Rochester tuning question time

[Racin_jason]

Recently I bought a 81 with a 350 topped by a Rochester M4ME carb..

Before you just jump on the replace it with an Edelbrock train, you'll have to know I'm just in the process of getting this truck running and would like to (for the time being) keep things the way they are.

..After diagnosing a few vacuum issues i was able to get the truck to a good driving position.

BUT! When I stick my foot to the floor I experience a drastic loss of power and hesitation. The guy that I bought the truck from said that he was experiencing the same problem when he put the truck away last fall and he was told that the choke was the issue. When I took the truck out this morning after replacing said vacuum lines with the choke propped open it was still an issue. Any thoughts on resolving this issue?


Also, this morning when after i replaced the vac lines I attempted to connect a vacuum gauge and fiddle with the air/fuel mix. The gauge that i had wouldn't read any vacuum unless i was to blip the throttle.. possible a faulty vacuum gauge or something else? Any thoughts here?

With the weather becoming warmer and such i've been working to get this thing on the road so i can enjoy it, hopefully i can gain a little insight in to these problem,

thanks folks, you rock!

[geezer#99]

Pics would help of your carb. Both sides and from the front.
Could be several things.
Accelerator pump not working.
Secondary air valve set too loose.
Lack of timing.
To check pump just look inside the carb when you stroke the throttle. Should see 2 strong shots of fuel.
Your vac gauge is fine. You had it hooked to a ported vac nipple.

[Racin_jason]

The accelerator pump seems to be in good shape. Two nice strong jets like you say. Timing is set 12° at idle and 36° on at 3000 rpm. Next chance I'll get I'll look for the proper nipple for the vacuum gauge.

I was winding about the secondary side, it doesn't seem to move if I give it a blip or two

[geezer#99]

Are you stock or do you have headers?
Have you proved your timing tab/balancer are correct?

[Racin_jason]

Everything is all stock. Timing tabs look like the original to the best of my knowledge they haven't moved.

[geezer#99]

You might just have a cold intake. Crossover could be plugged or heat riser not working.
If it still does it with the motor completely warmed up then bump your timing up until it pings and see if that helps.

[Guilty-by-Design]

i went through this on my 82 with a 305 and the quadrajet i replaced all vacuum lines, vacuum advance, removed and blocked off the egr, new cap, rotor, and plugs. also installed new timing chain and rebuilt the carb. but i still had a bad hesitation sometimes resulting in stalling.

if i remember right my vacuum guage was reading about 17 hg
and the only thing i could find wrong is the throttle shafts on my carb had alot more play than i thought they should have

my fix was an Edelbrock 1406

[Wrecked1982]

once had similar problem on a 4 barrels, the secondaries upper plates were opening too fast .it was missing a small rod on passenger the side of the carb. that connect to the vacuum module

[Liberty]

I personally LOVE the QuadraJet, and properly tuned they are one of the best carbs ever made. Just a TON of people don't know how to adjust them so they go with simpler carbs.
The QJets are kind of a booger to tune though lol.

12 might be kinda high. I THINK mine is set to 8 at idle. You might just have to rebuild your carb or pop a fresh QJet on. My truck had that same problem for years until I swapped the carb for a rebuilt QJet. My old one was just wore out plain and simple. Supposedly the choke was out on my old one too.

[geezer#99]

Originally Posted by Liberty

I personally LOVE the QuadraJet, and properly tuned they are one of the best carbs ever made. Just a TON of people don't know how to adjust them so they go with simpler carbs.
The QJets are kind of a booger to tune though lol.

12 might be kinda high. I THINK mine is set to 8 at idle. You might just have to rebuild your carb or pop a fresh QJet on. My truck had that same problem for years until I swapped the carb for a rebuilt QJet. My old one was just wore out plain and simple. Supposedly the choke was out on my old one too.

Running 8 degrees is like buying 10 gallons of gas and only putting 9 in the tank and 1 on the ground.
Think of the lost power and mileage!

[86c20]

redo your timing with the vac you will hear it run better or worse as you turn the dizzy go as high as you can on the vac that will put you right under ping on kick back on starter and yhou will be running fine timimg wise. been doing it that way for years as i have no timimg makes on my truck at all. i have found right at 20 or just north seems good for my truck but i live at sea level so you may be lower.

qjet is a good carb but like said hard to tune. i dont mess with mine to much but mine has given me 9 years of use with no choke and just now is starting to be on the down hill. really thinking about sending it out for a rebuild if i can find some one close

[Liberty]

Originally Posted by geezer#99

Running 8 degrees is like buying 10 gallons of gas and only putting 9 in the tank and 1 on the ground.
Think of the lost power and mileage!

Im not sure what Im running, after some sleep I think 12 is standard on these trucks isn't it? Id have to ask my mechanic what we ended up setting to. I typically don't futz around too much on the timing lol.