Fuel pressure and vapor lock advice needed

[280zwitha383]

(Things to keep in mind while reading this post:

I'm running a stock mechanical fuel pump in an 82 ZX with a 383 280 dur cam Dart IE 215cc heads victor jr. intake. My carburetor is a 670cfm holley street avenger and it is spotless inside and ran great when I took it off of my truck)

 

I've been thinking about my fuel problems I'm having and I wanted input about my train of thought so here's my deal. At idle with the engine warm or cold I can hook a vacuum gauge up to the carb and it is constantly fluctuating so I can't properly tune my carb even though I'm pretty sure half a turn is pretty much right on because vacuum pressure pretty much tops out around there and the thing runs pretty good. I'm thinking this could be from low or inconsistent fuel pressure however I don't think the engine is getting starved for fuel at higher rpm because my acceleration is right on (atleast if it's not I'm really going to need some bigger tires). However, when I'm cruising between 2k and 3k rmp I can feel the engine cutting out slightly here and there and moreso when it has been running for a while. I know my underhood temperature is aweful because I can't even hold the throttle back on the carb once it's been running for a while because it's so hot (and I work with open fryers all day at work). So my question is do you think I have two separate problems? One being fuel pressure or something else causing my vacuum pressure to fluctuate and the other being vapor lock causing my sputtering at 2-3k rpm or is this all a vacuum problem. I haven't thought of holding the throttle down at say 2.5k rpm and seeing if the vacuum pressure still fluctuates which would cause the vacuum advance to also fluctuate. If it does fluctuate across the board what could be the cause of this? I have thought about simply running an electric fuel pump and rerouting the lines away from any exhaust which would seemingly eliminating both possibilites. Any help you guys give me would be greatly appreciated. ~Lance

[Pop N Wood]

You need to make absolutely certain you have no vacuum leaks.

[Alf]

first off, how many inches of mercury is it pulling at idle. Then how much is it fluctuating. This could be many different problems.

[280zwitha383]

It pulls about 11 psi while idling and only fluctuates around 1 psi. That might be normal but I don't remember my other engine doing that. I thought that it was fluctuating more than that when I posted last time, but I tested it again and that's all it did. I tightened all of my intake manifold bolts as well as my carburetor bolts so that might have made an improvement, I also plugged all the vacuum lines and then later hooked them back up with the gauge still on and it didn't fluctuate at a higher rate. Is some fluctuation normal? It seems to me like my truck doesn't fluctuate at all but I can't remember and at the moment it's too dark and cold to go outside and check it

[Alf]

some fluctuation is normal with a high performance cam. it could also mean that your fuel mixture isnt quite right yet. The sputtering may be a timing problem, what is it set at? I had a similar problem with my motor and once i found the optimum place for the timing it ran smooth.

[280zwitha383]

well in the process of all the testing to get the vacuum pressure I adjusted the timing, it is at 10* and 36* total timing. It was at 12* and 38* total.

[Alf]

you may want to try retarding it slighty by only about two degrees and see what happens. You should check your plugs too and see how they look, also check the gap.