383 Stumble/miss

[StrokedOne]

Hola fellow Chevy men (and women?),

Hola fellow Chevy men (and women?),

I come in need of assistance. I have a 1967 Chevy C-10 with a 383 in her (2 wheel drive auto tranny, no A/C). She has developed a VERY noticeable stumble/hesitation/miss while under load and almost seems to backfire through the exhaust. She seems to idle just fine but as soon as you put a load on her is when the issues begin. I changed the plugs/plug wires/cap and rotor. I have a Crane Fireball digital ignition. After all this I was I got frustrated with it so I decided to take it out to see what it would do. Once I "went through the gears". As I expected it "fluttered" until I let off the throttle... then as I got back down to a cruising speed and pressed the throttle again it wanted to die. I had to feather the throttle for a few seconds before it would get going again. I was thinking maybe a fuel issue but, I just had the carb (Holley 750 vacuum sec.) rebuilt about 8 months ago and then I checked the fuel for water, it's clean.
I'm at a lose here. She was running great up till this point. I first noticed it about 7 months ago but went away for 6 months and just got to work on it. It is driving me crazy. Any help would be greatly appreciated. I miss cruising in my ole truck
Thank you in advanced

[IAFF2407]

sounds like your carb is advance to far?

[Scott68-93-97]

Spark plugs or coil, if its not pinging the timing is probably not an issue I would look at the coil first since they usually fail under a load, If both are fine check your valves my 68 did that when a exhaust valve was to tight

[Scott68-93-97]

Originally Posted by IAFF2407

sounds like your carb is advance to far?

you mean the dizzy , and a retarded spark causes backfire throught the exhaust, to far advanced would fire through intake

[StrokedOne]

Thanks for the advice..
I was thinking the same thing about the coil and the valves..
But I figured the coil either worked or not worked.. and I did adjust the valves (hyd flat tappet)..I think I did them right..it's been a while.. still the exact same thing.. I will see about getting a coil (a cheap one to trouble shoot with) I have an after market one and would hate to spend the money too find out it's something else..lol

And
I'm not sure how to check the carb... nothing was touched for a good 3 or 4 months. All was good and then this..

Thanks again

[BCOWANWHEELS]

I,D SAY ITS THE POWER VALVE IN THE CARB. darn caps need to remove the button.......

[Scott68-93-97]

Originally Posted by StrokedOne

Thanks for the advice..
I was thinking the same thing about the coil and the valves..
But I figured the coil either worked or not worked.. and I did adjust the valves (hyd flat tappet)..I think I did them right..it's been a while.. still the exact same thing.. I will see about getting a coil (a cheap one to trouble shoot with) I have an after market one and would hate to spend the money too find out it's something else..lol

And
I'm not sure how to check the carb... nothing was touched for a good 3 or 4 months. All was good and then this..

Thanks again

Coils fail a lot under a load power brake it a little and see if it misses

[pitt]

it sounds like the carb.. i had the same problem until i rebuilt mine.which is an edelbrock and as you stated it also sat for several months and the insides got all gunked up... also it might not be getting enough air.

[StrokedOne]

Thanks for the info.. I was thinking it maybe a fuel issue.. and to answer the question ..the card 8 months ago..was suppose to read... had the carb rebuilt 8 months ago..sorry..got ahead of myself...

As for the coil, I did the power brake trick and as soon as it gets under load it "stumbles". if you hold it at 2000 RPM you have here it "stumble". I got out and held the rpm at 2000 with my hand and you can see the motor have a definite shake to it at the same time you hear the stumble..or what ever you'd want to call it...

[Scott68-93-97]

Throw a cheapy in it and see what happens

[Bucky71]

When the optical sensor went in my Mallory Dizzy, it would hesitate and then backfire through the exhaust. I repalced the sensor and all is well. Yours sounds more like a fuel problem though.

[StrokedOne]

OK..so I went out and did some more trouble shooting and this is what I found.. the # 1 exhaust valve was hardly moving.. I pulled the valve and found the valve shot as too the cam lobe just about gone.. guess it's to summit I go.lol..wife is loving me.. (pictured it the #1 intake and exhaust lifters)
I hope once this is taken care of my issues will be over...

[Scott68-93-97]

What cam was in it?