Need your opinons!

[BMSJaX]

Alright I have an odd 'problem' with my 350 and I think I know what it is but I'd like to know your opinions without tellin you my thoughts to see if we think alike before I go through the effort of fixin it to find out I was wrong.

Symptoms:
1. Poor fuel economy- 10 MPG or less when I should be gettin 12 to 15 (Q-jet 750cfm)
2. Badly fouled spark plugs(Only 2 months old and are BLACK)
3. Slightly low vacuum(fluctuates between 12-15 at idle)
4. Poor low-end power with great top-end power
5. Cannot run with proper timing settings(6-12 adv base and it dies on take-off in first of if you hit the throttle harder than feathering it)
6. Timing by 'feel' and it runs great but the mark is way off the scale(20-30 adv range base)

Alright tell me what you think!

[65gmc930]

It sounds like you slipped a timing chain.

[TheDark1]

The ring on the balancer could have moved.

[markeb01]

My guesses –

Because it’s a Q-Jet my first guess would be to check the plug in the bottom of the fuel bowl for leaks. This will certainly contribute to fouled plugs. Most people epoxy them in place during a rebuilt, and one outfit has a screw-in solution (I haven’t read it yet but I’ve read it’s on this website): http://www.cliffshighperformance.com/.

Any of the following can contribute to fouled plugs and low manifold vacuum - Intake manifold end seals that are not sealing properly, intake side gaskets, carb to manifold gaskets, leaking vacuum hoses, or even a leaking vacuum advance canister.

As noted above, the timing chain could be shot or jumped a tooth - or – if the timing cover/timing tag is not original, it could be in the wrong location. Some aftermarket covers with the bolt on timing tab do not correctly orient the mark. You can somewhat check the condition of the chain by watching the timing mark with a timing light while you raise and lower the rpm. It should move somewhat smoothly up and down. If it jumps all over it could be the slop in the chain is waving throwing the timing off.

The vacuum advance could be dead. Easy to check with a vacuum pump or timing light.

The accelerator pump in the carb could be dead or connected on the incorrect link setting. Easy to check by looking down the carb throats and operating the throttle linkage.

And then there’s the option of checking vacuum gauge diagnostics, which may reveal bad valves, springs, etc. Good luck and let us know what you find.

[62gmc910]

I would go with the slipped timing chain ,it retards the cam thus lowering swept compression (bad mileage, fouled plugs, poor bottom end power,probably poor starting)also indicated by the need for so much initial timing, and the big indicator poor bottom end but good top end power

[BMSJaX]

Yep, my thoughts were a retarded cam. Though I think the previous owner did it on purpose. But if I'm in there I might as well change the timing chain. But do I get a single or double row set? Or will either work?

[Corts60]

A double is definitely a safe bet. There is nothing wrong with a single roller but a double roller gives that little bit of piece of mind and it can handle more power. Now, before you start pulling anything apart, be sure that the PO didn't put an early style harmonic balancer with a later style timing cover, ie: a balancer that is made to be time'd in the center of the cover vise an off-set (later model) timing mark. It's not common but I've had it happen to me.

Also, be sure that you replace one part at a time. If you start replacing a bunch of different things at once, your never gonna know what exactly the problem was and that, to me, is more frustrating than the problem itself.

And be sure to get the basics down first: compression test, firing order, fuel filter yadda, yadda.....

[BMSJaX]

Alright so I looked into the mixed balancer/cover idea and found that a balancer with a 30 deg offset would put the timing mark at the top of the balancer so I just hooked up my timing light, advanced the dial to 30 degrees and the mark was right on 12 so I adjusted it to 8 test drove it and it runs great! Looks like your probably right Corts60. I will still get a new timing chain and it looks like it might be time for a new balancer as well and when I put them in I'll check to make sure timing marks align and everything. Thanks for all the help guys!

[ruffrida2005]

Maybe you should teach your retarted cam some school work to brighten it up. Sorry I just had to.