Ok, so I did search and didn't see an answer, so hear goes.. I put a fresh rebuilt (2nd time..) 4150 carb on my 65 327/350.. Issue I have now is that when I stomp on it I get a slight hesitation before it goes.. I tried the timing set at 6, 8 and 10 BTC with similar results. The best I can tell the vacumn advance does work when I throttle the engine.. Should I put it at 12 or is that to much and back it off? I'm not sure how the distributor is set as far as weights go. I guess I should do the Lars trick of find TDC, but is getting cold here in the north east.. Any other idea's I should try.. I appreicated any help... BTW the carb is running nicer now..

thanks,

/joe

 

Do you know the accelerator pump and linkage are adjusted correctly? It must give an immediate burst of fuel when the linkage is moved or you'll get hesitation.

 

Sounds like the accelerator pump may be coming on a little late. There are specifications for adjusting the accelerator pump in the rebuild page with the kit.

You should adjust it or tweak the linkage and cam so that the discharge nozzles begin to squirt fuel at the slightest throttle movement. You should have a decent shot and it should be consistent for the travel of the throttle.

Timing should be ok at 10 degrees. The vacuum can will not show movement when “static” revving the engine. IF you are observing a timing movement while free revving the engine it is fly weight movement.

The only way to tell if the vac can is open at idle is to unplug it and see if the timing goes down. You should have full vacuum advance at idle, plus the initial and depending on idle speed, the centrifugal (fly weights).

Total idle timing should be vacuum + initial. Or around 30*

Unplug the vacuum advance line, and plug it off.
Next, set the initial timing to 10 degrees BTDC. Timing should read 10*
Next plug the vacuum can back in and it should add another 15-20* for a total of 25-30*

Now, rev the engine to around 3000 RPM and the centrifugal should add some more.

Mark

 

The first thing I would do is a visual inspection of all of your vacuum fittings and hoses. Make sure their not old and cracked. Any vacuum hoses that are hard or hold their shape should be replaced. Next, I would adjust the floats on the front first and then the back to make sure a dribble of gas is coming out of the screw out plug holes on the side of the float bowls. Do this adjustment with the engine running at idle. Next, I would set the idle as low as possible with the idle throttle screw. Attach a vacuum gauge to a manifold vacuum port on the carb or manifold and read the vacuum. Adjust the primary idle mixture screws in on each side until the idle starts to drop and the vacuum decreases. Then adjust the screws out on each side until the idle smooths out for the highest vacuum reading. Then use the idle throttle adjustment screw to set the idle speed to the proper speed.

If by chance you have a four corner idle adjustment system, close down the secondary screws completely while you adjust the primaries. Then just crack the secondaries to see if the vacuum needle improves. If so, open them up to achieve the best idle. If you have vacuum secondaries, make sure the correct spring is in the diaphragm chamber and the small ball bearing is in its proper place. Many people take this steel ball out thinking that it will improve the secondary operation. It won't and could cause your diaphragm to open the secondaries slightly causing a lean condition when accelerating from idle. Also, if you disassembled the vacuum diaphragm housing and installed a new vacuum diaphragm, make sure that the edge of the diaphragm is showing all around the housing. It is very easy to tear the diaphragm or have it move out of position when installing the cover and compressing the spring inside. If torn, a vacuum leak could occur.

Holleys have several small cork and rubber gaskets around vacuum orifices where the choke housing attaches and where the vacuum can attaches to the carb housing. Any of these vacuum passages can leak if the gaskets are not replaced with new ones when rebuilding occurs.

Two of the best tools you can have in the toolbox are a vacuum gauge and a Mityvac hand vacuum pump to check things such as distributor vacuum cans and cvacuum diaphragms on Holleys. Good Luck.

 

Well the bushing on the linkage from the peddle looks a little hokey, so I'll replace that monday.. Also can the return springs be to much.. They are pretty beefy ??

Update.. Just took it for a drive again..I have it idling real nice and smooth at about 850-900 but still have the same issues.. When the car is stationary and I goose the throttle, I do see the gas coming out real nice and smooth, with no hesitation... Anything other idea's?? Floats??BTW it is a Holley 4150 4bbl...

Thanks,

/jc