Timing is way off...

[RockyMtnSierra]

Help! I am going back and forth with my timing, vacuum advance, etc.

I have a 86 Sierra with a 305, new Holley carb, new intake manifold and new exhaust manifold. I don't expect that info to help, but I'm sure someone would ask.

Here's my issue: my initial timing is running somewhere around 35 degrees. I can set timing for factory (6 Btdc - but my elevation is at 8600' so I prefer to try and run it ~ 12 BTDC) but it runs awful. Poor gas mileage, no power, hesitates, the works also vacuum pressure drops about 5lbs (from 15 to 10).

What could cause this? Bad timing chain? Any way to check without removing the timing cover? Anything else I can try - I don't want to go on and on but I feel I've tried everything!!)

(I should say this first as I know it'll be the first comment: yes I removed the advance before setting the timing and the idle is around 650rpm. No vacuum leaks)

 

[Rusty Nail]

Ask @bucket , he's real smart....

 

[Camar068]

just googling (chevy 350 altitude timing) in an attempt to learn more...I found all of the following to be consistent across all the post I read:

1. more air
2. less fuel (lean the carb out a bit)
3. Advance the timing more (read this on fewer than the 2 above....read more so your comfortable with it)

Hope it helps

 

[RockyMtnSierra]

Thanks for the responses. I don't need help timing at altitude. I am just trying to figure out why my timing would be so far off. I would guess it sits anywhere between 30 and 38 BTDC at idle.

I've confirmed that TDC is in fact TDC.

One thing that I also find a little odd is my #1 wire on my dizzy sits at like 2 o'clock compared to say 5 ish on a regular dizzy. Could that have something to do with it?

 

[RockyMtnSierra]

I guess confirming the marks on the balancer to TDC would mean it's probably not the timing chain. Also confirms the balancer is not off...

 

[74 Shortbed]

Sounds like the mechanical advance is stuck and not returning, pop the cap and rotor and see if you can move it back and forth by hand, if you can't you're lacking lubrication on the shaft, who's distributor you using??..

 

[SkinnyG]

^^^ I agree - check there first.

 

[rich weyand]

Thanks for the responses. I don't need help timing at altitude. I am just trying to figure out why my timing would be so far off. I would guess it sits anywhere between 30 and 38 BTDC at idle.

I've confirmed that TDC is in fact TDC.

One thing that I also find a little odd is my #1 wire on my dizzy sits at like 2 o'clock compared to say 5 ish on a regular dizzy. Could that have something to do with it?

Last paragraph first. That just means the disti was stabbed in the wrong place to get the normal 5:00 position. No issue there.

Let me understand. You set the timing to 12* BTDC with the vacuum disconnected. With the vacuum back connected, you read between 30 and 38 degrees BTDC at idle? Is that right?

If so, no problem. Vacuum advance should be around 20 degrees, so 12+20 = 32* BTDC at idle would be normal.

You might not yet have enough advance dialed in for base timing. I am running base timing of 17* BTDC at 800 feet above MSL.

 

[Rusty Nail]

Why don't you get a really long flathead and turn the oil pump the way you want it to be if you dont like 2o'clock? Lol?

 

[HotRodPC]

You mentioned it already, make sure the balancer hasn't slipped and is accurate since you're obviously timing with a light. And yes, it's possible that enough slop in the timing chain can throw your reading off too. If the chain has that much slop in it, then your valve timing can be off a bit too but unless the chain has jumped time it should still be tolerable and you should be able to get it to run fair to good.

With all that said, are you sure your problem isn't in the carb adjustment or jetting for your altitude? Just suggesting it so you're not dwelling on only 1 thing that can be causing your poor performance and bad mpg.

 

[vkh]

I agree with 74 Shortbed, it sounds allot like frozen weights to me. I had it happen to my truck, ran like **** and we had a hell of a time trying to track it down. Kept checking timing and fiddling with carb until we found it. Then it was just a matter of some wd40 and working it.

 

[MikeB]

Not sure this is applies to your problem, but some mid-80s dampers had the TDC mark near the 12:00 position for use with a "sight tube" viewer. Using one of these dampers with a traditional pointer bolted to the timing cover will make timing look 20 degrees more advanced than it is. You'll have the opposite problem if older damper is used with sight tube timing cover. I have run into the first problem twice over the years.

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[Green79Scottsdale]

Did the '86 trucks run the CCC (computer controlled carb) system? Did a proper non-CCC dist. get installed when the non-CCC Holley got put on? That can cause problems if the conversion is not done correctly. I could be talking out my arse too.

 

[1987 GMC Jimmy]

Did the '86 trucks run the CCC (computer controlled carb) system? Did a proper non-CCC dist. get installed when the non-CCC Holley got put on? That can cause problems if the conversion is not done correctly. I could be talking out my arse too.

They did in California. Even if it wasn't a Computer Command Control truck, it would still come with the four wire ESC distributor, knock sensor, vacuum switch, and ESC controller, which would all need to be plugged in and wired up to work right. It would be simpler to stab a new regular HEI distributor in there, but it shouldn't be too hard to get the ESC working if it's not.

 

[HotRodPC]

You can also do some wire twisting and do away with the ESC and still keep the ESC dizzy and Control Module installed and it works just like a standard HEI dizzy. By twisting some wires, you're just killing off the ability for the Ignition Control Module to advance and retard timing.