Need some advice tuning new engine

[RDJ]

I'm pretty much a rank amateur mechanic. But I built an engine and it runs. I couldn't have done it without the help of this forum :grin:. After the initial break in, I had a couple of oil leaks and the intake wasn't sealed correctly. I fixed this stuff and now I need some help to dial it in.

I starts and idles just fine. There is a slight bog when I step on it from idle, and then when I hit about 4700 rpms, it kind of sputters or surges. Then when it gets above there somewhere, it takes off again and I have had the engine up to about 6500 rpms, but at that point my foot is off the gas.

I've messed with the timing. I currently have it set at 12 initial and approx 30 total. The vacuum pod hasn't been hooked up yet. I have the hoses plugged. It was dieseling after I turned off the engine at higher initial. It still did a couple of times at this setting but hasn't the last three or four times I've run the engine.

Carb issue? I have adjustable roller rockers. Can the valves be too tight? (my slant six has a solid cam that I check the valve lash each year, and I don't know much about the hydraulic cam).


The engine is a 408 smallblock
Edelbrock 800 cfm Thunder AVS carb w/electric choke
stock edelbrock heads w/ hughes springs (bought from Hughes with the cam)
Hughes 3237 hydraulic cam (232/237 dur @ .50, 540/548 lift)
Eddie air gap intake
10.2:1 compression
Hughes roller rockers

TTI headers, X-pipe, turbo mufflers

3,000 stall Spec-Rite converter

727 tourqueflite
3.23 suregrip 8 3/4 rear

FBO "stockish" ignition (recurved dist by them)

 

[bad440]

set the timing total at 34 degrees. the fbo dist is a very good piece. hook up the vacume adv. buy the step up spring kit for the carb. get a vac. gauge and check the vac. the spring kit should get rid of the bog as you step on it .

 

[70aarcuda]

you are going to need the lighter stepup springs on the metering rods with that cam...

i used their older 230/237 hydraulic in a 360 with stock eddy heads..

set the timing correctly....and connect vacum advance to the timed port on the carb..

adjusting hydraulic lifters....are adjusted in the same sequence as a solid...but instead of setting a lash with feeler gauge...you are setting preload..

once you get to zero lash....no clearance you are adding preload....so you turn (tighten) the adjuster another 1/2 turn....

a compression test will tell ya if the valves are too tight...you will have no compression as the valve will not close....

 

[TurdFerguson]

If it's bogging when stabbing the throttle, it could be too much pump shot.
Once it hit the 4700 range it could be either really lean and laying over or even detonating at that point.
It does sound like the the primary rods need lifting out of the jet to allow more fuel-step up spring need to be weaker/lighter.
With that compression and those heads/chambers, I recommend 30-32* total.

But only testing will tell you how much timing it really likes.

 

[RDJ]

Thanks! The carb had the orange springs, and I changed them to the pink. It helped a lot! Pretty damn easy to change out the springs. I just took it for a short cruise, and it surged slightly a couple of times at the higher rpms, but didn't a couple of other times. I pushed it to over 6000 rpms and it ran good. Anybody know how many rpms an engine like this can go to?

Unfortunately, there are a lot of cars on the road right now. I live on a kind of rural road that is good for going fast, but right now a school down the road is getting out and the soccer moms in SUVs rule.

Should I mess with the the secondary opening sooner or thinner metering rods? I don't have much time to today, but I may try the blue springs later to see what the difference is. Thanks again.