Oldbuilder
Member
Okay folks,,, I've got a idle problem and just can't get it figured out so here's the best I can give ya.
Here's what it's doing,,, won't idle below 1500-1700 RPM and when shut off it will backfire after a few seconds or sometimes quite a few seconds,,, that's the one that scares the crap out of me cause I'm not expecting it LOL,, I get relaxed when it doesn't happen within a few seconds.
350 SBC engine,,,
Engine was rebuilt almost back to stock. I added an upgraded hydraulic cam .488 lift and roller tip 1.6 ratio rockers, an RPM Performer dual plane intake non-air gap, and a Holley 670 Street avenger carb.
Heads are 1968-1970 cast steel 487X from a Corvette with 2.0 X 1.6 valves. Header exhaust into flow master pipes and mufflers. So nothing outrageous here. At least I don't' think so.
When setting the valves, was told to tighten the nut until the push rod was making contact with the lifter then 1/2 to 3/4 turn,,, I think that was wrong and they were too tight. Also while driving they backed off and were rattling pretty bad. Not sure if it's flattened a lobe or two or bent a valve. Will check all that later this week with a 1" travel indicator if I can figure a way to mount it.
Got everything set the best I knew and fired up the engine. Couldn't get it to idle below 1500-1700 RPM. Even after doing all the adjusting I know about, this isn't my first rodeo but it's been a while since I've run into any problems.
Went back and disconnected all the vacuum lines and plugged off the open ports. That seemed to help for a while but the back firing after shut down started. Somewhere there has to be an ignition source I'd think.
Anyways, this last time I pulled the valve covers and checked everything there was no give (cushion) in the lifters so I set them all with a .010" feeler gage and fired it back up. The first few times I shut it off all was good on the back fire but idle was still high.
Part of me thinks there has to be a vacuum leak somewhere and I've heard it can be on the inside of the lifter valley with aluminum intakes not fitting right. ma I hope not.
So chime in crew and don't be shy,,,, it's been a long battle and I'm about to shoot something if you get my drift ha ha ha .
Later Ya'll,
Grego
Here's what it's doing,,, won't idle below 1500-1700 RPM and when shut off it will backfire after a few seconds or sometimes quite a few seconds,,, that's the one that scares the crap out of me cause I'm not expecting it LOL,, I get relaxed when it doesn't happen within a few seconds.
350 SBC engine,,,
Engine was rebuilt almost back to stock. I added an upgraded hydraulic cam .488 lift and roller tip 1.6 ratio rockers, an RPM Performer dual plane intake non-air gap, and a Holley 670 Street avenger carb.
Heads are 1968-1970 cast steel 487X from a Corvette with 2.0 X 1.6 valves. Header exhaust into flow master pipes and mufflers. So nothing outrageous here. At least I don't' think so.
When setting the valves, was told to tighten the nut until the push rod was making contact with the lifter then 1/2 to 3/4 turn,,, I think that was wrong and they were too tight. Also while driving they backed off and were rattling pretty bad. Not sure if it's flattened a lobe or two or bent a valve. Will check all that later this week with a 1" travel indicator if I can figure a way to mount it.
Got everything set the best I knew and fired up the engine. Couldn't get it to idle below 1500-1700 RPM. Even after doing all the adjusting I know about, this isn't my first rodeo but it's been a while since I've run into any problems.
Went back and disconnected all the vacuum lines and plugged off the open ports. That seemed to help for a while but the back firing after shut down started. Somewhere there has to be an ignition source I'd think.
Anyways, this last time I pulled the valve covers and checked everything there was no give (cushion) in the lifters so I set them all with a .010" feeler gage and fired it back up. The first few times I shut it off all was good on the back fire but idle was still high.
Part of me thinks there has to be a vacuum leak somewhere and I've heard it can be on the inside of the lifter valley with aluminum intakes not fitting right. ma I hope not.
So chime in crew and don't be shy,,,, it's been a long battle and I'm about to shoot something if you get my drift ha ha ha .
Later Ya'll,
Grego