Mixture.. Damit!

[Broken_down?]

ok got the intake manifold gaskets in a few days ago and what a difference it made. No more sputtering at all. But now that the main problem is now fixed I have a back fire with an occational flame coming out of carb. Re-timed to 6 dg, 30 dwell, .35 gap, 700 rpm @ idle New ignition coil, points, condensor, rotor, cap, wires, plugs, ignition, belts, valve cover gaskets, exhuast gaskets. Checked for burnt valves and dead cyclinders (none), compression on all 8 was 120. Did timing from Top dead center and placed rotor to wire one etc..

Heres what happening. When I first time it, she runs great around town. Speed verys from 10 to 45 max. But when I hit the highway to open her up performance degrades so bad so fast that it starts back fireing, stalling major hesatation, serious missing to the point where the truck kinda jerks like the engine died (not sure how to explain that last one). Every so often it will backfire and a puff of smoke will come out. I am assuming this is unburnd fuel and at the price of gas that just plain hurts. When I get back I check the timing and it is still @ 6 dg and has not advanced/retarted. Plugs are not totaly black but they are working on it. I am leaning towards the idea that my mixture is way off as it does not seem to be at the "right" timing anywhere between 4 and 10 dg. Another thing and not sure if this could be or not but recently I replaced my water pump, thermostat 180 dg, radiator. Before the temp guage was very accurate. But with the new pump it takes dam near the entire day to get past the cold into the normal heat range. It used to run just above the cold mark and I knew it was acurate as I blew my alternator belt a few times on the way home from work it she heated righht up. So is there a possibility that she is running to cool?

1. How do you set the mixture?
2. truck running to cool?

Thanks for any help!


Rich

[GMCPaul]

You will find directions to set fuel mixture on our tech tips page here
http://www.gmcpauls.com/Tech%20Tips1.htm
The directions are in bottom article how to use vacuum gauge.
Sounds to be timing related to me though, I'd check where you are sourcing the vacuum advance from it should be a ported source no vacuum at idle with vacuum coming on as you open throttle, also check the vacuum advance mechanism to see if its functioning. Fuel/Air mixture will not cause the motor to backfire. Most often when I find a motor displaying the systems your is its points related and the points are not opening fully enough but your dwell is correct in this regards, with it backfiring through the carb this says timing is off and motor is sending a spark to the cylinder before the intake valve is fully closed.
Can you rev motor up with no problem in park and only have a problem with getting RPM's and speed up when moving????
Using the vacuum gauge chart on our tech tips page it can solve many timing & valve train related problems, check the motor at idle with vac. gauge and while driving, its a great tool for diagnosis of problems like this.
GMCPaul

[GMCPaul]

PS also check to be sure you dropped the distributor in correctly, 1 tooth off towards the advanced side and you would have the same problem.
GMCPaul

[Broken_down?]

Can you rev motor up with no problem in park and only have a problem with getting RPM's and speed up when moving????

When at idle there is no backfire or any thing bad. Yes this only happens when you start hitting higher RPM's while moving fast. I am sure we got the distor in right. BUt i the event It is 1 tooth off how would you know if it was?


Rich

[Broken_down?]

you know I was just readin your facts and guages number 2 says: A intermittent fluctuation at idle indicates a ignition miss or sticking valves. I noticed that my idle kinda fluctuates never staying steady @ 700. this being usually between 700 to 750 or 800 to 850 etc.. could thisbe caused by sticking valves?

Rich

[GMCPaul]

Pull #1 plug and place finger over plug hole and rotate motor until you feel air trying to push out hole then watch timing mark on harmonic balancer and stop rotating it when its at TDC, now your on compression stroke for #1 pull cap and see if its pointed at #1 terminal, depending on the age of motor and prior problems you had the timing chain could be worn and a backfire has caused timing chain to jump and thrown off timing, I have also seen the rubber dampner on the harmonic balancers tear and allow the outer ring to rotate on the balancer and this then throws the timing line off so when you think your setting it at 6deg BTDC actually ends up being 2deg BTDC.
Before trying anything use the vacuum gauge to troubleshoot it.
GMCPaul

[GMCPaul]

Sticking valves or a worn timing chain can cause idle speed fluctuation but if it was timing chain you can see timing fluctuating some at harmonic balancer, sticking valve will cause backfire but 1 sticking valve should not be robbing the motor of power as bad as you describe.
GMCPaul

[jhwkns]

Seems like a worn camshaft to me. Those are the symptoms. G/L

[Sweet72]

Sounds valve train related to me, not ignition or carb.

[dwaite72lnghrn]

When you set it up like paul said with the vacuum check to be sure all of your plug wires are correct adjacent firing plug wires (like 5&7 backwards) will do the same thing.

[jostrans68]

my truck did the same thing it was valve adjustment I has several that seemed to tight when i readjusted it ran great for a while then back to it. Mine was solved it turned out the guy i had do my heads screwed me on hardened seats my valves have droped into the cyl head 1/4" or better thus making the adjustment tighter as they wore. but I had all the same symptoms as you Good luck my .02 Jack

[race-n-jason]

I agree, sounds like valves are out of adjustment. Granted if you have hydraulic lifters, adjustment is fairly simple. It will only require removal of your valve covers and the ability to hand crank your engine (i.e. removal of spark plugs, access to front of crank pully).

Find TDC of compression stroke, completely loosen valve, then tighten while hand turning the pushrod until you feel resistance then tighten another 3/4 turn. Repeat for every cylinder (ideally in the fireing order).

[Broken_down?]

ALL HAIL... KING OF THE DUMBASSES -----> broken_down?

6 and 8 thats all need be said...

rich

[cableguy0]

lol dont feel bad man its happened to everyone