Built sbc stumbling under load

[gwandro]

I have a built sbc that I’m trying to get dial in. Running into a problem with it having a stumble/spuddering at high rpm under load. No problems when revving in neutral. Has done the same on 2 different carbs. It has an electric fuel pump. Maybe lose fuel pressure? Not really sure. Might look into getting a fuel pressure gauge and seeing what I get

 

[Ricko1966]

Maybe an ignition misfire,that would my 1st check. Spray under hood with salt water after dark,power brake it and look for lightning under hood.

 

[squaredeal91]

What carb are you running? And what other carb did you try?

 

[PrairieDrifter]

Usually an ignition issue. What's base and total timing?

Will it clear up above a certain rpm?

 

[Vbb199]

I say misfire or vacuum leak causing a misfire

 

[gwandro]

Holley at first then switched to edelbrok off another truck of mine that runs great

 

[gwandro]

Holley at first then switched to edelbrok off another truck of mine that runs great

 

[gwandro]

Usually an ignition issue. What's base and total timing?

Will it clear up above a certain rpm?

Starts at 3800 in 2nd gear and 3000 if I’m on it in 3rd

 

[PrairieDrifter]

Starts at 3800 in 2nd gear and 3000 if I’m on it in 3rd

Is it a fall on its face stumble or more like a misfire? Could be pinging.

We need to know your timing.

I've found that most off the shelf carbs are tuned pretty lean.

 

[Vbb199]

Seems like that rpm in 3rd might be indicative of the mechanical advance curve? Maybe too much timing total

 

[gwandro]

What carb are you running? And what other carb did you try?

Had a Holley and changed to a edelbrok

 

[xm20k]

Need more info
Is it a stock rebuild?
Is it a performance build ie. big came and/or high compression?
What distributor? HEI or aftermarket?
What size carb?