Hey guys, I have a '68 Camaro with a 350 in it. I do not know much about the engine except that it has a single plane edelbrock intake, hooker headers (1 5/8 inch), vacuum advance electronic distributor, pretty lumpy solid cam and a holley street avenger 670 cfm carb. The trans is a turbo 350 and it has 4:10 gears. At full throttle the car flies, smooth, strong acceleration. When I'm just cruising along at approximately 30-40 mph the car is holding back. It doesn't feel like a missfire, feels like it's starving for fuel. Any suggestions? I changed the fuel filter, no help. Also at idle the car tends to load up a bit. I have it set to idle at about 750rpms in gear. Any suggetions would be appreciated.

 

Start with basics like checking fuel pressure (probably not or you'd back fire under full throttle) and float level.

Cause of loading is the big cam, might also be cause of the way it feels at 40. With a big cam a lot of times you have to open idle stop screw to get it to idle. this exposes the transfer slots in carb. Richens the mixture excessively. Cure is to drill a hole in each primary butterfly between front edge and shaft. Start with 1/16" and work your way up to ~ 1/8" max.

After drilling, set stop so that ~.050" max of the transfer slot shows. Pop carb back on. If it idles ok, hole is proper size, idles too low, needs more air, drill out a little bigger till the idle is acceptable. Right now the idle mix screws probably have no effect due to the idle slots dumping in so much fuel. Once you do the fix, you should have some mixture control.

High idle with a big cam can cause the advance weights in distributor to kick out adding timing. So you think you have 8-12 initial, might actually have zero. So you might have very little timing at 30-40 and too rich a mixture. Try setting it to 14-16 initial, but you also have to put timing tape on your balancer to make sure you don't have more than 36-38 total at > 3,500 rpm.

If you want to learn Holleys, there is an excellent book by HP Books on them. You can get it on ebay.

 

Thanks alot for the info. I will get the book and give your suggestions a try.

 

With 4.10 gears, single plane intake, high idle speed and solid lift, lumpy cam, its likely that when you're going 30-40mph your rpm's are lower than where your engine starts making power. The reason the problem goes away during heavy acceleration is because your engine rpm's are up in the cam's operational band. The reason the car loads up at stop is because the stall speed isnt high enough.

 

As for suggestions...

If this is a race car, live with it.
If this is a street car, swap out the solid cam for a 270 or 280 hydraulic Comp Cam and a dual plane intake. This will still give you plenty of power, but make it way more streetable.

 

I had that similar problem with my 350. I also had a 670 street avenger. It would run lean at cruisng speeds and kind of seem like it would miss it also had a off idle bog. No mater what I did with that carb i couldn't fix it. I bought a 650 Speed Demon and without any tuning to the carb the problem was GONE!!!