Vacuum Leak??!!??

[madmopar]

Be easy on me as I am somewhat of a newbee . I am having problems with my race only 340 (engine details at bottom). It seems that when I first fire it up, it runs fine but when it starts warming up it takes a lot of effort to keep it running. It almost acts like it is grunting like it is under load. A couple weeks ago at a test & tune, ended up jetting up 10 #'s and it's still running lean. From that point on is when it started running like crap. I replaced the gaskets in the carb think I did something while changing jets.Also I put a vacuum gauge on it and the needle bounces between 2 and 5 inches at idle. I am by myself most of the time so it has been hard to keep it running and run out and check the engine. Any help would be greatly appreciated!!
340 ci,.040 over, 11.5 to 1,
Comp Cams 305 duration hyd,.525 lift, Comp Pro-magnum lifters,Comp Pro-magnum roller rockers,AED Holley 750 cfm double pumper, edelbrock Performer RPM,MSD 6al, MSD Billit distributer, TF727, manual valve body, Continental 4000 stall converter

[amxauto-x]

We like picking on newbies. Just kidding. Welcome to the web site.

My first thought is a leak in the intake manifold gasket. But you should check and spray water/soap test all vacumn fittings in the intake. Then use the soap on all the edges of the intake. Then spray it at the base of the carb for leaks. If you have power brakes then you should spray some on the fitting that is on the booster. This is a start.

[sixpackgut]

madmopar, you do know you cold start a mopar from under the hood?

[sixpackgut]

madmopar, you do know you could start a mopar from under the hood?

[darren509]

My car was doing somthing similar to yours and I finally checked the distributor cap; an MSD billet small block, the center of the cap that has the metal nub had a crack in it going all the was to one of the contacts. After spraying with electrical cleaner, I found what looks like spider webs of cracks on three terminals. $12.00 cap and now its good. Hope your problem will be as cheap and easy as mine.

[creative1]

i dunno about that camshaft, it is way more radical than mine, but the vacuum should be steady, i think, even if it is low. i know that some cams only produce about 10" of vacuum, maybe less. because your vacuum is fluctuating, i would investigate things that cause that... burned or bent valves, incorrect valve lash, worn valve guides, or even dislodged valve seats, something that affects one or two cylinders. even a holed piston could cause the vacuum to fluctuate (but then you would almost certainly have other problems readily apparent). vacuum leaks (like manifold gaskets) tend to cause low vacuum readings, but they are pretty stable. it is most likely to be a mechanical problem of which there are many possible causes. even bent pushrods can cause it.