340 timing

[culp71]

so I've been reading a bunch of various forums regarding timing.
so my 71 340 cuda essentially stock engine, (w Electronic Distributor)
I ran it for first time, broke in cam, set timing, adjusted carb etc, idle down to 700 all seemed to run great.
I had set it at 5 degree BTC @ 900 rpms. turned it off.

It sat 2 days while getting other things wrapped up, I went to start and it took quit a bit to restart. various cranking, throttle input, etc.
it did start and seem to run ok but not as well as before,
what I am looking for is a simple estimation of the timing to be set at.

I know this topic is highly argued, but I am just looking for a normal base line for a streetable car setup.


So if I set carb idle up to 3000, vacuum advance disconnected, set to 30-36 BTDC, reconnect vacuum, set idle to 900 and should have around 10-18 BTDC @ idle.

sound like a good starting point?

[Chryco Psycho]

No
Ask Neil  @nsmall
We just went through this with his , he will tell you how much difference this made on his 340
If you are going to set timing at 2500-3000 rpm with the vacuum disconnected do not reconnect it or it will over advance , you can stuff a ball brg inside the hose so it looks stock or use an allen wrench & dial out all of the vacuum advance by turning counterclockwise to the end
IS your dist mechanical advance adjustable internally .
I would start with a 16* at idle & a 20* advance curve , if it is adjustable this is easy to do , if not you either need a limiter plate or weld the advance slots so you have around 35* at RPM
Basically engine want more initial advance to start & idle well , with a shorter curve to full advance
Most cams are not designed as the factory did them Unless you use the specific MP repop cam , not sure what cam you used , but the factory cams had 115* lobe separation tis made a lot of idle vacuum & worked better for emissions etc & allowed a different timing set up [ yes they were worried about emissions even in 69 !] Most replacement cams are ground on 112* separation yeah Only 3* difference but it makes a huge difference .
So you need to do a couple of things limit the mech advance , if you are going to run vacuum advance you need to limit that just to get enough advance at idle & not over advance with rpm or eliminate the vacuum as I always do .

[Cudakiller70]

Just did the same thing. 71 340 4 speed. I'm 18 degrees @ 900 (seems like it might take a little more) and 32 degrees total @ 3000. I set the initial timing, then to get total timing where I want it, I still have to tweak my distributor with springs and or limiter plate. Have stock electronic distributor also.
Could the hard starting be fuel evaporation from carb bowls? I added an electric fuel pump and have no problem starting after sitting.
I am far from a tuner, but so far car fires right up and runs strong.

[HP_Cuda]

Wow, I didn't know using vacuum advance could add 15 degrees!

No wonder folks get into trouble when using it. 

[Chryco Psycho]

Yes but at least on Mopars it is easily adjusted with a small allen wrench

[nsmall]

Chrycho Psycho helped me big time and all I can say is my car runs like a beast now.

I had to change my curve, it was crazy long, change the springs, and change the timing.  Running strong and efficient now.

@culp71 I recommend sending Chrycho a PM if you get stuck and he will help you out.  Its shocking how much better my 340 runs.

[Shane Kelley]

On 340's I actually prefer to lock the timing @35 BTC.     Just a bump of the key and it fires right up and throttle response is instant. Every time I try different springs and advance curves I always end up going back to locking the timing advance. When I would run the lighter spring for quick advance I would have issues getting them to return all the way and causing it to idle high until I shut it off and fire it back up. Now I run mini starters so I'm not sure if factory starter will have issues or not cranking over the motor with that much timing. But I think it would do fine. Something to think about.

As previously stated don't run the vacuum advance. That will always cause problems.

[gzig5]

This topic is very timely, I was just about to start a topic on initial timing.  I've been trying to figure out my timing all week.  Got the new tank and fuel line in, mounted the rebuilt carb and got it to fire and idle.  I didn't have a helper to hold brake in gear so set the idle mixture adjustment screws on the carb to get 19 inches of vacuum and set the idle to 850 rpm while in park.  Vacuum advance is disconnected.  Went to check the timing with my new light and the timing mark was not visible.  I was planning on setting it to 8-10 degrees advanced.  Some investigation revealed that the distributor was installed 180 degrees out.  Found approximate TDC on #1 compression, and installed distributor so the rotor points at left front of the intake and rewired the cap.  While doing that I found the mark on the damper and highlighted it with a silver Sharpie.  I also added a line about 1.5" advanced and another ~2.2" advanced, just slapped them on because I was guessing the TDC mark was hiding under the water pump.  Got it started and adjust the distributor by ear for best idle.  I now see the extra marks I make with the light and it has an advance function that tells me my best idle is at ~34 degrees.  Go down to 25-ish and it idles like crap and dies.  Still doesn't idle all that great yet.  I have not driven  the car yet.  This is freaking me out.  I am suspecting the timing chain skipped, cam was installed wrong, or the damper has failed.  I'm in the process of making a piston stop to verify TDC on #1 is correct on the damper.  It is a 71 340 in a 73 Cuda with 727 auto trans.  I really have no info on the motor.  Cam sounds fairly stock or is a mild aftermarket.  Chrysler electronic ignition and distributor, Holley 650 DP, LD4B intake, and headers with crushed tubes that probably don't help anything.

I was not aware you could set the timing to 35 and lock it out.  How do I tell if that was done?
What's this about dialing out the advance with an allen wrench? 

I haven't touched one of these motors in 30 years and the learning curve has been steep.  I was going to start tearing the front of the engine apart after verifying TDC to check the timing chain so I'd appreciate some guidance on other potential causes.  I've been trying to read up all week but haven't found a case similar to mine yet.

[Shane Kelley]

If you follow Chryco's instructions you should be pretty good.

Locked out timing. Meaning there is no mechanical, or vacuum advance. The distributor is locked to where only the shaft rotates with the motor. This is done a few different ways. The most common is tack welding the weights on a stock distributor. I have also seen where you drill and tap the weights to fasten them to their base plate. Some aftermarket distributors come with hardware to achieve this. I run a stock style in my RR that is welded. I run a Mopar Performance billet distributor in my Cuda and it has a couple allen head bolts that allows you to lock the timing.

I'm sure somebody will chime in how locked timing sucks for this or that reason and I'm not saying that it's the best way. I'm just saying that's how I run them and it seems to work really well. The throttle response is instant because it doesn't have to wait for the timing curve to advance.

[scf100]

Good stuff on the 340......... mine has slight pinging in above 60 mph
So was gonna look at timing

Running diff brands of gas no change

360 block ,340 heads purple cam think 10-1 compression

[Shane Kelley]

Automatics tend to be more sparkknock prone.

Some guys have tried the locked timing and experienced spark knock and or hard starting. Both of my motors have aluminum heads so cast iron heads may or may not have those issues. Aluminum heads tend to have less spark issues compared to the factory ones.

For you guys that don't have lots of experience doing stuff like this I highly recommend Chryc'o's method. 

[HP_Cuda]

Well here's one for ya, what kind of timing light are you using?

I have an old one where if you don't clip it to the number 1 wire in the direction of the arrow you get readings that are way off.

This topic is very timely, I was just about to start a topic on initial timing.  I've been trying to figure out my timing all week.  Got the new tank and fuel line in, mounted the rebuilt carb and got it to fire and idle.  I didn't have a helper to hold brake in gear so set the idle mixture adjustment screws on the carb to get 19 inches of vacuum and set the idle to 850 rpm while in park.  Vacuum advance is disconnected.  Went to check the timing with my new light and the timing mark was not visible.  I was planning on setting it to 8-10 degrees advanced.  Some investigation revealed that the distributor was installed 180 degrees out.  Found approximate TDC on #1 compression, and installed distributor so the rotor points at left front of the intake and rewired the cap.  While doing that I found the mark on the damper and highlighted it with a silver Sharpie.  I also added a line about 1.5" advanced and another ~2.2" advanced, just slapped them on because I was guessing the TDC mark was hiding under the water pump.  Got it started and adjust the distributor by ear for best idle.  I now see the extra marks I make with the light and it has an advance function that tells me my best idle is at ~34 degrees.  Go down to 25-ish and it idles like crap and dies.  Still doesn't idle all that great yet.  I have not driven  the car yet.  This is freaking me out.  I am suspecting the timing chain skipped, cam was installed wrong, or the damper has failed.  I'm in the process of making a piston stop to verify TDC on #1 is correct on the damper.  It is a 71 340 in a 73 Cuda with 727 auto trans.  I really have no info on the motor.  Cam sounds fairly stock or is a mild aftermarket.  Chrysler electronic ignition and distributor, Holley 650 DP, LD4B intake, and headers with crushed tubes that probably don't help anything.

I was not aware you could set the timing to 35 and lock it out.  How do I tell if that was done?
What's this about dialing out the advance with an allen wrench? 

I haven't touched one of these motors in 30 years and the learning curve has been steep.  I was going to start tearing the front of the engine apart after verifying TDC to check the timing chain so I'd appreciate some guidance on other potential causes.  I've been trying to read up all week but haven't found a case similar to mine yet.

[Chryco Psycho]

Good stuff on the 340......... mine has slight pinging in above 60 mph
So was gonna look at timing

Running diff brands of gas no change

360 block ,340 heads purple cam think 10-1 compression

Pull off the vacuum hose on the dist , insert an Allen wrench & dial it back a number of full turns , it has 14 turn range
@scf100

[gzig5]

Well here's one for ya, what kind of timing light are you using?

I have an old one where if you don't clip it to the number 1 wire in the direction of the arrow you get readings that are way off.

Innova 5568 Digital Timing light.  There is no mention of arranging the clip one way or the other so I don't think that is an issue.

[HP_Cuda]

The newer ones it shouldn't matter but look at the clip which goes around the plug wire.

If it has an arrow imprinted make sure it's pointing in the right direction.