I cant get my new engine to run smooth. Seems untunable.

[Ricko1966]

If you checked for vacuum leaks with carb cleaner at the base you'd have caught that.

 

[AyWoSch Motors]

I had said earlier that disconnected ad capped all tye vacuum ports, but i relized i missed the vaccuum advance on the distributor. I undid that and capped it off, and it actaully idled down a tiny bit and smoothed out a little, not sure why. I played with the idle screw and was able to get down to about 1100, without it dying, but it sounded rough, so i turned it up to about 14-1500.
Wired in a tach in the egine bay temporarily, so i can see what its doing.

I put my vaccum gauge on the port where i have the vac advace now (left side manifold vac) and it reads about 3.5-4 inches. I put it on the port where i had the vac advance (right side manifold vac), and it read 5-6 inches..
Shouldnt it be around 20ish?

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

 

[AyWoSch Motors]

If you checked for vacuum leaks with carb cleaner at the base you'd have caught that.

Well i was focusing more on the base plate and the gaskets. I didn't spray it on the linkage. I had to have the sprayer close to where i was spraying cause the wind was blowing it away. Ill try that tomorrow.

 

[Ricko1966]

I was just saying I'd have thought that was already checked.my bad. Vacuum readings that low I would assume you are on a ported vacuum source,not a manifold vacuum source plug that port. Find a manifold vacuum port. Now turn your idle way down with the throttle stop screw and adjust your mixture with the mixture screws until you have maximum steady vacuum. Take your vacuum gauge off hook that port to your vacuum advance and turn the throttle stop screw down to idle speed. I think your problem will be gone.

 

[wanderinthru]

Worn out throttle shaft bore on the Q jet. Pretty common problem. They suck air around the shaft, and it makes them idle high. PITA to fix, you have to take the shaft out, drill them out and put a new bushing. I've never done one.

Thinking this as well. Worth a check for sure.

 

[BSquared]

I did not see this discussed earlier. What's the PCV valve situation on this engine build? Have you tried plugging the port(s) on the carb where the PCV valve(s) attach?

Sounds like a huge vacuum leak to me.

 

[DoubleDingo]

Hmmmm, that might explain it. Never heard of that.

Yeah, it's common. The original q-jet on my '81 has a worn throttle shaft. It ran well and then it started acting weird. I found a bunch of vacuum leaks and fixed them. It ran better, but it still acted up once in a while. I couldn't figure it out. And then the throttle would stick open from time to time. I couldn't figure that out either. So, out of desperation, after work one day, I pulled off the air cleaner and inspected everything. It looked fine. Then I grabbed the throttle arm and went to turn it, and it was sloppy as heck. I could replicate the throttle sticking open, and also it not sticking. I swapped on a rebuilt carb I had as backup that didn't have a wobbly throttle shaft, and the problem was fixed. Except it would backfire when I left off the gas too quickly, that I could never fix, so I had to be mindful of how quickly I let off the gas.

 

[Ricko1966]

Did you ever get this fixed?

 

[AyWoSch Motors]

Did you ever get this fixed?

No, looking for a new carburetor as we speak.

I did change the the vac advace port, capped off all other ports. Tuned it a bit back and forth and got it to run pretty smooth and i got the idle down to about 1400. Its running smoother and its driveable, so im happy for now.
Still going to look for a new better carb though.

 

[Ricko1966]

No, looking for a new carburetor as we speak.

I did change the the vac advace port, capped off all other ports. Tuned it a bit back and forth and got it to run pretty smooth and i got the idle down to about 1400. Its running smoother and its driveable, so im happy for now.
Still going to look for a new better carb though.

Have you verified it is leaky throttle shaft bushings?

 

[Ricko1966]

Memory has kicked in.One of my employees years ago, was converting a tpi firebird to carburetor. He got the wrong intake gaskets. So put some duct tape over your pcv hole on the valve cover. Make sure your oil cap fits tight.Plug the pcv valve hose. Pull the dipstick, hook your vacuum gauge to the dipstick tube and start your car.If you are pulling vacuum at distick tube you have a vacuum leak into the lifter galley.

 

[Conejo_K10]

With vacuum that low, I would 2nd the intake gasket theory - something is misaligned or just the wrong gasket.

An issue I've had with the q-jet base gasket is with the plastic inserts. Often they're too thick, disallowing the compression of the gasket and thereby leaking. Typically I sand down the inserts to assure gasket compression.

 

[AyWoSch Motors]

Memory has kicked in.One of my employees years ago, was converting a tpi firebird to carburetor. He got the wrong intake gaskets. So put some duct tape over your pcv hole on the valve cover. Make sure your oil cap fits tight.Plug the pcv valve hose. Pull the dipstick, hook your vacuum gauge to the dipstick tube and start your car.If you are pulling vacuum at distick tube you have a vacuum leak into the lifter galley.

Well I dry fit the gaskets on the heads before i installed it, everything seemed to line up perfectly

 

[Ricko1966]

Well I dry fit the gaskets on the heads before i installed it, everything seemed to line up perfectly

What I told you to do would take less than 5 minutes,and then we could rule out intake gaskets. I actually don't even think it would take 5 minutes.

 

[Snoots]

Hmmmm, that might explain it. Never heard of that.

Happens more often than people care to admit. It IS a PITA to do but is not all that hard unless you're in a hurry. Take your time and it will be time well spent. Cliff Ruggles sells a complete kit to do the job and it comes with instructions.