1978 K5 Blazer Stumbles Until Warmed Up

[Egg_Head]

1978 Blazer with 400 CUI, Edelbrock carb & intake. When I first start it even in mild weather, she'll stumble like there is a bad plug wire or 2. Yesterday she was even backfiring out the passenger side exhaust when putting a load on the engine but not when revving in neutral. Once she's good and warmed up runs and idles smooth. MSD wires & coil are fairly new as are plugs, cap & rotor. Any thoughts?

 

[bigt61]

My guess would be the carb. Ethanol, even 10%, doesn't play well with older cars.

 

[Chris142]

Could be a loose valve guide too.vacuum leak?

 

[NHGUY]

You probably removed the cold air heat stove by adding an open element air cleaner,or else the flapper valve (vacuum controlled) is not selecting warm air/cold air very well.

 

[DSparks]

Carb/choke...basically lean till it warms up....typical of carbed vehicles..work on the choke...adust it closed a little more and make it stay on longer...basic stuff ....

 

[Errtt]

"Yesterday she was even backfiring out the passenger side exhaust"

I'd re-check the wires/plugs for that side, if nothing back to vacuum lines & carb.

 

[Trav]

+1 Typical choke opening to early problem, what model carb is it?

 

[Egg_Head]

Edelbrock 4 bbl 600 CFM with electric choke, basically a Carter.

 

[CT8]

Originally Posted By: Trav
+1 Typical choke opening to early problem, what model carb is it?
Fisrt thing to check.

 

[turtlevette]

Originally Posted By: bigt61
Ethanol, even 10%, doesn't play well with older cars.


It plays extremely well. You just have to turn a few screws.

If it were me, I'd just let it warm up. You can mess around with the choke forever and never get it right. The carters are not very sophisticated carbs.

 

[jhs914]

Originally Posted By: DSparks
Carb/choke...basically lean till it warms up....typical of carbed vehicles..work on the choke...adust it closed a little more and make it stay on longer...basic stuff ....


^^^^^
This. Take it from an old guy who remembers carbs and their quirks.

 

[Pop_Rivit]

As others have said, that sounds a lot like choke issues, especially those automatic chokes from that era. Some were so problematic that there were manual choke conversion kits for folks that didn't want to constantly fight with them.

Originally Posted By: bigt61
My guess would be the carb. Ethanol, even 10%, doesn't play well with older cars.


Interesting. I have 4 vintage carbureted engines ranging from 1940-1952 and all run just fine on E10.

 

[Kruse]

Originally Posted By: Pop_Rivit

Interesting. I have 4 vintage carbureted engines ranging from 1940-1952 and all run just fine on E10.


Yea, the only problems I've ever had with E10 was when it first came out in my area, IIRC, about 1981. The stuff would clean out everything from the tank all the way to the carb and plug fuel filters. For the car that I was driving at the time, I went through three fuel filters in about a week. After that, I never had to change the fuel filter again. The local gas station even had a notice on the cash register counter that explained that the benefit (or problem) of gasohol, as it was called back then, was that all the varnish and deposits that had accumulated in your car's fuel system would be purged. They were right.

 

[Trav]

Originally Posted By: Egg_Head
Edelbrock 4 bbl 600 CFM with electric choke, basically a Carter.

On the choke housing there are marks along with a mark on the choke cap.
Loosen the three screws and turn it one line tighter (should be CCW). Repeat until it clears up
When you loosen the screws make sure the cap spring has tension on it, it may have missed the lever when they assembled it.

 

[The_Eric]

Originally Posted By: Pop_Rivit
As others have said, that sounds a lot like choke issues, especially those automatic chokes from that era. Some were so problematic that there were manual choke conversion kits for folks that didn't want to constantly fight with them.

Originally Posted By: bigt61
My guess would be the carb. Ethanol, even 10%, doesn't play well with older cars.


Interesting. I have 4 vintage carbureted engines ranging from 1940-1952 and all run just fine on E10.



Even though his vehicle is a '78, his carb is not. In the first post he mentioned installing an Edelbrock carburetor with an electric choke. This would be a fairly new piece, produced in the last few years with an all electric heated choke coil. They're fairly simple- no manifold heated parts or hot air tubes to fuss with.



As for the quip about ethanol, I tend to agree- it works fine. Like Pop_Rivit, my wife and I have used it cumulatively for 40+ years and 400,000+ miles in everything from outdoor power equipment to old tractors to cars/trucks- all with nary a problem. I wish people would quit playing the blame game.

 

[artificialist]

Have you removed smog devices or not?

Sometimes when an EGR valve gets stuck open, it affects cold performance more than warm performance. In addition, with all those vacuum lines, I'm sure some are leaking, and some of those hoses might have been routed incorrectly by the last owner.

Some of those smog devices are connected to vacuum switching valves that are operated by the engine coolant. It wouldn't surprise me if those get stuck open or closed.