misfiring problem help!!!!!!

[mike78nc]

I have looked everywhere and can't seem to find anyone with the same problem. Me and my dad just build a 350. We put new 375 hp angle plug heads on it with an aluminum air gap intake. Also a new cam with 230 duration and .495 lift. It also has an 800 quadrajet on it. The motor is 1970 model 350 4 bolt main. The motor is in a 1985 GMC pickup. The problem we are having is no power. The truck has no power at all. The truck has a splutter out the tail pipes and it also has a few plugs that are soot black when we pull them. This means they are getting no fire right? We originally thought that it was the cam or the heads, but we ran a compression test and all of the cylinders had great compression. Can anyone help me because I am stumped.

[bowtiemanchevyman]

Have you check your timing if it to retarted or advance you will lose power and have the spark at the wrong time and not get a full burn. make sure your number one is right on. befor you doanything else.

[mike78nc]

We have changed the timing a lot we have it to a point now where it cranks perfect but another thing i forgot to tell is that we can set it to idle at 900 but when i put it in gear it will die. should i try using a timing light to set it? We have been doing it by ear

[deth_1970]

I would use the timing light, and also hook a vacuum gauge to it, and check for vacuum leaks

[mike78nc]

ok i will definitely try that now thanks guys i'll post back after i try that

[bowtiemanchevyman]

i would frist make sure you have TDC and set you timing to 12 BTDC then move it to get it fine tuned.after that check with a vac. gauge to see if you got 15-20 vac.

[mike78nc]

how do you check the vac? where do you check it?

[bowtiemanchevyman]

you find which one of the ports has full time vac. most of the time its the one that hook up to the heater. what type of card do you have? if its a edelbrock it the one on the passenger side. on holley its most of the time the sec. one back on the passenger side of the card. if u can figure it out post a pic and ill tell u

[mike78nc]

i have a quadrajet

[RPOZ11]

I am having a similar but different issue than you.

I just worked on my truck today.

On my QuadraJet, I used the port above the baseplate.
Stand facing the engine from the front of the vehicle, on the lower right hand side (driver's side) of the front of the carb, there should be a port there.
Note :
If your carb is not the original QuadraJet on your Truck from GM, double check to see what carb you have.
There will be a 7 or 8 digit part # on the driver's side of the body of the carb near the carb linkage.
Try isolating what each port vacuum supplies.

I measured with my Vacuum Gauge 0" vacuum pull at idle; 15-20" vacuum pull thru 3500 rpms.

This is the Vacuum Gauge that I use...
(Sorry for such a big image)

[mike78nc]

alright cool i will go and get me a timing light and vac gauge and run those tests thanks everyone i will post back in the next couple days and let everyone know whats going on.

[bowtiemanchevyman]

Originally Posted by RPOZ11

I am having a similar but different issue than you.

I just worked on my truck today.

On my QuadraJet, I used the port above the baseplate, on the lower right hand side (driver's side) of the front of the carb.

I measured with my Vacuum Gauge 0" vacuum pull at idle; 15-20" vacuum pull thru 3500 rpms.

This is the Vacuum Gauge that I use...
(Sorry for such a big image)

and its the left side. and is that what you rread when u ran your truck if so you dont have any vac. and need to find out why

[jjzepplin]

Once chased a misfire down to a broken rocker (twice actually). Pop the valve covers and check for movement, pulled studs etc.