Technical Timing Trouble with a SBC 350

Hi all. New to the community and to car building in general. I have a 1949 Ford Club Coupe that has a 1972(?) Small Block Chevy 350 and TH350 transmission. Right now, I'm having trouble with timing.

After reading this forum for days, I've learned a TON from all of you. I know that SBC's "like" about 12 degrees BTDC initial timing and you should end up with a total timing of about 35 degrees BTDC, without the vacuum advance hooked up. By 2500 - 3000 RPM, the full amount of mechanical advance should be in showing you your total timing.

Here's the problem that I am having. When I set my initial timing at 12 degrees BTDC, my idle speed is around 1400 RPM. There's no room to lower the idle on the carb so to get it to my desired idle speed of 700 - 800 RPM, I need to move the distributor clockwise to get the RPM's to where I need them to be. When I do this and then hit the timing tape with the timing light, the 0 degree setting on the damper timing tape is, well, somewhere else, not registering any numbers on the tape. All I see is bare damper. Because of this, I don't have a start point for my initial idle speed, nor does a number show up when I rev the engine to 3k RPM or wherever the timing stops advancing to find the total timing.

It should be noted that I (the rookie) was the one that had to find TDC on the #1 cylinder and add the timing tape to the correct spot on the damper. With this initial setting, it did allow the car to turn over and run, but I'm stuck with not being able to time it because of what can only be described as a misplaced timing tape. But I don't think this is what the problem is. I'm reluctant to even check for TDC on #1 again because I went through the procedure for setting TDC like 4 times, to make sure it was right. Coupled with the fact that this initial setting made the engine run pretty well too is making me think this is something else than that. But, like I said, I'm a rookie at this and I'm looking to figure out where I went wrong. I'm hoping someone here can provide me with the correct insight into this. If you need more info, please ask. Thank you!

 

Are you setting the timing at idle, with the vacuum advance line disconnected, and plugged, transmission in drive, and idle set?

 

Oh, and what carburetor is on this, and have you checked for vacuum leaks?

 

How did you find exactly TDC? Lippy

 

You should be able to lower your idle to the point the car dies.

 

I did the method where you screw a fitting into the #1 plug hole and through that adapter is another threaded section that allows for an internal threaded rod to be used as a stop for the piston. Rotate the engine clockwise slowly until you hit that stop you threaded into the #1 cyl. Mark this line on your damper at 0 degrees. Rotate the engine counterclockwise very slowly until the piston travels down and then back up to meet the stop threaded into the cyl and mark this other stop point on the damper. Depending on how far down the cyl #1 the stop was, you may have two marks pretty close to one another. The center distance between these two marks should in theory be TDC.

 

Lower on the carb or on the rotation of the distributor? I tried it on my carb but there was no adjustment left to lower the idle. The only way to get the idle where I wanted it was to rotate the distributor clockwise. Rotate it far enough and yes the engine stalls.

 

I am setting the idle first but I'm only able to achieve my desired idle by rotating the distributor clockwise (retard?). The vacuum advance line is disconnected and plugged. I've never heard of setting timing with the transmission engaged. Is this something you are supposed to do that would require an extra person to hold the brake while the trans is engaged? All the videos I watched on this subject, the timing was set while the vehicle was in park to find your total timing.

 

You don't need it to be in drive to check timing, I suspect you have a vacuum leak causing too fast idle speed.

 

Sorry. The carb is an Edelbrock 650 cfm Performer series

 

If you can't lower idle on the carb, you may have other issues.

 

Dick, the more I think about it, the more this makes sense. Now how the F^#@! do I track down a vacuum leak like this one? I guess I'll stand over the engine tonight for a few hours and look at hoses, caps, cracks, looseness in carb mount, etc. Any other usual suspects you have as some favorites to check?

 

Either you have a linkage problem [something not allowing the flaps to close completley] or a vacuum leak [I've had good luck w/ a peice of 3/8 fuel hose asa stethoscope to listen for a hiss]

 

Well, which manifold is that Edelbrock on? You can bolt a square bore Edelbrock to a spread bore manifold (and some combo spread/square bore manifolds), bit it will not seal, without the thin plate, and two gaskets designed to prevent that exact leak.


I would wager that every single one of the members of this board, that has installed a gasket, has had one just not quite seal. It happens.

If you have power brakes, disconnect that hose on the booster, and plug it, to see if you have a booster leak.

You can try spraying a little starting fluid, or carb cleaner around sealing areas, while the engine is running. If the idle speeds up, look there. Don't over-do it and start a fire.

 

I will have to go back over the exact part numbers of intake and the plate/2 gaskets, but It's an Edelbrock Performer Carb and Performer Air Gap Intake. I don't have the exact part numbers for you right now, but I will post them later when I get home.

 

I always set them in drive, with the idle speed properly set.

No-load idle is not an accurate or meaningful place to set timing. You cannot drive the car like that.

 

It's probably a fine match in terms of components. Just make sure that any unused ports for vacuum are capped, and if you are not using the one in the back, that it has a plug in it.

 

Welcome and extra credt for being so articulate in your descriptions, we rarely get that, much easier to help when we have this much information.
Never had a problem finding tdc using the finger in #1 hole and having helper bump starter over. Just to be sure, #1 is right side front facing engine, but you knew that.
Are you sourcing vacuum from above or below throttle blades?
Is there a bolt-on timing pointer on the timing cover or the spot welded version?
These should be plenty dependable for the average street engine as long as they match the correct keyway location on the harmonic balancer.


This vvvvv

 

^^^^This^^^^. This is an excellent point.

If the engine has been gone through, and you don't know the history, there could be a parts mismatch.

GM moved the timing pointer, thee times, over about a 40º range. It all bolts together, but you could easily end up with a timing mark/pointer misalignment. Toss in some aftermarket parts, and who knows what exactly could be going on.

 

I'm guessing vac leak also. Is the motor warmed up and the electric choke set right?

 

X2 on this. Normally, we have to extract about every little detail, one post at-a-time.

Clarity is king. Thank you!

 

Like gimpsy said..spray around the engine..What I thought was a vacuum leak once was actually an intake gasket that hadnt completely sealed on the intake runner...so spray around the intake to head surface too..just lightly like he said dont over do it. I also saw you said you had no more room to rotate the distributor. Is this due to a physical restriction in the engine compartment? I have sometimes also had to try and lift the distributor up and try and drop it in 1 or 2 teeth over from what I thought was actual TDC to allow me a little extra room to regard the timing...I would try this if you find no vacuum or gasket leaks.

Sent from my VS995 using The H.A.M.B. mobile app

 

Make sure the choke high idle cam is not holding the throttle open.

 

I assume you have the vacuum ports on the carb capped off?

 

I've run into this a few times and it was a nightmare, until we figured out what was happening.

 

Are you running a throttle rod or cable? Either way you should be able to adjust the idle down as others have said...look at the idle screw...is it touching the linkage arm on the carb like it's supposed to? In other words...is the idle tang on the carb arm resting on the screw? I'd disconnect the linkage and see if you don't have enough travel in your accelerator linkage. Disconnect it and see if the idle screw does something then....

 

Also, make sure that the idle tang is not bent, propping the throttle open.

 

When you say you plugged the vacuum advance, did you unplug it at the carb and plug the port on the carb or did you unplug it at the carb and plug the hose? The carb needs the port plugged not the vacuum advance. Just checking.

 

TDC in relation to the timing plate on the engine was determined by the piston stop method so it doesn't matter which timing plate is on the engine.

At 1400 rpm the centrifugal advance is probably already advancing the timing. You need to get the idle down.

 

Disconnect linkage. Back off all idle screws. Hold a couple fingers over the carb primaries, like you're choking it . If it doesn't try to stall, you've got a big time vacuum leak. Most likely at the mounting flange.