|01-10-2013 04:33 PM|
To help get the lean, diluted charge burned before the piston is too far back down the cylinder past TDC, the spark has to happen earlier- and this is done by advancing the timing from stock the setting.
The catch to this, is the total timing (base plus mechanical) has to stay below a certain point, about 36 degrees BTDC for non fast burn heads. So if you add initial timing, you have to check to see that there's not too much mechanical timing, and if there is, you have to limit it. One way of limiting the mechanical advance is shown in the photo below.
Click on the photo to read more about this:
To check to see if adding initial timing will help, you can use a timing light to set the timing to about 16 degrees BTDC. This should allow you to turn the curb idle speed screw CCW to lower the idle. Don't drive the vehicle like this- this is just to see if adding timing will help.
|01-10-2013 09:25 AM|
Did they re-jet the carb?
My car is having the exact same problem and I'm trying to fix it myself and just wondering exactly what they did to your carb to get the timing right.
My motor is a:
freshly rebuild Chevy 5.7L SBC 350.
Block has been bored 40 over
Edelbrock RPM airgap intake
Holley 600cfm carb
New Comp 268 cam kit.
New flat top pistons providing a 9.5:1 compression ratio
|05-07-2011 01:26 PM|
Ding ding ding, carb opinions win.
I personally use the weird bendy/loopy straws for tdc
|05-06-2011 04:09 PM|
Thanks to all that replied. I cheated a bit in my resolution. I took it to a local hotrod shop and paid $120 for my education. Turms out the engine was indeed 60 degrees advanced and it took some carb tuning to get it right @ 15 initial and 35 total.
Well, I'm still learning and now I know that a poorly adjusted carb can cause issues with timing. I also now know that if I'm buying a new part such as a carb, don't buy it if someone has obviously messed with it and returned it.
Just thought I'd post this for the archives.
|05-04-2011 06:24 PM|
Sorry we got off on the wrong foot. I sometimes lack diplomacy and am too blunt. I think that's a sign of my age....however that's not a valid excuse.
|05-03-2011 09:55 PM|
I too would like to help and see him get it right, skip the ball park and just do the precise verification was my take on it. I meant no offence, my bad with the wise crack.
I assumed that the crank rotation was by hand with plugs out, but that is just me.
Anyway quite the thread hope he/we can fix it.
|05-03-2011 09:38 PM|
I think we need to remember we're trying to help a guy that isn't a gearhead. I agree that a piston stop and rotating both directions, split the difference, etc is the correct way to find TDC. However, someone could.....without thinking...hit the starter and destroy an engine. Piston stops in assembled engines in the car are for experienced people. I was just trying to help him find TDC safely. It's hard to hurt a piston with a straw.
Maybe you and I need to stop making smart *** comments to each other and try to help the guy.
|05-03-2011 09:38 PM|
|cobalt327||My opinion for THIS case- being as how the error is like 20-plus degrees (so it can be easily seen w/o minute of degree accuracy)- is that anything that can safely be used through a plug hole as a rough indicator of TDC will suffice. It's only to see that there IS an error. Once it has been determined an error exists, TDC should be correctly and accurately found and the damper and/or tab corrected or replaced as needed.|
|05-03-2011 09:27 PM|
|Custom10||Thats funny,,,maybe a piston stop? U should really take a pill. Every bit of advice has been about first verifying TDC and personally I have never used a straw.|
|05-03-2011 08:44 PM|
What the hell would you recommend, sticking his biggest screwdriver in to feel the piston coming up. Give me a break.
|05-02-2011 11:56 PM|
Looking at the rockers on #1 and aligning the damper line to the tab tells you nothing.
Physically confirm TDC and see if the timing tab/damper line agree- I will guarantee you they will not- providing all else is correct. As far off as you are, you could even use a foot long piece of soft copper wire to use as a feeler down the #1 sparkplug hole and rotate the engine by hand until the wire stops rising. This will be somewhat inaccurate, but more than good enough to see the error at the damper/timing tab.
The following is from another post I made on this:
|05-02-2011 11:37 PM|
Just an observation,,,Since this is not a milk shake I would avoid a straw to get to TDC
|05-02-2011 10:16 PM|
I agree...start with the basic's.
Set float level and check that fuel isn't running into carb at idle. Turn the idle screws out 2-2 1/2 turns.
Check TDC. Make SURE piston is at tdc. Look in the spark plug hole. Stick a soda straw in the hole and feel the piston reach TDC.
Check firing order on plug wires. 1-8-4-3-6-5-7-2 CW rotation
Basic's (Forgive me for being very basic but I want to be sure. Besides all of us get brain farts occasionally).
|05-02-2011 09:40 PM|
|dklong||you need to use a dead stop on # 1cylinder to verify the harmonic balancer is ligning up with the timing pointer, if it is'nt ligning up either you are using the wrong timing cover or balancer , or the balancer has spun on its rubber ring, an other problem could be a bad distributor ( i seen a few chevy 4.3 and 5.7 engine be working bad and put the timing light on them and the timing would at 40 plus degrees with no one adjusting the timing, the star wheel is usually cracked or has spun on the distributor.|
|05-02-2011 09:38 PM|
|cool rockin daddy||
Start over. Pull the heads. Change the gaskets. Verify piston at TDC before putting heads back on. Verify where the timing mark on balancer is. CHANGE THE CAM AND THROW THE THUMPR INTO A LAKE AS FAR AS YOU CAN THROW IT. Put heads back on engine. Follow any one of the trued and tried methods of setting the valves. Something is way wrong with your setup and starting over is the only way to get to the bottom of it.
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