vortec heads on . WOW

[JMZ]

We drove around yesterday. Seems to have made a big difference, but I think my carb is dumping to much fuel when you mash it to the floor. It sputters and bogs a lot. It does better in first and second,when the load on the engine is not that much. The q-jet was bad and the holly 750 was a little better. The holly is not mine but a friend is gonna let me run it indefinitly. If the holly was mine I could have swapped it for a 600 yesterday. Timing is at 7tdc. We have an accel hei super coil on it. The holly has been sitting a while, runs good other than the bogging.It has 65 jets in he front. Could it be the power valve?

 

[Lonnie]

Does the bogging only occur at full throttle? Is this 750 Holley a Double Pumper with mechanical secondaries..... if so it is most likely bogging because it is too large for a 350 in a heavy truck. A 750 vac secondary will work well, or a 600-650 Doubler pumper is the max size recommended.
Lonnie

 

[JMZ]

It is a 750 vacume. It is popping through the carb a little also. I am going to put a power valve in it. What kind of spark plug gap should I be running. I want to find an Edelbrock carb.

 

[Thunder]

You may have to put a stiffer spring it the vacume module that controlls the secondaries. It sounds like the secondaries are opening too soon, letting too much air in without enough velocity. A stiffer spring will allow the secondaries to open later in the RPM band when yourr engine can handle more air/fuel
Most auto parts stores that have holley performance parts carry the spring kit needed to tune it for your engine. they only cost around 15.00
If it has backfired back thru the carb the power valve is prolly bad.
To get the rite power valve:
Put a vacume guage on it
Get the vacume at idle
divide the reading by 2 to get the proper size power valve.
EX: 15 Hg at idle divided by 2 = 7.5 hg power valve

 

[TX Mudder]

Hey, what intake are you using?
Did you buy the aftermarket self-aligning rockers ($$$) or get GM stamped steel ones?
What kind of valve covers are you using?
Thanks
-- Mike

 

[JMZ]

The heads and intake came off a marine engine. The intake has PCM on it, but it looks like an edlebrock I saw at Auto Zone except for the bolt pattern , I think it is a dual plane highrise. The heads were complete with the center bolt valve covers. My friend that I got them from said it was a late model motor.It has a 99 stamped on the heads or block can`t remeber. Ithink I need an edelbrock carb. At least thats what my mechanic buddys tell me.

 

[CaptCrunch]

Basically... if you just drive the truck daily then go with an Edelbrock or Carter AFB. They are super simple and don't require much work. They will suck on uneven slopes though. Holley will be slightly better offroad, but they tend to need more maintance tuning. Quadrajets work great off road and are a pretty good choice for a daily driver. I would personally use the Quad, but an Edelbrock is simplier for the less mechanical.

 

[sosamantx]

kewl, i'd say check the power valve (as well), and out of curosity how'd you do the linkage??

fyi, i'd probably gap them at least .045 (you did mention HEI??) /forums/images/icons/wink.gif

 

[JMZ]

I fabricated a throttle bracket out of a piece of 10ga. flat strip and part of the factory bracket and bolted to the back drivers side carb bolt.

 

[79Beast]

Your engine will bog when the secondaries open if the vaccum advance is not coming in fast enough. Also, the secondaries could be opening too fast. Way to many variables. Try leaning the mixture a little at a time.