1969 Blazer - running real rough

[fear_nothing]

This is how I got home today. It backfired pretty hard, and was a bear to restart. When it did start it didn't seem like it was firing on all cylinders. Did I mention that the backfire started a small fire in the carb? I had to hit it with a small fire extinguisher blast. That was more excitement that I needed. Truck has been running rough for a while, I'm guessing I need my carb rebuilt. So I'll throw in all the factors for a better diagnosis.

1. I've been running without an air cleaner for a couple days, I can't find the right size locally go figure. A new threaded stud in the carb fixes that I guess.
2. The truck bogs down when I lay into the throttle, it sputters and will die if I stay into it.
3. Old gas maybe I had some old gas [6 months old] laying around, mixed that with some new gas and put that in Sunday
4. Exhaust leak, it backfires through the muffles when running, especially when I let off the gas suddenly
5. Cooling, been fighting this since I got the truck, I'm running a 165 degree thermostat it normally stays around 190 but will spike to 220 ish in traffic.
- it needs a shroud and larger fan.

Yeah that's one hell of a list, the fire didn't damage anything. I kept the blast small to avoid getting that white power everywhere. What should I be focusing on? Bad gas, exhaust leak, carb, cooling?
This all happened a couple hours ago, it fires right up when its cool.

thanks!

 

[rampage]

Maybe the choke is sticking.

But I do know that that is one sweet looking Blazer!
Don't know about that faux door window frame though. Maybe it'll grow on me.

 

[ekajkrats]

Don't take me as a pro at this, but here are my 2cents.

On my 72 the backfiring bogging and dying, had to do with the PO not setting the distributor right so timing was all jacked up. Then he just turned the idle up to avoid bogging when the gas was stepped on.

When i replaced the dizzy I then had to adjust the carb. I have a edlebrock (also from PO) and it required me adjusting the air fuel, as well, I replaced the plunger, and adjusted the floats (at the same time i added the off road needle and seats for the carb i have). once the carb was refreshed i had to mess with the a/f mixture screws and the idle screw.

Messing with the floats, plunger and mixture screws is what got rid of the bog, the idling and the dying for me. I believe backfire through the exhaust means too rich or timing isn't right, and should be fixed by adjusting the mixture.

As for cooling I haven't had to trouble shoot that yet. I run a 195 thermostat and it never moves once it gets warm.

I think most will tell you, get rid of the gas and get the air cleaner on there. Rebuilding the carb will also get rid of any vacuum leaks that can cause issues.

You may also want to say what carb you have, as there are probably experts for that exact one on here.

Sorry if this wasn't all that helpful.

-jacob

 

[K5_Fla]

sounds like a timing, vacume, fuel or carb issue. Get fresh gas in there, change fuel filter, make sure timing and vacume are correct then see where you are at.

 

[y5mgisi]

I also vote timing.

 

[fear_nothing]

Maybe the choke is sticking.

But I do know that that is one sweet looking Blazer!
Don't know about that faux door window frame though. Maybe it'll grow on me.

Thanks, funny enough I never noticed the "faux door"

I have an Edelbrock carb, its been forever since I rebuilt one. Is it worth the time/money to perform a DIY rebuild or just have a shop do it?

 

[rampage]

Do it yourself, that's why you're here isn't it? Get to know your truck and give it a little TLC. Lots of people here can walk you through the rebuild, me not being one of them.

 

[rompinstompinmudmonkey]

Bad gas (low octane) and timing too advanced will cause a back fire. Also, if the timing is advanved too much the engine will run warm, but I think the larger problem for running hot is the missing fan shroud.

Start with some fresh gas and checking the timing. Also, if you have a Holley carb, you will need to replace the power valve. Every time the engine backfires through a Holley carb the power valve blows - a blown power valve will also cause a hesitation and stumble.

 

[fear_nothing]

Well I've taken care of the low hanging fruit, snugged up the headers that cured the majority of the exhuast leaks and replaced the fuel filter. Timing is next on my list.

 

[Eason]

My '77 was acting exactly like you described when I first got it. I drained the old gas and replaced the fuel filter, then sprayed the carb with carb cleaner several times and it did the trick. It did start acting up again once, but then I sprayed the carb again and it runs great now.

 

[fear_nothing]

Rebuilt the carb this weekend, wasn't as hard as I thought. Its been about 15 years since I last rebuilt one, I had to consult yout tube and the instyructions many times. I got it to run however it its running rich, and it's idling too fast. It backfires through the muffles each time I shut it down.

It sets off my neighbors truck alarm every time so thats a bonus
-we all have a neighbor we don't like right?

Also replaced the 3 finned fan w/ a 5 finned version. Located a shroud but its not the right year and will require some customization.

So what should I be looking for with the carb? It doesn't seem to kick down, IE tap the throttle and normally it idles down.

thanks!

 

[fear_nothing]

Calling CK5 carb gurus, could I get a couple of you to weigh in?

 

[ekajkrats]

Not a guru, but reading this thread still, you turned the idle screw counter clockwise to bring down the idle after making a/f mixture adjustments (assuming those were made)?

Consult the manuals at edelbrock for adjusting the carb too if you haven't already: http://www.edelbrock.com/automotive_new/misc/tech_center/install/1000.shtml

Rich fuel/carbon buildup can cause that type of backfire.

 

[454Sub]

Backfiring is usually a result of the plug firing when the exhaust valve is open, popping out the carb is the opposite, firing when intake valve is open. I would set timing first, x degrees base timing on whatever you are comfortable with, try 8 advanced. Then make sure the dizzy is connected to a PORT manifold vac source, meaning one that has little vac at idle and builds vac as rpms rise. Then maybe try replacing the 160 thermostat with a 180, the 160s empties the radiator to fast and does not dissipate heat effectively, they are best used on boosted or very high heat engines. Hopefully that will get it idling decently enough, then start messing with the air mix screws, bowl levels and idle settings. Always set the hard parts first, timing and such, as they wont change once the engine is set. Best way in my personal experience.

On the Edlebrock them air mix needles you have to move both them the same amount, and after a certain amount of turning either direction, you have to change a needle setting i believe, the manual describes this, but not very well. LOL

 

[ashman]

dude, just saw this thread and it reminded me I owe you a pm.

sorry, I been slackin'

 

[fear_nothing]

Great news, my K5 is back to its old self again. Dare I say better than when I got it. I turned over the tires when I stomped on it

So what did I do.

1. Messed around w/ the air and fuel mixture settings, no change
2. Took the carb off and rechecked all measurements and tolerances. Didn't change anything. However it seemed to run alot better.
3. Noticed the distributor had worked itself loose, adjusted until the idle sounded right.

Those steps removed the backfire, and any sluggishness. However a road test uncovered some "bogging down" After some additional investigation the choke seems to be staying closed. I've got it forced open at the moment & its running like a raped ape

The google box says this a common problem, not getting a full 12V to open the electric choke. So I've got a little more tinkering left, but it would seem the hard part is done. Thanks for all the suggestions!