I have a fresh rebuild that I am trying to get to run right. 351M to a 400. Edelbrock intake and AVS carb. From Edelbrock tech line to adjust for my elevation of 5300 ft I changed metering rod and to a 92 secondary jet, from 95. All ignition is stock. Comp cam, basically an RV grind. From what I have read the factory cam had a 4° offset timing ground into it. With the new cam do I need to have a different base, mech/vacuum timing? Timing is currently set at 12°. Pretty sure I have all the vacuum lines in factory setup. Except for those that have no place to go due to different intake/carb. Those have been capped off.
The problem I am having is the engine will not accelerate. It started out running ok until the secondaries kicked in. Then it would lose power. Now I can barely go 30MPH. Power falls flat with any attempt to go faster. Still idles ok. Acts like it is not getting fuel but checked all that. 100 miles ago it seemed like to would run worse after about 20 miles on the road. Like a lack of fuel. Now it doesn't like to take any load. Might be a separate issue, but the other day it quit on me and wouldn't start until the following morning. Looking for any help before I start shotgunning new parts. Some of my thoughts for the heat issue are bad ignition coil or ignition module. With the lose of power, I'm lost. Timing curve? Any feedback would be much appreciated. Thanks in advance.

 

Mechanical or electronic fuel pump?

12 degrees is your base/initial/idle timing?

Pictures pictures pictures.

We need more info before we start diving into answers.

 

Mechanical fuel pump. 12° initial timing.
Basically in stock configuration. Except the engine has just been rebuilt. Only 350 miles on rebuild. All new internals except connecting rods. Stock heads with new valve train and mild port job. New Edelbrock AVS 650 carb and performer intake. I didn't notice any cracked vacuum hoses. I do have a front intake gasket leak that is letting some oil out that I will fix later. Factory exhaust manifold, single pipe back. I still need to pass visual and tailpipe emissions.
I understand that you will need more info. Not sure what to tell you. Questions? Thanks.
Clint

 

Do you have a fuel pressure regulator?

Carbs are finicky with fuel pressure. Edelbrock's tend to like anywhere between 4.5-5.5 psi (check your carb manual for what they recommend). Your mechanical pump will be producing a lot more than that without a pressure regulator to turn it down.

 

Could be a myriad of issues....vacuum leak, stuck choke, fuel filter, lean condition, accelerator pump, fuel pressure, timing, etc.....

 

I would go back and recheck timing as it sounds like the dist. may have turned if not clamped down good.

Does the truck run a cat? If so how old is it and the muffler? I ask because it also acts like a plugged exh. system.
As a test you could disconnect the exh pipe before cat / muffler and take it on a test drive.

Could pick up a 2nd IGN box as a spare and try it and if it does not fix it keep it under the seat.
Dave ----

 

"Bigger" than stock cams like more initial timing.....bump your ignition timing up to ~14* BTDC - 16* BTDC. 12* BTDC is for stock cams.

Have you addressed the fuel pressure issue like Aaron-71 suggested?

Ignition coil test: with all the wires removed, the primaries want to be ~ 1 ohm -1.3 ohms.
The secondaries want to be ~ 8 K Ohms - 11 K Ohms.
Make sure the engine is up to operating temperature.....feel the coil. Is it hot to the touch or just warm?

The ICM can be tested at a local parts store but make sure it's hot or very warm. When cold these bad boys will show it's good...unless it's completely pooched. Heat is the mortal enemy of the ICM.

 

It's tough to run down the cause, and get the carb tuned when it's acting up. The best thing I ever did for this was install an Air / Fuel Ratio Gauge. It takes all the guess out of carb tuning. You no longer have to ask yourself, "Was that stumble because of a lean or a rich condition, or was it timing?" You'll know by watching the gauge as you transition through different throttle positions. I also like to use a vacuum gauge with the AFR gauge.

 

Thanks for all the feedback. I had the ICM tested today. It wasn't hot and tested good. I might heat it up and bring it back. I did pick up a spare coil while I was there. I'll test the old one to the values mentioned after I heat it up some too. I'll try each suggestion until I figure it out. Thanks again for the feedback.
Clint

 

Heat the coil to operating temps: Set your OVEN to 200*....on Bake....Cook it for 20 minutes then quickly measure the primaries and secondaries.

 

Is it popping out the carb at all? How did you break in the cam and what oil are you running?

 

Will this work in the Microwave?

BRB

 

Yeah, hahaha....an easy way to tell The Warden you need a new Nuker.....and some remodeling....but, what a light show!

 

Dangit!!! Now ya tell me

 

I think it's important to realize that too much fuel can also make the engine hesitate and not generate power. After a bit you can actually tell the difference just by feel / listening (difference between not enough fuel or too much fuel)