Power Loss

[wilcoxl]

I have a 358 Cu In Chev that I run on a 3/8 Dirt Track.

I have had a power problem at 5800 to 6300 RPMS I have replaced the Fuel Line, Fuel Filter had the Carburetor reconditioned by the Manufacture and have rebuilt the Elbrock fuel pump. I have replaced the Cam, I have installed a 18 VIP Battery with a new HEI, DUI Dist (battery runs dist only) no Alternator. Jets 74 Plug gap 0.70

Problem When I run about a lap or so the car just starts to quit, when I pump the foot feed it Ba Ba through the Carburetor but if I quite pumping just for a second the car will quit, but the second you hit the switch it will start and set their and run. You take off and bring it up to max power it does the same thing again . Also it just does not have that crisp sound like it used to when it is up to power.

Got any Ideas I need Help "Thanks"

[carsandcycles]

You sound like you did the right things for fuel delivery, however, it still sounds like a lean condition. You could look for other fuel restrictions between your fuel tank and carb. connector. (crimps in the line, foreign matter blocking flow, etc.) Maybe do a fuel pressure test to see how much volume your pump is delivering. Check your plugs also, their condition can tell you alot.

[jmedved]

Yeah, it sounds like Fuel to me....If you're running a Fuel Cell, take the top off, and examine the hose for the pick-up, it's probably kinked, or the end of the hose is being pinched somehow....don't forget to examine the Fuel Cell Vent, it may be clogged just enough to prevent air from getting into the tank at the rate you're pumping gas out of it......Just continue working your way toward the carb, one part at a time till you find a delivery problem....don't forget the push rod for the fuel pump, and as a matter of fact, make sure the cam eccentric (lobe) that actuates the fuel pump push rod is also OK, it may seem like a lot of work, but I hope everything works out for you. The other thing that may cause a problem is you may have a Big-block fuel pump, that someone tried to fit to your engine with a little creativity.........GOOD LUCK....BY THE WAY... It's only my opinion, but do yourself a favor, and get rid of that Fuel Pump that you rebuilt, and replace it with another famous (not rebuildable) fuel pump...even one out of the junk yard (stock) will be better for your application, as there is nothing to loosen-up...like all those diaphram/lower chamber bolts....BTW, who recommended the .070 sparkplug gap??? With a HEI, you should run closer to .045 with a good racing plug like the Autolite R3539 (or is it R3935??)...A good investment would be to change over the HEI to a MSD HEI module & coil available from Summit (it maintains the stock look of the, stock HEI distributor but runs like stink) I've seen 7900 RPM with a "stock looking" HEI distributor in a modified 358 with 9:1 compression...of course, it didn't live a long life at that RPM. (about 15 laps on a 1/2 mile dirt track) I think the rods, naw, the crank, naw, the pistons, naw it was possibly the cam that gave out first (you're right everything was trash)

[Gearhead52]

Wilcoxl,

I would investigate the things suggested and go a little further.

I don't know what kind of cam you have but at 6300 my guess it ain't stock.

I also don't know any of the rules or restrictions you have in your class like, 2 barrel carb, must weigh a certain amount, must pull a certain amount of vacuum at what rpm, must use factory cast iron parts ?????

My guess is that part of the problem is you may have worn out the valve springs which will drain power at high rpm. When they get soft and they aren't a high seat presure spring they will bounce on the seat at high rpm and drain off power and will actually prevent any high rpm. If you have any broken springs they will cause a backfire at mid rpm ranges.

Have you checked them lately ??? Not just for breaks but seat presure and installed hight ??

How much advance you running ??? 30, 36, 38 ?? What rpm is it all in at ??

Got a fuel presure gauge you can run on the car while doing a hot lap ???

[justen]

also check your fuel pump, and gas preasure in the gas line or any kinkys in the gas line will most definitely run like crap at high rpms

I had a problem like this with my racecar. I'm on a 3/8 asphalt track, and mine would break up at the end of the straightaway, about 6700 rpm. One of the fittings on the suction line on my fuel cell was loose. It was sucking air and causing a lean out miss. I had the pickup tube work its way above the foam in the cell once too. I just zip-tied a large nut to the end of it to keep it from floating up again. Good luck

[lou]

thats a lot of revs, what kind of valve train do you have? it could be valve floating