355 Looses power around 5000rpm

[thatclappedsilverado]

95 k1500 with a 355 10.25:1 with speedmaster 195 alu. heads, and a comp xe274 with 1.6 rockers .519/.522.
Issue im having is i had an edelbrock carb on it and had nothing but issues and it finnaly crapped out on me the other week. Put a holley 650 mechanical secondary on it and it now idles and runs fine up to about 5000rpm. After that it acts like a natural rev limiter, i know its not valve float, but im pretty stumped with it right now. carb is jetted as close i can tell to what i need with 69/75 jets and a 6.5 pv timing is at 18* at idle and 34* total all in by 3500rpm. 3/8 fuel line from tank to carb with a bypass regulator set at 6.5 psi with the stock tbi pump. Was told combo should make around 400hp/tq

 

[Komet]

How do you know its not valve float? What's the seat pressure of your springs vs the recommendation for a xe274?

 

[thatclappedsilverado]

How do you know its not valve float? What's the seat pressure of your springs vs the recommendation for a xe274?

It ran fine up to 6500 rpm with the edelbrock when it would want to work. and closed is 145 and open is 360 and comp reccomends 290lbs open and 110 closed. in theyre reccomended parts list.

 

[evilunclegrimace]

It ran fine up to 6500 rpm with the edelbrock when it would want to work. and closed is 145 and open is 360 and comp reccomends 290lbs open and 110 closed. in theyre reccomended parts list.

what CFM was the Edelbrock carb? what is your cam specs@ .050?

 

[thatclappedsilverado]

what CFM was the Edelbrock carb? what is your cam specs@ .050?

650cfm same as the holley, and cam is 230/236 @ 50 and .519/.522

 

[Supercharged111]

I'd stick a wideband in there to see what the AFRs are.

 

[thatclappedsilverado]

I'd stick a wideband in there to see what the AFRs are.

plugs look pretty good in it not rich not lean but thats the plan, gotta save up some cash just bought a cam kit and hp tuners and wideband for my other truck

 

[PlayingWithTBI]

plugs look pretty good in it not rich not lean but thats the plan

Any peppering on the plugs?
www.dynamicefi.com/SparkPlug.php

Spark Plugs

When you changed carbs did you change anything else, like fuel pump/pressure? Maybe vacuum leak?

FYI Comp Cams Dyno results for that cam used a 750 CFM carb

You must be registered for see images attach

 

[thatclappedsilverado]

not that i noticed, doesnt ping from what i can hear. ill have to pull them again and look over them completely. And nothing else changed when swapping carbs other than having to add a 1" spacer to clear the fuel line on my intake. All the local guys that build engines told me to stick with a 650 on it. Doing the calculations the most i got was 677cfm which was on the high end of street stuff. And no no vaccum leak, sprayed around the intake/carb with some starting fluid and no change to rpm. Possible the floats are too low? Or loosing fuel pressure or something? Possible bad regulator? Bad fuel(fuel is 89 thats like a week old.

 

[Erik the Awful]

Jetting adjusts your mixture in the lower 3/4 of the rpm range. In the upper range you change the mixture with the air bleeds (aka emulsion tubes). They work the opposite of jets. Smaller air bleeds richen the mixture, larger air bleeds lean the mixture.