General Engine Question - Vacuum Leak

[Ed McGettigan]

In addition to my 1964 Corvette, I also have a 1966 Lemans with with a 1967 Pontiac 400cid engine. Last week, I put an edelbrock manifold and Holley carb on the Lemans.

I now have the following problems:

- at start up, while the choke is on and the engine cold - it has a strong idle and then starts to die and then stalls. Vacuum reading is about 15. It does have an aggressive cam.

- once it warms up, it stays running and the vacuum reading is steady at 17. The timing is correct and it drives well, however, it occasionally backfires through the carb on mild acceleration from a coast.

I really only know enough about engines to get myself in trouble, therfore, my question is - does this sound like a vacuum leak?? I've sprayed all around the manifold and carb with carb cleaner to try to detect a vacuum leak by the rpm change but have not been able to detect anything. Any help would be appreciated...

Ed

[Dave #35697]

Re: General Engine Question - Vacuum Leak

Ed,
There are adjustments to the carb for "cold running",cold idle should be around 950 rpm until it warms up and your choke should be partially open until the choke thermostat opens it.If the timing is set correctly check the adjustment on the accelerator pump if there is one.
I have corrected a pop by simply advancing the timing a couple of degrees.
If the engine is not stalling at idle and is relatively smooth at idle,I doubt it is a leak.
Dave

[Clem Z.]

Re: General Engine Question - Vacuum Leak

the dieing with the choke on is caused by the choke pull off is opening the choke too far on startup. the back fire could be caused by too low a float level,the accelerator pump discharge is late,check for play in the pump linkage. the pump squirter should put out fuel if you just touch the throttle linkage.

[Ed McGettigan]

Re: General Engine Question - Vacuum Leak

Thanks guys! The carb that I put on is the Holley Street Avenger 670cfm - new - right out of the box. Do these typically need to be checked for all the settings?? I thought these were set at the factory??

[Clem Z.]

Re: General Engine Question - Vacuum Leak

they are set to a std but every engine will need fine tuning. the floats sometimes get moved because of the way they throw the boxes around. were there not instructions in the box on tuning the carb?

[Ed McGettigan]

Re: General Engine Question - Vacuum Leak

Hi,
They do provide instructions on fine tuning but the way it is written, it made it sound to me that it wouldn't need any adjustments???? I'll give some adjusting a shot - with the help of someone who knows what they are doing!!! Thanks for your help...