb. This works as a one-way valve (along w/the under squirter check) to allow fuel to go out via the accelerator nozzle, and fuel to enter to refill the pump as the pump returns after a shot.

Then, under the squirter there's another needle valve or ball.

The umbrella just gets replaced, the ball and bail can have the seat re-formed by carefully tapping a used check ball into the seat. Same thing for the under squirter check, if needed.

[cobalt327]

Originally Posted by kyle86

Oh also made a little J looking limiter plate out of some scrap kind of like the pic Cobalt327 posted.

Don't know if it'll help but it looks good! lol

[kyle86]

EDIT: It's not totally fixed haha false alarm. For the most part detination went way by limiting the advance. Right now I'm at 42 total including vac advance. That means my vac advance is limited to 10*. I can still however hear a slight bit of what I think is pre-ignition. It's so faint I think I might just be paranoid. I do think it is something tho because it doesn't really happen when going downhill, mostly just uphill.

Possible reasons I've been thinking about
1: I'm 1 jet size too lean, should try going from a 72 jet to a 73
2: Vacuum advance rateis comming in too early.
3: Secondaries might be trying to open up some and leaning it out. I have the purple spring in it right now.
4: What oldbogie was saying about fuel loosing velocity.
5: I have a hot spot somewhere in the cylinder. Some of my plugs have dark burns on the insulators. Also sometimes it will try to diesel after I cut the ignition. No idea what's up with that.


Also, I'm running 93 octane that has the 10% ethanol in it.

[kyle86]

Originally Posted by cool rockin daddy

"Your ported vacuum of 20" seems high"

Agree. I would put a con in that provides 15 and see what happens.

What? That's my manifold vacuum reading at cruse rpm. What's wrong with that?

[bubbahotep]

Is 15' intial and 32' total correct for your engine? I thought a 383 would be at 20' idle 36-38' total.

Edit: the reason I ask is because I had my 383 at low timing once and that forced me to have my idle-speed screw on the carb set too far down (to raise my rpm). I had similar issues as you. This board solved all that

[Custom10]

Originally Posted by kyle86

What? That's my manifold vacuum reading at cruse rpm. What's wrong with that?

The cruise RPM he listed was low about 2300 if I remember, now every engine will have its own characteristics but at that RPM with the cam he is running 20" does seem high. From my experience with my 383 and a 221 duration cam at 50 thou (less duration than his) I am pulling only about 14-15" at that RPM at a steady state cruise, the only time I come to 20" is if I am off the pedal and the gearing is causing the truck to decelerate but I have an 1405eddy and am on manifold vacuum. That is why I asked about checking his vac gage to be sure it was accurate. If the gage is off then it will hamper his tuning setup.

[bubbahotep]

Originally Posted by Custom10

The cruise RPM he listed was low about 2300 if I remember, now every engine will have its own characteristics but at that RPM with the cam he is running 20" does seem high. From my experience with my 383 and a 221 duration cam at 50 thou (less duration than his) I am pulling only about 14-15" at that RPM at a steady state cruise, the only time I come to 20" is if I am off the pedal and the gearing is causing the truck to decelerate but I have an 1405eddy and am on manifold vacuum. That is why I asked about checking his vac gage to be sure it was accurate. If the gage is off then it will hamper his tuning setup.

Same here. My brake canister is usually 10-15 reserve vac, rarely gets higher on my 383