setting timing in 68 c-10 with 250

[dwmurry2006]

Ok so I got my other hei distributor from skip white and forgot to put #1 at tdc. before I pulled the distributor out of the block.

I brought #1 cyl to tdc compression stroke. Timing mark on balancer lined right up with 0 on timing tab on gear cover. Then set distributor in pointing rotor to #1 spark plug hole and set the cap on and wired it up. I fired it up and adjusted distributor til the idle sounded nice. However when i shot it with the timing light, I couldn't see the timing mark. so i retarded it back til the timing mark was at about 10* on the tab. Took her for a spin and it was real hesitant and back fired alot like she was too retarded. So i advanced it back to where it sounded good at idle and didnt back fire and she felt real good lots of power. Hit it with the timing light at its at like 30*??? the timing mark on the balancer is about at 12 o'clock straight up and down. My buddy said i didnt get the distributor set in right.
I pulled the cap with the engine at tdc compression stroke, rotor pointing right at #1 spark plug, the poll on the cap is correct with the right wire going to the right cylinder.
So I have absolutely no idea what my timing is set at.

I looked at the inside of the cap and theyre firing right on the edge of the brass terminals. not near the middle, like right on the edge.

I'm guessing my other problem is related to this... I can't run my vacuum advance at all. When i plug in the vacuum line and give it gas it starts running really rough and like its loosing fire or something. and then as I let off the accelerator it lets off a huge backfire. If I slam the gas wide open it revs up just fine, You just can't ease up on it or cruise. Something is not right and I need to figure it out.

I would really appreciate any help. You guys are all very knowledgeable and I thank you all for the help you've provided thus far.

[LandonL]

You sure it was the compression stroke? Set the timing with vac advance off, as you probably know. If the damper mark lined up on the 0, you'll probably be targeting 4 degrees before, as thats the stock setting. Others set to 12 I believe. The vacuum advance may be bad. I'm no expert, but someone else may know.

[dwmurry2006]

I tested for tdc compression by turning the fan over by hand with thumb over hole. Is it possible for me to have set timing on exhaust stroke and the truck still run? Because it runs just fine except with the vacuum advance. and the timing mark being way off.

[LandonL]

Only way to know for sure (as far as I know) is to take the timing cover off and look at the two gears. There's two distinct marks and when they align that's the compression stroke. It could've run with it opposite, not sure if it's possible. If you just stuck your hand on the hole it could've been the exhaust stroke. Since you took the distributor out that would've been the only other way to tell if it was the exhaust stroke or compression by telling which way the rotor was pointed.

Also, question to anyone reading this would the harmonic balancer mark point to the 0 on the exhaust stroke? If so, this is most likely the problem

[68gmsee]

You seem to have done everything correctly. It shouldn't be too much trouble to recheck the timing though.

You did it the way I do mine also. I remove the plug stick my finger or thumb until I start to feel pressure then finish with a long thin plastic or wooden dowl I feel the piston as it reaches the top. On the 250 you should be able to see it.

If it is all correct and lined up like the first time you checked, then make sure you unplug the vacuum advance line and plug it up. Also make sure there aren't any other vacuum leaks. If it's till off like you mentioned, make sure your distributor mechanical advance is working correctly.

After that, I don't know unless you have some mechanical problems like extremely worn cam/crank gears or dist gears.

[raycow]

If the engine runs best when the timing mark is obviously off, it means the outer ring on the balancer could have slipped. The only thing holding the ring is a rubber to metal bond which can deteriorate over time.

Don't worry about timing the engine on the exhaust stroke. The timing mark will be on 0 at TDC on the exhaust stroke but the engine just plain won't run like that. You would be off by a full revolution and firing #6 instead of #1.

Ray

[scrapmetalart]

Are you checking the timing with the vacuum advance disconnected?

[dwmurry2006]

Alright she is in time. Did the paper towel inthe spark plug hole trick. Did it 5 times to be safe. Checked out everytime. Rotor at number one and timing mark at 0* everytime. So i' still confused how is it so that I'm at tdc and 0* but with it idling smooth my mark is at the 12o'clock position.

My other question is do all hei distributor use a hall effecct for the vacuum adv. Cuz on my points dist. It moved the points plate. Cuz I still have the issue with not being able to use vac adv. It advances properly watching with timing light it just starts cutting out and bucking and jerking and ending with a big backfire out exhaust. I'm at my wits end i need to get this fixed. Its my daily driver.

[dwmurry2006]

Surely someone on here has ran into this problem. I really need some help.

[68gmsee]

Originally Posted by dwmurry2006

Alright she is in time. Did the paper towel inthe spark plug hole trick. Did it 5 times to be safe. Checked out everytime. Rotor at number one and timing mark at 0* everytime. So i' still confused how is it so that I'm at tdc and 0* but with it idling smooth my mark is at the 12o'clock position.

My other question is do all hei distributor use a hall effecct for the vacuum adv. Cuz on my points dist. It moved the points plate. Cuz I still have the issue with not being able to use vac adv. It advances properly watching with timing light it just starts cutting out and bucking and jerking and ending with a big backfire out exhaust. I'm at my wits end i need to get this fixed. Its my daily driver.

I guess you mean that it goes to 12 degrees advance?

So, are you saying that after you static time it to "0" and without reconnecting the vacuum advance you crank the engine and it will move to 12 deg advance?

As I mentioned above, the only thing I know that does that is mechanical advance.

if I were you I'd locate another HEI. Borrow one or find one in the junkyard so you can do another test.

[dwmurry2006]

basically my confusion arrises from when I had my points in my truck. When that distributor was in there I had the timing set at 4* btdc like I was told to do and it idled as smooth as that old worn out distributor would. you could shut it off put #1 at 0* tdc and pull the cap and the rotor pointed right at #1 pole on the cap.

Now with the hei in there you put #1 at 0* tdc with rotor pointed at #1 pole. start her up and set the timing to 8-10* btdc and its like its too retarded wont accelerate smoothly and when you let out of her she backfires and pops alot, and idles real slow... too retarded correct? so i forget the timing light and time it by ear and then use the light its a couple inches before the timing tab. so I honestly have no clue how many degrees I'm timed at. unless on the tab they go in increments of 1 degrees instead of multiples of 2 like i was told.

Holding the timing light while slowly revving it up the timing doesnt start advancing until like 2k rpms but it advances. (mechanical adv.)

[68gmsee]

Not sure what it's doing...

If you've checked everything including the firing order, vacuum advance, vacuum leaks, wires, plugs, etc., then about this time, I think I'd go back to my old distributor with the points and/or try a different HEI like I mentioned above.

[Jimmy S.]

It sounds like you have some sparkplug wires in the wrong order.

Start with #1 wire go clockwise,firing order 1 5 3 6 2 4

The marks on the timing tab are multiples of 2 degrees.

[dwmurry2006]

Checked the firing order its correct per jimmy s.'s info. So I guess I'll just deal with no vacuum advance, since she runs better than it did with points. Thank you all for your help in trying to figure this out.

[jpert]

DWmurry, Did you ever get your disrributor problem figured out? I have the same problem. I know an "old" GM man and he said they always set timing with a vacume gauge. Advance the timing until you get max vacume then back off distributor until the vacume drops one. When I do this the mark is at about 12 o'clock like you said. I have read that with HEI the vacume advance diaphram is 20 degrees or more and should be changed out with a 6 degree diaphram. My flyweight bushings are gone and I installed flyweights and bushings and springs from Mr gasket and that made it worse. I am still looking for someplace to purchase flyweight bushings to fit the original flyweights. Maybe you have the total answer!

[oily]

Quote:I looked at the inside of the cap and theyre firing right on the edge of the brass terminals. not near the middle, like right on the edge.

When the vacuum advance is hooked up, the rotor has moved away the edge of the brass terminal towards the next terminal. You end up with a large gap between the rotor and terminal.

[Wrenchbender Ret]

Some engines just don't run good with too much advance. I have run with out the vacuum advance hooked up it ran find & the MPG was normal. I 'm not recomending running without it normally as it helps driveability & MPG but on rare occasions if it runs better without it it is ok to run it that way.

[oily]

It has to do with rotor timing.
http://67-72chevytrucks.com/vboard/s...d.php?t=427872

[jpert]

I think that since a timing light uses the actual spark plug pulse to operate and the light shows #1 firing at 12 o'clock (crankshaft location) that is where the spark has occured. I am going to locate TDC compression on #1 with a dial indicator and compare with front cover timing tab. I don't think the problem is in the distributor. There is a reason this engine runs with initial timeing set to what appears to be 20 to 30. Also, don't replace the dapner until you are sure it has spun.

[Ticker]

If the engine has the heads on or is in the car, this is the easiest tool to use to find TDC; a piston stop.

http://www.summitracing.com/parts/SUM-900189/

[redhead69]

did you re-gap the plugs?

[slick copper]

I'm having this exact problem on my 250. Ever figure it out?
I just put in a new HEI dropped it in correctly and everything, but won't run with my vacuum advance hooked up, so I drove it around with no problems last night anyways. Someone

[geezer#99]

What did you set your timing at. I run 12* on mine. You did plug the vacuum line off to the vacuum can when you set your timing i assume.