Here is a question about a problem I am having. 1968 GS 455 Painless wiring harness with HEI connection. Comp cam perhaps about a little hotter than the stage 1 cam with B4B intake. At full throttle when revs hit about 4500 the vehicle acts as if it is running out of gas. What I have had tested, intake is sealing, changed carbs no difference, had HEI checked okay, Vehicle has perhaps 2000 to 3000 miles since getting rebuilt. My tech, and I disagree with him, thinks it might be the valves are not right. He has suggested pulling the heads and having them checked. Valves and springs came from T/A had their cam but it wiped a lobe. Three angle valve job 70 stage 1 heads stock. I am at a loss but I am thinking about pulling the tank and checking the rubber gas lines or something else fuel line related. Any thoughts? What am I missing?
Testing pressure and volume will answer the fuel question. It may very well be a valvetrain problem, too. Incorrect spring pressures, wrong stem heights, all have a role to play. Check the fuel system first, in my opinion. Devon
what do you mean running out of fuel like it backfires or it just starts cutting out? does it pop out the exhaust?
Either not enough fuel to keep up, or not enough coil to keep up, or valve float if running hydraulic valves. How old is the fuel pump? How old is the fuel filter? What coil are you running?
It certainly sounds like a fuel delivery problem, and that would be my first guess. Check your pick up in the tank, and all the fuel lines for restrictions. If the lines check out and your fuel pump is old, change it, they are relatively inexpensive. Early HEI's had a reputation for laying down at higher RPM's. They could not supply enough spark at higher RPM. That self contained coil can run pretty hot. The after market has taken care of that with improved high performance modules and coils. There are two different stock coils for the HEI. If memory serves, one coil had red and white wires, the other had red and yellow wires. I would imagine this had to do with module compatibility, but I'm not sure. The above is unlikely, but I thought I'd mention it. I'd look hard at the fuel delivery first.
I had someone suggest valve problems like the springs or valves. The springs are from a kit from T/A, one of their old 499/499 cams. It wiped a lobe, so I put a comp cam in that is more tame. If anything it is a little bit of overkill. The valves are from T/A stainless steel so I believe Mike is very careful about things like that. Think I will run down my gas and pull the tank, perhaps it is the sending unit. I believe it is origional so perhaps it needs some attention. Thanks.
If it's a valvetrain problem, the quality of the parts may not be an issue, but as I said already, spring installed heights or valve tip heights may be wrong, causing valvetrain geometry issues. Don't confuse the quality of the parts with the quality of the machine work and assembly. If you don't have those numbers from whomever did the work, the only way to verify the installation is to measure again. Devon
