Advice on engine vacuum...or lack of..

[Bob Carriere]

I am breaking the stride of the Hammond barn news 'cause I am frustrated.....

My engine won't suck!!!!

Here is the situation.

My rebuilt 261 was started by Dan.. the Wizard Man....

since then I have tweak the timing and it starts easy...but.. after all efforts I can only get about 9 inches of vacuum at idle and ONLY with the choke on full.....

Mixture screw is at 1 1/2...... further adjustments + or - made no difference.....

Comment by Dan was that I might be overcarburated..... yeah like having too much sex.....

I was running at the time Dan was here a NOS 7015011 Rochester B carb listed as suitable for a 261. In fact the same carburator on Stew's 261 works fine.

I checked the fuel pump for sufficient delivery of fuel..... squirts like the devil..... I checked every vacuum line and even removed the PCV in case it allowed too much air into the manifold... no changes.

Then I changed the carburator for the original 261 Rochester B carb that I rebuilt and got the same no idle response.

Now I can get a reasonable idle speed with a very steady 9 inch vacuum but only with full the choke on... with that setting it runs reasonably good.... racing the engine raises the vacuum to the 15 - 18 inch easily.... but again only with the choke on.

I do have a small ( I think) leak in the front intake manifold at port 1&2..... engine races in RPM when I squirt raw gas with a syringe near that port and an exhaust gas leak underneath at the rear port 3&4......

After engine was hot the bolts were retightened from center outward as recommended.

New one piece special thick manifold gasket is ordered and on the way....

I almost seems that, without the choke on, the engine does not develope enough vacuum to run......

Help.....What did I overlook....????

BooB