350sbc pops and spits under load

[JointTech]

just picked up old blue from the muffler shop. (headers and cherrybombs)
It popped and spit and generally ran like crap on the way home.
In neutral I can rev it no problem. in drive it will randomly die and fire and pop. Doesnt seem to matter if its heavy load or light/ fast or slow.
I just bought this thing and havent even changed the oil in it yet.
It has HEI ignition.
I did just get cap/rotor/wires/hei unit from Summit which Ill install with new plugs and an oil change this weekend. I havent done any timing in 15 years but I think I remember how.
I'm thinking timing or maybe the carb? I was way low on gas and only put in a couple gallons after leaving the shop. I wonder if I got some tank crud in the carb since it sat awhile before i bought it. I have driven it 20 miles or so since buying and it didnt do this until now.
I was also thinking plug wires not in order since they pulled them to put on the headers. But it purrs like a kitten when its not popping and spitting.

thoughts?

[mrein3]

Originally Posted by JointTech

...snip
But it purrs like a kitten when its not popping and spitting.

thoughts?

The last time I had this happen I had two valve seats that were gone. The time before that I had a flat lobe on the camshaft.

Do your general tune-up like you are planning. If it is still popping and spitting after that a compression test will tell you if a valve seat went bye-bye.

[406 Q-ship]

Burned valve

[CC69Rat]

Does it have headers on it? Maybe one of the new plug wires is too long, and laying against the header .. It has run long enough to burn through the boot and/or the wire and maybe it's arcing through the header at higher RPMs ?

Raise the hood at night and see if you see it arcing over to your header .. just something to try. I had a 406 in an old Firebird that as bad to burn through plug boots.

[BIG69GMC]

I would do the tune up and spray the carb to clean it out and see how it does afterwards, sounds like ur carb mixture is off
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[BIG69GMC]

Forgot to mention to spray carb cleaner before u install the new plugs so the old ones burn off all the crud, so u dont foul up the new plugs
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[CC69Rat]

I see now that I read it again, it has headers on it .. duh, sorry.

I would look for one arching through the header. Another consideration would be a restriction in the old exhaust setup. For example if you had it running slightly more lean/rich to compensate for the other setup .. now that you have headers and less restrictive exhaust the engine can handle a little more timing and even a slight carb adjustment.

[JointTech]

wow, thanks guys. I'll check for arcing tonight and will do the tuneup as planned tonight.
Other than a compression test is there a way to visually see anything about the valves? I can pull the valve covers but if I have to pull the heads its going to have to go to the shop.

[CC69Rat]

Pull your spark plugs..

the end of the plug should be a white / Milk chocolate color if it's burning clean. If you have one pulg that looks different (black / wet / oily looking) then the gas going into that cyl is not being burned efficiently. Could mean the plug is fouled out .. and $2 replacement would fix it .. It could also mean other problems such as a burned valve, maybe broken valve spring, .. etc. But, check the simple stuff first before you pull the heads.

.. just my .02.

[JointTech]

so i just saw it has an edelbrock intake
looks like GM 2bbl carb.
any idea what the weeping goo hole on the front is for? Looks like it has silicon coming out.


plug wires look like garbage but I can see they labeled each one when they took them off for the headers.
( as a side note $150 headers are really garbage. The paint is all burned off after a total of 3 miles lol) good times riding home with it popping and smoking all the paint and new pipe smell.
Those Cherrybomb vortex look sweet under there but I think Midas did a halfass job making everything pretty. And they beat up one muffler some it looks like.

[CC69Rat]

So, it ran fine when you took it in for the Exhaust work.

to make sure I am understanding, Midas put the headers AND mufflers on for you?

It's very possible they have a spark plug wire crossed. Have you checked the firing order and made sure your plug wires are on correctly?

the Odd numbered cyl are on the Drivers side. Starting from the front cyl, 1,3,5,7
The Even numbered are on the Pass side. Starting from the front cyl 2,4,6,8

you want to make sure (trace each wire down, make sure you hear it 'click' if you push the plug wire up on the spark plug) The Firing order is 1,8,4,3,6,5,7,2

So, you want to find #1 cyl. (Driver's side front) Trace that wire and find it on the distributor. #1 should be "pointing" pretty close to the #1 cyl. If you drew a line from the dist to #1, comparing it clockwise it should be in the same general area.

Counting clockwise around the distributor, make sure your firing order is 1,8,4,3,6,5,7,2 All the plug wires should follow this sequence and match the cyl it's connected to. It is possible if they installed your headers, they have one crossed. the most common one I have seen is 5 and 7. (I guess because they are right beside each other, and on the same side)

that would definitely cause it to sputter !

[JointTech]

the engine ran fine before taking it in. Fired up barely turning the key on the first spin.
They installed the headers and mufflers and new pipe. This morning it was cold (60 is cold in socal) and it seemed sluggish to turn over. low batteryish. And then it ran poppy/spitty on the way home.
Ill run check the plug wires now.
I figured the slow crank was cold plus the fact that it hasnt run for more than 2 minutes other than the 15mile trip home, so maybe the alternator hasnt had time to kick the battery.

[JointTech]

you sir, are the F'n man.
5 and 7 were swapped. Swapped them back and she fired on half a key turn and damn she sounds good with the new exhaust.

thanks for the moral support and tips everyone. Im still obviously going to do the tuneup this weekend and if anybody knows what that crap leaking out of the carb is that'd be cool.

[CC69Rat]

Glad I could help you out man! Glad she's running smooth again ..

The goop leaking out of the carb might be old varnished up gas? Has the truck been sitting for a while? Over time the gas will 'varnish' up and it turns into like a jelly lookin stuff. .. Does it smell like paint thinner?

[JointTech]

yea it sat for 6 months to a year before i bought it. its really reddish almost like that high temp silicon and i thought maybe a hose was actually supposed to be in there or something? Or they just have random holes in carbs? lol its been 15 years since I got under a hood im rusty!!
Ill take a closer look/smell when i pop the hood next.
The whole engine bay needs to be cleaned up. I hate getting greasy just touching anything.
I'm thinking this engine has a light cam in it. Now that I can hear it it lopes more than a stock sbc. but Ill hold judgement till the tuneup.
I've never even had it over 1/4 throttle.