Mood swings; It runs good, bad, and ugly, all in the same 30 seconds

[mountainexplorer]

I'm starting to get annoyed at this. I've had 3 different carbs on this 350 I put in an '84.

No matter what, the motor at time idles perfect, and has good throttle response. Then I'll hit the gas again, and it will just plain out sputter, backfire, or even die. Then hit it again, it has a hesitation then opens up.

The last two carbs act the same way, and they both ran excellent on other motors. If it was a distributor/spark isssue, it should be more consistent, shouldnt it?

Sometimes it'll idle fine, then just die. Sometimes it will fire right up, other times you'll have to sit there and crank it and pump the throttle even when its warm.

With the latest carb which I KNOW is good, it's been doing this.

I'm tired of this thing being moody and changing it's mind every 30 seconds or less. /forums/images/graemlins/dunno.gif

 

[beater_k20]

check your valvesprings? i had my 355 do that years ago in my C10, i thought it was a carb issue, since i had just put an intake and a Holley carb on it. tinkered with the Holley and couldnt get it to go away, so i went back to my QJet. it did the same thing. i got tired of limping it around so i bought another truck and parked the C10. that was the beginning of the demise of the C10. the engine went into my TA and got an Edelbrock carb, and still had the very same problem. changed the valve springs to a set of new factory replacements, not only did it run better, but it felt like i picked up an extra 4 cylinders.

 

[mountainexplorer]

This motor "supposedly" was rebuilt not too long ago... but there is a clicking like it needs the valves adjusted.

I took it out and drove it, and it seemed to be fine now so far. Maybe it's past it's moodiness. If not, I guess I'll be pulling valve covers.

 

[socal chevy]

mine does the same thing.

 

[rjfguitar]

Hydralic lifters adjust automatically IIRC...

 

[diesel4me]

It could be an ignition problem(maybe the pick up coil or ignition coil is crapping out??)or perhaps water in the fuel passing thru the carb.The valve springs could be a suspect too--I never thought of that--I'll bet my van's 307 needs new ones--it runs like what you described,and I changed nearly everything,carb,distributor,timing chain,etc.
/forums/images/graemlins/crazy.gif