urban_cowboy

Changing jets around will just be hunting in the dark until you pull the plugs and inspect a good number of them. As 67mustang302 said, you need to look at the top of the porcelen for WOT coloring. It should be tan...not black...not white.

my77stang has a good point. If you are floating valves, the cam cannot work correctly. It is just like having a wrongly lobed cam because the valves are not following the correct timing. Typically at high rpm, you need stiffer springs to maintain contact between the valves and the rest of the timing system. 5500 is not very high rpm to have valve float, but if you have weak springs, it could happen.

Fuel starvation could also be an issue. What pump and fuel pressure are you running at those rpms?

racin66coupe

the valve springs that are in it are more than enough for high rpm's
the pump is just a stock replacement one, i dont know about he psi

urban_cowboy

What estimated horsepower & torque is this motor? With a stock pump and fuel line, you could be running low on fuel at WOT at higher rpms.

Will the motor rev to 6500 and stay there for a minute or so while out of gear under no load?

racin66coupe

hmm i havent tried that, it wont hurt the motor? the fuel line is 3/8 with a return like same diameter

urban_cowboy

Haha, not any more than running it at those rpms on the track for an hour . I do this all the time when working on a close tune for jetting and air bleeds. It will run a little easier without load, but if you you are having problems with fuel flow, air flow, or exhaust flow, it might show up.

As for the fuel pump, it and that -6AN line might be too small for your fuel needs at race rpms...something to check out.

racin66coupe

hmm yeah ill try to rev it to 6500 once i get the carb all rebuilt and see what happens

67mustang302

Even a stock pump is more than enough for his engine. Those hobby stock type engines are lucky if they can even produce 300-350hp out of a 350 inch engine. Pull the plugs and cut the threaded portion off, the base of the insulator should ideally have a very thin greyish ring about 3/4 of the way to all the way around it. Once it's all the way around it starts getting thicker. Anything more than about 1mm of width and you're too rich. 3/4 of a turn is typically lean best power, anything less is too lean. The ground strap should also show a color change(bluing metal or a greyish zone moving to copper) at about the apex of the strap. Closer to the tip is too little timing, closer to the plug body is too much. Also look for a greyish or brownish ring at the insulator tip where the electrode comes out, "ring around the electrode" as it were. A ring about .020 wide all the way around is a good indication of correct timing also, less ring = too much timing, thicker ring = not enough timing.

my77stang

i still say retard the cam anyways if you can - its good for some extra top end powwa

67mustang302

Yeah, if the rules allow every bit helps, provided the cam isn't specifically ground for that type of restricted racing, then it's designed to function best straight up.